JP2012174712A - Organic light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element which can be expected to exhibit superior emission characteristics by preventing the luminous efficiency from lowering due to residue of a bank material especially between a hole injection layer and a hole transport layer.SOLUTION: A bank 5 is formed on one surface of a substrate 10 after formation of a positive electrode 2 before formation of a hole injection layer 4. An organic EL element 1 is configured by sequentially laminating a hole transport layer 6A, a light-emitting layer 6B, and a negative electrode 8 on the hole injection layer 4. The hole injection layer 4 is a tungsten oxide layer having a thickness of 2 nm or more deposited under specified deposition conditions. In the electron state thereof, the occupied level is made to exist in a range of bond energy which is 1.8-3.6 eV lower than the lowest bond energy in the valence band. Consequently, hole injection barriers can be reduced between the positive electrode 2 and the hole injection layer 4, and between the hole injection layer 4 and the hole transport layer 6A.

Description

  The present invention relates to an organic electroluminescent device (also referred to as an organic light emitting device, hereinafter referred to as “organic EL device”), which is an electroluminescent device, and particularly over a wide luminance range from low luminance to high luminance for light source applications, The present invention relates to a technique for driving an organic EL 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 EL element. The organic EL element is a current-driven light-emitting element and has a configuration in which a functional layer containing an organic material is provided between a pair of electrodes including an anode and a cathode. The functional layer includes a light emitting layer, a buffer layer, and the like. A hole injection layer for injecting holes may be disposed between the functional layer and the anode. In the case where an organic EL panel is produced by arranging a plurality of organic EL elements in a pattern such as a matrix on a substrate, insulation is performed so as to partition the organic EL elements for each organic EL element or for each predetermined arrangement. A partition wall (bank) made of a material is formed.

  For driving the organic EL element, electroluminescence is generated by applying a voltage between the pair of electrodes and recombining holes injected from the anode into the functional layer and electrons injected from the cathode into the functional layer. Use the phenomenon. Since it is self-luminous, its visibility is high, and since it is a complete solid element, it has excellent impact resistance. Therefore, its use as a light-emitting element and a light source in various display devices has attracted attention.

  Organic EL elements are roughly classified into two types depending on the type of functional layer material used. The first is a vapor deposition type organic EL element in which an organic low molecular weight material is mainly used as a functional layer material and is formed by a vacuum process such as a vapor deposition method. Secondly, a coating type organic EL element is formed by using an organic polymer material or an organic low molecular weight 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.

  Therefore, an attempt to realize the enlargement of the organic EL panel using a coating type organic EL element has begun. As described above, in the coating type organic EL element, 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 light emission efficiency of organic EL elements are also actively conducted. In order for the organic EL element to emit light efficiently and 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 EL elements 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, even when an organic EL element having the above-described advantages is manufactured, there are problems.
That is, when an organic EL panel or the like is manufactured, an anode and a hole injection layer are sequentially formed on a substrate, and then a partition wall material is applied and patterned to prepare a predetermined pattern of partition walls. Thereafter, a region hole transport layer, a light emitting layer, and the like partitioned by the partition are sequentially formed. At this time, a residue may remain between the hole injection layer and the hole transport layer when the partition wall material is patterned. Since this residue hinders the movement of holes during driving, it causes a decrease in luminous efficiency in the light emitting layer.

In order to improve the light emission efficiency of the organic EL element and the organic EL panel using the organic EL element, improvement of this problem is desired.
The present invention has been made in view of the above problems, and is expected to exhibit excellent light emission characteristics, particularly by preventing a decrease in light emission efficiency due to bank material residues between the hole injection layer and hole transport. An object of the present invention is to provide an organic EL element that can be used.

  In order to solve the above-described problems, one embodiment of the present invention provides an anode, a partition wall provided in contact with the anode so as to define an anode portion in the light-emitting portion, and a contact with the anode portion in the light-emitting portion. And a tungsten oxide layer provided in contact with at least a part of the surface of the partition corresponding to the light emitting portion and a contact with the tungsten oxide layer so as to cover the anode portion. A layer including an organic material and a cathode provided on a side different from the anode with respect to the layer including the organic material, and the tungsten oxide layer has the lowest valence band in its electronic state. It has a configuration in which it has an occupied level in a binding energy region that is 1.8 to 3.6 eV lower than the binding energy, and the film thickness is 2 nm or more.

  In the organic EL element of one embodiment of the present invention, the hole injection layer is configured as a layer having a thickness of 2 nm or more containing tungsten oxide. This hole injection layer has an occupied level in a bonding 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 the organic EL device according to one aspect of the present invention, the occupation level of the hole injection layer is used, the Fermi level of the anode and the occupation level of the hole injection layer, and the occupation level of the hole injection layer. And the hole injection barrier between the first layer and the highest occupied orbit (HOMO) of the functional layer can be made extremely small. As a result, the organic EL element of one embodiment of the present invention has high hole injection efficiency, can be driven at a low voltage, and can be expected to exhibit excellent light emission efficiency.

  In addition, the organic EL device of one embodiment of the present invention can stabilize the hole injection barrier between the anode and the hole injection layer in a normal manufacturing process without particularly strictly adjusting and maintaining the surface state of the anode. Can be kept small. Therefore, it is not necessary to highly control the surface state of the anode in order to produce an organic EL element having a stable performance, and a large organic EL panel can be easily manufactured at a relatively low cost, and has excellent feasibility.

  Thus, in the organic EL element of one embodiment of the present invention, the hole injection barrier between the anode and the hole injection layer is extremely small, and so-called Schottky ohmic connection is formed. Since the hole flow due to the Schottky ohmic connection is dominant between the anode and the hole injection layer, even if a partition wall residue exists between them, the hole injection efficiency is not significantly affected. In the present invention, by utilizing this point, by forming the partition after forming the anode and before forming the hole injection layer, the residue of the partition wall material is mainly left between the anode and the hole injection layer. It is intended to maintain a good hole injection efficiency by preventing it from remaining with the cathode as much as possible, and to expect an excellent light emission efficiency.

1 is a schematic cross-sectional view showing a configuration of an organic EL element according to Embodiment 1. FIG. 5 is a process diagram for explaining a method of manufacturing the organic EL element 1 according to Embodiment 1. FIG. 5 is a process diagram for explaining a method of manufacturing the organic EL element 1 according to Embodiment 1. FIG. 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 EL element. It is a device characteristic figure which shows the relationship curve of the current density of organic electroluminescent 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 the influence confirmation test of a partition residue. It is a graph which shows the characteristic of a voltage and efficiency, and the lifetime characteristic which were measured in the influence confirmation test of a partition wall residue. It is process drawing explaining the manufacturing method of the conventional organic EL element 1X. It is typical sectional drawing which shows the structure of the conventional organic EL element 1X. 5 is a schematic cross-sectional view showing a configuration of an organic EL element according to Embodiment 2. 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 EL 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. 36 is a diagram (a) showing a peak fitting analysis result related to the sample α shown in FIG. 35 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. It is a figure explaining the process which produces a brightness | luminance change plot from the two-dimensional Fourier-transform image shown in FIG. 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 electroluminescent panel which concerns on a modification. It is sectional drawing which shows a part of organic electroluminescent panel which concerns on a modification.

[Outline of One Embodiment of the Present Invention]
An organic light-emitting element which is one embodiment of the present invention includes an anode, a partition provided in contact with the anode so as to define a light-emitting region on the anode, a light-emitting region on the anode, and the light-emitting region A tungsten oxide layer provided so as to be in contact with at least a part of a partition corresponding to the layer, a layer containing an organic material provided in contact with the tungsten oxide layer, and a layer containing the organic material A cathode provided on a side different from the anode, and the tungsten oxide layer occupies a 1.8 to 3.6 eV lower binding energy in the electronic state than the lowest binding energy in the valence band. It was set as the structure which has a level and the film thickness is 2 nm or more.

  As described above, since the hole injection layer has the occupied level and the film thickness, at least the hole injection barrier between the anode and the hole injection layer can be suppressed small. Therefore, a high hole injection efficiency from the anode to the hole injection layer is exhibited at the time of driving, a good low voltage driving can be realized, and an excellent luminous efficiency can be expected. Further, since the hole injection layer has the occupied level and the film thickness, stable hole injection efficiency from the anode to the hole injection layer can be maintained without depending on the surface state of the anode.

  As another aspect of the present invention, the partition material may have a residue amount less between the tungsten oxide layer and the cathode than between the anode and the tungsten oxide layer.

  As described above, a stable hole injection efficiency of the anode and the hole injection layer is utilized, and the amount of the residue of the partition material is less between the tungsten oxide layer and the cathode than between the anode and the tungsten oxide layer. As a result, a decrease in hole injection efficiency due to the residue can be prevented, and an organic light-emitting device with excellent luminous efficiency can be realized.

As another aspect of the present invention, the tungsten oxide layer may be a hole injection layer, and the layer containing an organic material may be a functional layer.
As another aspect of the present invention, the interface between the hole injection layer and the anode may be configured such that the difference between the binding energy of the occupied level and the Fermi level of the anode is within ± 0.3 eV. .

As a result, the anode and the hole injection layer can be Schottky ohmic connected satisfactorily, and the hole injection efficiency from the anode to the hole injection layer can be improved.
As another aspect of the present invention, the hole injection layer may have a 1.8 to 3.6 eV lower than the lowest binding energy in the valence band in the UPS spectrum representing the relationship between the binding energy and the photoelectron intensity or its normalized intensity. A configuration having a raised shape in a low binding energy region may be employed.

  As another aspect of the present invention, the hole injection layer may be 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 the normalized intensity. A configuration having a raised shape in a low binding energy region may be employed.

  As another aspect of the present invention, the hole injection layer has a UPS spectrum that represents the relationship between the binding energy and the photoelectron intensity or its normalized intensity, and is 2.0 to less than the lowest binding energy in the valence band. A structure having a shape expressed as a function different from an exponential function over a low binding energy region of 3.2 eV may be employed.

  As another aspect of the present invention, since the hole injection layer has the occupied level, the binding energy of the occupied level is the highest coverage of the functional layer at the interface between the hole injection layer and the functional layer. It can also be set as the structure located in the vicinity of the binding energy of an occupied track.

  As a result, in addition to suppressing the hole injection barrier between the anode and the hole injection layer, the hole injection barrier between the hole injection layer and the functional layer can also be effectively reduced to further improve the hole injection efficiency. Is preferred.

  As another aspect of the present invention, at the interface between the hole injection layer and the functional layer, a difference between the coupling energy of the occupied level and the coupling energy of the highest occupied orbit of the functional layer is within ± 0.3 eV. It can also be set as the structure which is.

Thereby, the hole injection efficiency from the hole injection layer to the functional layer can be further increased.
As another aspect of the present invention, the tungsten oxide layer contains a hexavalent tungsten atom having a maximum valence and a pentavalent tungsten atom lower than the maximum valence, and an oxide having a particle size of nanometer order. It can also be set as the structure containing a tungsten crystal.

  In the organic EL element according to one embodiment of the present invention, the hole injection layer is made of tungsten oxide, and a part of the tungsten atoms constituting the tungsten oxide has a valence lower than the hexavalence that is the maximum valence of tungsten. By doing so, a hole conduction site can be provided in the film of the hole injection layer. In addition to this, the surface of the hole injection layer contains a tungsten oxide crystal having a particle size on the order of nanometers, so that the surface of the crystal and the grain boundary have many hole conduction sites. Many are formed in the layer. As a result, the hole conduction path can be extended in the film thickness direction of the hole injection layer, so that efficient hole conduction can be realized with a low driving voltage. Here, the “size on the order of nanometers” refers to a size of about 5 to 10 nm and is smaller than the film thickness of the hole injection layer.

As another aspect of the present invention, the ratio W ⁵⁺ / W ^{6+ of the} number of pentavalent tungsten atoms and the number of hexavalent tungsten atoms may be 3.2% or more. Thereby, better hole conduction efficiency can be obtained.

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 layer, a first component corresponding to the 4f _7/2 level of a hexavalent tungsten atom is lower than the first component. A configuration in which the second component exists in the binding energy region can also be adopted.

  As another aspect of the present invention, the second component may be present in a binding energy region that is 0.3 to 1.8 V lower 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, the tungsten oxide layer has a bond energy that is 1.8 to 3.6 eV lower than the lowest bond energy in the valence band in the electronic state due to the presence of the pentavalent tungsten atom. A configuration having an occupied level in the region can also be employed.

As another aspect of the present invention, the tungsten oxide layer may include a plurality of the tungsten oxide crystals having a particle size of 3 to 10 nanometers.
As another aspect of the present invention, the tungsten oxide layer has a linear structure that is regularly arranged at intervals of 1.85 to 5.55 cm in a lattice image observed by a transmission electron microscope. It can also be.

  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 functional layer may include an amine material.
Further, as another aspect of the present invention, the functional layer includes a hole transport layer that transports holes, a light emitting layer that emits light by recombination of injected holes and electrons, adjustment of optical characteristics, or use of an electronic block The buffer layer may be at least one of the buffer layers used in the above.

Further, as another aspect of the present invention, it may be configured to exist in a binding energy region that is 2.0 to 3.2 eV lower than the lowest binding energy in the valence band.
As another aspect of the present invention, the tungsten oxide layer can be provided in contact with at least the upper surface of the anode.

  Further, as another aspect of the present invention, the tungsten oxide layer is provided so as to cover a part or more of the side surfaces of the partition wall corresponding to the light emitting portion while being in contact with the upper surface of the anode. You can also

Moreover, it can also be set as a display apparatus provided with the organic light emitting element of any aspect of this invention mentioned above as another aspect of this invention.
Or as another aspect of this invention, it can also be set as a light-emitting device provided with the organic light emitting element of any aspect of this invention mentioned above.

The organic light emitting device manufacturing method according to another aspect of the present invention includes a first step of preparing an anode, a resin material is applied to the anode to form a resin material film, and the resin material film is formed A second step of forming a partition by patterning and partially opening the surface of the anode, and oxidizing the region surrounded by the opened surface of the anode and the surface of the partition A step of forming a tungsten layer, wherein a gas composed of argon gas and oxygen gas is used as a gas in a chamber of a sputtering apparatus, and the total pressure of the gas is more than 2.7 Pa and 7.0 Pa or less, and , there is a ratio to the total pressure of the oxygen gas partial pressure 50 to 70%, further deposition conditions input power density per target unit area is 1W / cm ² or more 2.8W / cm ² or less , Its film thickness A third step of forming the tungsten oxide layer to have a thickness of 2 nm or more; a fourth step of forming a functional layer containing an organic material on the formed tungsten oxide layer; and above the functional layer. And a fourth step of forming a cathode.

  Here, as another aspect of the present invention, in the third step, the tungsten oxide layer is raised in a binding energy region whose UPS spectrum is 1.8 to 3.6 eV lower than the lowest binding energy in the valence band. It is also possible to form a film so as to have the shape as described above.

  As another aspect of the present invention, the third step is different from the exponential function in that the differential spectrum of the UPS spectrum spans a binding energy region that is 2.0 to 3.2 eV lower than the lowest binding energy in the valence band. The tungsten oxide layer can be formed to have a shape expressed as a function.

As another aspect of the present invention, in the third step, the total pressure / input power density, which is a value obtained by dividing the total pressure by the input power density, is set to be larger than 0.7 Pa · cm ² / W. It can also be done.

As another aspect of the present invention, the third step can be performed such that the total pressure / input power density is smaller than 3.2 Pa · cm ² / W.
Further, as another aspect of the present invention, the resin material film between the tungsten oxide layer and the functional layer is formed by sequentially performing the third step and the fourth step after forming the partition wall in the second step. The amount of residue can be made smaller than the amount of residue of the resin material film between the anode and the tungsten oxide layer.
<Embodiment 1>
(Configuration of organic EL element)
FIG. 1 is a schematic cross-sectional view showing the configuration of the organic EL element 1 in the first embodiment.

  The organic EL element 1 is a coating type in which a functional layer is applied by a wet process to form a film, and includes a hole injection layer 4 and various functional layers (here, a hole transport layer) containing an organic material having a predetermined function. 6A and the light-emitting layer 6B) are disposed between the electrode pair composed of the anode 2 and the cathode 8 in a state where the light-emitting layer 6B and the light-emitting layer 6B) are stacked on each other.

Specifically, as shown in FIG. 1, the organic EL element 1 includes an anode 2, a hole injection layer 4, a hole transport layer 6A, a light emitting layer 6B, a cathode 8 (barium layer 8A and The aluminum layer 8B) is 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 EL element 1 from the outside.
(substrate)
The substrate 10 is a portion that becomes a base material of the organic EL element 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.

Although not shown, a TFT (thin film transistor) for driving the organic EL element 1 is formed on the surface of the substrate 10.
(Flattening film)
The planarizing film 11 is made of an insulating resin material such as polyimide or acrylic, and is provided to cover the surface of the substrate 10 and ensure flatness.
(anode)
The anode 2 is composed of a transparent conductive film made of ITO having a thickness of 50 nm. The structure of the anode 2 is not limited to this. For example, a transparent conductive film such as IZO, a metal film such as aluminum, APC (silver, palladium, copper alloy), ARA (silver, rubidium, gold alloy), MoCr (molybdenum) Alloy films such as NiCr (alloy of chromium) and NiCr (alloy of nickel and chromium) may be used, and a plurality of these films may be laminated.
(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 perform uniform film formation, and it is difficult to form a Schottky ohmic connection (contact) between the anode 2 and the hole injection layer 4 described below, which is not preferable. 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 made of tungsten oxide as much as possible, 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.
(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.
The bank 5 is not essential for the present invention, and is not necessary when the organic EL element 1 is used alone.
(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 EL element 1 is applied to an organic EL panel, a series of three elements 1 corresponding to each color of RGB 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 a known organic material. 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 EL element has 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 EL element other than the hole injection layer which is an object of the present invention.
(cathode)
The cathode 8 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.

An electron transport layer 7A is disposed between the light emitting layer 6B and the cathode 8. The electron transport layer 7A 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 EL element)
In the organic EL element 1 having the above configuration, since the occupied level near the Fermi surface exists in the hole injection layer 4, the occupied level near the Fermi surface and the highest occupied orbit of the hole transport layer 6A A so-called interface state connection is made between them, and the hole injection barrier between the hole injection layer 4 and the hole transport layer 6A is extremely small.

  Furthermore, in the organic EL element 1, a good Schottky ohmic connection is formed between the anode 2 and the hole injection layer 4, and the hole injection barrier is also kept small between the anode 2 and the hole injection layer 4.

  Thereby, in the organic EL element 1, when a voltage is applied to the organic EL element 1 at the time of driving, 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. Therefore, when manufacturing the organic EL element 1, it is not necessary to strictly control the surface state of the anode 2, and the element 1 having a relatively low cost and high hole injection efficiency, or a large-sized organic EL panel formed with a large number thereof. Can be manufactured with high yield.

Here, the “surface state of the anode” refers to the surface state of the anode immediately before the hole injection layer is formed in the standard manufacturing process of the organic EL element or the organic EL 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 for mass-producing large organic EL panels is not shown. . 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 panel, and has an occupied level in the vicinity of a predetermined Fermi surface. This is greatly different from the prior art in that efficiency is obtained and low voltage driving of the organic EL element is realized.

  Furthermore, in the organic EL element 1, in the manufacturing process, the bank 5 is formed after the anode 2 is formed and before the hole injection layer 4 is formed. Therefore, as shown in FIG. 2B, which will be described later, the residue 5R of the bank material 5X that can be generated after patterning the bank material 5X disposed on the substrate under fabrication with a photomask is mainly the anode 2 and the hole injection layer. It becomes the structure which remains between.

  As described above, in the organic EL element 1, the residue 5R is mainly present between the anode 2 and the hole injection layer 4, and therefore the residue 5R does not remain between the hole injection layer 4 and the hole transport layer 6A, or It is adjusted to become a very small amount. In this respect, the organic EL element 1 is different from the conventional organic EL element 1X in which the residue 5R is interposed between the hole injection layer 4 and the hole transport layer 6A as shown in FIG.

  As a result, excellent hole injection characteristics are exhibited between the hole injection layer 4 and the hole transport layer 6A without being substantially affected by the residue 5R (contamination). On the other hand, the Schottky ohmic connection is made between the anode 2 and the hole injection layer 4 as described above, and is hardly affected by the residue 5R. Therefore, good hole injection characteristics can be maintained.

As a result, excellent hole injection characteristics are exhibited also in the entire organic EL element 1, and good light emission characteristics can be expected.
Next, the whole manufacturing method of the organic EL element 1 is illustrated. 2 and 3 are diagrams illustrating a manufacturing process of the organic EL element 1.
(Manufacturing method of organic EL element)
First, the substrate 10 on which the planarizing film 11 is formed is placed in a chamber of a sputtering film forming apparatus. Then, a predetermined gas is introduced into the chamber, and the anode 2 containing ITO having a thickness of 50 nm is formed on the planarizing film 11 based on the reactive sputtering method (FIG. 2A). In this figure, in addition to the anode 2, metal parts 2a and 2b formed during patterning are also shown.

  The metal parts 2a and 2b include, for example, APC or an aluminum alloy, and can be another anode 2 (reflective anode) adjacent to the anode 2. In this case, the anode has a two-layer structure. A light emitting layer 6B is formed on the hole transport layer 6A above the hole transport layer 6A.

  Next, as one of the features of the first embodiment, a bank material (resin material film) containing, for example, a photosensitive resin material, preferably a fluorine-based material so as to cover the anode 2 and the metal portions 2a and 2b. 5X is disposed. After pre-baking, a photomask having a predetermined-shaped opening (bank pattern to be formed) is overlaid. Then, after partially exposing the bank material 5X by UV irradiation from above the photomask (FIG. 2B), the uncured excess bank material 5X is washed out with a developer. Finally, the bank 5 is completed by washing with pure water (FIG. 2C). At this time, the surface portion corresponding to the light emitting region of the anode 2 is exposed. At this time, as an actual problem, the residue 5R of the bank material 5X can remain on the surfaces of the anode 2 and the metal parts 2a and 2b, but this residue 5R exists between the next hole injection layer 4 and Therefore, it is possible to suppress a decrease in hole injection characteristics for the reason described above.

  Here, FIGS. 29A to 29E are diagrams for sequentially explaining examples of manufacturing steps of a conventional organic EL element. Conventionally, after forming the anode 2 and the metal parts 2a and 2b, the hole injection layer 4 is formed (FIG. 29A), and then the bank material 5X is uniformly disposed. Patterning is performed by performing UV irradiation through a photomask to form banks 5 (FIGS. 29B and 29C). Therefore, the residue 5R remains at the interface between the hole injection layer 4 and the hole transport layer 6A when the hole transport layer 6A is formed (FIGS. 29C and 29D). Thereafter, when the light emitting layer 6B, the electron transport layer 7, the cathode 8, and the sealing layer 9 are formed in this order, the conventional organic EL element 1X is formed. However, due to the influence of the residue 5R, the hole injection efficiency is not excellent, and a configuration in which a problem remains in the light emission efficiency can be obtained.

  In general, in the bank 5, in order to appropriately apply an appropriate amount of ink or the like of the light emitting layer material and prevent color mixing between the adjacent light emitting regions, the bank material 5X is given water repellency, The surface may be subjected to water repellent treatment. Conventionally, in order to remove the residue 5R remaining at the interface between the hole injection layer 4 and the hole transport layer 6B, the carbon component of the residue 5R is decomposed by UV irradiation after the bank formation. Could be lost. On the other hand, in the manufacturing process of the organic EL element 1, it is not necessary to positively remove the residue 5 </ b> R by UV irradiation, so that the water repellency of the bank 5 is not impaired. Therefore, a sufficient amount of the ink can be applied between the adjacent banks 5 by utilizing the water repellency of the banks 5.

  Next, the hole injection layer 4 is formed so as to contact the surface portion corresponding to the light emitting region of the anode 2 and the surface of a part of the bank 5 corresponding to the light emitting region. As a film forming method, it is preferable to use a reactive sputtering method. In particular, when the present invention is applied to a large-sized organic EL panel that requires film formation of a large area, there is a possibility that unevenness occurs in the film thickness and the like when the film is formed by vapor deposition. If the film is formed by the reactive sputtering method, it is easy to avoid such film formation unevenness.

  Specifically, the target is replaced with metallic tungsten, and a reactive sputtering method 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, the metal tungsten released by the sputtering phenomenon reacts with the oxygen gas to become the tungsten oxide film 4X, and is uniformly formed on each surface of the anode 2, the metal portions 2a, 2b, and the bank 5 of the substrate 10. (FIG. 2 (d)).

As described later, the tungsten oxide film 4X is formed under a gas pressure (total pressure) of more than 2.7 Pa and 7.0 Pa or less, and a ratio of the oxygen gas partial pressure to the total pressure of 50% or more and 70%. a less, 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 hole injection layer 4 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. Since the hole injection layer 4 is formed after the bank 5 is formed, basically the residue 5R of the bank material 5X does not remain on the surface of the hole injection layer 4.

Subsequently, a portion of the tungsten oxide film 4X exposed from the resist P is etched through a pattern formation process (FIG. 2E) by photolithography using the resist P. Examples of the etching process include gas etching using a mixed gas of CF ₄ and O ₂ . Then, the hole injection layer 4 is formed by removing the resist P with, for example, an alkali solution or the like (FIG. 2F).

  Here, in Embodiment 1, since the hole injection layer 4 is formed by sputtering after the bank 5 is formed, not only the surface portion of the anode 2 corresponding to the light emitting region but also the side surface of the bank 5 corresponding to the light emitting region. Also, the hole injection layer 4 can be formed. The bank 5 may be appropriately coated with an appropriate amount of light emitting layer material ink or the like and may have water repellency in order to prevent color mixing between adjacent light emitting areas. By forming the hole injection layer 4 having good wettability with respect to the surface portion (side surface), the wettability in the side surface region of the bank 5 can be improved and the ink can be applied densely. In order to obtain this effect, it is desirable to form the hole injection layer 4 on the side surface of the bank 5 up to the maximum height of the bank 5, but a part of the side surface (for example, a side region of 80% or less from the maximum height of the bank). ), It is possible to ensure appropriate wettability.

In addition, when securing the wettability of the surface of the bank 5 does not matter so much, the hole injection layer 4 can be formed only at least on the upper surface of the anode 2 corresponding to the light emitting region.
Subsequently, as shown in FIG. 3A, the surface of the hole injection layer 4 exposed between the adjacent banks 5 contains an amine-based organic molecular material by a wet process such as an inkjet method or a gravure printing method. The composition ink 6AX is added dropwise to volatilize and remove the solvent. Thereby, the hole transport layer 6A is formed (FIG. 3B).

  Next, a composition ink containing an organic light emitting material is dropped on the surface of the hole transport layer 6A in the same manner, and the solvent is volatilized and removed. Thereby, the light emitting layer 6B is formed (FIG. 3C). When applying any of the ink for the hole transport layer 6A and the light emitting layer 6B, the hole injection layer 4 having good wettability formed on the side surface of the bank 5 can apply the ink densely and uniformly, and the hole transport. The layer 6A and the light emitting layer 6B can be formed appropriately.

  In addition, the formation method of the hole transport layer 6A and the light emitting layer 6B is not limited to this, and methods other than the inkjet method and the gravure printing method, for example, a dispenser method, a nozzle coating method, a spin coating method, an intaglio printing, a relief printing, etc. The ink may be dropped and applied by this method.

Next, the electron transport layer 7A is formed on the surface of the light emitting layer 6B and the exposed hole injection layer 4 and each surface of the bank 5 by a vacuum deposition method (for example, barium) (FIG. 3D). .
Subsequently, 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 7A by a vacuum deposition method. Thereby, the cathode 8 is formed (FIG. 3E).

  3D and 3E, the electron transport layer 7A and the cathode 8 are also formed on the bank 5, but the electron transport layer is formed in a region other than the upper portion of the bank 5 by performing masking. 7A and the cathode 8 can also be formed sequentially.

  Next, a sealing layer 9 is provided on the surface of the cathode 8 for the purpose of preventing the organic EL element 1 from being exposed to the atmosphere (FIG. 3 (f)). 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 EL element 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 EL element 1 can be driven at a low voltage.

As a tungsten oxide film forming method for obtaining such performance, a DC magnetron sputtering apparatus is used, the target is metallic tungsten, the substrate temperature is not controlled, and the chamber gas 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 EL element, carriers that form current are both holes and electrons. Therefore, in addition to the hole current, the electron current is reflected in the electrical characteristics of the organic EL element. 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 device is obtained by replacing the cathode 8 in the organic EL device 1 of FIG. 1 with gold. That is, as shown in FIG. 4, 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 device 1A) in which a hole transport layer 6A made of organic polymer TFB, a light emitting layer 6B made of F8BT which is an organic polymer having a thickness of 70 nm, and a cathode 8 made of gold having a thickness of 100 nm are sequentially laminated. 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 1A (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 1A 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 1A, 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 drive voltage for each film formation condition of the total pressure, oxygen gas partial pressure, and input power of each hole-only element 1A obtained by the experiment. In Table 3, element No. of each hole only element 1A. Is indicated by a boxed number.

  5A to 5C are graphs summarizing the film formation condition dependence of the drive voltage of each hole-only element 1A. Each point in FIG. 5A is an element No. from left to right. The drive voltages of 4, 10, and 2 are represented. Each point in FIG. 5B is an element No. from left to right. The drive voltage of 13, 10, 1 is represented. Furthermore, 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. 5A, the dependence of the driving voltage on the total pressure is at least in the range where the total pressure exceeds 2.7 Pa and 4.8 Pa or less under the conditions of the oxygen gas partial pressure 50% and the input power 500 W. 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. 5B, the oxygen gas partial pressure dependence of the driving voltage is at least 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. 5 (c), the dependence of the driving voltage on the input power is abruptly increased when the input power exceeds 500 W under a total pressure of 4.8 Pa and an oxygen gas partial pressure of 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 1A, the 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. 6, 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 1A.

  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 element 1A. The hole-only element 1A has the same configuration as the organic EL element 1 except for the cathode. Therefore, also in the organic EL element 1, the film injection condition dependency of the hole injection efficiency from the hole injection layer 4 to the hole transport layer 6A is essentially the same as that of the hole only element 1A. In order to confirm this, each organic EL element 1 using the hole injection layer 4 under the deposition conditions A, B, and C was fabricated.

  As shown in FIG. 1, each specifically produced organic EL element 1 is formed with an anode 2 made of an ITO thin film having a thickness of 50 nm 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 EL elements 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 explanation, in FIG. 7, the organic EL element 1 under the film formation condition A is BPD-A, the organic EL element 1 under the film formation condition B is BPD-B, and the organic EL element 1 under the film formation condition C is used. Was described as BPD-C.

  As shown in FIG. 7, BPD-A has the fastest rise of the current density-applied voltage curve and higher current density at the lowest applied voltage than BPD-B and BPD-C. . 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 EL elements 1 described above, a light emission intensity-current density curve showing the relationship of the 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 EL element 1 as in the case of the hole only element 1A. Is done. That is, in the organic EL element 1 of the experiment, tungsten oxide constituting the hole injection layer 4 is a DC magnetron sputtering apparatus, 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 a DC magnetron sputtering apparatus different from the DC magnetron sputtering apparatus used in this experiment is used, the input power is adjusted so that the input power density satisfies the above conditions according to the target size. In addition, the hole injection layer 4 that realizes the organic EL element 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.

  In addition, when the hole injection layer 4 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, the substrate temperature is room temperature at least before film formation. However, the substrate temperature may increase by several tens of degrees Celsius during film formation.

The organic EL element 1 in which the hole injection layer 4 is produced under the film forming condition A is the organic EL element 1 according to 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 EL element 1 of Embodiment 1 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 FIG. 9B, 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 1B under the film formation condition A will be referred to as sample A, the sample 1B under the film formation condition B as sample B, and the sample 1B under the film formation condition C as sample C.

  Samples A, B, and C were all deposited in a sputtering apparatus and then transferred into 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. 10 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. 10 has the above basic structure, which has a tungsten trioxide crystal or an amorphous structure in which the order of the crystal is disordered (but the bond is not broken and the above 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. 10 corresponds to the band gap between the valence band and the conduction band, but as this UPS spectrum shows, this region is different from the valence band in tungsten oxide. 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. 11 shows UPS spectra in the region (y) of each tungsten oxide layer 12 in Samples A, B, and C. The spectrum intensity shown in FIG. 11 was normalized by the value of the peak top of the peak (ii) located 3-4 eV higher than the point (iii) in FIG. FIG. 11 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. 11, 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 the injection layer, excellent hole injection efficiency can be exhibited in the organic EL element.

  Here, it has been found that the steeper degree of the protrusion tends to increase the hole injection efficiency. Therefore, as shown in FIG. 11, a region having a binding energy lower by about 2.0 to 3.2 eV than 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 the samples A, B, and C shown in FIG. 11 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. 12 are the same horizontal axis positions as in FIG.
According to the differential curve shown in FIG. 12, 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. 11 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. 11 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. 11, 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. 13, 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 exposure to the atmosphere. 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. 14 is an XPS spectrum of the tungsten oxide layer 12 of Sample A after the atmospheric exposure. For comparison, the UPS spectrum (same as FIG. 10) 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. 14, the point (iii) in the figure is the same horizontal axis position as in FIG. 10, and the horizontal axis indicates the relative binding energy with respect to the point (iii) as in FIG. 11. Further, a line corresponding to (i) of FIG. 10 in the XPS spectrum is indicated by (i) ′ in FIG.

  As shown in FIG. 14, 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, separately from the structure of the organic EL element 1 shown in FIG. 1, a sample 1B (FIG. 1B) formed by forming a tungsten oxide layer 12 on a conductive silicon substrate 10S. 9) was used. This is merely a measure for preventing charge-up during measurement, and the structure of the organic EL element 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 EL element 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 1B, 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 1B 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. 15 is an energy diagram at the interface between the tungsten oxide layer having an occupied level near the Fermi surface of the present invention and the α-NPD layer.
In FIG. 15, first, in the tungsten oxide layer (corresponding to the hole injection layer), the lowest binding energy in the valence band (denoted as “the upper end of the valence band” 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. 10, 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. 15 was obtained by repeating ultrahigh vacuum deposition. Since no charge-up was confirmed during the UPS measurement, in FIG. 15, 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. 15, 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 top 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.

Furthermore, FIG. 15 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. 15 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, as described above, the tungsten oxide layer and the α shown in FIG. 15 are formed at each interface between the deposited film of molybdenum oxide having the same physical properties as tungsten oxide and α-NPD and F8BT. -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 EL 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 element HOD-A and the organic EL element 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. 16 (b), even if the implantation site (x) exists in the tungsten oxide layer where the raised structure near the Fermi surface does not exist, such as the samples B and C described above, the number density thereof is 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.

  On the other hand, as shown in FIG. 16A, the tungsten oxide layer having a raised structure near the Fermi surface, such as the above-described sample A, has abundant implantation 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. 17 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. 10), which is found 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. 17 is completely different from that in FIG. 15, 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, the interface state connection is not at all. 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 into the highest occupied orbit of α-NPD from the upper end of the second in-gap state, 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 light emission efficiency of the hole-only device 1A and the organic EL device 1 under the respective film forming conditions. That is, the difference in characteristics between the hole-only element 1A and the organic EL element 1 under the deposition conditions A, B, and C is that the organic EL element 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.

In summary, the fact that the organic EL device of the present invention has excellent hole injection efficiency can be explained as follows.
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 EL element 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.

  As shown in FIGS. 18 and 19, when the anode is made of IZO, the surface of the anode is subjected only to pure water cleaning (FIG. 18), and further subjected to dry etching after pure water cleaning ( In FIG. 19), the hole injection barrier between the Fermi level of the anode and the highest occupied orbit of the functional layer has a considerable size of more than 1 eV, and the size of the barrier is not enough for the treatment of the IZO surface. It can be seen that there is a large fluctuation due to the difference.

  As shown in FIGS. 20 and 21, even when the anode is made of ITO, the surface of the anode is only cleaned with IPA (isopropanol) (FIG. 20). It can be seen that there is also a hole injection barrier with a considerable height in the processed one (FIG. 21).

  As shown in FIGS. 18 to 21, in the conventional organic EL element, 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.

  Meanwhile, 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 are shown in FIGS.

  22 and 23 show the case where the anode is made of IZO. Similarly to FIGS. 18 and 19, the surface of the anode was cleaned only with pure water (FIG. 22), and further subjected to dry etching after pure water cleaning (FIG. 23), respectively. A hole injection layer of the present invention is laminated thereon.

  24 and 25 show the case where the anode is made of ITO. Similar to FIGS. 20 and 21, the surface of the anode was subjected only to IPA cleaning (FIG. 24), and further treated with oxygen plasma after IPA cleaning (FIG. 25). The hole injection layer of the present invention is laminated.

  Further, FIG. 26 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.

The following can be understood from the results shown in FIGS.
First, in all of FIGS. 22 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 near 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. 22 to 26, a good Schottky ohmic connection with 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. 22 and 23 and the ITO anode of FIGS. 24 and 25, the difference in binding energy between the Fermi level of the anode and the upper end of the in-gap state when the hole injection layer thickness 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 device has the same configuration and manufacturing method except for the film thickness of the hole-only device 1A of FIG. 2 and 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 EL 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 organic EL element is obtained by changing the cathode made of gold into a layered structure 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 EL elements are all the same except for the thickness of the hole injection layer, all the characteristics are the same as long as a constant Schottky ohmic connection can be formed between the anode and the hole injection layer. It should be.

Each organic EL element having a 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 EL element.

  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. Accordingly, as in the case of the hole-only device, in the organic EL 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 drive life of the element was evaluated using the organic EL element. The organic EL 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 in Table 1 and FIGS. 5 to 8, 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.

  Similar to the method used in FIG. 15, when the hole injection layer and the UPS measurement under the respective film formation conditions were repeated on the ITO anode, the film formation was performed when the hole injection layer had a thickness of about 2 nm or less. 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. 11, the presence or absence of a raised structure near the Fermi surface varied depending on the film formation 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. 5-8 will depend on film-forming conditions.

  As described above, as discussed using each experimental data, the anode and hole injection layer in the present invention have good hole injection characteristics. Since this effect is considered to be predominantly Schottky ohmic connection formed between the anode and the hole injection layer, even if the residue 5R of the bank 5 slightly exists between the anode and the hole injection layer, Not so badly affected.

Therefore, in the organic EL element 1 according to the first embodiment, the residue 5R is prevented from remaining, the hole injection layer and the hole transport layer are formed at a clean connection interface, and the bank residue 5R is mainly left between the anode and the hole injection layer 4. As a result, excellent luminous efficiency can be expected.
(Confirmation test on the effects of bank residue)
Next, a confirmation test was performed on the influence of the bank residue on the driving voltage, light emission efficiency, and life characteristics of the organic EL element.

  First, FIG. 27 shows the configuration of a sample used for the effect confirmation test of the partition residue. As Sample S1 (Comparative Example), a hole injection layer made of the tungsten oxide layer of the present invention was laminated on the anode, and a configuration not including bank residue was prepared (FIG. 27A). In this sample S1, there is no bank residue between the hole injection layer and the anode and the upper surface of the hole injection layer, and the surface is kept clean.

  Next, as sample S2 (comparative example), a structure was prepared in which the hole injection layer made of the tungsten oxide layer of the present invention was laminated on the anode, and the bank residue was adhered to the upper surface of the hole injection layer (FIG. 27 ( b)).

  Next, as Sample S3 (Example), a structure was prepared in which a hole injection layer made of a tungsten oxide layer of the present invention was laminated on the anode, and a bank residue was adhered between the anode and the hole injection layer ( FIG. 27 (c)).

  Using these samples S1, S2, and S3, an element having a stacked configuration similar to that of the organic EL element 1 of the first embodiment was manufactured. The voltage and efficiency characteristics of each element immediately after fabrication were measured. The result is shown in FIG. In this figure, two samples S1, S2, and S3 are produced, and the measurement results of driving an element using these samples S1, S2, and S3 are shown. As a result, it was confirmed that the elements using any of the samples S1, S2, and S3 have characteristics that are almost the same as those of the elements immediately after fabrication.

Next, the element using each sample S1, S2, and S3 was driven for a long time, and the lifetime characteristic was measured. The result is shown in FIG.
As shown in the figure, it was confirmed that the element using the sample S3 as an example exhibited excellent long-life characteristics almost the same as the sample S1 of the comparative example having no residue at all in the bank. On the other hand, Sample S2 in which bank residue is present on the upper surface of the hole injection layer did not emit light abruptly within a relatively short time from the start of driving, and exhibited short life characteristics.

From these results, when the hole injection layer is formed of the tungsten oxide layer formed under certain conditions of the present invention, even if there is a bank residue between the anode and the hole injection layer, the residue on the hole injection layer It was found that an organic EL device having excellent life characteristics can be obtained if there is no. It is most important that there is no bank residue between the hole injection layer and the hole transport layer, considering that the element of Sample 2 including the hole injection layer using the same tungsten oxide layer has a short lifetime, If this condition can be satisfied, it can be said that even if some bank residue is present between the anode and the hole injection layer, the life characteristics are hardly affected.
<Embodiment 2>
<Overall configuration of organic EL element 1C>
FIG. 31A is a schematic cross-sectional view showing the configuration of the organic EL element 1C according to the present embodiment. FIG. 31B is a partially enlarged view near the hole injection layer 4A.

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

Specifically, the organic EL element 1C has an anode 2, an ITO layer 3, a hole injection layer 4A, a hole transport layer 6A, a light emitting layer 6B, an electron injection layer 7B, a cathode 8, The stop layer 9 is laminated in the same order. Hereinafter, the difference from the organic EL element 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 EL element 1 </ b> C, the ITO layer 3 is separated from the anode 2, but the ITO layer 3 can also be regarded as a part of the anode 2.
(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 EL element 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 EL element 1C) and the section (About the film forming conditions for the hole injection layer 4A).
Here, in the second embodiment, since the tungsten oxide layer constituting the hole injection layer 4A is formed under the predetermined film forming 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 EL element 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 EL element 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 second embodiment includes both a case where the hole injection layer 4A is made of only a nanocrystal structure and a case where the hole injection layer 4A is made 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 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 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.
(Electron injection layer 7B, cathode 8, sealing layer 9)
The electron injection layer 7B 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 EL element 1C from the outside.

  The sealing layer 9 has a function of suppressing the organic EL element 1C from being exposed 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 EL element, it is preferably formed of a light transmissive material.

Also in the organic EL element 1C of the second embodiment having the above configuration, substantially the same effect as that of the organic EL element 1 of the first embodiment can be expected.
That is, in the manufacturing process of the organic EL element 1C, the bank 5 is formed after the ITO layer 3 is formed and before the hole injection layer 4A is formed. Accordingly, the residue 5R of the bank material 5X exists mainly between the ITO layer 3 and the hole injection layer 4A, and the residue 5R does not remain or is adjusted to a very small amount between the hole injection layer 4A and the hole transport layer 6A. ing.

  As a result, excellent hole injection characteristics are exhibited between the hole injection layer 4A and the hole transport layer 6A without being substantially affected by the residue 5R (contamination). On the other hand, the Schottky ohmic connection is made between the ITO layer 3 and the hole injection layer 4A as shown in the above experimental results, and the hole conductivity is hardly affected by the residue 5R. Therefore, good hole injection characteristics can be maintained.

Thereby, excellent hole injection characteristics are exhibited also in the entire organic EL element 1C, and good light emission characteristics 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 second embodiment, the hole injection layer is formed by forming tungsten oxide constituting the hole injection layer 4A under predetermined film formation conditions. By making the nanocrystal structure intentionally exist in 4A, the hole conduction efficiency is improved, and the organic EL element 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. The film formation method of the hole injection layer 4A is not limited to this, and the film can 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 EL element 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 condition of the above parameters (total pressure / power density) for forming the nanocrystal structure of the second embodiment is 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 1D shown in FIG. 32 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. 32, the hole-only element 1D is obtained by changing the organic EL element 1C of FIG. 31 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 injection layer 7B 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 1D, 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 element 1 </ b> D composed of the hole injection layer 4 </ b> A having five film forming conditions of α to ε shown in Table 8 was produced. Hereinafter, the hole only element 1D formed under the film formation condition α is HOD-α, the hole only element 1D formed under the film formation condition β is HOD-β, and the hole only element 1D formed under the film formation condition γ is HOD. The hole-only element 1D formed under the film formation condition δ is referred to as HOD-δ, and the hole-only element 1D formed under the film formation condition ε is referred to as HOD-ε.

  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.

FIG. 33 shows the relationship between the applied voltage and current density of each hole-only element 1D. 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 1D. 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 element 1D, 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 1D strongly reflects the difference in hole conduction efficiency of the hole injection layer 4A.

  As shown in Table 9 and FIG. 33, 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 1D has been described above. The hole-only device 1D is the same as the organic EL 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 EL element 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 1D.

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

  Each organic EL element 1C is obtained by changing the organic EL element 1C of FIG. 31 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 injection layer 7B and the cathode 8 made of an aluminum layer were set to 5 nm and 100 nm, respectively.

  Each organic EL element 1C produced under the deposition 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. 34 shows the relationship between the applied voltage and current density of each organic EL element 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 EL element 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. 34, 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 EL element 1C as in the case of the hole only element 1D. That is, even in the organic EL element 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.

  Further, 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 EL element 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 EL element produced under film formation conditions α and β. It is. Hereinafter, an organic EL element including a hole injection layer manufactured under film forming 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)
Pentavalent tungsten atoms are present in the tungsten oxide layer constituting the hole injection layer 4A of the organic EL element 1C of the second 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) is 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. 35, 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. 36A shows the analysis result of the sample α, and FIG. 36B shows the analysis result of the sample ε.
In both figures, the broken lines (sample α, sample ε) are measured spectra (corresponding to the spectra in FIG. 35), and the two-dot chain line (surface) is the component (W ^sur 5p _3/2 , W ^sur 4f _{5) / 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 spectrums of the broken line and the solid line in FIG. 36 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. 36 (a), the component (5) attributed to the corresponding pentavalent (0.3 to 1.8V lower than the component (W ⁶⁺ ) attributed to the hexavalent ( W ⁵⁺ ) can be confirmed. On the other hand, in the sample ε of FIG. 36B, such a component attributed to pentavalent cannot be confirmed. For easy understanding, an enlarged view of a circled portion is shown on the right side of each of FIGS. 36 (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 EL element tends to decrease as the ratio 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)
Similar to the hole injection layer 4 of the first embodiment, the hole injection layer 4A made of tungsten oxide of the second embodiment has an occupied level near the Fermi surface. 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. . Thereby, the organic EL element of Embodiment 2 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 EL element of the second embodiment 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.
In each of samples α to ε, after hole injection layer 4A was formed in the sputtering apparatus, it was transferred to a glove box connected to the sputtering apparatus and filled with nitrogen gas, and kept in a state where it was 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. 37 shows a UPS spectrum in the region (y) of each hole injection layer 4A of the 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. 37, 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 2 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 EL element of Embodiment 2 can exhibit excellent hole conduction efficiency.

  The characteristics of the series of hole-only devices and organic EL devices described in the second 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 the injection sites (x) are present in the hole injection layer 4A at such a number density that can be confirmed by UPS, as will be described with reference to FIG. 14 in the first embodiment. . 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 second 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. 38 is a diagram for explaining the structure of a tungsten oxide crystal. As described above, the tungsten oxide according to the second embodiment has a composition ratio of tungsten to oxygen of approximately 1: 3. Therefore, here, description will be made by taking tungsten trioxide as an example.

As shown in FIG. 38, the crystal of tungsten trioxide 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. 38, for the sake of simplification, the octahedrons are shown in an orderly arrangement like rhenium trioxide, but actually the octahedrons are 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 second embodiment having pentavalent tungsten atoms, which is 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 second 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. Therefore, it is considered that hole conduction is facilitated at a low voltage, and excellent hole conduction efficiency can be exhibited in the organic EL element 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)
A nanocrystal structure exists in the tungsten oxide layer constituting the hole injection layer 4A of the second embodiment. 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 second embodiment, the cross section of the hole injection layer 4A is observed, and 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. 39 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. 39, the size of this crystal can be seen as a nano size 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 the sample α in FIG. 39, any one of the nanocrystals is shown 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. 40 shows the result of two-dimensional Fourier transform of the TEM observation photograph of FIG. 39 (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. 39, and thus shows the periodicity of the TEM observation photograph. Specifically, the two-dimensional Fourier transform image of FIG. 40 was created by performing Fourier transform on the TEM photograph of FIG. 39 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-mentioned “unintelligibility” 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. 41 is a diagram showing an outline of the creation method, and shows a sample α as an example.

  As shown in FIG. 41 (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 from the center point to the X axis in the figure at 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. 41B 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, the plot created by the method described with reference to FIG. 41 and indicating the relationship between the distance from the center point and the normalized luminance at each distance is referred to as a “luminance change plot”.

42 and 43 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”.
42 and 43, 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. 44 is a diagram showing an outline of the evaluation method, and shows samples α and ε as examples.

  44 (a) and 44 (b) are luminance change plots of samples α and ε, respectively, and FIGS. 44 (a1) and 44 (b1) 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 more accurately determine the “peak width L of peak P1,” the luminance change plots of FIGS. 44 (a1) and (b1) are first-order differentiated and shown in FIGS. 44 (a2) and (b2). . 44 (a2) and 44 (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 EL element 1C having the hole injection layer 4A under the film forming conditions γ and δ has a good hole conduction efficiency as described above.

The value of the peak width L in Table 13 shows 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 therefore the regularity and order in the TEM photograph of FIG. 39 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 contrary, 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. 39 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 second 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 under each film forming condition of the second 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. 45B 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 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.

  When the holes 14 reach the surface of the nanocrystal 15 in FIG. 45 (b), 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. 45 (a) 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. 45 (a), 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 organic EL device of the present invention is not limited to a configuration using a single device. An organic EL light-emitting device can be configured by integrating a plurality of organic EL elements as pixels on a substrate. Such an organic EL light-emitting device can be implemented by appropriately setting the film thickness of each layer in each element, and can be used as, for example, a lighting device. Or it can also be set as the organic electroluminescent panel which is an image display apparatus.

  In the second embodiment, the rising position of the peak P1 shown in FIG. 44 is the position at which the differential value first becomes 0 from the peak top of the peak P1 toward the center point in FIGS. 44 (a2) and (b2). did. However, the determination method of the rising position of the peak P1 is not limited to this, and for example, referring to FIG. 44 (a1), an average value of normalized luminance near the peak P1 is used as a base line, and the base line 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 EL element 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 property 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 an organic EL panel is manufactured using the organic EL element of the present invention, the bank shape is not limited to a so-called pixel bank (a cross-shaped bank), and a line bank can also be adopted. FIG. 46 shows a configuration of an organic EL 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 first and second embodiments, an organic material is used as the bank material, but an inorganic material can also be used. In this case, the bank material layer can be formed by coating, for example, as in the case of using an organic material. The removal of the bank material layer can be performed by forming a resist pattern on the bank material layer and then performing etching using a predetermined etching solution (tetramethylammonium hydroxide oxide (TMAH) solution or the like).

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.
In the above embodiment, the hole transport layer is formed by using a so-called wet process such as an ink jet method. However, the present invention is not limited to this. For example, the hole transport layer is formed by using a so-called dry process such as an evaporation method. It is also possible to do. In this case, as described in the above embodiment, it is not necessary to etch the hole injection layer by the pattern formation step (FIG. 2 (e)). That is, as shown in the cross-sectional view of FIG. 47, the hole injection layer 4 can be uniformly formed so as to include the top of the bank 5. As a result, the manufacturing process can be simplified, and the bank surface is covered with the hole injection layer, so that the residue remaining between the bank and the hole injection layer must be reliably confined. Can do.

  The organic EL device of the present invention can be used for display devices for mobile phones, display devices such as televisions, various light sources, and the like. In any application, it can be applied as an organic EL element that is driven at a low voltage in a wide luminance range from low luminance to 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.

DESCRIPTION OF SYMBOLS 1, 1C Organic EL element 1B Photoelectron spectroscopy measurement sample 1A, 1D Hall-only element 2 Anode 3 ITO layer 3A IZO layer 4X Thin film (tungsten oxide film)
4, 4A Hole injection layer 5X Bank material layer 5 Bank 6A Hole transport layer 6B Light emitting layer 7A Electron transport layer 7B Electron injection layer 8 Cathode 9 Sealing layer 10, 10S Substrate 11 Planarization film 12 Tungsten oxide layer 13, 15 Nanocrystal 14 holes 16 amorphous structure DC DC power supply

Claims (34)

The anode,
A partition provided in contact with the anode so as to define a light emitting region on the anode;
A tungsten oxide layer containing tungsten oxide provided in contact with a light emitting region on the anode and at least a part of a partition corresponding to the light emitting region;
A layer containing an organic material provided in contact with the tungsten oxide layer;
A cathode provided on a side different from the anode with respect to the layer containing the organic material,
The tungsten oxide layer 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, and the film thickness is 2 nm or more.
Organic light emitting device. The amount of residue of the partition material is less between the tungsten oxide layer and the cathode than between the anode and the tungsten oxide layer,
The organic light emitting device according to claim 1. The tungsten oxide layer is a hole injection layer;
The organic light emitting device according to claim 1, wherein the layer containing the organic material is a functional layer. The organic light emitting device according to claim 3, wherein, at the interface between the hole injection layer and the anode, a difference between a binding energy of the occupied level and a Fermi level of the anode is within ± 0.3 eV. The hole injection layer raised in a binding energy region 1.8 to 3.6 eV lower than the lowest binding energy in the valence band in the UPS spectrum representing the relationship between the binding energy and the photoelectron intensity or the normalized intensity thereof. The organic light emitting device according to claim 3, having a shape. The hole injection layer is 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. It has a shape. The organic light emitting element as described in any one of Claims 3-5. The hole injection layer extends over 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. The organic light-emitting device according to claim 3, having a shape expressed as a function different from an exponential function. Since the hole injection layer has the occupied level, the binding energy of the occupied level is positioned in the vicinity of the binding energy of the highest occupied orbit of the functional layer at the interface between the hole injection layer and the functional layer. The organic light emitting device according to any one of claims 3 to 7. 9. The difference between the binding energy of the occupied level and the binding energy of the highest occupied orbit of the functional layer is within ± 0.3 eV at the interface between the hole injection layer and the functional layer. The organic light emitting device according to one item In the tungsten oxide layer,
The organic light-emitting device according to claim 1, wherein the organic light-emitting device includes a tungsten oxide crystal having a nanometer-order particle size, and a hexavalent tungsten atom having a maximum valence of 6 and a pentavalent tungsten atom lower than the maximum valence. 11. The organic light emitting device according to claim 10, wherein a ratio W ⁵⁺ / W ^{6+ of the} number of pentavalent tungsten atoms and 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 layer, a first component corresponding to the 4f _7/2 level of a hexavalent tungsten atom and a second component exist in a lower binding energy region than the first component. The organic light emitting device according to claim 10. The organic light-emitting device according to claim 13, wherein the second component is present in a binding energy region that is 0.3 to 1.8 V lower than the peak-top binding energy of the first component. The organic light emitting element according to claim 13 or 14, 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 the pentavalent tungsten atom, the tungsten oxide layer 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. The organic light-emitting device according to claim 10. The organic light emitting device according to any one of claims 10 to 16, wherein the tungsten oxide layer includes a plurality of the tungsten oxide crystals having a particle size of 3 to 10 nanometers. The tungsten oxide layer has a linear structure regularly arranged at intervals of 1.85 to 5.55 mm in a lattice image obtained by observation with a transmission electron microscope. The organic light emitting element as described. The organic light-emitting device according to claim 18, wherein a concentric bright portion centering on a center point of the two-dimensional Fourier transform image appears in the two-dimensional Fourier transform image of the lattice image. 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. The organic light emitting device according to claim 19, wherein two or more appear. 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 organic light emitting element according to claim 20, wherein the peak width is smaller than 22 when the distance corresponding to the position of the peak top is 100. The functional layer includes an amine-based material,
The organic light emitting element according to any one of claims 1 to 21. The functional layer is at least one of a hole transport layer that transports holes, a light emitting layer that emits light by recombination of injected holes and electrons, and a buffer layer that is used for optical property adjustment or electronic block applications. The organic light emitting element according to any one of claims 1 to 22. The organic light emitting element according to any one of claims 1 to 23, wherein the occupied level 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. The organic light emitting element according to any one of claims 1 to 24, wherein the tungsten oxide layer is provided in contact with at least an upper surface of the anode. The tungsten oxide layer is provided so as to cover a surface of a part or more of a side surface of a partition corresponding to the light emitting unit while being in contact with an upper surface of the anode. Organic light emitting device.   A display apparatus provided with the organic light emitting element as described in any one of Claims 1-24.   A light-emitting device provided with the organic light-emitting element as described in any one of Claims 1-24. A first step of preparing an anode;
Applying a resin material to the anode to form a resin material film, patterning the resin material film and partially opening the surface portion of the anode, thereby forming a partition;
A step of forming a tungsten oxide layer on a region surrounded by the open surface portion of the anode and the surface portion of the partition wall, wherein a gas composed of argon gas and oxygen gas is used as a chamber of a sputtering apparatus; And the total pressure of the gas 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 further per target unit area in the charged deposition conditions power density is 1W / cm ² or more 2.8W / cm ² or less, and a third step of forming the tungsten oxide layer as its thickness is greater than or equal to 2 nm,
A fourth step of forming a functional layer containing an organic material with respect to the formed tungsten oxide layer;
A fourth step of forming a cathode above the functional layer;
The manufacturing method of the organic light emitting element which has this. In the third step, the tungsten oxide layer is formed so as to have a raised shape in a binding energy region whose UPS spectrum is 1.8 to 3.6 eV lower than the lowest binding energy in the valence band. Item 30. A method for producing an organic light-emitting device according to Item 29. In the third step, the differential spectrum of the UPS spectrum has a shape expressed as a function different from the exponential function over a binding energy region that is 2.0 to 3.2 eV lower than the lowest binding energy in the valence band. 30. The method of manufacturing an organic light-emitting element according to claim 29, wherein the tungsten oxide layer is formed on the substrate. 30. The organic light-emitting element according to claim 29, wherein in the third step, the total pressure / input power density, which is a value obtained by dividing the total pressure by the input power density, is greater than 0.7 Pa · cm ² / W. Method. 33. The method of manufacturing an organic light emitting element according to claim 32, wherein in the third step, the total pressure / input power density is smaller than 3.2 Pa · cm ² / W. After the partition is formed in the second step, the residual amount of the resin material film between the tungsten oxide layer and the functional layer is changed to the anode and the tungsten oxide by sequentially performing the third step and the fourth step. 30. The method for manufacturing an organic light-emitting element according to claim 29, wherein the amount is less than a residue amount of the resin material film between layers.