JP2012174346A - Organic light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic light-emitting device in which high reliability and a long life can be expected by effectively preventing moisture absorption to a planarization film.SOLUTION: A planarization film 11, a coating film 20, a positive electrode 2, and a hole injection layer 4 are formed on one surface of a substrate 10. The planarization film 11 is coated with the coating film 20. An organic light-emitting device 1 is constituted by laminating a hole transport layer 6A, a light-emitting layer 6B, and a negative electrode 8 sequentially on the hole injection layer 4. The coating film 20 and the hole injection layer 4 are tungsten oxide layers having a thickness of 2 nm or more deposited under certain deposition conditions, so as to have an electronic state where an occupied level exists in a range of bond energy which is 1.8-3.6 eV lower than the lowest bond energy in a valence band. A source electrode 17 and the positive electrode 2 are connected electrically with the coating film 20 interposed therebetween.

Description

  The present invention relates to an organic electroluminescent device (also referred to as an organic EL device, hereinafter referred to as an “organic light emitting device”) that is an electroluminescent device, and particularly over a wide luminance range from low luminance to high luminance such as a light source. The present invention relates to a technique for driving an organic light emitting element with low power.

In recent years, research and development of various functional elements using organic semiconductors has been promoted.
As a typical functional element, there is an organic light-emitting element that is a current-driven light-emitting element.
A configuration example of an organic light emitting device 1X using a conventional organic light emitting element is shown in FIG.

  An insulating planarizing film (interlayer insulating film) 11 for reducing the level difference and ensuring flatness is formed on the upper surface of the TFT substrate 10 on which the TFT elements as drive elements are arranged. An anode 2 made of aluminum or aluminum alloy is disposed on the planarizing film 11 so as to be electrically connected to the source electrode (current extraction terminal) 17 of the TFT element. A hole injection layer 4 is formed on the anode 2 to increase the hole injection efficiency. Further, a functional layer (hole transport layer 6A, light emitting layer 6B) containing an organic material is provided on the upper surface of the hole injection layer 4, and an electron transport layer 7, a cathode 8, and a sealing layer 9 are sequentially disposed.

  FIG. 34 shows the configuration of the organic light emitting device 1X using one organic light emitting element, but the organic EL display panel in which a plurality of organic light emitting elements are arranged in a pattern such as a matrix on the TFT substrate 10 is used as an organic EL display panel. In the case of manufacturing a light emitting device, a partition (bank) 5 made of an insulating material is formed so as to partition the organic light emitting elements for each organic light emitting element or for each predetermined arrangement.

  When driving the organic light emitting device 1X, a voltage is applied between a pair of electrodes composed of the anode 2 and the cathode 8, and holes injected from the anode 2 and electrons injected from the cathode 8 are recombined in the light emitting layer 6B. The electroluminescence phenomenon generated by doing so is utilized.

  Organic light-emitting elements have high visibility due to self-luminescence, and are excellent in impact resistance because they are completely solid elements, so they are attracting attention for use as light-emitting elements and light sources in various display devices. ing.

  Organic light-emitting elements are roughly classified into two types depending on the type of functional layer material used. The first is a vapor-deposited organic light-emitting device in which an organic low-molecular material is mainly used as a functional layer material and is formed by a vacuum process such as a vapor deposition method. Second, a coating-type organic light-emitting device is formed by using an organic polymer material or an organic low-molecular material having good thin film formability as a functional layer material and forming the film by a wet process such as an inkjet method or a gravure printing method.

  Up to now, vapor-deposited organic EL elements have been developed for reasons such as high luminous efficiency of light-emitting materials and long drive life (for example, see Patent Documents 1 and 2). Practical use has started for small TVs.

  The vapor deposition type organic EL element is suitable for a small-sized organic EL panel, but it is not always easy to apply it to, for example, a 100-inch class full-color large-sized organic EL panel. The factor lies in manufacturing technology. When an organic EL panel is manufactured using a vapor deposition type organic EL element, a mask vapor deposition method is generally used when forming a light emitting layer separately for each color (for example, R, G, B). However, when the panel has a large area, it becomes difficult to maintain the alignment accuracy of the mask due to the difference in thermal expansion coefficient between the mask and the glass substrate, and thus it is not always easy to manufacture a normal display. In order to overcome these problems, there is a method of using a white light emitting layer on the entire surface and providing an RGB color filter to avoid separate coating, but in this case, the light that can be taken out is 1/3 of the light emission amount. In principle, the power consumption increases.

  Thus, attempts have been made to realize the enlargement of the organic display EL display panel by using a coating type organic light emitting element. As described above, in the coating type organic light emitting device, the functional layer is manufactured by a wet process. In this process, since the positional accuracy when the functional layer is separately applied to a predetermined position does not basically depend on the substrate size, there is a merit that a technical barrier against an increase in size is low.

  On the other hand, research and development for improving the luminous efficiency of organic light-emitting elements are also actively conducted. In order for the organic light emitting device to efficiently emit light with low power consumption and high luminance, it is important to efficiently inject carriers (holes and electrons) from the electrode to the functional layer. In general, in order to inject carriers efficiently, it is effective to provide an injection layer for lowering an energy barrier (injection barrier) during injection between each electrode and a functional layer. Among these, as the hole injection layer, an organic low molecular vapor deposition film such as copper phthalocyanine (CuPc), a coating film made of an organic polymer solution such as PEDOT: PSS, an inorganic vapor deposition film such as molybdenum oxide, a sputtered film, etc. Is used. In particular, organic light emitting devices using molybdenum oxide have been reported to improve hole injection efficiency and lifetime (see, for example, Patent Document 3). The hole injection layer is formed on the surface of the anode made of a transparent conductive film such as ITO or IZO, a metal film such as aluminum, or a laminate thereof.

Japanese Patent No. 3369615 Japanese Patent No. 3789991 JP 2005-203339 A

Th. Kugler et al. , Chemical Physics Letters 310, 391 (1999). Jingze Li et al. , Synthetic Metals 151, 141 (2005). Hiromi Watanabe et al., Proceedings of the 7th Regular Meeting of Organic EL Discussion Meeting 17 (2008). Hyunbok Lee et al. Applied Physics Letters 93, 043308 (2008). Yasuo Nakayama et al., Proceedings of the 7th Regular Meeting of Organic EL Discussion Group 5 (2008). Kaname Kanai et al. Organic Electronics 11, 188 (2010). I. N. Yakovkin et al. , Surface Science 601, 1481 (2007).

However, the conventional organic light emitting device has the following problems.
The planarizing film is generally composed of an organic material such as an acrylic resin or a polyimide resin, but has a characteristic of absorbing moisture. Moisture is adsorbed to the planarizing film in atmospheric moisture, etching, rinsing or the like in the manufacturing process. When the adsorbed moisture moves to the functional layer side, the functional layer is deteriorated, causing problems such as peripheral light-emitting shrink, reduction in light-emitting efficiency, and life deterioration. Further, since the planarizing film expands due to moisture adsorption, the peeling of the anode disposed on the planarizing film occurs with the expansion. Due to such problems, there is a problem that normal light emission driving of the organic light emitting device cannot be performed.

  The present invention has been made in view of the above problems, and an object thereof is to provide an organic light-emitting device that can be expected to have high reliability and long life by effectively preventing moisture adsorption on a planarizing film. And

  In order to solve the above-described problems, an organic light-emitting device according to one embodiment of the present invention includes a driving element having a current extraction terminal and an opening at a position corresponding to the current extraction terminal. Covering the surface of the insulating film including the provided insulating film and the inner peripheral surface of the opening of the insulating film, and electrically connected to the current extraction terminal of the drive element through the opening A conductive coating film, a pixel electrode provided on the opposite side of the coating film from the insulating film, and electrically connected to the coating film; and the pixel electrode And a light emitting layer including an organic material having a light emitting property, and a counter electrode provided on the side opposite to the pixel electrode with respect to the light emitting layer.

  In the organic light-emitting device of one embodiment of the present invention, the insulating film is covered with respect to the insulating film that covers the driving element and has an opening corresponding to the current extraction terminal. A conductive coating film is provided so as to be electrically connected.

  Accordingly, the insulating film receives a shielding effect by the coating film, and moisture adsorption from the outside to the insulating film is suppressed, and moisture movement from the insulating film to the light emitting layer side can be prevented. As a result, it is possible to prevent deterioration of the functional layer and deterioration of the light emission characteristics due to moisture adhesion, maintain good light emission characteristics, and expect a longer life.

In addition, since the expansion of the insulating film is suppressed by preventing the insulating film from absorbing water, it is possible to simultaneously avoid film peeling of the pixel electrode formed on the insulating film.
Note that the “pixel electrode” referred to in one embodiment of the present invention may be either an anode or a cathode.

3 is a schematic cross-sectional view showing a configuration of each organic light-emitting device according to Embodiments 1 and 2. FIG. FIG. 5 is a schematic cross-sectional view showing a configuration of each organic light emitting device according to Embodiments 3 and 4. 2 is a wiring diagram of a TFT substrate in the organic light emitting device according to Embodiment 1. FIG. FIG. 5 is a process diagram illustrating a method for manufacturing the organic light-emitting device according to Embodiment 1. FIG. 5 is a process diagram illustrating a method for manufacturing the organic light-emitting device according to Embodiment 1. FIG. 5 is a process diagram illustrating a method for manufacturing an organic light emitting device according to Embodiments 2, 3, and 4. It is typical sectional drawing which shows the structure of a hole only element. It is a graph which shows the dependence of the drive voltage of a hole only element with respect to the film-forming conditions of a hole injection layer. It is a device characteristic figure which shows the relationship curve of the applied voltage and current density of a Hall only element. It is a device characteristic figure which shows the relationship curve of the applied voltage and current density of an organic light emitting element. It is a device characteristic figure which shows the relationship curve of the current density of an organic light emitting element, and emitted light intensity. It is typical sectional drawing which shows the structure of the sample for photoelectron spectroscopy measurements. It is a figure which shows the UPS spectrum of a tungsten oxide layer. It is a figure which shows the UPS spectrum of a tungsten oxide layer. It is a figure which shows the differential curve of the UPS spectrum of FIG. It is a figure which shows the UPS spectrum of the tungsten oxide layer exposed to air | atmosphere. It is a figure which shows collectively the UPS spectrum and XPS spectrum of the tungsten oxide layer of this invention. It is an interface energy diagram of the tungsten oxide layer and α-NPD layer of the present invention. It is a figure for demonstrating the effect of the injection site of a hole injection layer and a functional layer. 4 is an interfacial energy diagram between a tungsten oxide layer and an α-NPD layer under film formation conditions C. It is an interfacial energy diagram of an IZO anode cleaned with pure water and a functional layer. It is an interface energy diagram of the IZO anode and functional layer which were dry-etched after pure water cleaning. It is an interfacial energy diagram of an ITO anode cleaned by IPA and a functional layer. It is an interfacial energy diagram of an ITO anode treated with oxygen plasma after IPA cleaning and a functional layer. It is an interface energy diagram of an IZO anode cleaned with pure water and a hole injection layer of the present invention. It is an interface energy diagram of the IZO anode which carried out the dry etching process after pure water washing | cleaning, and the hole injection layer of this invention. It is an interfacial energy diagram of an ITO anode cleaned with IPA and a hole injection layer of the present invention. It is an interfacial energy diagram of the ITO anode treated with oxygen plasma after IPA cleaning and the hole injection layer of the present invention. It is an interface energy diagram of an aluminum anode and the hole injection layer of this invention. It is typical sectional drawing which shows the structure of the sample used for a performance confirmation test. It is a graph which shows the connection (contact) resistance value of a TFT electrically conductive film and an anode about an Example and a comparative example. It is the photograph which shows the mode of the metal oxide film which generate | occur | produced on the anode surface facing a ITO layer conventionally, and sectional drawing corresponding to this. It is the photograph which shows the structure which has arrange | positioned the tungsten oxide film (WOx) between the ITO layer and the anode in this invention, and sectional drawing corresponding to this. It is typical sectional drawing which shows the structure of the conventional organic light-emitting device 1X. 6 is a schematic cross-sectional view showing a configuration of an organic light emitting device according to Embodiment 5. FIG. It is typical sectional drawing which shows the structure of a hole only element. It is a device characteristic figure which shows the relationship curve of the applied voltage and current density of a Hall only element. It is a device characteristic figure which shows the relationship curve of the applied voltage and current density of an organic light emitting element. _{W5p 3/2,} W4f 5/2 by HXPS measurement of the tungsten oxide layer _is a diagram showing a spectrum attributed to _{W4f 7/2.} FIG. 40 is a diagram (a) showing a peak fitting analysis result related to the sample α shown in FIG. 39 and a diagram (b) showing a peak fitting analysis result related to the sample ε. It is a figure which shows the UPS spectrum of a tungsten oxide layer. It is a figure for demonstrating the structure of a tungsten trioxide crystal | crystallization. It is a cross-sectional TEM photograph of a tungsten oxide layer. It is a figure which shows the two-dimensional Fourier-transform image of the TEM photograph shown in FIG. FIG. 45 is a diagram illustrating a process of creating a brightness change plot from the two-dimensional Fourier transform image shown in FIG. 44. It is a figure which shows the two-dimensional Fourier-transform image and luminance change plot in sample (alpha), (beta), and (gamma). It is a figure which shows the two-dimensional Fourier-transform image and brightness | luminance change plot in sample (delta) and (epsilon). Luminance change plots ((a) and (b)) of samples α and ε, enlarged views ((a1) and (b1)) near the peak appearing closest to the center point in each luminance change plot, and (a1) It is a figure ((a2), (b2)) which shows the 1st derivative of each brightness | luminance change plot of (b1). A diagram (a) schematically showing hole conduction when the tungsten oxide layer is mainly formed with a nanocrystal structure, and a diagram (b) schematically showing hole conduction when mainly formed with an amorphous structure. It is. It is a top view which shows a part of organic electroluminescence display panel which concerns on a modification.

[Outline of One Embodiment of the Present Invention]
An organic light-emitting device according to an aspect of the present invention includes a driving element having a current extraction terminal, an insulating film that covers the driving element and has an opening provided at a position corresponding to the current extraction terminal, The insulating film covers the surface of the insulating film including the inner peripheral surface of the opening, and is electrically connected to the current extraction terminal of the driving element through the opening. A coating film, a pixel electrode provided on the opposite side of the coating film from the insulating film, electrically connected to the coating film, and provided corresponding to the pixel electrode; A light emitting layer containing an organic material having a property and a counter electrode provided on the opposite side of the pixel electrode with respect to the light emitting layer are provided.

  As another aspect of the present invention, the coating film has an occupied level in a binding energy region that is 1.8 to 3.6 eV lower than the lowest binding energy in the valence band in its electronic state, In addition, a tungsten oxide film containing tungsten oxide having a thickness of 2 nm or more can be employed.

  As another aspect of the present invention, the difference between the binding energy of the occupied level and the Fermi level of the pixel electrode is within ± 0.3 eV at the interface between the tungsten oxide film and the pixel electrode. You can also.

  Further, as another aspect of the present invention, a conductive film is provided in contact with the current extraction terminal of the drive element, and the tungsten oxide film is provided in contact with the conductive film, The interface between the tungsten oxide film and the conductive film may be configured such that the difference between the binding energy of the occupied level and the Fermi level of the conductive film is within ± 0.3 eV.

  As another aspect of the present invention, the tungsten oxide film is provided in contact with the current extraction terminal of the drive element, and at the interface between the tungsten oxide film and the current extraction terminal, A difference between the occupation level binding energy and the Fermi level of the current extraction terminal may be within ± 0.3 eV.

  As another aspect of the present invention, the tungsten oxide film has a thickness of 1.8 to 3.3 lower than the lowest binding energy in the valence band in the USP spectrum representing the relationship between the binding energy and the photoelectron intensity or its normalized intensity. A configuration having a raised shape in a binding energy region as low as 6 eV may be employed.

  As another aspect of the present invention, the tungsten oxide film has a thickness 1.8 to 3.3 lower than the lowest binding energy in the valence band in the XPS spectrum representing the relationship between the binding energy and the photoelectron intensity or its normalized intensity. A configuration having a raised shape in a binding energy region as low as 6 eV may be employed.

  As another aspect of the present invention, the tungsten oxide film has a UPS spectrum that represents the relationship between the binding energy and the photoelectron intensity or its normalized intensity, and is 2.0% lower than the lowest binding energy in the valence band. A configuration having a shape expressed as a function different from an exponential function over a binding energy region of ~ 3.2 eV may be employed.

  As another aspect of the present invention, the tungsten atoms constituting the tungsten oxide film have a hexavalent state that is the maximum valence that the tungsten atoms can take and a pentavalent that is lower than the maximum valence. In addition, the tungsten oxide film may include a tungsten oxide crystal having a particle size on the order of nanometers.

As another aspect of the present invention, W ⁵⁺ / W ⁶⁺ which is a value obtained by dividing the number of pentavalent tungsten atoms by the number of hexavalent tungsten atoms is 3.2% or more. You can also

As another aspect of the present invention, the W ⁵⁺ / W ⁶⁺ may be 3.2% or more and 7.4% or less.
As another aspect of the present invention, in the hard X-ray photoelectron spectroscopy spectrum of the tungsten oxide film, a second binding energy region lower than the first component corresponding to the 4f _7/2 level of the hexavalent tungsten atom is used. It can also be set as the structure in which a component exists.

  As another aspect of the present invention, the second component may be present in a binding energy region lower by 0.3 to 1.8 eV than the peak top binding energy of the first component.

As another aspect of the present invention, the area intensity of the second component may be 3.2 to 7.4% with respect to the area intensity of the first component.
As another aspect of the present invention, due to the presence of tungsten atoms lower than the maximum valence, in the electronic state of the tungsten oxide film, the bond is 1.8 to 3.6 eV lower than the lowest binding energy in the valence band. A configuration having an occupied level in the energy region can also be adopted.

As another aspect of the present invention, the tungsten oxide film may include a plurality of tungsten oxide crystals having a particle size of 5 to 10 nm.
As another aspect of the present invention, a linear structure regularly arranged at intervals of 1.85 to 5.55 mm may appear in the lattice image of the tungsten oxide film observed with a transmission electron microscope. it can.

  As another aspect of the present invention, a concentric bright portion centered on the center point of the two-dimensional Fourier transform image may appear in the two-dimensional Fourier transform image of the lattice image.

  As another aspect of the present invention, in the plot representing the relationship between the distance from the center point and the normalized luminance that is a numerical value obtained by standardizing the luminance of the two-dimensional Fourier transform image at the distance, the normalized A configuration in which one or more luminance peaks appear in addition to the center point may be employed.

  As another aspect of the present invention, the distance corresponding to the peak top position of the normalized luminance that appears closest from the center point in the plot, and the rising position of the peak of the normalized luminance The peak width may be smaller than 22 when the difference from the distance is a peak width and the distance corresponding to the position of the peak top is 100.

As another aspect of the present invention, the light emitting layer may include an amine material.
As another aspect of the present invention, the occupied level in the tungsten oxide film is present in a binding energy region that is 2.0 to 3.2 eV lower than the lowest binding energy in the valence band. You can also

  In another aspect of the present invention, a conductive film is provided in contact with the current extraction terminal of the driving element, and the coating film is provided in contact with the conductive film. It can also be.

As another aspect of the present invention, the coating film may be provided in contact with the current extraction terminal of the drive element.
As another aspect of the present invention, the coating film may be a metal oxide film.

  As another aspect of the present invention, the insulating film covers the driving element, and includes a first insulating film provided with a first opening at a position corresponding to the current extraction terminal; And a second insulating film that covers the first insulating film and has a second opening that communicates with the first opening at a position corresponding to the first opening. You can also.

As another aspect of the present invention, the first insulating film can be made of an inorganic material, and the second insulating film can be made of an organic material.
As another aspect of the present invention, a conductive film is provided in contact with the current extraction terminal of the drive element in the first opening, and the conductive film is provided in the second opening. On the other hand, it can also be set as the structure by which the said coating film is provided in contact.

As another aspect of the present invention, the conductive film may be a metal oxide film.
As another aspect of the present invention, the coating film may be provided in contact with the current extraction terminal of the drive element in the first opening.

  As another aspect of the present invention, the apparatus further includes a substrate, the drive element is formed on the substrate, the insulating film is formed on the substrate so as to cover the drive element, The covering film is formed on the substrate so as to cover the insulating film and to be in contact with the substrate by spreading outside the region where the insulating film is formed. You can also.

  Further, as a method for manufacturing an organic light emitting device which is one embodiment of the present invention, a first step of forming a driving element having a current extraction terminal, an insulating film covering the driving element is formed, and the insulating film A second step of forming an opening at a position corresponding to a current extraction terminal; and covering a surface of the insulating film including an inner peripheral surface of the opening of the insulating film, and through the opening, A third step of forming a conductive coating film electrically connected to the current extraction terminal, and the coating film on the opposite side of the coating film to the coating film; A fourth step of forming electrically connected pixel electrodes, a fifth step of forming a light emitting layer containing a light emitting organic material corresponding to the pixel electrodes, and the light emitting layer with respect to the light emitting layer. A sixth step of forming a counter electrode on the side opposite to the pixel electrode It was intended to include.

  Further, as another aspect of the present invention, in the second step, a conductive film is formed in contact with the current extraction terminal of the drive element, and in the third step, the conductive film is A coating film can also be provided in contact.

As another aspect of the present invention, the conductive film can be a metal oxide film.
As another aspect of the present invention, in the third step, the coating film can be provided in contact with the current extraction terminal of the drive element.

As another aspect of the present invention, the coating film may be a metal oxide film.
As another aspect of the present invention, in the second step, a first insulating film that covers the driving element is formed, and the first insulating film has a first position at a position corresponding to the current extraction terminal. A first sub-process for forming the opening, and a second insulating film that covers the first insulating film, and communicates with the first opening at a position corresponding to the first opening. And a second sub-process for forming the second opening.

As another aspect of the present invention, the first insulating film may be made of an inorganic material, and the second insulating film may be made of an organic material.
As another aspect of the present invention, in the second step, the current extraction of the drive element is further performed in the first opening between the first sub step and the second sub step. A third sub-step of forming a conductive film in contact with the terminal, wherein in the third step, the coating film may be provided in contact with the conductive film in the second opening. it can.

As another aspect of the present invention, the conductive film may be a metal oxide film.
As another aspect of the present invention, in the third step, the coating film may be provided in contact with the current extraction terminal of the drive element in the first opening. it can.

As another aspect of the present invention, in the third step, the coating film is a tungsten oxide film, and the tungsten oxide film is a gas composed of argon gas and oxygen gas in a chamber of a sputtering apparatus. The total pressure of the gas is more than 2.7 Pa and 7.0 Pa or less, and the ratio of the partial pressure of oxygen gas to the total pressure is 50% or more and 70% or less. in the film formation conditions input power density is 1W / cm ² or more 2.8W / cm ² or less, can be formed to have a film thickness is greater than or equal to 2 nm.
<Embodiment 1>
(Configuration of organic light emitting device 1)
FIG. 1 is a schematic cross-sectional view showing the configuration of the organic light emitting device 1 according to the first embodiment.

  The organic light emitting device 1 is a coating type in which a functional layer is applied by a wet process to form a film, and an anode 2 is formed on the upper surface of a TFT substrate 10 (hereinafter simply referred to as the substrate 10) formed with TFT driving elements. The anode 2 and the cathode in a state where the coating film 20, the hole injection layer 4, and various functional layers (here, the hole transport layer 6A and the light emitting layer 6B) including an organic material having a predetermined function are laminated. 8 is interposed between the electrode pairs.

  Specifically, as shown in FIG. 1, the organic light emitting device 1 has a planarization film 11, a coating film 20, an anode 2, a hole injection layer 4, a hole transport layer 6 </ b> A, light emission, on one side main surface of a substrate 10. The layer 6B and the cathode 8 (barium layer 8A and aluminum layer 8B) are laminated in the same order. A power source DC (not shown) is connected to the anode 2 and the cathode 8 so that power is supplied to the organic light emitting device 1 from the outside.

Note that FIG. 1 shows an apparatus configuration including one organic light emitting element. However, the organic light emitting device 1 according to the first embodiment can be an organic EL display panel in which a plurality of organic light emitting elements are arranged.
(substrate)
The substrate 10 is a portion that becomes a base material of the organic light emitting device 1, and includes, for example, alkali-free glass, soda glass, non-fluorescent glass, phosphate glass, borate glass, quartz, acrylic resin, styrene resin, and polycarbonate resin. , Epoxy resin, polyethylene, polyester, silicon resin, or an insulating material such as alumina.

  FIG. 1 shows only the source electrode 17 (source / drain wiring) that is a current extraction terminal, but a TFT (thin film transistor) (not shown) is provided on the upper surface of the substrate 10 as a drive element of the organic light emitting device 1. ) The element is formed corresponding to the light emitting region.

FIG. 3 is a wiring diagram showing the pixel circuit 130 of the TFT element.
As shown in FIG. 3, the pixel circuit 130 includes a first transistor 140 that operates as a switching element, a second transistor 150 that operates as a driving element, and a capacitor 160 that stores data to be displayed in a corresponding light emitting region. Is done.

  The first transistor 140 includes a gate electrode 141 connected to the gate wiring 121, a source electrode 142 connected to the source wiring 122, and a source electrode 143 connected to the capacitor 60 and the gate electrode 151 of the second transistor 150. And a first semiconductor film (not shown). In driving, when a voltage is applied to the connected gate wiring 121 and source wiring 122, the first transistor 140 stores the voltage value applied to the source wiring 122 in the capacitor 160 as display data.

  The second transistor 150 includes a gate electrode 151 connected to the source electrode 143 of the first transistor 140, a source electrode 152 connected to the power supply wiring 123 and the capacitor 160, and a source electrode 153 connected to the anode 2 ( And the second semiconductor film (not shown). The second transistor 150 supplies a current corresponding to the voltage value held by the capacitor 160 from the power supply wiring 123 to the anode 2 through the source electrode 153 (17). As described above, the organic light emitting device 1 employs an active matrix system in which display control is performed for each light emitting region located at the intersection of the gate wiring 121 and the source wiring 122.

(Source electrode 17)
The source electrode 17 is a current extraction terminal of the drive element, and is made of a metal such as Ag, Cu, Al, Mo, MoW, or an alloy thereof.
(Flattening film)
The planarizing film 11 is made of an insulating resin material such as polyimide resin or acrylic resin, and is provided to cover the surface of the substrate 10 to reduce the step and ensure flatness. In the planarizing film 11, an opening (contact hole) is formed at a position corresponding to the source electrode 17 while avoiding the light emitting region, and the source electrode 17 is exposed to the outside.

(Coating film)
The coating film 20 is made of a tungsten oxide film, which is a conductive film formed with the same configuration, based on the same film formation conditions as those of the hole injection layer 4 to be described later, and covers the entire surface (upper surface portion 11t, In order to cover the side surface portion 11s and the hole inner side surface portion 11h), the upper surface of the substrate 10 is formed so as to expand and come in contact with the outer surface of the planarization film 11 formation region. The film thickness can be adjusted as appropriate, but a film thickness of 2 nm or more is preferable in order to achieve Schottky ohmic connection with at least the anode 2. Moreover, in order to maintain a stable film thickness in the manufacturing process and prevent moisture adsorption to the planarizing film 11, a film thickness of about 30 to 40 nm is preferable.

  By covering the surface of the planarizing film 11 with the upper surface portion 20t, the side surface portion 20s, and the hole inner portion 20h of the coating film 20, moisture adsorption from the outside to the planarizing film 11 is prevented. Further, by interposing the coating film 20 between the source electrode 17 and the anode 2, generation of a metal oxide film on the surface of the anode 2 (particularly the bottom surface portion 2 h) is prevented, and the source electrode 17 and the anode 2 Good continuity is achieved.

  In the case where the organic light emitting device 1 is configured as an organic EL display panel provided with a plurality of organic light emitting elements, the planarizing film 11 is uniformly formed for each organic light emitting element. In this case, the side surface portion 11 s of the planarizing film 11 is formed only in each organic light emitting element located at the peripheral end portion of the substrate 10. In the organic light emitting device formed on the inner surface side of the substrate 10, only the upper surface portion 11t of the planarizing film 11 is formed.

Hereinafter, in order to provide an understanding of the present embodiment and thus the present invention, the conventional configuration and the present invention will be described in comparison.
Conventionally, in an organic light emitting device, an ITO film (indium tin oxide) or an IZO film (indium zircon oxide) is provided so as to cover a current extraction terminal of a drive element, and further, an aluminum film is brought into contact with the ITO film or the IZO film. Alternatively, an anode made of an aluminum alloy may be provided.

  In this configuration, the purpose of providing the ITO film or the IZO film so as to cover the current extraction terminal of the drive element is that the planarization layer is formed by an etching process such as dry etching for forming an opening (contact hole) of the planarization film. It is to prevent direct damage from being applied to the current extraction terminal of the drive element facing downward.

  By the way, according to the above configuration, an aluminum metal oxide film may be formed in the vicinity of the interface with the ITO film or the IZO film in the anode. Since the metal oxide of aluminum generally exhibits insulating properties, the conduction between the current extraction terminal and the anode may deteriorate over time.

  As described above, according to the configuration in which the ITO film or the IZO film is provided in contact with the anode, it is difficult to achieve the purpose of “providing good conduction between the current extraction terminal and the anode” in the present embodiment. It is.

On the other hand, the configuration which is one embodiment of the present invention described above focuses on the matter of “preventing direct damage to the current extraction terminal of the drive element” which is a problem different from the present invention. In addition, since it is considered that the problem to be solved of the present invention has not been sufficiently recognized, the present embodiment and the structure of the present invention are based on the above structure. It is considered difficult to get to.
(anode)
The anode 2 is made of aluminum (Al) or an aluminum alloy (aluminum cobalt lanthanum (ACL) alloy or the like) having a thickness of 50 nm. The configuration of the anode 2 is not limited to this. For example, a transparent conductive film such as ITO and IZO, APC (alloy of silver, palladium, copper), ARA (alloy of silver, rubidium, gold), MoCr (alloy of molybdenum and chromium) ), NiCr (nickel and chromium alloy), etc., or a plurality of these films may be laminated.

  The anode 2 can be configured by laminating a transparent electrode on the reflective anode. In this case, aluminum, silver, or the above alloy using these is used as the reflective anode. The thickness of the reflective anode is preferably 100 nm or more. On the other hand, ITO and IZO can be configured as transparent electrodes. The film thickness of the transparent electrode is preferably about 50 nm.

The anode 2 is formed on the upper surface of the planarization film 11 corresponding to the light emitting region while covering the inner peripheral surface of the contact hole formed in the planarization film 11. The bottom surface portion 2 h of the anode 2 inside the contact hole is electrically connected to the source electrode 17 through the hole inner portion 20 h of the coating film 20.
(Hole injection layer)
The hole injection layer 4 is configured as a layer having a thickness of 2 nm or more (here, 30 nm as an example) using tungsten oxide (in the composition formula WOx, x is a real number in a range of 2 <x <3). . If the film thickness is less than 2 nm, it is difficult to form a uniform film, and it is difficult to form a Schottky ohmic connection (contact) between the anode 2 and the hole injection layer 4 described below. Since the Schottky ohmic connection is stably formed when the film thickness of tungsten oxide is 2 nm or more, if the hole injection layer 4 is formed with a film thickness larger than this, stable holes from the anode 2 to the hole injection layer 4 are formed. Injection efficiency can be expected.

The hole injection layer 4 is preferably composed only of tungsten oxide, but may contain a trace amount of impurities as long as it can be mixed at a normal level.
Here, the hole injection layer 4 is formed under specific film formation conditions. Thereby, in the electronic state, an occupied level exists in a binding energy region that is 1.8 to 3.6 eV lower than the upper end of the valence band, that is, the lowest binding energy in the valence band. This occupied level is the highest occupied level of the hole injection layer 4, and its binding energy range is closest to the Fermi level (Fermi surface) of the hole injection layer 4. Therefore, hereinafter, this occupied level is referred to as “occupied level near the Fermi surface”.

  The existence of the occupied level near the Fermi surface allows so-called interface level connection at the stacked interface between the hole injection layer 4 and the functional layer (here, the hole transport layer 6A), and the highest coverage of the hole transport layer 6A. The binding energy of the occupied orbit becomes substantially equal to the binding energy of the occupied level in the vicinity of the Fermi surface of the hole injection layer 4.

  Here, “substantially equal” and “interface state connection made” mean that the lowest binding energy at the occupied level near the Fermi surface at the interface between the hole injection layer 4 and the hole transport layer 6A. And the lowest binding energy in the highest occupied orbital means that the difference is within a range of ± 0.3 eV.

Furthermore, the “interface” here refers to a region including the surface of the hole injection layer 4 and the hole transport layer 6A at a distance within 0.3 nm from the surface.
Further, the occupied level in the vicinity of the Fermi surface is preferably present in the whole hole injection layer 4, but may be present at least at the interface with the hole transport layer 6A. Note that such an occupied level in the vicinity of the Fermi surface is not possessed by all tungsten oxides. In particular, at the inside of the hole injection layer and at the interface with the hole transport layer 6A, a predetermined composition described later is provided. It is a unique level that can be formed for the first time depending on the film conditions.

Furthermore, the hole injection layer 4 is characterized by forming a so-called Schottky ohmic connection at the interface with the anode 2.
The “Schottky ohmic connection” referred to here is a difference between the Fermi level of the anode 2 and the lowest binding energy at the occupied level in the vicinity of the Fermi surface of the hole injection layer 4 described above from the surface of the anode 2. A connection that is small within ± 0.3 eV at a position where the distance to the hole injection layer 4 side is 2 nm. The “interface” here refers to a region including the surface of the anode 2 and a Schottky barrier formed on the hole injection layer 4 side from the surface.

For the same reason as the hole injection layer 4 described above, interface state connection (Schottky ohmic connection) is also formed between the coating film 20 and the source electrode 17 and between the coating film and the anode 2. .
(bank)
On the surface of the hole injection layer 4, a bank 5 made of an insulating organic material (for example, an acrylic resin, a polyimide resin, a novolac type phenol resin, or the like) has a stripe structure or a cross beam structure having a certain trapezoidal cross section. Formed. An inorganic material may be used as the bank material.

The bank 5 is not an essential component of the present invention, and may be omitted when only one organic light emitting element is formed in the organic light emitting device 1.
(Functional layer)
On the surface of the hole injection layer 4 partitioned in each bank 5, a functional layer including a hole transport layer 6A and a light emitting layer 6B corresponding to one of RGB colors is formed. When the organic light emitting device 1 is applied to an organic EL display panel, a series of three elements 1 corresponding to RGB colors are set as one unit (pixel, pixel), and are arranged in parallel on the substrate 10 over a plurality of units. .
(Hall transport layer)
The hole transport layer 6A has a function of transporting holes injected from the hole injection layer 4 to the light emitting layer 6B. As the hole transport layer 6A, a hole transporting organic material is used. The hole transporting organic material is an organic substance having a property of transmitting generated holes by a charge transfer reaction between molecules. This is sometimes called a p-type organic semiconductor.

  As the material for the hole transport layer 6A, either a high molecular material or a low molecular material may be used. When forming the upper light emitting layer, the material of the hole transport layer 6A preferably contains a crosslinking agent so as not to be mixed with the material of the light emitting layer. Examples of the material for the hole transport layer 6A include a copolymer containing a fluorene moiety and a triarylamine moiety, and a low molecular weight triarylamine derivative. As an example of the crosslinking agent, dipentaerythritol hexaacrylate or the like can be used. In this case, it is preferable to be formed of poly (3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT: PSS) or a derivative thereof (such as a copolymer).

A buffer layer can be separately provided between the hole transport layer 6A and the light emitting layer 6B. The buffer layer is TFB (poly (9,9-di-n-octylfluorene-alt- (1,4-phenylene-((4-sec-butylphenyl) imino) -1), which is an amine organic polymer having a thickness of 20 nm. , 4-phenylene)).
(Light emitting layer)
The light emitting layer 6B is made of F8BT (poly (9, 9-di-n-octylfluorene-alt-benzothiadiazole)) which is an organic polymer having a thickness of 70 nm. However, the light emitting layer 6B is not limited to the structure made of this material, and can be configured to include an organic material having a known light emitting property. For example, the oxinoid compounds, perylene compounds, coumarin compounds, azacoumarin compounds, oxazole compounds, oxadiazole compounds, perinone compounds, pyrrolopyrrole compounds, naphthalene compounds, anthracene compounds, fluorene compounds, fluoranthene compounds described in JP-A-5-163488, Tetracene compound, pyrene compound, coronene compound, quinolone compound and azaquinolone compound, pyrazoline derivative and pyrazolone derivative, rhodamine compound, chrysene compound, phenanthrene compound, cyclopentadiene compound, stilbene compound, diphenylquinone compound, styryl compound, butadiene compound, dicyanomethylenepyran Compounds, dicyanomethylene thiopyran compounds, fluorescein compounds, pyrylium compounds, An apyrylium compound, a serenapyrylium compound, a telluropyrylium compound, an aromatic aldadiene compound, an oligophenylene compound, a thioxanthene compound, an anthracene compound, a cyanine compound, an acridine compound, a metal complex of an 8-hydroxyquinoline compound, a metal complex of a 2-bipyridine compound, A fluorescent substance such as a complex of a Schiff salt and a group III metal, an oxine metal complex, or a rare earth complex can be given.

The functional layer in the present invention includes a hole transport layer that transports holes, a light-emitting layer that emits light by recombination of injected holes and electrons, a buffer layer that is used for optical property adjustment or electronic block applications, etc. Or a combination of two or more layers, or all layers. Although the present invention is directed to the hole injection layer, the organic light emitting device includes layers that perform the required functions, such as the hole transport layer and the light emitting layer described above, in addition to the hole injection layer. The functional layer refers to a layer necessary for the organic light emitting device other than the hole injection layer which is a subject of the present invention.
(cathode)
The cathode 8 is an electrode provided on the side opposite to the anode 2 with respect to the light emitting layer 6B, and is configured as a laminate of a barium layer having a thickness of 5 nm and an aluminum layer having a thickness of 100 nm, or any one of these. Is done.

An electron transport layer 7 is disposed between the light emitting layer 6B and the cathode 8. The electron transport layer 7 can be formed of a barium layer. Therefore, when the cathode 8 is formed by sequentially laminating a barium layer and an aluminum layer, the barium layer may be regarded as an electron transport layer (or electron injection layer).
(Operation and effect of organic light emitting device)
In the organic light emitting device 1 having the above configuration, a coating film 20 made of a tungsten oxide film formed under predetermined film forming conditions so as to have the electronic state is formed at least between the source electrode 17 and the anode 2. Yes.

  When the anode 2 is formed using aluminum or an aluminum alloy by forming the coating film 20 made of this tungsten oxide film, the aluminum component is an oxygen component in the atmosphere, an oxygen component derived from the planarizing film 11, or the like. The reaction prevents the formation of a metal oxide film on the surface of the anode 2. Further, as will be described later, since the tungsten oxide film can form a good Schottky ohmic connection with at least the anode 2, holes can be injected well into the light emitting layer 6 B side, which can contribute to exhibiting excellent luminous efficiency. .

  The reason why it is difficult to form a metal oxide film on the surface of the anode 2 is not clear at this stage. However, since the tungsten oxide film has an oxygen defect structure, oxygen atoms existing in and around the anode 2 This is considered to be because the minutely formed oxide is taken into the tungsten oxide film and diffused and removed. Therefore, even if a minute oxide is formed, it does not become a film shape, but remains in a minute state, and a decrease in conductivity can be prevented. According to this principle, even when the anode 2 is made of a material other than aluminum or an aluminum alloy, the problem associated with the generation of the metal oxide film can be improved by the same action.

  Here, in FIGS. 32A and 32B, a TEM photograph showing a configuration in which an aluminum oxide layer is formed between a conventional relay electrode made of ITO and an anode made of an aluminum alloy, The cross-sectional view which illustrated the structure is shown. A thin aluminum oxide layer is formed on the lower surface of the anode facing the relay electrode, leading to a decrease in conduction between the anode and the relay electrode.

  On the other hand, in FIGS. 33 (a) and 33 (b), a coating film (WOx) made of a tungsten oxide film of the present invention is formed between a relay electrode made of ITO and an anode made of an aluminum alloy. And a cross-sectional view illustrating the structure of the photograph.

By forming the coating film (WOx), it can be confirmed that the generation of the aluminum oxide layer on the lower surface of the anode is effectively suppressed.
In the organic light emitting device 1, the entire surface of the planarizing film 11 (upper surface portion 11 t, side surface portion 11 s, and hole inner side surface portion 11 h) is covered with the coating film 20, so that moisture from the outside to the planarizing film 11 can be obtained. Adsorption is suppressed. As a result, moisture movement from the planarizing film 11 to the light emitting layer 6B side is suppressed, the light emitting layer 6B is altered, and the occurrence of reduction of the light emitting region (so-called light emitting shrink) can be prevented. As a result, good light emission characteristics can be maintained and a longer life can be expected. Furthermore, since the expansion of the planarizing film 11 due to water absorption can be suppressed, the problem that the anode 2 peels off due to the expansion can also be avoided. The “moisture” referred to here does not matter in any form of liquid or gas.

  Furthermore, as another effect of the organic light emitting device 1, in the hole injection layer 4 formed by forming the tungsten oxide film, the occupied level near the Fermi surface exists, A so-called interface state connection is made between the highest occupied orbit of the hole transport layer 6A, and the hole injection barrier between the hole injection layer 4 and the hole transport layer 6A is extremely small.

  Further, in the organic light emitting device 1, a good Schottky ohmic connection is formed between the anode 2 and the hole injection layer 4, and the hole injection barrier is kept small between the anode 2 and the hole injection layer 4.

  Thereby, in the organic light emitting device 1, when a voltage is applied to the organic light emitting device 1 during driving, holes are transferred from the Fermi level of the anode 2 to the occupied level near the Fermi surface of the hole injection layer 4 and from the occupied level near the Fermi surface. Holes are injected relatively smoothly into the highest occupied track of the transport layer 6A at a low voltage, and high hole injection efficiency is exhibited. And in a light emitting layer 6B, a favorable light emission characteristic will be exhibited because a hole recombines with an electron. Specifically, the difference between the Fermi level of the anode 2 and the lowest binding energy at the occupied level near the Fermi surface of the hole injection layer 4, and the lowest binding energy at the occupied level of the hole injection layer 4, The difference from the lowest binding energy in the highest occupied orbit of the hole transport layer 6A is suppressed within ± 0.3 eV, and the hole injection efficiency is greatly enhanced.

  As in the experiment described later, the Schottky ohmic connection formed between the anode 2 and the hole injection layer 4 is greatly influenced by the degree of the surface state of the anode 2 (including characteristics such as work function). However, it has high stability. For this reason, it is not necessary to strictly control the surface state of the anode 2 in manufacturing the organic light emitting device 1, and the element 1 having a relatively high cost and high hole injection efficiency, or a large-sized organic EL display formed by a large number of them. Panels can be manufactured with good yield.

Here, the “surface state of the anode” refers to the surface state of the anode immediately before the formation of the hole injection layer in the standard manufacturing process of the organic light emitting device or the organic EL display panel.
Here, the structure itself using tungsten oxide as the hole injection layer has been reported in the past (see Non-Patent Document 2). However, the film thickness of the optimum hole injection layer obtained in this report is about 0.5 nm, and the film thickness dependence of the element characteristics is large, and the practicality of mass-producing large organic EL display panels has been shown. Absent. Further, it is not shown that an occupied level near the Fermi surface is positively formed in the hole injection layer. The present invention provides a hole injection layer made of tungsten oxide that is chemically stable and can withstand the mass production process of a large organic EL display panel, and has an occupied level in the vicinity of a predetermined Fermi surface. This is significantly different from the prior art in that injection efficiency is obtained and low voltage driving of the organic light emitting device is realized.

Hereinafter, other embodiments of the present invention will be described focusing on differences from the first embodiment.
<Other embodiments>
FIG. 1B is a schematic cross-sectional view of the organic light emitting device 1A according to the second embodiment. In this configuration example, a first insulating film (insulating film 18) is formed on the upper surface of the TFT substrate 10, and a second insulating film (planarizing film 11) covering the insulating film 18 is formed thereon. ing. The insulating film 18 is composed of an inorganic film such as SiN or an organic SOG film. The insulating film 18 has a contact hole (first opening), and the contact hole and the contact hole (second opening) of the planarization film 11 are provided in communication with each other in the thickness direction.

  Next, FIG. 2A is a schematic cross-sectional view of an organic light-emitting device 1B according to Embodiment 3. In this configuration example, a relay electrode (top metal film) 19 made of a metal oxide such as ITO or IZO is formed on the surface of the source electrode 17. The relay electrode 19 is disposed for the purpose of protecting the surface of the source electrode 17.

  In this case, conventionally, when the anode 2 made of aluminum or an aluminum alloy is in direct contact with the relay electrode 19, the oxygen component in the relay electrode 19 reacts with the aluminum component in the anode 2. There is a risk of generating a film. In the present third embodiment, the coating film 20 is interposed between the relay electrode 19 and the anode 2 to prevent the metal oxide film from being generated on the anode 2 and to prevent the metal oxide film on the relay electrode 19 from being generated. Occurrence can also be prevented. In the organic light emitting device 1B, the coating film 20 forms a Schottky ohmic connection to both the anode 2 and the relay electrode 20, and can exhibit excellent electrical connectivity.

2B is a schematic cross-sectional view showing the organic light emitting device 1C according to the fourth embodiment. This configuration is a combination of the second and third embodiments, and includes both the insulating film 18 and the relay electrode 19. The covering film 20 is provided in contact with the source electrode 17 through the second opening (contact hole) of the insulating film 18. As a result, the effects of Embodiments 2 and 3 can be exhibited synergistically.
<Method for manufacturing organic light-emitting device>
Next, an overall manufacturing method of the organic light emitting device 1 is illustrated. 4 and 5 are diagrams illustrating the manufacturing process of the organic light emitting device 1.
(Method for manufacturing organic light emitting device)
First, a substrate 10 on which a TFT drive element is formed is prepared (FIG. 4A). In the figure, only the source electrode 17 is shown as the TFT drive element.

  When manufacturing the apparatus 1A of the second embodiment, as shown in FIG. 6A, a material such as SiN is used on the substrate surface other than the upper surface of the source electrode 17, and a vacuum evaporation method, a CVD method, a sputtering method, or the like is used. The insulating film 18 is formed by the method described above. When an organic material is used, the insulating film 18 can be formed by coating.

  When manufacturing the device 1B of the third embodiment, as shown in FIG. 6B, a film is formed on the source electrode 17 by using a material such as ITO or IZO by a method such as sputtering, and relayed. The electrode 19 is formed.

  When manufacturing the device 1C of the fourth embodiment, the insulating film 18 and the relay electrode 19 can be formed by sequentially performing the steps of FIGS. 6A and 6B (FIG. 6). (C)).

  Next, an organic material film such as an acrylic resin or a polyimide resin is applied and formed on the upper surface of the substrate 10. Thereafter, based on a method such as a photolithography method, the arrangement position of the source electrode 17 is opened as a contact hole. Thereby, the planarizing film 11 is formed (FIG. 4B).

  Next, a coating film 20 is formed using a method such as reactive sputtering so as to cover the upper surface of the source electrode 17 and the entire surface of the planarization film 11. In particular, when the present invention is applied to a large-sized organic EL display panel that requires film formation in a large area, if the film is formed by vapor deposition or the like, the film thickness of the coating film 20 may be uneven. If the film is formed by reactive sputtering, it is easy to avoid such film formation unevenness.

  Specifically, the target is metallic tungsten, and reactive sputtering is performed. Argon gas as a sputtering gas and oxygen gas as a reactive gas are introduced into the chamber. In this state, argon is ionized by a high voltage and collides with the target. At this time, metallic tungsten released by the sputtering phenomenon reacts with oxygen gas to form a tungsten oxide film, which is uniformly formed on the substrate 10 (FIG. 4C).

As described later, the tungsten oxide film is formed under a gas pressure (total pressure) of more than 2.7 Pa and not more than 7.0 Pa, and a ratio of the oxygen gas partial pressure to the total pressure is 50% or more and 70% or less. a is, it is preferable to further charge power per target unit area (input power density) is set to be 1W / cm ² or more 2.8W / cm ² or less. By passing through this process, the coating film 20 having an occupied level in a binding energy region 1.8 to 3.6 eV lower than the lowest binding energy in the valence band is formed at least on the surface layer.

  In order to prevent the generation of the metal oxide film of the anode 2 and to achieve a good electrical connection between the source electrode 17 (or the relay electrode 19) and the anode 2, the inner side of at least the inside of the contact hole. It is necessary to provide the coating film 20 (hole inner portion 20h) at a position corresponding to the surface portion 11h, and to electrically connect the bottom surface portion 1h of the anode 2 at the hole inner portion 20h.

  On the other hand, in order to prevent moisture adsorption on the planarizing film 11, the entire surface of the planarizing film 11 is covered with the coating film 20. In order to ensure this effect, in addition to the upper surface portion 11t of the planarizing film 11, the covering portion 20 is provided so as to cover the side surface portion 11s and the hole side surface portion 11h. Thus, if the coating film 20 is provided widely, it is possible to effectively block moisture adsorption to the planarizing film 11 in the wet etching or water washing steps in the manufacturing process. In addition, it is possible to expect the effect of preventing the generation of the metal oxide film on the surface of the anode 2 and ensuring the electrical connection between the source electrode 17 (or the relay electrode 19) and the electrical connection of the anode 2.

  Next, based on a method such as reactive sputtering, an anode material film 2X made of aluminum or aluminum alloy having a thickness of 50 nm is uniformly formed on the planarizing film 11 and the upper surface of the source electrode 17 (FIG. 4). (D)).

  Next, a resist R is formed on the anode material film 2X, and the anode 2 is patterned by a known photolithography method (FIGS. 4E and 4F). This patterning can be performed by wet etching using a mixed solution of phosphoric acid and acetic acid as an etchant.

  Next, the hole injection layer 4 made of a predetermined tungsten oxide film is formed so as to cover the entire surface of the anode 2 by the same method as the method of forming the coating film 20 based on a method such as reactive sputtering (FIG. 5). (A)). Thereby, the hole injection layer 4 having the same characteristics as the coating film 20 is obtained. By this step, it is possible to effectively prevent the anode 2 from being encapsulated by the hole injection layer 4 and the coating film 20 and forming a metal oxide film on the surface of the anode 2.

  Next, for example, a bank material (resin material film) containing a photosensitive resin material, preferably a fluorine-based material, is applied on the hole injection layer 4 and prebaked to form a bank material film. Thereafter, a photomask having a predetermined-shaped opening (a bank pattern to be formed) is overlaid. Then, based on a known photolithography method, the bank material film is partially exposed by UV irradiation from above the photomask, and the uncured excess bank material 5 is washed out with a developer. Finally, the bank 5 having a predetermined shape is completed by washing with pure water (FIG. 5B).

  In addition, also when using an inorganic material for bank material, it can apply | coat and provide similarly to the above. After the application, patterning is performed based on a photolithography method, and an unnecessary bank material film can be removed by etching using a predetermined etching solution (tetramethylammonium hydroxide (TMAH) solution or the like).

  Subsequently, a composition ink containing an amine-based organic molecular material is dropped onto the surface of the hole injection layer 4 corresponding to the light emitting region exposed between the adjacent banks 5 by a wet process such as an inkjet method or a gravure printing method. The solvent is removed by volatilization. Thereby, the hole transport layer 6A is formed (FIG. 5C).

  Next, a composition ink containing an organic light emitting material is dropped on the surface of the hole transport layer 6A by the same wet process as described above, and the solvent is volatilized and removed. Thereby, the light emitting layer 6B is formed (FIG. 5D).

  The formation method of the hole transport layer 6A and the light emitting layer 6B is not limited to these methods, and methods other than the inkjet method and the gravure printing method, such as a dispenser method, a nozzle coating method, a spin coating method, intaglio printing, letterpress printing, etc. The ink may be dropped and applied by a known method.

  Next, a film is formed on the surface of the light emitting layer 6B and the exposed hole injection layer 4 and the surface of the bank 5 by a vacuum deposition method using barium or aluminum material. Thereby, the electron transport layer 7 is formed (FIG. 5D).

  Subsequently, based on the same film formation method as that for the electron transport layer 7, a barium layer, an aluminum layer, or a metal layer formed by stacking these layers is formed on the surface of the electron transport layer 7 by vacuum deposition or the like. Thereby, the cathode 8 is formed (FIG. 5E).

  Next, in order to suppress the organic light emitting device 1 from being exposed to the atmosphere, a sealing layer 9 is provided on the surface of the cathode 8 (FIG. 5F). The sealing layer 9 can be formed of a material such as SiN (silicon nitride) or SiON (silicon oxynitride), for example, and is provided so as to internally seal the element 1. Alternatively, instead of the sealing layer, a sealing can that can spatially isolate the entire element 1 from the outside can be provided. When the sealing can is used, the sealing can can be formed of the same material as that of the substrate 10, for example, and a getter that adsorbs moisture and the like is provided in the sealed space.

The organic light emitting device 1 is completed through the above steps.
<Various experiments and discussion>
(Tungsten oxide film forming conditions)
In the first embodiment, tungsten oxide constituting the hole injection layer 4 is formed under predetermined film formation conditions so that the hole injection layer 4 has the occupied level near the Fermi surface, and the hole injection layer 4 The hole injection barrier between 4 and the hole transport layer 6A is reduced so that the organic light emitting device 1 can be driven at a low voltage. This tungsten oxide film is similarly used as the coating film 20.

As a film formation method of tungsten oxide for obtaining such performance, a DC magnetron sputtering apparatus is used, the target is metallic tungsten, the substrate temperature is not controlled, the gas in the chamber is composed of argon gas and oxygen gas, The gas pressure (total pressure) is more than 2.7 Pa and 7.0 Pa or less, and the ratio of the oxygen gas partial pressure to the total pressure is 50% or more and 70% or less, and the input power per unit unit area (input power) density) is set to the film formation condition to be 1W / cm ² or more 2.8W / cm ² or less, it is considered to be preferable that a film is formed by reactive sputtering.

The effectiveness of the film forming conditions was confirmed by the following experiments.
First, in order to ensure the evaluation of the dependency of the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A on the film formation conditions, a hole-only element was manufactured as an evaluation device.

  In the organic light emitting device, the carriers for forming a current are both holes and electrons. Therefore, the electrical current of the organic light emitting device reflects the electron current in addition to the hole current. However, in the hole-only device, since the electron injection from the cathode is hindered, the electron current hardly flows and the total current is composed of almost only the hole current, that is, the carrier can be regarded as almost only the hole. Suitable for evaluation.

  The specifically produced hole-only element is obtained by replacing the cathode 8 in the organic light emitting device 1 of FIG. 1 with gold. That is, as shown in FIG. 7, an anode 2 made of an ITO thin film having a thickness of 50 nm is formed on a substrate 10, and a hole injection layer 4 made of tungsten oxide having a thickness of 30 nm is formed on the anode 2, and an amine-based material having a thickness of 20 nm. A structure (hole-only element 1D) in which a hole transport layer 6A made of TFB that is an organic polymer, a light-emitting layer 6B that is made of F8BT that is an organic polymer having a thickness of 70 nm, and a cathode 8 that is made of gold having a thickness of 100 nm are sequentially stacked. did. Note that the bank 5 is omitted to constitute an evaluation device.

  In this manufacturing process, the hole injection layer 4 was formed by a reactive sputtering method using a DC magnetron sputtering apparatus. The gas in the chamber was composed of at least one of argon gas and oxygen gas, and metallic tungsten was used as the target. The substrate temperature was not controlled, and the argon gas partial pressure, oxygen gas partial pressure, and total pressure were adjusted by the flow rate of each gas. As shown in Table 1 below, the film formation conditions are such that the total pressure, the oxygen gas partial pressure, and the input power are changed, whereby a hole provided with the hole injection layer 4 formed under each film formation condition. Only element 1D (element No. 1-14) was obtained. Hereinafter, the oxygen gas partial pressure is expressed as a ratio (%) to the total pressure.

  Table 2 shows the relationship between input power and input power density of the DC magnetron sputtering apparatus.

Each produced hall-only element 1D was connected to a DC power source DC, and a voltage was applied. The applied voltage at this time was changed, and the current value that flowed according to the voltage value was converted to a value (current density) per unit area of the element. Hereinafter, the “drive voltage” is an applied voltage at a current density of 10 mA / cm ² .

  It is estimated that the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A is higher as the drive voltage is lower. This is because, in each hole-only device 1D, the manufacturing method of each part other than the hole injection layer 4 is the same, so the hole injection barrier between two adjacent layers excluding the hole injection layer 4 is considered to be constant. Further, as described later, it has been confirmed by another experiment that the cathode 2 and the hole injection layer 4 used in the experiment are in a Schottky ohmic connection. Therefore, the difference in drive voltage depending on the film formation conditions of the hole injection layer 4 strongly reflects the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A and the hole conduction efficiency of the hole injection layer 4 itself.

  Here, it is said that the hole conduction efficiency of the hole injection layer 4 influences the element characteristics in each experiment of the first embodiment in addition to the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A. Conceivable. However, it is clear from the evaluation result of the energy diagram described later that the hole injection barrier between the hole injection layer 4 and the hole transport layer 6A is strongly reflected in the characteristics of the element.

  In the first embodiment, the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A is mainly considered, and the hole conduction efficiency of the hole injection layer 4 is considered in the second embodiment.

  Table 3 shows the values of the driving voltage for each film-forming condition of the total pressure, oxygen gas partial pressure, and input power of each hole-only device 1D obtained by the experiment. In Table 3, element No. of each hole only element 1D. Is indicated by a boxed number.

  8A to 8C are graphs summarizing the film formation condition dependence of the driving voltage of each hole-only element 1D. Each point in FIG. 8A corresponds to an element No. from left to right. The drive voltages of 4, 10, and 2 are represented. Each point in FIG. 8B corresponds to the element No. from left to right. The drive voltage of 13, 10, 1 is represented. Further, each point in FIG. The drive voltages of 14, 2, and 8 are represented.

  In this experiment, when the total pressure is 2.7 Pa and the oxygen gas partial pressure is 100%, when the total pressure is 4.8 Pa and the oxygen gas partial pressure is 30%, the total pressure is 4.8 Pa and the oxygen gas partial pressure. When the total pressure was 4.8 Pa and the oxygen gas partial pressure was 100%, film formation could not be performed due to the limitations of the sputtering apparatus such as the gas flow rate.

  First, as can be seen from FIG. 8A, the dependence of the driving voltage on the total pressure is at least in the range where the total pressure is over 2.7 Pa and 4.8 Pa or less under the conditions of 50% oxygen gas partial pressure and 500 W input power. In FIG. 5, a clear reduction in drive voltage was confirmed. It was found by another experiment that this tendency continues at least until the total pressure is 7.0 Pa or less. Therefore, it can be said that the total pressure is desirably set in the range of more than 2.7 Pa and 7.0 Pa or less.

  Next, as can be seen from FIG. 8B, the dependency of the driving voltage on the oxygen gas partial pressure is at least an oxygen gas partial pressure of 50% to 70% under the conditions of a total pressure of 2.7 Pa and an input power of 500 W. In this range, it was confirmed that the driving voltage decreased with the increase of the oxygen gas partial pressure. However, when the oxygen gas partial pressure increased more than this, the driving voltage was confirmed to be increased by another experiment. Therefore, it can be said that the oxygen gas partial pressure is preferably 50% or more and the upper limit is preferably suppressed to about 70%.

  Next, as can be seen from FIG. 8 (c), the dependence of the driving voltage on the input power is rapidly over 500 W when the total pressure is 4.8 Pa and the oxygen gas partial pressure is 50%. Was confirmed to rise. Therefore, it is considered that the input power should be suppressed to 500 W or less. In addition, element No. of Table 3 As can be seen from FIGS. 1 and 3, even when the input power is 500 W, the driving voltage rises if the total pressure is 2.7 Pa or less.

Next, among the hole-only elements 1D, element No. The current density-applied voltage curves of 14, 1, and 7 are shown in FIG. In the figure, the vertical axis represents current density (mA / cm ² ), and the horizontal axis represents applied voltage (V). Element No. No. 14 satisfies all the desirable conditions of the total pressure, oxygen gas partial pressure, and input power described above. On the other hand, element No. 1 and 7 do not partially satisfy the above desirable conditions.

  Here, for the following description, regarding the film formation conditions of the hole injection layer 4 (and the tungsten oxide layer 12 described later), the element No. No. 14 film forming conditions are film forming conditions A and element no. No. 1 film formation condition B, element No. The film formation condition 7 is referred to as film formation condition C. In accordance with this, in FIG. 14 is HOD-A, element no. 1 is HOD-B, element no. 7 was also described as HOD-C.

  As shown in FIG. 9, HOD-A has the fastest rise in current density-applied voltage curve compared to HOD-B and HOD-C, and a high current density is obtained at the lowest applied voltage. . Thereby, it is estimated that HOD-A is superior in hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A compared to HOD-B and HOD-C. HOD-A is an element having the lowest drive voltage among the hole-only elements 1D.

  The above is the verification regarding the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A in the hole-only device 1D. The hole-only device 1D has the same configuration as the organic light emitting device 1 except for the cathode. Accordingly, also in the organic light emitting device 1, the dependency of the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A on the film formation conditions is essentially the same as that of the hole only element 1D. In order to confirm this, each organic light emitting device 1 using the hole injection layer 4 under the deposition conditions A, B, and C was fabricated.

  As shown in FIG. 1, each of the organic light emitting devices 1 specifically manufactured has an anode 2 made of an ITO thin film having a thickness of 50 nm formed on a substrate 10 and further made of tungsten oxide having a thickness of 30 nm on the anode 2. Hole injection layer 4, hole transport layer 6A made of TFB, which is an amine-based organic polymer having a thickness of 20 nm, light emitting layer 6B made of F8BT, which is an organic polymer having a thickness of 70 nm, barium having a thickness of 5 nm, and a thickness of 100 nm The cathode 8 made of aluminum was sequentially laminated. Note that the bank 5 is omitted because of the evaluation device configuration.

The produced organic light emitting devices 1 under the film forming conditions A, B, and C were connected to a DC power source DC, and a voltage was applied. The current density-applied voltage curve at this time is shown in FIG. In the figure, the vertical axis represents current density (mA / cm ² ), and the horizontal axis represents applied voltage (V).

  For the following description, in FIG. 10, the organic light emitting device 1 under the film forming condition A is BPD-A, the organic light emitting device 1 under the film forming condition B is BPD-B, and the organic light emitting device 1 under the film forming condition C is used. Was described as BPD-C.

  As shown in FIG. 10, BPD-A has the fastest rise of the current density-applied voltage curve compared to BPD-B and BPD-C, and a high current density is obtained at the lowest applied voltage. . This is the same tendency as HOD-A, HOD-B, and HOD-C, which are hole-only elements having the same film forming conditions.

Furthermore, for each of the organic light emitting devices 1 described above, a light emission intensity-current density curve showing the relationship of light emission intensity according to the change in current density is shown in FIG. In the figure, the vertical axis represents emission intensity (cd / A), and the horizontal axis represents current density (mA / cm ² ). This shows that the emission intensity of BPD-A is the highest at least in the measured current density range.

From the above results, it is speculated that the film formation condition dependency of the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A is also acting in the organic light emitting device 1 as in the case of the hole only element 1D. Is done. That is, in the organic light emitting device 1 of the experiment, tungsten oxide constituting the hole injection layer 4 is a DC magnetron sputtering device, the target is metallic tungsten, the substrate temperature is not controlled, and the gas in the chamber is argon gas and oxygen. It is composed of gas, the total pressure is over 2.7 Pa and 7.0 Pa or less, the ratio of the oxygen gas partial pressure to the total pressure is 50% or more and 70% or less, and the input power density is 1 W / cm ² or more. When a film is formed by a reactive sputtering method under a film forming condition of 2.8 W / cm ² or less, the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A is good, thereby achieving excellent low voltage driving and high It is estimated that luminous efficiency is realized.

  In the above description, the input power condition is again expressed as the input power density based on Table 2. When using a DC magnetron sputtering apparatus different from the DC magnetron sputtering apparatus used in this experiment, the input power is adjusted so that the input power density satisfies the above conditions according to the size of the target. In addition, the hole injection layer 4 that realizes the organic light emitting device 1 with excellent low voltage driving and high luminous efficiency can be obtained. Note that the total pressure and oxygen partial pressure do not depend on the size of the apparatus or the target.

  Further, when the hole injection layer 4 is formed by the reactive sputtering method, the substrate temperature is not intentionally set in a sputtering apparatus arranged in a room temperature environment. Therefore, at least the substrate temperature before film formation is room temperature. However, the substrate temperature may increase by several tens of degrees Celsius during film formation.

The organic light emitting device 1 in which the hole injection layer 4 is produced under the film forming condition A is the organic light emitting device 1 of the first embodiment, and has an occupied level near the Fermi surface described above. This will be discussed later.
(Electron state of hole injection layer)
The tungsten oxide constituting the hole injection layer 4 of the organic light emitting device 1 of the first embodiment has an occupied level near the Fermi surface. The occupied level in the vicinity of the Fermi surface is formed by adjusting the film forming conditions shown in the previous experiment. Details are described below.

Experiments were conducted to confirm the existence of occupied levels in the vicinity of the Fermi surface in tungsten oxide formed under the above-described film formation conditions A, B, and C.
Samples for photoelectron spectroscopy measurement were produced under each film forming condition. As the configuration of the sample, as shown in 1E shown in FIG. 12, a tungsten oxide layer 12 (corresponding to the hole injection layer 4) having a thickness of 10 nm is formed on the conductive silicon substrate 10S by the reactive sputtering method. Was formed. Hereinafter, the sample 1E under the film formation condition A will be referred to as sample A, the sample 1E under the film formation condition B as sample B, and the sample 1E under the film formation condition C as sample C.

  Samples A, B, and C were all deposited in a sputtering apparatus and then transferred to a glove box connected to the sputtering apparatus and filled with nitrogen gas, and kept in a state where they were not exposed to the atmosphere. . And it enclosed with the transfer vessel in the said glove box, and mounted | worn with the photoelectron spectrometer. Thereby, ultraviolet photoelectron spectroscopy (UPS) measurement was performed without exposing the tungsten oxide layer 12 to the air after film formation.

  Here, the UPS spectrum generally reflects the state of the occupied level such as the valence band from the surface of the measurement object to a depth of several nm. Therefore, in this experiment, the state of the occupied level in the surface layer of the tungsten oxide layer 12 was observed using UPS.

UPS measurement conditions are as follows. In Samples A, B, and C, since the conductive silicon substrate 10S was used, no charge-up occurred during measurement.
Light source: He I line Bias: None Emitting angle: Substrate normal direction measurement point interval: 0.05 eV
FIG. 13 shows a UPS spectrum of the tungsten oxide layer 12 of Sample A. The origin of the binding energy on the horizontal axis is the Fermi level of the conductive silicon substrate 10S, and the left direction is the positive direction.

Hereinafter, the occupied levels of the tungsten oxide layer 12 will be described with reference to FIG.
In general, in the UPS spectrum shown by tungsten oxide, the largest and steep rise is uniquely determined. A tangent line passing through the rising inflection point is defined as a line (i), and an intersection with the horizontal axis is defined as a point (iii). Thereby, the UPS spectrum of tungsten oxide is divided into a region (x) located on the high bond energy side from the point (iii) and a region (y) located on the low bond energy side.

  Here, according to the composition ratio of the tungsten oxide layer 12 shown in Table 4 below, the ratio of the number of tungsten atoms to oxygen atoms in samples A, B, and C is approximately 1: 3. This composition ratio was determined by X-ray photoelectron spectroscopy (XPS). Specifically, using the photoelectron spectrometer, as in the UPS measurement, the tungsten oxide layer 12 is subjected to XPS measurement without exposure to the atmosphere, and tungsten and oxygen at a depth of several nm from the surface of the tungsten oxide layer 12 are measured. The composition ratio was estimated. In Table 4, the conditions for forming the tungsten oxide layer 12 are also shown.

  From this composition ratio, in any of Samples A, B, and C, the tungsten oxide layer 12 has an atomic arrangement based on tungsten trioxide, that is, six oxygen atoms are 1 in at least a range of several nm from the surface. It is considered that the basic structure has a structure in which octahedron bonds to two tungsten atoms and the octahedrons share an apex oxygen atom. Therefore, the region (x) in FIG. 13 has the basic structure of the tungsten trioxide crystal or the amorphous structure in which the order of the crystal is disordered (however, the bond is not broken and the basic structure is maintained). Is an area corresponding to a so-called valence band. In addition, this inventor measured the X-ray absorption fine structure (XAFS) of the tungsten oxide layer 12, and confirmed that the said basic structure was formed in any of the samples A, B, and C.

  Therefore, the region (y) in FIG. 13 corresponds to the band gap between the valence band and the conduction band, but as shown in the present UPS spectrum, tungsten oxide is also separated from the valence band in this region. It is known that there may be a number of occupied levels. This is a level derived from another structure different from the basic structure, and is a so-called inter-gap level (in-gap state or gap state).

  Next, FIG. 14 shows UPS spectra in the region (y) of the tungsten oxide layers 12 in the samples A, B, and C. The intensity of the spectrum shown in FIG. 14 was normalized by the value of the peak top of the peak (ii) located 3 to 4 eV higher than the point (iii) in FIG. FIG. 14 also shows the point (iii) at the same horizontal axis position as the point (iii) in FIG. The horizontal axis is expressed as a relative value (relative binding energy) with respect to the point (iii), and the binding energy decreases from left to right.

  As shown in FIG. 14, in the tungsten oxide layer 12 of Sample A, the region from the position of binding energy approximately 3.6 eV lower than the point (iii) to the position of binding energy approximately 1.8 V lower than the point (iii). In addition, the presence of a peak can be confirmed. The clear rising position of this peak is indicated by a point (iv) in the figure. Such a peak cannot be confirmed in the samples B and C.

  In the present invention, tungsten oxide having a structure in which it rises (not necessarily has a peak shape) in a region having a binding energy of about 1.8 to 3.6 eV lower than the point (iii) in the UPS spectrum is converted into a hole. By using it as an injection layer, excellent hole injection efficiency can be exhibited in an organic light emitting device.

  Here, it has been found that the steeper degree of the protrusion tends to increase the hole injection efficiency. Therefore, as shown in FIG. 14, a region having a binding energy lower by about 2.0 to 3.2 eV from the point (iii) is a region where the raised structure is relatively easy to confirm and the raised portion is relatively steep. It can be said that it is particularly important.

  Hereinafter, the raised structure in the UPS spectrum is referred to as “a raised structure near the Fermi surface”. The occupied level corresponding to the raised structure in the vicinity of the Fermi surface is the aforementioned “occupied level in the vicinity of the Fermi surface”.

Next, in order to clarify the raised structure in the vicinity of the Fermi surface, the differential of the normalized intensity in the UPS spectrum of samples A, B, and C shown in FIG. 14 was calculated.
Specifically, using the graph analysis software “IGOR Pro 6.0”, the binomial smoothing (smoothing factor is set to 1) is performed 11 times on the UPS spectrum shown in FIG. went. This is to smooth the variation factors such as background noise during UPS measurement, to smooth the differential curve, and to clarify the following discussion.

The differential curve obtained by this processing is shown in FIG. Points (iii) and (iv) in FIG. 15 are the same horizontal axis positions as in FIG.
According to the differential curve shown in FIG. 15, in the tungsten oxide layers 12 of the samples B and C, the differential value is 0 in the region (v) from the bond energy measurable by the photoelectron spectrometer to the point (iv). In the region (vi) from the point (iv) to about 1.2 eV on the high binding energy side, the differential value increases almost at the rate of increase toward the high binding energy side. It only increases gradually. The shapes of the differential curves of the samples B and C in the regions (v) and (vi) are almost similar to the UPS spectra of the samples B and C shown in FIG. Therefore, it can be said that the shape of the UPS spectrum and its differential curve in the regions (v) and (vi) of the samples B and C are exponential shapes.

  On the other hand, the tungsten oxide layer 12 of the sample A shows a steep rise from the vicinity of the point (iv) toward the high binding energy side, and the shape of the differential curve in the regions (v) and (vi) is exponential. The shape of the curve is clearly different. It is confirmed that such a sample A has a raised structure in the vicinity of the Fermi surface, which begins to rise near the point (iv) in the spectrum before differentiation in FIG. 14 and is different from the exponential spectrum shape. it can.

  In other words, the characteristics of Sample A have, in other words, an occupied level in the vicinity of the Fermi surface in a range approximately 1.8 to 3.6 eV lower than the lowest binding energy in the valence band. In the range of approximately 2.0 to 3.2 eV lower than the lowest binding energy, the raised structure near the Fermi surface corresponding to this range can be clearly confirmed by the UPS spectrum.

  Next, exposure to the atmosphere was performed at room temperature for 1 hour on the tungsten oxide layers 12 of Samples A, B, and C in which the UPS spectra of FIG. 14 were measured without being exposed to the air after film formation. And UPS measurement was performed again, and the change of the spectrum by this was confirmed. The UPS spectrum in the region (y) is shown in FIG. The method of taking the horizontal axis is the same as in FIG. 14, and points (iii) and (iv) in the figure are the same horizontal axis positions as in FIG.

  According to the UPS spectrum shown in FIG. 16, in the tungsten oxide layers 12 of the samples B and C, the raised structure in the vicinity of the Fermi surface cannot be confirmed as before the atmospheric exposure. On the other hand, in the tungsten oxide layer 12 of the sample A, although the intensity and the spectral shape change after exposure to the atmosphere, the presence of the raised structure near the Fermi surface can still be confirmed. As a result, it can be seen that Sample A can maintain the characteristics before being exposed to the atmosphere even if it is exposed to the atmosphere for a certain period of time, and has a certain stability with respect to the surrounding atmosphere.

  In the above, the UPS spectra measured for samples A, B, and C were discussed, but the raised structure near the Fermi surface should be confirmed in the same manner in the spectrum obtained by XPS or hard X-ray photoelectron spectroscopy. Can do.

  FIG. 17 is an XPS spectrum of the tungsten oxide layer 12 of Sample A after the atmospheric exposure. For comparison, the UPS spectrum (same as in FIG. 13) of the tungsten oxide layer 12 of Sample A was overwritten.

  The XPS measurement conditions are the same as the UPS measurement conditions described above, except that the light source is Al Kα rays. However, the interval between measurement points was set to 0.1 eV. In FIG. 17, the point (iii) in the figure is the same horizontal axis position as in FIG. 13, and the horizontal axis indicates the relative binding energy based on the point (iii) as in FIG. 14. Further, the line corresponding to (i) of FIG. 13 in the XPS spectrum is indicated by (i) ′ in FIG.

  As shown in FIG. 17, the raised structure in the vicinity of the Fermi surface in the tungsten oxide layer 12 of Sample A is approximately 1.8 lower than the lowest binding energy in the valence band in the XPS spectrum as in the case of the UPS spectrum. The existence of a bulge structure of a considerable size can be clearly confirmed within a range of ~ 3.6 eV. In another experiment, a raised structure near the Fermi surface was also confirmed in the spectrum of hard X-ray photoelectron spectroscopy.

  In the above measurement, as a sample for photoelectron spectroscopy measurement, apart from the structure of the organic light emitting device 1 shown in FIG. 1, a sample 1E (FIG. 1) formed by forming a tungsten oxide layer 12 on a conductive silicon substrate 10S. 12) was used. This is merely a measure for preventing charge-up during measurement, and the structure of the organic light-emitting device of the present invention is not limited to this configuration.

  According to another experiment conducted by the inventor of the present application, the structure of the organic light emitting device 1 shown in FIG. 1 (the structure in which the anode 2 made of ITO and the hole injection layer 4 made of tungsten oxide are sequentially laminated on one surface of the substrate 10). ), And UPS and XPS measurements were performed, charge-up occurred during the measurement of the tungsten oxide layer under the deposition conditions B and C.

However, if a neutralizing gun that cancels charge-up is used in combination, the absolute value of the binding energy indicated by each occupied level of the hole injection layer 4 (for example, the binding energy when the Fermi level of the photoelectron spectrometer itself is used as the origin). (Value) may differ from that of the tungsten oxide layer 12 of the sample 1E, but at least in the range from the band gap to the lowest binding energy in the valence band, a spectrum having the same shape as the sample 1E is obtained. ing.
(Consideration of hole injection efficiency from hole injection layer to functional layer)
In the hole injection layer made of tungsten oxide, the principle that the occupied level in the vicinity of the Fermi surface, which can be confirmed as a raised structure in the vicinity of the Fermi surface by UPS spectrum or the like, affects the hole injection efficiency from the hole injection layer to the functional layer is as follows. Can be thought of as

  It has been reported from the results of experiments and first-principles calculations that the occupied levels in the vicinity of the Fermi surface found in tungsten oxide thin films and crystals are derived from structures similar to oxygen defects.

  Specifically, the bond trajectory between 5d orbitals of adjacent tungsten atoms formed by depletion of oxygen atoms, or the 5d orbital of tungsten atoms alone existing in the film surface or in the film without being terminated by oxygen atoms, It is presumed that the occupied level near the Fermi surface is derived. If these 5d orbitals are in a semi-occupied or non-occupied state, it is assumed that when they come into contact with organic molecules, electrons can be extracted from the highest occupied orbitals of organic molecules for mutual energy stabilization. Is done.

  In fact, in tungsten oxide and molybdenum oxide having many common physical properties such as catalysis, electrochromism, and photochromism, when a layer made of α-NPD, which is an organic low molecule, is laminated on the thin film, the α-NPD molecule There is a report that an electron moves to a molybdenum oxide thin film (refer nonpatent literature 3).

  The inventor of the present application has described that in tungsten oxide, a semi-occupied 5d orbital of a single tungsten atom having a lower binding energy than a bonding orbital between adjacent 5d orbitals of tungsten atoms or a structure similar thereto occupies near the Fermi surface. I think that it corresponds to a level.

FIG. 18 is an energy diagram at the interface between the tungsten oxide layer having an occupied level near the Fermi surface and the α-NPD layer of the present invention.
In FIG. 18, first, in the tungsten oxide layer (corresponding to the hole injection layer), the lowest binding energy in the valence band (denoted as “upper valence band top” in the figure) and the occupancy quasi near the Fermi surface. The lowest binding energy at the occupied level in the vicinity of the Fermi surface, which corresponds to the rising position of the position (denoted as “in-gap state upper end” in the figure), is shown. In the UPS spectrum, the upper end of the valence band corresponds to the point (iii) in FIG. 13, and the upper end of the in-gap state corresponds to the point (iv) in FIG.

  Further, when α-NPD (corresponding to a functional layer) is laminated on the tungsten oxide layer, the film thickness of the α-NPD layer, the binding energy of the highest occupied orbit of α-NPD, and the vacuum The relationship with the level is also shown. Here, the binding energy of the highest occupied orbit of α-NPD is the binding energy at the peak rising position of the highest occupied orbit in the UPS spectrum, in other words, the lowest in the highest occupied orbit of α-NPD. Binding energy.

  Specifically, while the tungsten oxide layer formed on the ITO substrate is moved back and forth between the photoelectron spectrometer and the ultrahigh vacuum deposition apparatus connected to the apparatus, UPS measurement and α-NPD The energy diagram of FIG. 18 was obtained by repeating ultra-high vacuum deposition. Since no charge-up was confirmed during UPS measurement, in FIG. 18, the binding energy on the vertical axis is expressed as an absolute value with the Fermi level of the ITO substrate as the origin.

  From FIG. 18, in the range where the thickness of the α-NPD layer is at least 0 to 0.3 nm, that is, in the vicinity of the interface between the tungsten oxide layer and the α-NPD layer, the upper end of the in-gap state of the tungsten oxide layer, It can be seen that the binding energies of the highest occupied orbitals of α-NPD are substantially equal, that is, the states are connected to each other (the above-described interface state connection state). Note that “equal” here includes a slight difference in practice, and specifically refers to a range within ± 0.3 eV.

Further, FIG. 18 shows that the interface state connection is realized not by chance but by the interaction between tungsten oxide and α-NPD.
For example, the change in vacuum level (vacuum level shift) at the interface is that the electric double layer is formed on the interface with the tungsten oxide layer side negative and the α-NPD layer side positive from the direction of the change. Indicates. In addition, since the magnitude of the vacuum level shift is as large as 2 eV, it is appropriate that the electric double layer is formed not by physical adsorption but by an action similar to a chemical bond. That is, it should be considered that the interface state connection is realized by the interaction between tungsten oxide and α-NPD.

The inventor of the present application infers the following mechanism as a specific interaction.
First, the occupied level in the vicinity of the Fermi surface is derived from the 5d orbit of a tungsten atom constituting a structure similar to an oxygen defect, as described above. This is hereinafter referred to as “the raised W5d trajectory”.

  When the highest occupied orbit of the α-NPD molecule approaches the W5d orbit of the raised structure on the surface of the tungsten oxide layer, the raised structure is separated from the highest occupied orbit of the α-NPD molecule for mutual energy stabilization. Move to the W5d orbit. As a result, an electric double layer is formed at the interface, and vacuum level shift and interface level connection as shown in FIG. 18 occur.

  More specifically, the highest occupied orbitals of amine organic molecules such as α-NPD are generally distributed with the electron density biased toward the nitrogen atoms of the amine structure, and the unshared electron pairs of the nitrogen atoms are mainly distributed. It has been reported many as a result of the first principle calculation that it is configured as a component. From this, it is presumed that electrons move from the unshared electron pair of the nitrogen atom of the amine structure to the W5d orbit of the raised structure, particularly at the interface between the tungsten oxide layer and the amine organic molecule layer.

  As supporting the above inference, the tungsten oxide layer and the α shown in FIG. 18 are formed at each interface between the molybdenum oxide vapor-deposited film having the same physical properties as tungsten oxide and α-NPD and F8BT as described above. -There are reports of interface state connection similar to the interface state connection of the NPD layer (see Non-Patent Documents 4, 5, and 6).

  The excellent hole injection efficiency for the functional layer of the hole injection layer of the organic light emitting device of the present invention can be explained by the above interface state connection. That is, an interface state connection occurs between a hole injection layer made of tungsten oxide having an occupied level near the Fermi surface and an adjacent functional layer, and the binding energy at the rising position of the occupied level near the Fermi surface The binding energy at the rising position of the highest occupied orbit of the functional layer becomes almost equal. Hole injection occurs between the connected levels. Therefore, there is almost no hole injection barrier between the hole injection layer and the functional layer of the present invention.

  However, it is unlikely that tungsten oxide that does not have a structure similar to oxygen defects, which is a factor for forming an occupied level near the Fermi surface, actually exists. For example, even in tungsten oxides such as the aforementioned samples B and C that do not have a raised structure in the vicinity of the Fermi surface in the photoelectron spectroscopy spectrum, it is reasonable to think that there are very few structures similar to oxygen defects. .

  On the other hand, as shown in the previous experiment, the reason why the hole-only device HOD-A and the organic light-emitting device BPD-A having the hole injection layer 4 corresponding to the tungsten oxide layer 12 of the sample A exhibit excellent low voltage driving is shown. Will be described with reference to FIG.

  When the functional layer is stacked on the tungsten oxide layer, the highest occupied orbital of the organic molecules constituting the functional layer interacts with the occupied level near the Fermi surface of the tungsten oxide layer. Sites with high electron density of the highest occupied orbital (for example, nitrogen atom of amine structure in amine organic molecule; indicated by “injection site (y)” in the figure) and structure similar to oxygen defect on the surface of tungsten oxide layer ( (Indicated by “injection site (x)” in the figure) needs to approach (contact) to an interacting distance.

  However, as shown in FIG. 19 (b), the number density of the tungsten oxide layer, such as the above-described samples B and C, where there is no raised structure in the vicinity of the Fermi surface is present even if the implantation site (x) is present. In the UPS spectrum, it is so small that it does not reach the raised structure near the Fermi surface. Therefore, the possibility that the injection site (y) is in contact with the injection site (x) is very low. Since holes are injected where the injection site (x) and the injection site (y) are in contact, it can be seen that the efficiency of the samples B and C is extremely poor.

  In contrast, as shown in FIG. 19A, the tungsten oxide layer having a raised structure near the Fermi surface, such as the above-described sample A, has abundant injection sites (y). Therefore, it is highly likely that the injection site (y) is in contact with the injection site (x), and the hole injection efficiency from the hole injection layer to the functional layer is high.

  In order to make the series of discussions so far more reliable, the α-NPD layer is also applied to the tungsten oxide layer under the film formation condition C in which the raised structure in the vicinity of the Fermi surface cannot be confirmed at all, similarly to FIG. The energy diagram at the interface was measured.

  FIG. 20 shows the result. Here, as described above, in the tungsten oxide layer, the upper end of the in-gap state corresponding to the raised structure near the Fermi surface could not be confirmed. Therefore, as another candidate of the level used for hole injection, a structure different from the raised structure (see (z in FIG. 13), which is seen on the higher binding energy side than the position of the raised structure near the Fermi surface in the UPS spectrum. )) Rising position (denoted as "second in-gap state upper end") and the valence band upper end are shown in FIG.

  However, the highest occupied orbit of α-NPD in FIG. 20 is completely different from that in FIG. 18 and is not approaching the upper end of the second in-gap state or the upper end of the valence band at all, that is, no interface state connection is made. Not happening. This means that neither the second in-gap state nor the valence band interacts with the highest occupied orbital of α-NPD. Even if holes are injected from the upper end of the second in-gap state into the highest occupied orbit of α-NPD, the injection barrier is 0.75 eV, which is very large compared to the case of FIG.

  This difference in the injection barrier is considered to have a great influence on the driving voltage and the light emission efficiency of the hole-only element 1D and the organic light emitting device 1 under the respective film forming conditions. That is, the difference in characteristics between each of the hole-only elements 1D and the organic light emitting device 1 under the film forming conditions A, B and C is that the organic light emitting device of the present invention has excellent hole injection efficiency from the hole injection layer to the functional layer. It is thought to strongly suggest this.

Summarizing the above, it can be explained as follows that the organic light-emitting device of the present invention has excellent hole injection efficiency.
First, a hole injection layer made of tungsten oxide has a raised structure near the Fermi surface in its photoelectron spectroscopy spectrum. This means that a structure similar to an oxygen defect and an occupied level in the vicinity of the Fermi surface derived therefrom are present at least on the surface of the hole injection layer.

The occupied level in the vicinity of the Fermi surface itself has an effect of connecting the interface level with the highest occupied orbital of the organic molecule by taking electrons from the organic molecule constituting the adjacent functional layer.
Therefore, if there is a structure similar to oxygen defects on the surface of the hole injection layer, there is a high probability that the occupied level in the vicinity of the Fermi surface and the site where the electron density of the highest occupied orbit of the organic molecule is high will come into contact. Thus, the interface state connection effect occurs efficiently, and excellent hole injection efficiency from the hole injection layer to the functional layer appears.
(Consideration of hole injection efficiency from anode to hole injection layer)
Next, the stability of Schottky ohmic connection (dependence on the anode material and surface state) formed between the anode and the hole injection layer made of tungsten oxide of the present invention will be described.
[Hole injection barrier between anode and hole injection layer]
First, energy diagrams in the vicinity of the interface between the anode and the functional layer in an organic light emitting device having a conventional configuration in which the anode and the functional layer are directly laminated are shown in FIGS. Here, α-NPD was used as the functional layer. Further, the binding energy on the vertical axis in the figure is expressed in absolute value with the Fermi level of the anode as the origin.

  When the anode is made of IZO as shown in FIGS. 21 and 19, only the pure water cleaning is performed on the surface of the anode (FIG. 21), and the dry etching process is further performed after the pure water cleaning ( In FIG. 22), the hole injection barrier between the Fermi level of the anode and the highest occupied orbit of the functional layer is a considerable size exceeding 1 eV, and the size of the barrier for the treatment of the IZO surface is high. It can be seen that there is a large fluctuation due to the difference.

  As shown in FIGS. 23 and 21, even when the anode is made of ITO, the surface of the anode is only cleaned with IPA (isopropanol) (FIG. 23). It can be seen that there is a hole injection barrier with a considerable height in the processed one (FIG. 24).

  As shown in FIGS. 21 to 21, in the conventional organic light emitting device, the hole injection barrier between the anode and the functional layer varies considerably depending on the type of the anode material and the surface state of the anode, and the barrier itself is large. It can be confirmed that there is room for improvement in terms of drive voltage.

  On the other hand, FIGS. 25 to 26 show energy diagrams in the vicinity of the interface between the anode and the hole injection layer of the present invention when the anode and the hole injection layer made of tungsten oxide of the present invention are stacked.

  25 and 23 show the case where the anode is made of IZO. As in FIGS. 21 and 19, the surface of the anode was cleaned only with pure water (FIG. 25), and further subjected to dry etching after pure water cleaning (FIG. 26), respectively. A hole injection layer of the present invention is laminated thereon.

  27 and 25 show a case where the anode is made of ITO. Similarly to FIGS. 23 and 21, the surface of the anode was subjected only to IPA cleaning (FIG. 27), and further treated with oxygen plasma after IPA cleaning (FIG. 28). The hole injection layer of the present invention is laminated.

  Further, FIG. 29 shows a case where the anode is made of aluminum. After forming the anode, the hole injection layer of the present invention is laminated without being exposed to the atmosphere so that the surface is not naturally oxidized.

From the results shown in FIGS. 25 to 26, the following can be understood.
First, in all of FIGS. 25 to 26, when the thickness of the hole injection layer is less than about 2 nm, the binding energy at the upper end of the in-gap state, which is the rising position of the occupied level in the vicinity of the Fermi surface, changes relatively steeply. However, it is almost constant at a film thickness of 2 nm or more. The constant binding energy value is very close to the Fermi level of the anode, and the difference is within ± 0.3 eV. In other words, in all of FIGS. 25 to 26, a good Schottky ohmic connection having a Schottky barrier width of about 2 nm is realized between the anode and the hole injection layer of the present invention. means.

  Further, in the IZO anode of FIGS. 25 and 23 and the ITO anode of FIGS. 27 and 25, the difference in binding energy between the Fermi level of the anode and the top of the in-gap state when the film thickness of the hole injection layer is 2 nm or more is Regardless of the surface state, the values are almost the same (a shift of 0.02 eV at most).

  Therefore, the following can be said. First, regardless of whether the anode material is IZO, ITO, or aluminum, the anode and the hole injection layer of the present invention are in Schottky ohmic connection if the thickness of the hole injection layer is 2 nm or more. Furthermore, even if the surface state of the anode has undergone at least any of the above-described treatments, this connection is not only kept good, but also the degree of connection (the above-mentioned bond energy difference) depends on the surface state of the anode. Without depending on the difference of. It maintains a very stable and constant situation.

  From these results, if the hole injection layer made of tungsten oxide of the present invention is used, various operations for making the work function and surface state of the anode constant, that is, the anode material is strictly selected, or just before the hole injection layer is formed. Even without special considerations such as maintaining the surface state of the anode at a high level, good hole injection efficiency from the anode to the hole injection layer can be expected.

  In summary, the hole injection layer made of tungsten oxide in the present invention has an occupied level in the vicinity of the Fermi surface, and is hardly affected by the work function and surface state of the anode due to the action of the level. Realizes Schottky ohmic connection with the anode. Specifically, when the distance from the anode surface to the hole injection layer side is 2 nm, the difference in binding energy between the anode Fermi level and the occupied level is ± 0.3 eV. Is within. As a result, the hole injection barrier between the anode and the hole injection layer can be considerably relaxed.

Here, the hole injection layer of the present invention has a very small hole injection barrier with the functional layer due to the action of the occupied level as described above. Therefore, holes can be injected from the anode to the hole injection layer and from the hole injection layer to the functional layer with almost no barrier. In this way, not only the hole injection barrier between the hole injection layer and the functional layer but also the hole injection barrier between the anode and the hole injection layer is relaxed, thereby further improving the low voltage driving of the device. realizable. Furthermore, if the hole injection efficiency is improved, the load applied to the element during driving is reduced, so that the driving life of the element can be expected to be extended.
[Confirmation of stability of Schottky ohmic connection]
As described above, the hole injection layer made of tungsten oxide of the present invention can form a stable Schottky ohmic connection with the anode as long as the film thickness is 2 nm or more. This was also confirmed by the characteristics of the element.

First, using a hole-only element, the film thickness dependence of the hole injection efficiency from the anode to the hole injection layer in the hole injection layer of the present invention was evaluated.
The hole-only element has the same configuration and manufacturing method as the hole-only element 1D of FIG. 7 except for the film thickness of the hole injection layer 4A. Specifically, the hole injection layer was formed under the above-described film formation condition A, and the film thickness was in the range of 5 to 30 nm. For comparison, an element in which the hole injection layer was omitted, that is, an anode and a buffer layer were directly laminated (hereinafter referred to as “film thickness 0 nm”) was also produced. The film thicknesses of the other layers are 50 nm for the ITO anode, 20 nm for the buffer layer made of TFB, 80 nm for the light emitting layer made of F8BT, and 100 nm for the cathode made of gold.

  In the hole-only element, except for an element having a thickness of 0 nm, all the hole injection layers are formed under the film formation condition A. Therefore, it is considered that the hole injection efficiency from the hole injection layer to the buffer layer is all equivalent. Further, the configuration other than the film thickness of the hole injection layer is the same. Therefore, the characteristics of the hole-only device should be mainly influenced by the thickness of the hole injection layer and the degree of formation of the Schottky ohmic connection between the anode and the hole injection layer.

  Here, first, the influence of the electrical resistance of the hole injection layer is considered. The resistance of the hole injection layer increases as the thickness of the hole injection layer increases. However, it was confirmed by another experiment that the resistivity of the hole injection layer under the film formation condition A was 1/100 or less of the buffer layer and the light emitting layer. Therefore, the difference in resistance due to the difference in film thickness of the hole injection layer hardly contributes to the characteristics of the hole-only element.

  Therefore, all the hole-only elements should have the same characteristics as long as a constant Schottky ohmic connection can be formed between the anode and the hole injection layer, except for an element having a thickness of 0 nm.

Each hole-only element having a thickness of the prepared hole injection layer having a thickness of 0 nm, 5 nm, and 30 nm was connected to a DC power source, and a voltage was applied. The applied voltage at this time was changed, and the current value that flowed according to the voltage value was converted to a value (current density) per unit area of the element. Hereinafter, the “drive voltage” is an applied voltage at a current density of 10 mA / cm ² .

  Table 5 shows the drive voltage of each hole-only element.

  The driving voltage of the element having a film thickness of 0 nm is considerably high. This is presumably because a large hole injection barrier is formed between the anode and the functional layer because the hole injection layer of the present invention is not provided. On the other hand, it can be seen that the driving voltage is kept low in each of the elements having a film thickness of 5 nm and 30 nm, and the value thereof is almost the same regardless of the film thickness. As a result, when the thickness of the hole injection layer is at least 5 nm or more, a substantially constant Schottky ohmic connection is formed between the anode and the hole injection layer of the present invention, and a good transfer from the anode to the hole injection layer is achieved. It is considered that hole injection efficiency has been realized.

Next, also in the organic light emitting device, the film thickness dependency of the hole injection efficiency from the anode to the hole injection layer in the hole injection layer of the present invention was evaluated.
The organic light-emitting element is obtained by changing the cathode made of gold into a stacked layer of a barium layer (film thickness: 5 nm) and an aluminum layer (film thickness: 100 nm) in the configuration of the hole-only element. The thickness of the hole injection layer was in the range of 2 to 30 nm.

  Since the organic light-emitting elements are all the same except for the thickness of the hole injection layer, all the characteristics are the same as long as a certain Schottky ohmic connection can be formed between the anode and the hole injection layer. It should be.

Each of the organic light emitting devices having a film thickness of 2 nm, 5 nm, 15 nm, 20 nm, and 30 nm of the prepared hole injection layer was connected to a DC power source, and a voltage was applied. The applied voltage at this time was changed, and the current value that flowed according to the voltage value was converted to a value (current density) per unit area of the element. Hereinafter, the “drive voltage” is an applied voltage at a current density of 10 mA / cm ² .

  Table 6 shows the driving voltage of each organic light emitting device.

  The drive voltage is low and good. In consideration of variations in the thickness of each layer, which are inevitably generated in the production of the element, these driving voltages do not depend on the film thickness and can be regarded as sufficiently equal. Thus, as in the case of the hole-only device, in the organic light-emitting device, when the thickness of the hole injection layer is 2 nm or more, a substantially constant Schottky ohmic is provided between the anode and the hole injection layer of the present invention. It is considered that a connection has been formed.

Subsequently, the relationship between the film thickness of the hole injection layer of the present invention and the driving life of the element was evaluated using the organic light emitting element. The organic light emitting element has the same configuration as that used in Table 6. In addition, the film thickness of the hole injection layer was in the range of 2 to 30 nm, and for comparison, an element having a film thickness of 0 nm was prepared without the hole injection layer 4A.

  Each element has the same configuration except for the thickness of the hole injection layer. Therefore, if a constant Schottky ohmic connection can be formed between the anode and the hole injection layer, the same life can be expected.

Each element having a film thickness of the produced hole injection layer of 0 nm, 2 nm, 5 nm, and 30 nm was connected to a DC power source and driven at a constant current of 10 mA / cm ² , and the change in emission luminance with the driving time was measured.

  Table 7 shows the luminance reduction time until the luminance decreases to 60% at the start of driving in each element.

  From this, first, it can be seen that an element having a film thickness of 0 nm has a rapid decrease in luminance, that is, a short lifetime. This is because the hole injection layer of the present invention is not provided, so that a large hole injection barrier is generated between the anode and the functional layer, and it is necessary to increase the drive voltage in order to flow a constant current, and the load on the element It is thought that the increase in the value has a great influence.

  On the other hand, each element having a film thickness of 2 nm, 5 nm, and 30 nm has a slower luminance drop than that of an element having a film thickness of 0 nm, that is, has a long lifetime. This is presumably because the hole injection layer of the present invention effectively relaxes the hole injection barrier, lowers the driving voltage, and reduces the burden on the device.

  Each of the elements with film thicknesses of 2 nm, 5 nm, and 30 nm is good and shows the same level of luminance reduction. Therefore, if the thickness of the hole injection layer is 2 nm or more, a substantially constant Schottky ohmic connection is formed between the anode and the hole injection layer of the present invention. Therefore, the thickness of the hole injection layer is 2 nm or more. These elements are considered to have the same driving voltage and the same life.

  From the above experiment, it was also confirmed by element characteristics that the hole injection layer made of tungsten oxide of the present invention can form a stable Schottky ohmic connection with the anode when the film thickness is 2 nm or more.

  In the elements used in the measurements of Table 1 and FIGS. 8 to 18, the Schottky ohmic connection of the present invention is made between the anode and the hole injection layer regardless of the film formation conditions of the hole injection layer. This is formed by surface treatment of the ITO anode. Details are described below.

  Similarly to the method used in FIG. 18, when the film formation of the hole injection layer under each film formation condition and the UPS measurement were repeated on the ITO anode, the film formation was performed when the film thickness of the hole injection layer was within about 2 nm. Regardless of the conditions, a raised structure near the Fermi surface was confirmed, forming a Schottky ohmic connection with the anode. However, as the film thickness increased, as shown in FIG. 14, the presence or absence of a raised structure near the Fermi surface varied depending on the film forming conditions.

  This is presumably because the surface of the ITO anode was subjected to argon ion sputtering treatment before the hole injection layer was formed to clean the ITO anode and oxygen defects were formed on the surface.

  That is, by forming an oxygen defect on the surface of the ITO anode, immediately after the start of film formation of the hole injection layer, oxygen atoms of tungsten oxide are easily deprived to the ITO side, and therefore only in the vicinity of the interface, There are many structures similar to oxygen defects in the hole injection layer. For this reason, the Schottky ohmic connection of the present invention is formed between the anode and the hole injection layer.

If the film thickness becomes several nm or more after the start of the film formation of the hole injection layer, the film is uniformly formed with the film quality determined by each film formation condition, so the film thickness of the hole injection layer is 30 nm. And the characteristic of the element used by the measurement of FIGS. 8-18 will depend on film-forming conditions.
(Confirmation test for contact resistance between anode and source electrode)
Next, as shown in FIG. 30, samples of comparative examples and examples were manufactured, and the conductivity effect by the tungsten oxide film (WOx) of the present invention was confirmed.

  Specifically, as shown in FIG. 30A, a TFT conductive film (corresponding to a source electrode) is formed, and film formation conditions of the present invention (conditions for forming Wox with a film thickness of 2 nm or more) are formed thereon. Based on this, a tungsten oxide film (corresponding to a coating film) having a thickness of 20 μm was formed. On this tungsten oxide film, an anode made of an aluminum alloy was formed to obtain an example sample.

On the other hand, as shown in FIG. 30 (b), an anode made of an aluminum alloy was formed directly on the TFT conductive film to obtain a comparative sample.
The resistance values were measured using the samples according to these examples and comparative examples. The result is shown in FIG.

  As shown in the figure, the resistance value of the comparative example sample was higher than that of the example sample. This is presumably because the conductivity between the TFT conductive film and the anode was lowered as a result of the formation of the metal oxide film on the anode surface facing the TFT conductive film.

  On the other hand, the example sample showed better low resistance than the comparative example. It is considered that the formation of the tungsten oxide film suppresses the generation of the metal oxide film and maintains the conductivity between the TFT conductive film and the anode.

From the above experiment, the superiority of the present invention was confirmed.
<Embodiment 5>
<Overall configuration of organic light emitting device 1C>
FIG. 35A is a schematic cross-sectional view showing a configuration of an organic light emitting device 1C according to the fifth embodiment.

FIG. 35B is a partially enlarged view in the vicinity of the hole injection layer 4A.
The overall structure of the organic light emitting device 1C is the same as that of the organic light emitting device 1, but the crystal structure of the tungsten oxide layer constituting the coating film 20A and the hole injection layer 4A is different.

  The organic light emitting device 1C is a coating type in which a functional layer is applied by a wet process to form a film, in which a hole injection layer 4A and various functional layers including an organic material having a predetermined function are stacked on each other. Thus, it has a configuration interposed between the electrode pair composed of the anode 2 and the cathode 8.

Specifically, the organic light emitting device 1 </ b> C has a coating film 20 </ b> A, an anode 2, an ITO layer 3, a hole injection layer 4 </ b> A, a hole transport layer 6 </ b> A, a light emitting layer 6 </ b> B, and an electron transport layer 7 with respect to one side main surface of the substrate 10. The cathode 8 and the sealing layer 9 are laminated in the same order. Hereinafter, the difference from the organic light emitting device 1 will be mainly described.
(ITO layer 3)
The ITO (indium tin oxide) layer 3 is interposed between the anode 2 and the hole injection layer 4A and has a function of improving the bonding property between the layers. In the organic light emitting device 1C, the ITO layer 3 is separated from the anode 2, but the ITO layer 3 can be regarded as a part of the anode (the anode 2 is a first anode and the ITO layer 3 is a second anode).
(Hole injection layer 4A)
Similar to the hole injection layer 4 of the first embodiment, the hole injection layer 4A is formed of a tungsten oxide layer having a thickness of at least 2 nm (here, 30 nm as an example) formed under predetermined film formation conditions. The The ITO layer 3 and the hole injection layer 4A are in Schottky ohmic connection, and the Fermi level in the vicinity of the Fermi surface at a position where the distance from the surface of the ITO layer 3 to the hole injection layer 4A side is 2 nm. The difference with the lowest binding energy is within ± 0.3 eV, and so-called Schottky ohmic connection is achieved. As a result, in the organic light emitting device 1C, the hole injection barrier between the ITO layer 3 and the hole injection layer 4A is relaxed as compared with the conventional configuration, and good low-voltage driving is possible. The effect of this Schottky ohmic connection is kept good even if there is some residue 5R of the bank 5 between the ITO layer 3 and the hole injection layer 4A.

  The tungsten oxide constituting the hole injection layer 4A is a real number in the range of 2 <x <3 in the composition formula WOx. The hole injection layer 4A is preferably made of tungsten oxide with as high a purity as possible, but may contain a trace amount of impurities that can be mixed at a normal level.

The details of the predetermined film forming conditions for the hole injection layer 4A will be described in detail in the section (Method for manufacturing the organic light emitting device 1C) and the section (About the film forming conditions for the hole injection layer 4A).
Here, in the fifth embodiment, since the tungsten oxide layer constituting the hole injection layer 4A is formed under the predetermined film formation conditions, as shown in the enlarged sectional view of FIG. The crystal 13 is included in large numbers. The grain size of each crystal 13 is on the order of nanometers. For example, the hole injection layer 4A has a thickness of about 30 nm, whereas the crystal 13 has a grain size of about 3 to 10 nm. Hereinafter, the crystal 13 having a particle size of the order of nanometers is referred to as “nanocrystal 13”, and the layer structure composed of the nanocrystal 13 is referred to as “nanocrystal structure”. The hole injection layer 4A may include an amorphous structure in addition to the nanocrystal structure.

  In the hole injection layer 4A having the nanocrystal structure as described above, the tungsten atoms constituting the tungsten oxide are distributed so as to have a maximum valence state that the tungsten oxide can take and a valence state lower than the maximum valence. is doing. In general, a structure similar to an oxygen defect may exist in the tungsten oxide layer. The valence of the tungsten atom not included in the structure similar to the oxygen defect is hexavalent, while the valence of the tungsten atom included in the structure similar to the oxygen defect is lower than the hexavalence. In general, there are many structures similar to oxygen defects on the surface of the crystal.

  Therefore, in the organic light emitting device 1C, in addition to the relaxation of the hole injection barrier between the ITO layer 3 and the hole injection layer 4A described above, pentavalent tungsten atoms are distributed in the hole injection layer 4A, and the structure is similar to an oxygen defect. It is desired to further improve the hole conduction efficiency by forming. That is, by providing the hole injection layer 4A made of tungsten oxide with a nanocrystal structure, holes injected from the ITO layer 3 into the hole injection layer 4A conduct oxygen defects present at the crystal grain boundaries of the nanocrystal 13. As a result, the number of paths through which holes are conducted can be increased, leading to an improvement in hole conduction efficiency. Thereby, in the organic light emitting device 1C, the drive voltage can be reduced efficiently.

  The hole injection layer 4A is made of tungsten oxide having high chemical resistance, that is, hardly causing unnecessary chemical reaction. Therefore, even when the hole injection layer 4A comes into contact with a solution or the like used in a process performed after the formation of the same layer, damage to the hole injection layer 4A due to dissolution, alteration, decomposition, or the like can be suppressed. . As described above, since the hole injection layer 4A is made of a material having high chemical resistance, it is possible to prevent a decrease in hole conduction efficiency of the hole injection layer 4A.

  The hole injection layer 4A made of tungsten oxide in the fifth embodiment includes both a case where the hole injection layer 4A is composed of only a nanocrystal structure and a case where the hole injection layer 4A is composed of both a nanocrystal structure and an amorphous structure. The nanocrystal structure is preferably present in the entire hole injection layer 4A, but between the interface between the ITO layer 3 and the hole injection layer 4A and the interface between the hole injection layer 4A and the hole transport layer 6A. If the grain boundary is connected at one place, holes can be efficiently conducted from the lower end to the upper end of the hole injection layer 4A.

An example of using a layer containing a tungsten oxide crystal as a hole injection layer has been reported in the past. For example, Non-Patent Document 2 suggests that hole conduction efficiency is improved by crystallizing a tungsten oxide layer by annealing at 450 ° C. However, Non-Patent Document 2 does not describe the conditions for forming a tungsten oxide layer having a large area and the influence of tungsten oxide formed as a hole injection layer on the substrate on other layers on the substrate. Practical mass productivity of organic EL display panels is not shown. Further, it is not shown that a tungsten oxide nanocrystal having a structure similar to an oxygen defect is positively formed in the hole injection layer. The hole injection layer according to one embodiment of the present invention includes a tungsten oxide layer that hardly causes a chemical reaction, is stable, and can withstand a mass production process of a large organic EL display panel. Furthermore, it is greatly different from the prior art in that excellent hole conduction efficiency is realized by making the tungsten oxide layer positively have a structure similar to oxygen defects.
(Coating film 20A)
The covering film 20A is provided so as to cover the entire surface of the planarizing film 11 as in the first embodiment. Here, the coating film 20A is composed of the same tungsten oxide film as the hole injection layer 4A, and is composed of both a nanocrystal structure and a nanocrystal structure and an amorphous structure.
(Electron transport layer 7, cathode 8, sealing layer 9)
The electron transport layer 7 has a function of injecting electrons from the cathode 8 to the light emitting layer 6B. For example, barium with a thickness of about 5 nm, lithium fluoride with a thickness of about 1 nm, sodium fluoride, or a combination thereof Is preferably formed.

  The cathode 8 is composed of, for example, an ITO layer having a thickness of about 100 nm. A direct current power source DC is connected to the anode 2 and the cathode 8, and power is supplied to the organic light emitting device 1C from the outside.

  The sealing layer 9 has a function of suppressing exposure of the organic light emitting device 1C to moisture and air, and is formed of a material such as SiN (silicon nitride) or SiON (silicon oxynitride), for example. In the case of a top emission type organic light emitting device, it is preferably formed of a light transmissive material.

Also in the organic light emitting device 1C of the fifth embodiment having the above configuration, substantially the same effect as that of the organic light emitting device 1 of the first embodiment can be expected.
That is, by forming the coating film 20A made of a tungsten oxide film formed under predetermined film formation conditions, the metal oxide film in the vicinity of the bottom surface portion 2h of the anode 2 can be effectively prevented, and the anode 2 and the source electrode can be prevented. It is possible to ensure and maintain good electrical conductivity between 17. In addition, the coating film 20 can form a good Schottky ohmic connection with at least the anode 2, can inject holes into the light emitting layer 6 </ b> B side, and can contribute to exhibiting excellent luminous efficiency.

  Further, since the entire surface (upper surface portion 11t, side surface portion 11s, and hole inner side surface portion 11h) of the planarizing film 11 is covered with the coating film 20, moisture adsorption from the outside to the planarizing film 11 is suppressed, and the planarization film 11 is flat. There is almost no moisture movement from the conversion film 11 to the light emitting layer 6B side. Accordingly, it is possible to prevent the light emission characteristics from being deteriorated due to the alteration of the light emitting layer 6B, and to expect a long life while maintaining good light emission characteristics. Further, expansion of the planarizing film 11 due to water absorption can be suppressed, and film peeling of the anode 2 can be avoided.

In addition, since the device 1C is provided with the hole injection layer 4 similar to that of the device 1, an excellent Schottky ohmic connection is formed between the anode 2 and the hole injection layer 4A. Can be expected.
<Various experiments and considerations regarding film formation conditions of hole injection layer 4A>
(Regarding the film forming conditions of the hole injection layer 4A)
In addition to the effect of the Schottky ohmic connection between the anode 2 and the hole injection layer 4A, in the fifth embodiment, the tungsten oxide constituting the hole injection layer 4A is formed under predetermined film formation conditions, whereby the hole injection layer is formed. By intentionally having a nanocrystal structure in 4A, the hole conduction efficiency is improved, and the organic light emitting device 1C can be driven at a low voltage. The predetermined film forming conditions will be described in detail.

  A DC magnetron sputtering apparatus was used for film formation, and the target was metallic tungsten. The substrate temperature was not controlled. It is considered that the sputtering gas is preferably composed of argon gas, the reactive gas is composed of oxygen gas, and the respective gases are set to the same flow rate, and the film is formed by the reactive sputtering method. Note that the method for forming the hole injection layer 4A is not limited to this, and it may be formed by a method other than the sputtering method, for example, a known method such as a vapor deposition method or a CVD method.

  In order to form the hole injection layer 4A made of tungsten oxide having a nanocrystal structure, atoms and clusters flying to the substrate have a low kinetic energy that does not break the regular structure previously formed on the substrate. It is considered necessary to be able to reach the substrate and move together on the substrate with regularity. For this purpose, it is desirable that the film be formed at the lowest possible film formation rate.

  Here, from the experimental results to be described later, the above-described (1) to (4) are conceivable as film formation conditions that can realize the low film formation rate in the reactive sputtering method. The inventors of the present application obtained a hole injection layer made of tungsten oxide having a nanocrystal structure by forming a hole injection layer under these film formation conditions (1) to (4), and the driving voltage of the organic light emitting device was reduced. The reduction effect is confirmed.

Regarding the above (1), in the experiment described later, the total pressure has an upper limit value of 4.7 Pa, but it has been separately confirmed that the same tendency is exhibited up to at least 7.0 Pa. Regarding 2), in the experiment described later, the ratio of the oxygen gas partial pressure to the total pressure is set to 50%, but a reduction in driving voltage is confirmed at least 50% to 70%.

  Furthermore, supplementary explanation will be given regarding (4) above. When the flow rates of argon gas and oxygen gas are the same, the film quality is considered to be determined by the input power density and the total pressure. The input power density in (3) changes the number and kinetic energy of tungsten atoms and tungsten clusters that are sputtered and released from the target. In other words, by reducing the input power density, the number of tungsten released from the target is reduced, the kinetic energy is also reduced, the amount of tungsten flying to the substrate can be reduced and the kinetic energy can be reduced, and the film can be formed at a low film formation rate. Formation can be expected. The total pressure in (1) changes the mean free path of tungsten atoms and tungsten clusters released from the target. In other words, if the total pressure is high, the probability that tungsten atoms and tungsten clusters will repeatedly collide with the gas in the chamber before reaching the substrate increases, the flying directions of tungsten atoms and tungsten clusters are dispersed, and kinetic energy is also increased. By losing by collision, the amount of tungsten reaching the substrate can be reduced and the kinetic energy can be reduced, and film formation at a low film formation rate can be expected.

  However, it is considered that there is a limit to changing the film formation rate by independently controlling the input power density and the total pressure. Therefore, a value obtained by dividing the total pressure by the input power density was newly adopted as a parameter for determining the film formation rate, and the film formation condition (4) was determined.

Specifically, the conditions of the above parameters (total pressure / power density) for forming the nanocrystal structure of the fifth embodiment are 0.78 Pa · cm ² / W or more within the range of the experiment described later, 0.7Pa · ^cm 2 / W is considered necessary larger than, the more reliable is considered to be preferable at 0.8Pa · ^cm 2 / W or more. On the other hand, the upper limit value of the above parameter is 3.13 Pa · cm ² / W or less within the range of the experiment described later, and is considered to be smaller than 3.2 Pa · cm ² / W. Is considered to be preferably 3.1 Pa · cm ² / W or less. However, from the above consideration regarding the film formation rate and the nanocrystal structure, the lower the film formation rate, the better. Therefore, it is considered that the upper limit is not necessarily limited. From the above, the film formation condition (4) was determined.
It was confirmed by another experiment that the film formation rate was lower as the parameter value was larger and the film formation rate was higher as the parameter value was smaller.

Next, various experiments were conducted to confirm the effectiveness of the film formation conditions.
First, in order to evaluate the film conduction condition dependency of the hole conduction efficiency of the hole injection layer 4A, a hole-only element 1G shown in FIG. 36 was fabricated as an evaluation device. As described in the first embodiment, since the carriers flowing through the hole-only element can be regarded as only holes, the hole-only element is suitable for evaluating the hole conduction efficiency.

  As shown in FIG. 36, the hole-only element 1G is obtained by changing the organic light emitting device 1C of FIG. 35 to the configuration of the evaluation device, replacing the cathode 8 with a gold electrode, omitting the anode 2, and omitting the ITO layer 3 Is the anode, and the electron transport layer 7 and the bank 5 are omitted. Specifically, the layers are manufactured based on the above-described manufacturing method. The thickness of each layer is 30 nm for the hole injection layer 4A, 20 nm for the hole transport layer 6A made of TFB, 70 nm for the light emitting layer 6B made of F8BT, and gold. The cathode 8 was 100 nm.

  In the manufacturing process of the hole-only element 1G, the hole injection layer 4A was formed by a reactive sputtering method using a DC magnetron sputtering apparatus. The gas in the chamber was composed of at least one of argon gas and oxygen gas, and metallic tungsten was used as the target. The substrate temperature was not controlled, and the total pressure was adjusted by the flow rate of each gas. The partial pressures of argon gas and oxygen gas in the chamber are 50%, respectively.

  Each hole-only device 1 </ b> G composed of the hole injection layer 4 </ b> A having the five film formation conditions of α to ε shown in Table 8 was produced. Hereinafter, the hole only element 1G formed under the film formation condition α is HOD-α, the hole only element 1G formed under the film formation condition β is HOD-β, and the hole only element 1G formed under the film formation condition γ is HOD. The hole-only element 1G formed under the film formation condition δ is referred to as HOD-δ, and the hole-only element 1G formed under the film formation condition ε is referred to as HOD-ε.

  Each produced hall-only element 1G was connected to DC power supply DC, and a voltage was applied. The applied voltage at this time was changed, and the current value that flowed according to the voltage value was converted to a value (current density) per unit area of the element.

FIG. 37 shows the relationship between the applied voltage and current density of each hole-only element 1G. In the figure, the vertical axis represents current density (mA / cm ² ), and the horizontal axis represents applied voltage (V).
Table 9 shows the driving voltage of each hole-only element 1G. The “driving voltage” here is an applied voltage at a current density of 0.3 mA / cm ² .

  It can be said that the smaller the drive voltage, the higher the hole conduction efficiency of the hole injection layer 4A. This is because, in each hole-only device 1G, the configuration other than the hole injection layer 4A is the same, so the hole injection barrier between two adjacent layers excluding the hole injection layer 4A and the layers other than the hole injection layer 4A The hole conduction efficiency is considered constant. For the reasons described later, it is considered that the conduction efficiency of the hole injection layer 4A has a stronger influence on the device characteristics than the hole injection efficiency from the hole injection layer 4A to the hole transport layer 6A. Furthermore, it was confirmed in another experiment that the ITO layer 3 and the hole injection layer 4A used in the experiment have the Schottky ohmic connection of the present invention, as described in the first embodiment. . Therefore, it can be said that the difference in driving voltage depending on the film formation conditions of the hole injection layer 4A in each hole-only device 1G strongly reflects the difference in hole conduction efficiency of the hole injection layer 4A.

  As shown in Table 9 and FIG. 37, HOD-ε has the slowest rise of the current density-applied voltage curve and the highest drive voltage compared to other devices. Therefore, it is considered that HOD-α, β, γ, and δ are superior in hole conduction efficiency as compared with HOD-ε produced under film forming conditions that lower the total pressure and maximize the input power density.

  The verification regarding the hole conduction efficiency of the hole injection layer 4A in the hole-only device 1G has been described above. The hole-only device 1G is the same as the organic light-emitting device 1C except for the cathode 8 with respect to the essential parts related to the characteristics of the device. It is a configuration. Therefore, also in the organic light emitting device 1C, the film formation condition dependency of the hole conduction efficiency of the hole injection layer 4A is essentially the same as that of the hole only element 1G.

  In order to confirm this, an organic light emitting device 1C using a hole injection layer 4A formed under each film forming condition of α to ε was manufactured. Hereinafter, the organic light emitting device 1C formed under the film forming condition α is BPD-α, the organic light emitting device 1C formed under the film forming condition β is BPD-β, and the organic light emitting device 1C formed under the film forming condition γ is BPD. The organic light-emitting device 1C formed under −γ and the film formation condition δ is referred to as BPD-δ, and the organic light-emitting device 1C formed under the film formation condition ε is referred to as BPD-ε.

  Each organic light emitting device 1C is obtained by changing the organic light emitting device 1C of FIG. 35 to the configuration of the evaluation device, replacing the cathode 8 from ITO to aluminum, omitting the anode 2, and using the ITO layer 3 as the anode. Bank 5 is omitted. Specifically, the layers are manufactured based on the manufacturing method described above. The thickness of each layer is 30 nm for the hole injection layer 4A, 20 nm for the hole transport layer 6A made of TFB, 70 nm for the light emitting layer 6B made of F8BT, and 70 nm for the barium layer. The electron transport layer 7 was 5 nm, and the cathode 8 made of an aluminum layer was 100 nm.

Each organic light emitting device 1C having the produced film forming conditions α to ε was connected to a DC power source DC, and a voltage was applied. The applied voltage at this time was changed, and the current value that flowed according to the voltage value was converted to a value (current density) per unit area of the element.

FIG. 38 shows the relationship between the applied voltage and current density of each organic light emitting device 1C. In the figure, the vertical axis represents current density (mA / cm ² ), and the horizontal axis represents applied voltage (V).

Table 10 shows the driving voltage of each organic light emitting device 1C. The “driving voltage” here is an applied voltage at a current density of 8 mA / cm ² .

  As shown in Table 10 and FIG. 38, BPD-ε has the slowest rise of the current density-applied voltage curve and the highest drive voltage compared to other devices. This is the same tendency as the hole-only elements HOD-α to ε having the same film forming conditions.

  From the above results, it was confirmed that the film formation condition dependency of the hole conduction efficiency of the hole injection layer 4A is also acting in the organic light emitting device 1C as in the case of the hole only element 1G. That is, also in the organic light emitting device 1C, the hole conduction efficiency of the hole injection layer 4A is improved by performing the film formation under the film formation conditions in the range of the film formation conditions α, β, γ, and δ, thereby reducing the low voltage. It is considered that driving has been realized.

  In the above, the input power condition is represented by the input power density as shown in Table 8. When using a DC magnetron sputtering apparatus different from that used in this experiment, by adjusting the input power so that the input power density is in the above condition, a tungsten oxide layer having excellent hole conduction efficiency as in this experiment. 4A can be obtained. The total pressure and oxygen partial pressure do not depend on the apparatus.

  In addition, when the hole injection layer 4A is formed by the reactive sputtering method, the substrate temperature is not intentionally set in a sputtering apparatus disposed in a room temperature environment. Therefore, at least the substrate temperature before film formation is room temperature. However, the substrate temperature may increase by several tens of degrees Celsius during film formation.

  In addition, the inventor of this application has confirmed by another experiment that the drive voltage rises conversely when the oxygen partial pressure is increased too much. Therefore, the oxygen partial pressure is desirably 50% to 70%.

From the above experimental results, an organic light emitting device having a hole injection layer produced under film formation conditions α, β, γ, and δ is preferable for low voltage driving, and more preferably an organic light emitting device produced under film formation conditions α and β. It is. Hereinafter, an organic light-emitting device including a hole injection layer manufactured under film formation conditions α, β, γ, and δ is an object of the present application.
(Regarding the chemical state of tungsten in the hole injection layer 4A)
A pentavalent tungsten atom is present in the tungsten oxide layer constituting the hole injection layer 4A of the organic light emitting device 1C of the fifth embodiment. These pentavalent tungsten atoms are formed by adjusting the film forming conditions shown in the previous experiment. Details are described below.

  In order to confirm the chemical state of tungsten oxide deposited under the above-described deposition conditions α to ε, a hard X-ray photoelectron spectroscopic measurement (hereinafter simply referred to as “HXPS measurement”) experiment was performed. Here, generally, information from a hard X-ray photoelectron spectrum (hereinafter simply referred to as “HXPS spectrum”) up to several tens of nm in depth of the film of the measurement object, in other words, information on the bulk of the film is obtained. The measurement depth is determined by the angle formed by the surface normal and the direction in which photoelectrons are detected. In this experiment, in order to observe the state of the valence in the entire thickness direction of the tungsten oxide layer, the angle was adjusted and determined to be 40 °.

HXPS measurement conditions are as follows. During the measurement, no charge up occurred.
(HXPS measurement conditions)
SPring-8 beam line BL46XU is used.

Light source: Synchrotron radiation (energy 8 keV)
Bias: None Outgoing angle: 40 ° angle with substrate normal direction
Measurement point interval: 0.05 eV
Samples for HXPS measurement were prepared under the film formation conditions α to ε shown in Table 8. A 30-nm-thick tungsten oxide layer (considered as hole injection layer 4A) was formed on the ITO substrate formed on glass by the reactive sputtering method, thereby obtaining a sample for HXPS measurement. . Hereinafter, the HXPS measurement samples prepared under the film formation conditions α, β, γ, δ, and ε are referred to as sample α, sample β, sample γ, sample δ, and sample ε, respectively.

  HXPS measurement was performed on each hole injection layer 4A of samples α to ε. The resulting spectrum is shown in FIG. The horizontal axis is the binding energy, the Fermi level of the ITO substrate is the origin, and the left direction is the positive direction. The vertical axis represents the photoelectron intensity.

In the binding energy region shown in FIG. 39, three peaks are observed, and each peak is 5p _3/2 level (W5p _3/2 ), 4f _5/2 level of tungsten from the left to the right in the figure. It was assigned to be a peak corresponding to (W4f _5/2 ), 4f _7/2 level (W4f _7/2 ).

Next, peak fitting analysis is performed on each peak assigned to W5p _3/2 , W4f _5/2 , and W4f _7/2 of the spectrum of each sample using the photoelectron spectroscopic analysis software “XPSPEAK 4.1”. It was. First, the area intensity ratio of each component corresponding to W4f _7/2 , W4f _5/2 , W5p _3/2 is determined from the photoionization cross-sectional area with respect to the energy of hard X-rays as follows: W4f _7/2 : W4f _5/2 : W5p _3/2 = 4: 3: 10.5. Next, as shown in Table 11, the position of the peak top of the component (W ⁶⁺ 4f _7/2 ) attributed to the hexavalence of W4f _7/2 was adjusted to the binding energy of 35.7 eV. Next, the positions and half-widths of the peak tops of the components attributed to the surface photoelectrons of W5p _3/2 , W4f _5/2 , and W4f _7/2 , the component attributed to hexavalent, and the component attributed to pentavalent Was set within the range shown in Table 11. The initial value of the ratio of the Lorentzian function in the Gaussian-Lorentzian mixed function used for fitting each component was also set within the range shown in Table 11. Furthermore, the initial value of the area intensity of each component was arbitrarily set while maintaining the above intensity ratio. Then, the area intensity of each component is moved while maintaining the above intensity ratio, and the peak position of each component, the full width at half maximum, and the ratio of the Lorentzian function are moved within the range of Table 11, and optimization calculation is performed up to 100 times, The final peak fitting analysis result was obtained.

The final peak fitting analysis result is shown in FIG. FIG. 40A shows the analysis result of the sample α, and FIG. 40B shows the analysis result of the sample ε.
In both figures, the broken lines (sample α, sample ε) are measured spectra (corresponding to the spectrum of FIG. 39), and the two-dot chain line (surface) is the component (W ^sur 5p _3/2 , W ^sur 4f ₅ ) belonging to the surface photoelectrons. _{/ 2} , W ^sur 4f _7/2 ), the dotted line (W ⁶⁺ ) is a component attributed to hexavalence (W ⁶⁺ 5p _3/2 , W ⁶⁺ 4f _5/2 , W ⁶⁺ 4f _7/2 ), one-dot chain line ( W ⁵⁺ ) is a component (W ⁵⁺ 5p _3/2 , W ⁵⁺ 4f _5/2 , W ⁵⁺ 4f _7/2 ) attributed to pentavalent. A solid line (fit) is a spectrum obtained by adding the components indicated by the two-dot chain line, the dotted line, and the one-dot chain line. .

The spectra of the broken line and the solid line in FIG. 40 agree very well, that is, the peaks attributed to the levels of W5p _3/2 , W4f _5/2 , and W4f _7/2 are all in the hole injection layer 4A. The component (surface) attributed to photoelectrons from the surface, the component attributed to hexavalent (W ⁶⁺ ) and the component attributed to pentavalent (W ⁵⁺ ) contained in the hole injection layer 4A It can be seen that it can be explained well. .

In addition, in the sample α in FIG. 40A, a component (5) attributed to the corresponding pentavalent (0.3 to 1.8 V lower binding energy region than the component (W ⁶⁺ ) attributed to the hexavalent ( W ⁵⁺ ) can be confirmed. On the other hand, in the sample ε of FIG. 40B, such a component attributed to pentavalent cannot be confirmed. For ease of understanding, an enlarged view of a circled portion is shown on the right side of each of FIGS. 40 (a) and (b). According to this, it can be confirmed that there is a peak of W ⁵⁺ one-dot chain line (indicated by (c) in the figure) in the sample α, but it cannot be confirmed in the sample ε. Further, focusing on the details of the enlarged view, in sample α, there is a large “deviation” between the solid line (fit), which is the sum of the components of the peak fitting result, and the dotted line (W ⁶⁺ ) of only the hexavalent component. On the other hand, sample ε does not have the “shift” as much as sample α. That is, it is assumed that this “deviation” in the sample α suggests the presence of pentavalent tungsten atoms.

Next, W ⁵⁺ / W ⁶⁺ which is the ratio of the number of pentavalent tungsten atoms to hexavalent tungsten atoms in samples α to ε was calculated. This ratio was calculated by dividing the area intensity of the component attributed to pentavalent by the area intensity of the component attributed to corresponding hexavalence in the peak fitting analysis result of each sample.

In addition, the area intensity ratio of the component attributed to pentavalent and the component attributed to the corresponding hexavalent is the same value in terms of measurement in any of W5p _3/2 , W4f _5/2 , and W4f _7/2 become. In fact, the same value was confirmed in this study. Therefore, in the following discussion, only W4f _7/2 is used.

Table 12 shows W ⁵⁺ / W ⁶⁺ in W4f _7/2 of samples α to ε.

According to the values of W ⁵⁺ / W ⁶⁺ shown in Table 12, sample α has the highest proportion of pentavalent tungsten atoms in hole injection layer 4A, and then sample β, sample γ, and sample δ in this order. The ratio tends to be small, and the sample ε is the smallest. Further, comparing the results of Table 10 and Table 12, it can be seen that the driving voltage of the organic light emitting element tends to decrease as the proportion of pentavalent tungsten atoms in the hole injection layer 4A increases.

In addition, by calculating | requiring the composition ratio of tungsten and oxygen using said HXPS measurement, the ratio of the number of tungsten atoms and oxygen atoms in the hole injection layer 4A is average for the whole layer in both samples α to ε. It was confirmed that the ratio was approximately 1: 3. From this ratio, in any of samples α to ε, the hole injection layer 4A is considered to have an atomic arrangement based on tungsten trioxide in the basic structure almost entirely. In addition, this inventor performed the X-ray absorption fine structure (XAFS) measurement of 4 A of hole injection layers, and confirmed that the said basic structure was formed in all the samples (alpha)-(epsilon).
(Regarding the electronic state of the hole injection layer 4A)
The hole injection layer 4A made of tungsten oxide in the fifth embodiment has an occupied level in the vicinity of the Fermi surface, like the hole injection layer 4 in the first embodiment. By the action of the occupied level, the interface level connection is made between the hole injection layer 4A and the hole transport layer 6A, and the hole injection barrier between the hole injection layer 4A and the hole transport layer 6A is kept small. . As a result, the organic light emitting device of Embodiment 5 can be driven at a low voltage.

  The occupied level in the vicinity of the Fermi surface exists at the grain boundary of the nanocrystal not only in the above-described interface but also in the layer of the hole injection layer 4A as described later, and serves as a hole conduction path. . As a result, the hole injection layer 4A can obtain good hole conduction efficiency, and the organic light emitting device of Embodiment 5 can be driven at a lower voltage.

For each hole injection layer 4A of the samples α to ε, an experiment for confirming the existence of an occupied level in the vicinity of the Fermi surface was performed using UPS measurement.
Samples α to ε were all deposited in a sputtering apparatus and then transferred to a glove box connected to the sputtering apparatus and filled with nitrogen gas, and kept in a state not exposed to the atmosphere. And it enclosed with the transfer vessel in the said glove box, and mounted | worn with the photoelectron spectrometer. Thereby, UPS measurement was carried out without exposing the hole injection layer 4A to the air after film formation.

UPS measurement conditions are as follows. Note that no charge-up occurred during the measurement.
Light source: He I line Bias: None Output angle: Normal direction of substrate Measurement point interval: 0.05 eV
FIG. 41 shows a UPS spectrum in the region (y) of each hole injection layer 4A of samples α and ε. Here, the symbols such as the region (y) and the point (iii) are as described in the first embodiment, and the horizontal axis is the relative binding energy with the point (iii) as the origin.

  As shown in FIG. 41, in the hole injection layer 4A of the sample α, from the point (iii) where the binding energy is about 3.6 eV lower than the point (iii) which is the rising position of the valence band, about 1. from the point (iii). The raised structure in the vicinity of the Fermi surface described in the first embodiment can be confirmed in the region up to the position where the binding energy is 8V lower. On the other hand, such a raised structure cannot be confirmed in the sample ε. In the samples β, γ, and δ, the above-described raised structure was confirmed, and there was no significant difference from the sample α in the shape and normalized strength.

  However, the UPS measurement is an evaluation of the surface layer only. Therefore, it was confirmed by HXPS measurement of each hole injection layer 4A of samples α and ε whether the raised structure near the Fermi surface exists even over the entire film of hole injection layer 4A. On the other hand, it was still not confirmed in the sample ε.

  From the above experiment, it was confirmed that the hole injection layer 4A of Embodiment 5 has an occupied level in the vicinity of the Fermi surface. As described above, in the photoelectron spectrum, a tungsten oxide layer having a structure that is raised (not necessarily a peak) in a region having a binding energy of about 1.8 to 3.6 eV lower than the point (iii), that is, an occupancy quasi-near the Fermi surface. By using a tungsten oxide layer having a position as a hole injection layer, the organic light-emitting device of Embodiment 5 can exhibit excellent hole conduction efficiency.

  The characteristics of the series of hole-only devices and organic light-emitting devices described in the fifth embodiment include the hole injection efficiency from the ITO layer 3 to the hole injection layer 4A and the hole injection from the hole injection layer 4A to the hole transport layer 6A. It is considered that the hole conduction efficiency of the hole injection layer 4A has a greater influence than the efficiency. The reason is described below.

  In each hole injection layer 4A under the deposition conditions α, β, γ, and δ, as described above, a raised structure near the Fermi surface was confirmed in the UPS measurement. This means that, in FIG. 17 in the first embodiment, these hole injection layers 4A all have injection sites (x) with a number density that can be confirmed by UPS. . Further, the shape of the raised structure and the normalized strength are not much different in each of the α, β, γ, and δ hole injection layers 4A. Therefore, the number density of the injection sites (x) is each of α, β, γ, and δ. It is considered that the hole injection layer 4A has the same level. Then, considering that the film formation condition α is equivalent to the film formation condition A of the first embodiment, each of the α, β, γ, and δ hole injection layers 4A is injected into the hole transport layer 6A. It is considered that the injection site (x) has a sufficient number density with respect to the number density of the site (y). That is, the hole injection layers 4A under the film formation conditions α, β, γ, and δ can be regarded as having the same degree of hole injection efficiency from the hole injection layer 4A to the hole transport layer 6A.

However, although the drive voltages of HOD-α, β, γ, and δ in Table 9 are all good, there is an opening of 2.25V. Therefore, factors other than the hole injection efficiency from the hole injection layer 4A to the hole transport layer 6A influence the opening. In the fifth embodiment, since the Schottky ohmic connection is formed between the ITO layer 3 and the hole injection layer 4A as described above, the factor affecting the opening is the remaining one, that is, This is considered to be the hole conduction efficiency of the hole injection layer 4A itself.
(Consideration of the relationship between W ⁵⁺ / W ⁶⁺ value and hole conduction efficiency)
FIG. 42 is a diagram for explaining the structure of a tungsten oxide crystal. As described above, the tungsten oxide according to the fifth embodiment has a composition ratio of tungsten to oxygen of approximately 1: 3. Therefore, here, tungsten trioxide will be described as an example.

As shown in FIG. 42, the tungsten trioxide crystal has a structure in which six oxygen atoms are bonded to one tungsten atom in octahedral coordination, and the octahedrons share apex oxygen atoms. (In FIG. 42, for the sake of simplification, the octahedrons are shown in an orderly arrangement like rhenium trioxide, but the octahedrons are actually arranged slightly distorted.)
These tungsten atoms bonded to six oxygen atoms in octahedral coordination are hexavalent tungsten atoms. On the other hand, a tungsten atom having a valence lower than hexavalent corresponds to a disorder in which the octahedral coordination is disturbed in some way. Typically, one of the six coordinated oxygen atoms is missing and has an oxygen defect. At this time, the tungsten atom bonded to the remaining five oxygen atoms is pentavalent. Become.

  In general, when oxygen vacancies exist in metal oxides, in order to maintain electrical neutrality, electrons left by the missing oxygen atoms are supplied to metal atoms around the vacancies. Lower. The pentavalent tungsten atom is supplied with one electron in this way, and thus has one unshared electron pair together with one electron used for bonding with the missing oxygen atom. it is conceivable that.

The mechanism of hole conduction in the hole injection layer 4A of the fifth embodiment having pentavalent tungsten atoms inferred from the above is, for example, as follows.
A pentavalent tungsten atom can donate an electron to a hole from its unshared electron pair. Therefore, if pentavalent tungsten atoms are close to each other, holes can move by hopping between unshared electron pairs of pentavalent tungsten atoms by the voltage applied to the hole injection layer. is there. Furthermore, if the pentavalent tungsten atoms are substantially adjacent to each other, the overlap of the 5d orbitals corresponding to the unshared electron pair becomes large and can be easily moved without hopping.

That is, in the fifth embodiment, it is considered that holes are conducted between pentavalent tungsten atoms present in the hole injection layer 4A.
Based on the above assumption, in the hole injection layer 4A in which the value of W ⁵⁺ / W ⁶⁺ is large as in the sample α, that is, the ratio of pentavalent tungsten atoms is high, pentavalent tungsten atoms are closer and adjacent to each other. This facilitates hole conduction at a low voltage, and it is considered that excellent hole conduction efficiency can be exhibited in the organic light emitting device 1C.

In samples γ and δ, the value of W ⁵⁺ / W ⁶⁺ is not as high as that of sample α, but the device was driven at a favorable low voltage even if it was about 3.2%. From this, it is considered that the value of W ⁵⁺ / W ⁶⁺ should be about 3.2% or more.
(Regarding the fine structure of tungsten oxide in the hole injection layer 4A)
The tungsten oxide layer constituting the hole injection layer 4A of the fifth embodiment has a nanocrystal structure. This nanocrystal structure is formed by adjusting the film forming conditions. Details are described below.

In order to confirm the presence of the nanocrystal structure in each hole injection layer 4A formed under the film formation conditions α to ε in Table 8, a transmission electron microscope (TEM) observation experiment was performed.
The hole injection layer 4A in the sample for TEM observation was formed using a DC magnetron sputtering apparatus. Specifically, a 30-nm-thick tungsten oxide layer (considered as the hole injection layer 4A) was formed on the ITO substrate formed on glass by the reactive sputtering method.
Hereinafter, the TEM observation samples prepared under the film formation conditions α, β, γ, δ, and ε are referred to as samples α, β, γ, δ, and ε, respectively.

  Here, in general, TEM observation is performed by reducing the thickness direction of the sample with respect to the surface to be observed. In the fifth embodiment, the cross section of the hole injection layer 4A is observed, the cross section is produced by sample processing using a focused ion beam (FIB) apparatus, and further thinned to a thickness of about 50 nm. The conditions for FIB processing and TEM observation are as follows.

(FIB processing conditions)
Equipment used: Quanta200 (manufactured by FEI)
Acceleration voltage: 30 kV (final finish 5 kV)
Thin film thickness: about 50nm
(TEM observation conditions)
Equipment used: Topcon EM-002B (Topcon Technohouse)
Observation method: High-resolution electron microscopy Acceleration voltage: 200 kV
FIG. 43 shows a TEM observation photograph of a cross section of each hole injection layer 4A of samples α to ε. The magnification of the photograph follows the scale bar described in the photograph. The darkest part to the brightest part is divided into 256 gradations for display.

In each TEM photograph of the samples α, β, γ, and δ, a regular linear structure is confirmed due to the partial arrangement of bright portions in the same direction. It can be seen from the scale bar that the linear structures are arranged at intervals of approximately 1.85 to 5.55 cm. On the other hand, in the sample ε, the bright portions were irregularly dispersed, and a regularly arranged linear structure was not confirmed.
In general, in a TEM photograph, a region having the linear structure as described above represents one fine crystal. In the TEM photograph of FIG. 43, the size of this crystal can be seen as a nanosize of about 5 nm to 10 nm. Therefore, the presence or absence of the linear structure is paraphrased as follows. That is, in the samples α, β, γ, and δ, the nanocrystal structure of tungsten oxide can be confirmed, but in the sample ε, it cannot be confirmed, and almost the whole is considered to be an amorphous structure.

  In the TEM photograph of sample α in FIG. 43, an arbitrary one of the nanocrystals is illustrated by a white line outline. In addition, this outline is not an exact thing but an illustration to the last. This is because it is difficult to specify an accurate contour because the TEM photograph includes not only the outermost surface of the cross section but also the state of the lower layer. The size of the nanocrystal surrounded by this outline can be read as about 5 nm.

  FIG. 44 shows the result of two-dimensional Fourier transform of the TEM observation photograph of FIG. 43 (referred to as a two-dimensional Fourier transform image). This two-dimensional Fourier transform image is a wave number distribution in the inverse space of the TEM observation photograph of FIG. 43, and thus shows the periodicity of the TEM observation photograph. Specifically, the two-dimensional Fourier transform image of FIG. 44 was created by performing Fourier transform on the TEM photograph of FIG. 43 using image processing software “LAview Version # 1.77”.

In the two-dimensional Fourier transform images of the samples α, β, γ, and δ, relatively clear three or two concentric bright parts centered on the center point (Γ point) are confirmed. On the other hand, in the sample ε, this concentric bright part is unclear.
The above-described “unclearness” of the concentric bright portions indicates the disorder of the order in the TEM photograph of FIG. That is, the hole injection layer 4A of the samples α, β, γ, and δ in which concentric bright portions can be clearly confirmed has relatively high order and regularity, and the hole injection layer 4A of the sample ε has order and regularity. It is low.

  In order to clarify the above order, a graph showing the change in luminance with respect to the distance from the center point of the image was created from each two-dimensional Fourier transform image of FIG. FIG. 45 is a diagram showing an outline of the creation method, and shows a sample α as an example.

  As shown in FIG. 45 (a), a two-dimensional Fourier transform image is rotated in increments of 1 ° from 0 ° to 359 ° with the center point as the center of rotation, and the X axis in the figure from the center point every 1 ° rotation. Measure the luminance with respect to the distance in the direction. Then, all the measurement results for every 1 ° rotation were added and divided by 360 to obtain an average luminance (referred to as normalized luminance) with respect to the distance from the center point. FIG. 45B is a graph in which the distance from the center point is plotted on the horizontal axis and the normalized luminance at each distance is plotted on the vertical axis. Note that “Microsoft Office Picture Manager” was used to rotate the two-dimensional Fourier transform image, and image processing software “ImageNos” was used to measure the distance from the center point and the luminance. Hereinafter, a plot created by the method described with reference to FIG. 45 and showing the relationship between the distance from the center point and the normalized brightness at each distance is referred to as a “brightness change plot”.

46 and 47 show luminance change plots of samples α to ε. It can be seen that each sample has a peak indicated by an arrow separately from the high brightness portion at the center point. Hereinafter, the peak of the arrow that appears closest to the center point in this luminance change plot is referred to as “peak P1”.
46 and 47, it can be seen that the peak P1 of the samples α, β, γ, and δ has a sharp convex shape as compared to the peak P1 of the sample ε. The sharpness of the peak P1 of each sample was digitized and compared. FIG. 48 is a diagram showing an outline of the evaluation method, and shows samples α and ε as examples.

  48A and 48B are luminance change plots of samples α and ε, respectively, and FIGS. 48A1 and 48B1 are enlarged views near the peak P1. The “peak width L of the peak P1” indicated by “L” in the figure is used as an index indicating the “sharpness” of the peak P1.

  In order to determine the “peak width L of peak P1” more accurately, the luminance change plots of FIGS. 48 (a1) and (b1) are first-order differentiated and shown in FIGS. 48 (a2) and (b2). . In FIGS. 48 (a2) and 48 (b2), the value on the horizontal axis corresponding to the peak top of the peak P1 and the value on the horizontal axis corresponding to the position where the differential value first becomes 0 from the peak top toward the center point. The peak width L is defined as the difference between the two.

  Table 13 shows the values of the peak width L in the samples α to ε when the value on the horizontal axis corresponding to the peak top of the peak P1 is normalized as 100.

  As shown in Table 13, the peak width L is the smallest for the sample α, increases in the order of the samples β, γ, and δ, and is the maximum for the sample ε. Here, the peak width L of the samples γ and δ is not as small as the sample α. However, even if the value is about 21.9, the organic light emitting device 1C having the hole injection layer 4A under the film forming conditions γ and δ has good hole conduction efficiency as described above.

The value of the peak width L in Table 13 indicates the clarity of the concentric bright part closest to the center point in the two-dimensional Fourier transform image of FIG. The smaller the value of the peak width L, the smaller the spread of the concentric bright portion, and thus the regularity and order in the TEM photograph of FIG. 43 before the two-dimensional Fourier transform becomes higher. This is considered to correspond to an increase in the proportion of the area occupied by the nanocrystal structure in the TEM photograph. On the other hand, the larger the value of the peak width L, the larger the concentric bright portion spreads. Therefore, the regularity and order in the TEM photograph of FIG. 43 before the two-dimensional Fourier transform become lower. This is considered to correspond to a decrease in the proportion of the area occupied by the nanocrystal structure in the TEM photograph.
(Consideration of the relationship between nanocrystal structure and hole conduction efficiency)
The following was found from each experiment of the fifth embodiment. A hole injection layer having good hole conduction efficiency has an occupied level in the vicinity of the Fermi surface throughout the film, has a high proportion of pentavalent tungsten atoms, has a nanocrystal structure, and has high regularity and order of the film structure. On the other hand, the hole injection layer with poor hole conduction efficiency does not confirm the occupied level near the Fermi surface over the entire film, and the proportion of pentavalent tungsten atoms is very low, and the nanocrystal structure cannot be confirmed. Low regularity and order. The correlation between these experimental results will be discussed below.

First, the relationship between the nanocrystal structure (regularity of the film structure) and pentavalent tungsten atoms will be described.
As described above, the hole injection layer in each film forming condition of the fifth embodiment has a composition ratio of tungsten to oxygen of approximately 1: 3. Therefore, it is considered that the nanocrystal that is a factor of the regularity of the film structure seen in the hole injection layer under the film formation conditions α, β, γ, and δ is a microcrystal of tungsten trioxide.

  Here, in general, when an oxygen defect occurs inside a nanoscale microcrystal, the area affected by the oxygen defect becomes relatively large due to its small size, so that the microcrystal is greatly distorted. It becomes difficult to maintain the crystal structure. Therefore, it is unlikely that pentavalent tungsten atoms derived from a structure similar to an oxygen defect are included in the nanocrystal.

  However, this does not apply to the surface of nanocrystals and the grain boundaries between nanocrystals. In general, a structure similar to an oxygen defect, such as a so-called surface oxygen defect, is easily formed on a surface or grain boundary where the periodicity of the crystal is interrupted. For example, Non-Patent Document 7 shows that the surface of tungsten trioxide crystal has a structure in which half of the outermost tungsten atoms are not terminated by oxygen atoms, and the structure in which all the outermost tungsten atoms are terminated by oxygen atoms. More stable. In this way, it is considered that many pentavalent tungsten atoms that are not terminated by oxygen atoms are present on the surface or grain boundary of the nanocrystal.

  On the other hand, the hole injection layer under the film formation condition ε has almost no pentavalent tungsten atoms, nanocrystals are not confirmed, and the entire film has an amorphous structure with poor regularity. This is because the octahedron structure, which is the basic structure of tungsten trioxide, shares oxygen at the apex without interrupting each other (thus it does not become a pentavalent tungsten atom), but the octahedron structure is periodic. This is probably due to lack of order.

Next, the relationship between the occupied levels near the Fermi surface and pentavalent tungsten atoms will be described.
As described in the first embodiment, the occupied level in the vicinity of the Fermi surface is considered to be derived from a structure similar to an oxygen defect. The pentavalent tungsten atom is also derived from a structure similar to an oxygen defect. That is, the occupied level in the vicinity of the Fermi surface and the pentavalent tungsten atom are caused by the structure similar to the same oxygen defect. Specifically, as described in the first embodiment, the assumption that the 5d orbit that is not used for bonding with an oxygen atom of a pentavalent tungsten atom or the like is an occupied level in the vicinity of the Fermi surface is as follows. Many reports have been made.

  From the above, in the hole injection layer with good hole conduction efficiency, there are many pentavalent tungsten atoms adjacent to the surface and grain boundary of the nanocrystal, and therefore the 5d orbit of pentavalent tungsten atoms at the surface and grain boundary. It is inferred that there is a large overlap between them and there are continuous occupied levels near the Fermi surface. On the other hand, in a hole injection layer with poor hole conduction efficiency, it is surmised that the structure similar to oxygen defects and pentavalent tungsten atoms derived from it are hardly present in the amorphous structure, and therefore there are almost no occupied levels near the Fermi surface. The

  Next, the mechanism of hole conduction in the hole injection layer of the present invention will be further considered. Although it has already been considered that holes are conducted between pentavalent tungsten atoms existing in the hole injection layer 4A, it is possible to further infer a specific image from the correlation between the above experimental results. is there.

  First, hole conduction in a hole injection layer made of tungsten oxide mainly formed in an amorphous structure, such as a hole injection layer under film formation conditions ε, will be described. FIG. 49B is a diagram showing the conduction of the holes 14 when the amorphous structure 16 is dominant and the nanocrystals 15 are few (or not at all) in the hole injection layer. When a voltage is applied to the hole injection layer, hopping of the holes 14 occurs between the relatively close pentavalent tungsten atoms present in the amorphous structure 16. Under the force of the electric field, the holes 14 move to the buffer layer side while hopping between adjacent pentavalent tungsten atoms. That is, in the amorphous structure 16, the holes 14 move by hopping conduction.

  Here, when the number of pentavalent tungsten atoms is extremely small as in the hole injection layer under the film formation condition ε, the distance between the pentavalent tungsten atoms is long, and a very high voltage is required to hop between the long distances. Therefore, the driving voltage of the element becomes high.

  In order to avoid this increase in voltage, pentavalent tungsten atoms, and therefore, a structure similar to oxygen defects may be increased in the amorphous structure 16, and in fact, a tungsten oxide film is formed under predetermined conditions by, for example, vacuum deposition. Then, it is possible to produce an amorphous film containing a lot of structures similar to oxygen defects.

  However, in an amorphous film containing a large amount of such a structure similar to oxygen defects, chemical stability is lost, and in addition, obvious coloring derived from the light absorption phenomenon of a structure similar to oxygen defects occurs. Therefore, it is not practical for mass production of organic EL display panels. In this respect, the hole injection layer of the present invention has a composition ratio of tungsten to oxygen of approximately 1: 3, so that the entire film has few structures similar to oxygen defects and forms a crystal structure. Therefore, chemical stability is kept relatively good and coloring is reduced.

  In FIG. 49 (b), when the holes 14 reach the surface of the nanocrystal 15, there are many pentavalent tungsten atoms on the surface of the nanocrystal 15, and therefore, the vicinity of the Fermi surface where holes can be exchanged. If the occupying level is adjacent to the surface and is limited to the surface of the nanocrystal 15, the movement of the hole 14 is easy. However, in order for the hole 14 to reach the buffer layer, it must eventually pass through the amorphous structure 16, so the hole conduction efficiency is not improved.

  Next, hole conduction in the tungsten oxide layer having the nanocrystal structure of the present invention will be described. FIG. 49A is a diagram showing the conduction of the holes 14 in the case where there are few (or no) amorphous structures 16 in the hole injection layer and many nanocrystals 13 are present. First, in the same manner as described above, there are many pentavalent tungsten atoms adjacent to the surface or grain boundary of the nanocrystal 13, and therefore the occupied level near the Fermi surface where holes can be exchanged is It exists almost continuously at grain boundaries. In addition, in FIG. 49A, the presence of a large number of nanocrystals 13 further connects the respective surfaces and grain boundaries. That is, there is a continuous hole conduction path as shown by the thick arrows in the figure due to the surfaces and grain boundaries connecting the nanocrystals 13. As a result, when a voltage is applied to the hole injection layer, the hole 14 easily conducts the occupied level near the Fermi surface spreading on the connected surface and grain boundary, and reaches the buffer layer with a low driving voltage. It can be done.

From the above considerations, the structure of the metal oxide layer exhibiting good hole conduction efficiency includes (1) that there is a portion responsible for giving and receiving holes, and (2) that it is continuously present, Is considered important. Therefore, (1) a metal atom having a valence lower than the maximum valence that can be taken by itself is present in the layer, and (2) a metal oxide layer forming a nanocrystal structure is suitable for hole conduction. It can be said that it is a structure.
(Other matters)
The “occupied level” referred to in the present invention includes an electron level caused by an electron orbit occupied by at least one electron, that is, a so-called semi-occupied orbital level.

The film formation method of the hole injection layer of the present invention is not limited to the reactive sputtering method, and for example, a vapor deposition method, a CVD method or the like can be used.
The organic light emitting device of the present invention can be used as, for example, a lighting device or the like by appropriately setting the film thickness of each layer in each element when a plurality of organic light emitting elements are integrated on a substrate as pixels. Or it can also be set as the organic electroluminescent display panel which is an image display apparatus.

  In the fifth embodiment, the rising position of the peak P1 shown in FIG. 48 is defined as the position where the differential value first becomes 0 from the peak top of the peak P1 toward the center point in FIGS. 48 (a2) and (b2). did. However, the method for determining the rising position of the peak P1 is not limited to this. For example, referring to FIG. 48A1, the average value of normalized luminance in the vicinity of the peak P1 is used as a baseline, and the baseline and the peak P1 are determined. An intersection with a nearby graph can be set as the rising position of the peak P1.

  In the organic light emitting device 1C, since the anode 2 is formed of a thin film made of silver, the ITO layer 3 is formed thereon in order to improve the bonding between the layers. When the anode 2 is made of a material mainly containing aluminum, the bondability is improved. Therefore, the ITO layer 3 may be omitted and the anode may have a single layer structure.

  When a plurality of organic light emitting elements are formed as the organic light emitting device of the present invention to produce an organic EL display panel, the bank shape is not limited. In addition to the so-called pixel bank (cross-shaped bank) that defines each light emitting area, a line bank that defines a plurality of light emitting areas of the same color in parallel in one direction can also be adopted. FIG. 50 shows a configuration of an organic EL display panel in which a plurality of line banks 65 are arranged and light emitting layers 66a, 66b, and 66c adjacent in the X-axis direction are divided. When the line bank 65 is adopted, the light emitting layers adjacent to each other along the Y-axis direction are not defined by the bank element, but influence each other by appropriately setting the driving method, the area of the anode, the interval, and the like. It can be made to emit light without.

  In the present invention, one of the pixel electrode and the counter electrode may be an anode and the other may be a cathode. Therefore, for example, in the first embodiment, 2 can be a cathode (pixel electrode) and 8 can be an anode (counter electrode).

  The organic light emitting device of the present invention can be used for display elements for mobile phones, display elements such as televisions, light emitting devices, and various light sources. In any application, it can be applied as an organic light emitting device that is driven at a low voltage in a wide luminance range from a low luminance to a high luminance such as a light source. With such high performance, it can be widely used as various display devices for home or public facilities, or for business use, television devices, displays for portable electronic devices, illumination light sources, and the like.

1, 1A, 1B, 1C, 1F Organic light emitting device 1E Sample for photoelectron spectroscopy measurement 1D, 1G Hall-only element 2 Anode (pixel electrode)
2h Bottom part 2X Anode material film 3 ITO layer 4, 4A Hole injection layer 5 Bank 6A Hole transport layer 6B Light emitting layer 7 Electron transport layer 8 Cathode 9 Sealing layer 10, 10S Substrate 11 Planarization film (interlayer insulating film)
11s Side surface portion 11t Upper surface portion 11h Side surface portion in hole 12 Tungsten oxide layer 13, 15 Nanocrystal 14 Hole 16 Amorphous structure 17 (153) Source electrode 18 Insulating film 19 Relay electrode 20 Cover film (tungsten oxide film)
20s Side surface 20t Upper surface 20h Inside hole DC DC power supply

Claims (43)

A drive element having a current extraction terminal;
An insulating film covering the driving element and having an opening provided at a position corresponding to the current extraction terminal;
Covering the surface of the insulating film including the inner peripheral surface of the opening of the insulating film, and electrically connected to the current extraction terminal of the driving element through the opening. A coating film having,
A pixel electrode provided on the opposite side of the coating film from the insulating film and electrically connected to the coating film;
A light-emitting layer provided corresponding to the pixel electrode and including a light-emitting organic material;
A counter electrode provided on the opposite side of the light emitting layer from the pixel electrode;
An organic light emitting device comprising: The coating film has, in its electronic state, an occupied level in a binding energy region that is 1.8 to 3.6 eV lower than the lowest binding energy in the valence band, and the film thickness is 2 nm or more. The organic light-emitting device according to claim 1, which is a tungsten oxide film containing tungsten oxide. 3. The organic light emitting device according to claim 2, wherein a difference between a binding energy of the occupied level and a Fermi level of the pixel electrode is within ± 0.3 eV at an interface between the tungsten oxide film and the pixel electrode. A conductive film is provided in contact with the current extraction terminal of the drive element, and the tungsten oxide film is provided in contact with the conductive film,
3. The organic light emitting device according to claim 2, wherein, at the interface between the tungsten oxide film and the conductive film, a difference between the binding energy of the occupied level and the Fermi level of the conductive film is within ± 0.3 eV. The tungsten oxide film is provided in contact with the current extraction terminal of the drive element,
3. The organic light-emitting device according to claim 2, wherein a difference between a binding energy of the occupied level and a Fermi level of the current extraction terminal is within ± 0.3 eV at an interface between the tungsten oxide film and the current extraction terminal. . The tungsten oxide film was raised in a binding energy region 1.8 to 3.6 eV lower than the lowest binding energy in the valence band in the USP spectrum representing the relationship between the binding energy and the photoelectron intensity or its normalized intensity. Having a shape,
The organic light-emitting device according to claim 2. The tungsten oxide film raised in a binding energy region 1.8 to 3.6 eV lower than the lowest binding energy in the valence band in the XPS spectrum representing the relationship between the binding energy and the photoelectron intensity or its normalized intensity. Having a shape,
The organic light-emitting device according to claim 2. The tungsten oxide film spans a binding energy region that is 2.0 to 3.2 eV lower than the lowest binding energy in the valence band in the differential spectrum of the UPS spectrum representing the relationship between the binding energy and the photoelectron intensity or its normalized intensity. , Having a shape expressed as a function different from the exponential function,
The organic light-emitting device according to claim 2. The tungsten atoms constituting the tungsten oxide film are included in a hexavalent state that is the maximum valence that the tungsten atoms can take and a pentavalent state that is lower than the maximum valence, and
The tungsten oxide film includes a tungsten oxide crystal having a particle size of the order of nanometers.
The organic light-emitting device according to claim 2. 10. The organic light-emitting device according to claim 9, wherein W ⁵⁺ / W ⁶⁺ which is a value obtained by dividing the number of pentavalent tungsten atoms by the number of hexavalent tungsten atoms is 3.2% or more. The organic light-emitting device according to claim 10, wherein the W ⁵⁺ / W ⁶⁺ is 3.2% or more and 7.4% or less. In the hard X-ray photoelectron spectroscopy spectrum of the tungsten oxide film, a second component exists in a lower binding energy region than the first component corresponding to the 4f _7/2 level of hexavalent tungsten atoms.
The organic light-emitting device according to claim 9. The second component is present in a binding energy region lower by 0.3 to 1.8 eV than the peak top binding energy of the first component.
The organic light-emitting device according to claim 12. The organic light emitting device according to claim 12 or 13, wherein the area intensity of the second component is 3.2 to 7.4% with respect to the area intensity of the first component. Due to the presence of tungsten atoms lower than the maximum valence, in the electronic state of the tungsten oxide film, it has an occupied level in a binding energy region that is 1.8 to 3.6 eV lower than the lowest binding energy in the valence band. The organic light-emitting device according to claim 9. The tungsten oxide film includes a plurality of tungsten oxide crystals having a grain size of 5 to 10 nm.
The organic light-emitting device according to claim 9. In the lattice image of the tungsten oxide film observed by a transmission electron microscope, a linear structure regularly arranged at intervals of 1.85 to 5.55 mm appears.
The organic light-emitting device according to claim 9. In the two-dimensional Fourier transform image of the lattice image, a concentric bright portion centering on the center point of the two-dimensional Fourier transform image appears.
The organic light-emitting device according to claim 17. In a plot showing the relationship between the distance from the center point and the normalized brightness that is a numerical value obtained by standardizing the brightness of the two-dimensional Fourier transform image at the distance, the peak of the normalized brightness is 1 other than the center point. Appear more than one,
The organic light-emitting device according to claim 18. The difference between the distance corresponding to the position of the peak top of the normalized luminance that appears closest from the center point in the plot and the distance corresponding to the rising position of the peak of the normalized luminance is a peak width,
The peak width when the distance corresponding to the position of the peak top is 100 is smaller than 22.
The organic light-emitting device according to claim 19. The light emitting layer includes an amine-based material,
The organic light-emitting device according to claim 1. The organic light emission according to any one of claims 2 to 21, wherein the occupied level in the tungsten oxide film is present in a binding energy region that is 2.0 to 3.2 eV lower than the lowest binding energy in the valence band. apparatus. The organic light-emitting device according to claim 1, wherein a conductive film is provided in contact with the current extraction terminal of the drive element, and the coating film is provided in contact with the conductive film. The conductive film is a metal oxide film,
24. The organic light emitting device according to claim 23. The organic light-emitting device according to claim 1, wherein the coating film is provided in contact with the current extraction terminal of the drive element. The organic light-emitting device according to claim 1, wherein the coating film is a metal oxide film. The insulating film is
A first insulating film covering the driving element and having a first opening provided at a position corresponding to the current extraction terminal;
A second insulating film that covers the first insulating film and has a second opening that communicates with the first opening at a position corresponding to the first opening;
An organic light-emitting device according to claim 1. The first insulating film is made of an inorganic material, and the second insulating film is made of an organic material.
The organic light-emitting device according to claim 27. A conductive film is provided in contact with the current extraction terminal of the drive element in the first opening, and the coating film is in contact with the conductive film in the second opening. The organic light-emitting device according to claim 27. The organic light-emitting device according to claim 29, wherein the conductive film is a metal oxide film. The organic light-emitting device according to claim 27, wherein the coating film is provided in contact with the current extraction terminal of the drive element in the first opening. Furthermore, a substrate is provided,
The drive element is formed on the substrate;
The insulating film is formed on the substrate so as to cover the driving element;
The coating film is formed on the substrate so as to cover the insulating film and to be in contact with the substrate by spreading outside a region where the insulating film is formed. 2. The organic light emitting device according to 1. A first step of forming a drive element having a current extraction terminal;
A second step of forming an insulating film covering the drive element, and forming an opening in the insulating film at a position corresponding to the current extraction terminal;
The insulating film covers the surface of the insulating film including the inner peripheral surface of the opening, and is electrically connected to the current extraction terminal of the driving element through the opening. A third step of forming a coating film;
A fourth step of forming a pixel electrode electrically connected to the coating film on the opposite side of the coating film from the insulating film;
A fifth step of forming a light emitting layer containing an organic material having a light emitting property corresponding to the pixel electrode;
A sixth step of forming a counter electrode on the opposite side of the light emitting layer from the pixel electrode;
The manufacturing method of the organic light-emitting device containing this. In the second step, a conductive film that is in contact with the current extraction terminal of the drive element is further formed,
In the third step, the coating film is provided in contact with the conductive film.
34. A method of manufacturing an organic light emitting device according to claim 33. The method for manufacturing an organic light-emitting device according to claim 34, wherein the conductive film is a metal oxide film. In the third step, the coating film is provided in contact with the current extraction terminal of the drive element.
34. A method of manufacturing an organic light emitting device according to claim 33. The method for manufacturing an organic light-emitting device according to claim 33, wherein the coating film is a metal oxide film. The second step includes
Forming a first insulating film covering the drive element, and forming a first opening at a position corresponding to the current extraction terminal in the first insulating film;
A second sub-step of forming a second insulating film covering the first insulating film and forming a second opening communicating with the first opening at a position corresponding to the first opening; Including,
34. A method of manufacturing an organic light emitting device according to claim 33. The first insulating film is made of an inorganic material, and the second insulating film is made of an organic material.
39. A method of manufacturing an organic light emitting device according to claim 38. In the second step, a conductive film that is in contact with the current extraction terminal of the driving element is disposed in the first opening between the first sub step and the second sub step. Including a third sub-step of forming,
In the third step, the coating film is provided in contact with the conductive film in the second opening.
39. A method of manufacturing an organic light emitting device according to claim 38. 41. The method of manufacturing an organic light emitting device according to claim 40, wherein the conductive film is a metal oxide film. In the third step, the coating film is provided in contact with the current extraction terminal of the drive element in the first opening.
39. A method of manufacturing an organic light emitting device according to claim 38. In the third step, the coating film is a tungsten oxide film,
For the tungsten oxide film, a gas composed of argon gas and oxygen gas is used as the gas in the chamber of the sputtering apparatus, the total pressure of the gas is more than 2.7 Pa and 7.0 Pa or less, and the partial pressure of oxygen gas the total specific is not more than 50 to 70% with respect to pressure, further deposition conditions input power density per target unit area is 1W / cm ² or more 2.8W / cm ² or less of, its thickness Forming a film to be 2 nm or more,
34. A method of manufacturing an organic light emitting device according to claim 33.