WO2012169150A1

WO2012169150A1 - Organic electroluminescent element

Info

Publication number: WO2012169150A1
Application number: PCT/JP2012/003536
Authority: WO
Inventors: 松本　敏男
Original assignee: エイソンテクノロジー株式会社
Priority date: 2011-06-07
Filing date: 2012-05-30
Publication date: 2012-12-13
Also published as: JPWO2012169150A1; JP5922654B2

Abstract

Provided is a novel structure for an organic electroluminescent element which is capable of reducing a drive voltage, and which has a structure in which an insulating organic layer is disposed at a location that serves as a barrier to the movement of charges to a light-emitting layer, as a structure that allows electron charges to be moved in the direction of an anode, as viewed from a charge generation (carrier generation) location, and injected in the light-emitting layer, without using a strong electron-donating substance such as an alkali metal. The present invention pertains to an organic electroluminescent element characterized by having an anode, a cathode, a plurality of light-emitting units that includes a light-emitting layer and is positioned between the anode and the cathode, and intermediate layers that are positioned between the plurality of light-emitting units. The organic electroluminescent element is further characterized in that the intermediate layers each include an insulating organic layer that is disposed at a location that servers as a barrier to the movement of charges from the intermediate layer to the light-emitting unit, and a mixed layer comprising organic matter and a metal disposed adjacent to the insulating organic layer.

Description

Organic electroluminescent device

The present invention relates to an organic electroluminescent element (hereinafter sometimes abbreviated as “organic EL element”) used for a planar light source and a display element.

In recent years, an organic EL element having a light emitting layer made of an organic compound between an anode and a cathode, which are opposed to each other, has attracted attention as a means for realizing a large-area display element driven at a low voltage. Tang et al. Of Eastman Kodak Company has adopted a structure in which organic compounds having different carrier transport properties are stacked, and holes and electrons are injected in a balanced manner from the anode and the cathode, respectively, in order to increase the efficiency of the device. By making the thickness of the organic layer sandwiched between the anodes 200 nm or less, we succeeded in obtaining high luminance and high efficiency sufficient for practical application of 1000 cd / m ² and an external quantum efficiency of 1% at an applied voltage of 10 V or less. did.

For example, according to Patent Documents 1 to 6, it is said that a device capable of emitting light with a lower applied voltage can be provided by setting the film thickness of the entire organic layer sandwiched between the cathode and the anode to 1 μm or less. If the film thickness is in the range of 100 to 500 nm, an electric field (E = Vcm ⁻¹ ) useful for obtaining light emission with an applied voltage of 25 V or less is obtained.

The structure of the organic EL element has been developed on the basis of the structure shown by Tang et al. As described above. Recently, for example, as shown in Patent Document 7 and Patent Document 8, a structure sandwiched between electrodes. An organic EL element having a structure in which a plurality of light emitting units are stacked so that can be connected in series has been developed. This technology has been attracting attention as a technology that enables the organic EL device to dramatically extend its life, achieve high brightness required for light sources and illumination, and emit light uniformly over a large area. This is because the structure of the organic EL element of Tang et al. Which requires a large current despite the low voltage cannot satisfy these requirements.

Next, as described in Patent Document 8, the inventor of the present application devised and realized an organic EL element having a series type (tandem type) structure, and ITO (Indium Tin Oxide) or IZO (IZO ( A plurality of light emitting units can be connected in series by using a charge generation layer with low conductivity instead of a transparent electrode material such as Indium Zinc Oxide. In this organic EL element, only the region where the cathode and the anode intersect with each other emits light as in the conventional organic EL element, and the sputtering process that is essential for the formation of the transparent electrode becomes unnecessary. It is recognized as the most useful among the structures of organic EL elements, and has been widely known as a multiphoton organic EL element. The reason for being referred to as multiphoton is that if the number of light emitting units is set to a predetermined number or more, the number of photons exceeding the number of electrons passing through the organic EL element can be generated.

However, this multi-photon organic EL element has a problem that a manufacturing process several times as many as that of the conventional organic EL element is required. Further, a low-conductivity charge generation layer is formed by, for example, Patent Documents 9 to There is also a problem that it is difficult to control the manufacturing process because the chemical doping method described in Document 14 must be used.

The series organic EL element is suitable for emitting light over a large area with uniform intensity. When compared with the conventional organic EL element, the series organic EL element can increase the voltage V required to obtain the same luminance by multiplying by the number of units, and the current I is almost equal to the number of units. You can make it smaller by the amount you remove. As a result, the element resistance (ratio of voltage to current: VI ⁻¹ ) increases by approximately the square of the number of units, the voltage drop due to the surface resistance of the external electrode can be reduced, and a substantially uniform potential in the surface can be realized. Because.

Needless to say, the uniformity of the potential, in other words, the uniformity of the luminance, increases as the number of units increases. However, according to the present inventor's previous knowledge, when a luminance of 3000 cdm ⁻² or more necessary for illumination is required, a light emitting area of about 5 inches diagonal is approximately uniform in a laminate of several units. Although light emission can be realized, for example, when the light emission area is 15 inches or more diagonally, uniform light emission with such high brightness is impossible with a laminate of several units, and at least about 15 units are considered necessary. It is almost impossible to produce such a large number of unit laminates efficiently and at low cost.

The first reason why it is impossible to produce such a multi-unit laminate efficiently and at low cost is that the manufacturing method is complicated. That is, as proposed by the present inventors in Patent Document 8, the production of a charge generation layer provided for generating hole charges and electron charges is very complicated.

For example, in

claim

1 or 2 of Patent Document 8, the charge transfer complex formed at the contact interface formed by mixing or stacking a metal oxide having a strong electron-donating property and an amine-based organic compound having a high electron-accepting property is as if the charge is charged. It is described that an electron charge and a hole charge necessary for excitation of the luminescent substance are supplied from the generation layer to the light emitting unit. However, in actuality, in the configuration described in Patent Document 8, although electrons are generated in the metal oxide by the applied electric field at the interface, holes are generated in the amine organic compound. Thus, both the hole and electron charges are not automatically supplied to the light-emitting substance, and as shown in the specific examples, strong charges such as alkali metals are always present at the site in contact with the anode side of the charge generation layer. A technique is required for causing an electron donating substance to act on an electron transporting organic substance and promoting electron injection into the organic substance.

This is because there is a large energy difference between the electron transporting organic material and the metal oxide, and a strong electron donation such as an alkali metal is required to inject electrons generated in the metal oxide into the electron transporting organic material. This is because it is necessary to perform carrier doping with a conductive material and to effectively reduce the injection barrier with the electron transporting organic substance by the space charge of the ionized dopant.

When the injection efficiency is low, holes move predominantly in the light-emitting layer containing the light-emitting substance in the light-emitting unit located on the anode side of the charge generation layer, and the excess holes exist in excess in the charge generation layer. It undergoes a process in which current flows due to non-radiative recombination with electrons. The light emitting layer portion exists only as a hole current resistor, and the light emitting material does not emit light. That is, even if a multiphoton organic EL device is produced by forming a “charge generation layer made of a charge transfer complex” in Patent Document 8, no effect is actually obtained.

Examples of a method for supplying alkali metal into the film include a method in which alkali metal is directly evaporated by resistance heating (resistance heating vapor deposition method), a method using a film containing a compound containing alkali metal ions, and the like. Is proposed in Patent Document 8.

Furthermore, if an oxide, carbonate, composite oxide, composite carbonate, or the like containing an alkali metal ion is further deposited by electron beam evaporation, the electron beam evaporation method itself converts the metal in the compound from the ionic state to the metal. Since it is one of the means for reducing to an atomic state, as a result, an alkali metal can be allowed to act on an electron transporting organic substance. Furthermore, in exceptional cases, cesium carbonate (CsCO ₃ ) may be capable of producing metal cesium by reduction simply by resistance heating in vacuum without using an electron beam evaporation method.

For alkali metal compounds such as oxides, carbonates, composite oxides, composite carbonates and the like, for example, in Patent Document 9 or Patent Document 10, an electron injection layer or an intermediate cathode layer containing lithium carbonate or lithium oxide ( It is described that a layer called an interface layer is formed so as to be in contact with the anode side of the charge generation layer, and these documents do not clearly describe the vapor deposition method. If the film is formed by the usual resistance heating vapor deposition method regardless of the electron beam vapor deposition method, the alkali metal ions in the compound are not reduced to the metal, so that it becomes impossible to transport the electronic charge to the luminescent material as described above. This is easily verified by experiment.

When this alkali metal makes contact with the luminescent organic substance of the organic EL element, the luminescent organic substance loses its luminescent property due to its strong reducibility (this phenomenon is sometimes called luminescence quenching). In this manufacturing process, it is necessary to install it in a place separated from a manufacturing chamber for forming a layer made of an organic substance such as a light emitting layer. Therefore, when it is necessary to repeatedly manufacture substantially the same process many times, such as a multi-photon organic EL element having a plurality of light emitting units, a plurality of vapor deposition chambers are installed and what is between them. The process of forming the charge generation layer and the layer in contact therewith becomes complicated, and there is a problem that the product price is increased in combination with the complexity of the control of each process.

In contrast to the prior art as described above, the present inventors have conducted intensive studies, and the present inventors have proposed reducing substances such as alkali metals (strong electron donation) that have been indispensable for the structure of multi-photon organic EL devices that have been proposed and developed previously. An organic EL element that exhibits substantially the same performance as the conventional one has been proposed (Patent Document 11) while avoiding the use of an organic substance (thus greatly simplifying the manufacturing process). More specifically, as a result of intensive investigations, the present inventors have determined that an electron charge (radical anion state electron) in the direction of the anode as viewed from the charge generation site without using a strong electron donating substance such as an alkali metal. As a structure that can move (accepting semiconductor molecules) into the light-emitting layer, we have found a structure in which an insulating organic material layer is provided at a site that acts as a barrier against charge transfer to the light-emitting layer. The organic EL element which has was completed.

JP 59-194393 A JP-A 63-264692 Japanese Patent Laid-Open No. 2-15595 US Pat. No. 4,539,507 U.S. Pat. No. 4,769,292 US Pat. No. 4,885,211 Japanese Patent Laid-Open No. 11-329748 Japanese Patent No. 3933591 JP 2006-135145 A JP 2007-123611 A International publication WO2010 / 113493

However, the stack type organic EL element proposed in Patent Document 11 requires a driving voltage as high as that of the conventional organic EL element, and the present inventors have yet improved from the viewpoint of energy saving and the like. As a result, it was further studied that the structure of the organic EL element was repeated. And in the organic EL element in the above-mentioned patent document 11, if the charge injection into the light emitting layer can be made more efficient with respect to the element in which the insulating organic material layer is provided in the direction of the anode as viewed from the charge generation site, the driving voltage is set. The present inventors have found that a reduced stack type organic EL device structure can be obtained, and have completed the present invention. That is, the object of the present invention is a structure that does not use a strong electron donating substance such as an alkali metal and can be injected into the light emitting layer by moving the electron charge in the direction of the anode as viewed from the charge generation (carrier generation) site. An object of the present invention is to provide a new structure of an organic EL element that has a structure in which an insulating organic material layer is provided at a site that becomes a barrier against the movement of electric charges to a light emitting layer, and can further reduce the driving voltage.

In order to solve the above problems, the present invention provides:
The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units,
The intermediate layer is composed of an insulating organic layer provided in a portion that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit, and an organic material and a metal provided adjacent to the insulating organic layer. A mixed layer,
An organic electroluminescent element (hereinafter referred to as “organic EL element”) is provided. According to the present invention having such a configuration, it is possible to realize a stack type organic EL element that increases the efficiency of charge injection into the light emitting layer and suppresses an increase in driving voltage.

In the organic EL device of the present invention, the difference between the electron affinity of the organic substance constituting the mixed layer and the ionization potential of the layer adjacent to the side of the mixture layer opposite to the insulating organic layer side is 1 It is preferably 4 eV or less. According to the present invention having such a configuration, a sufficient carrier density can be generated, the efficiency of charge injection into the light emitting layer can be more reliably increased, and an increase in driving voltage can be suppressed.

In the organic EL device of the present invention, it is preferable that the organic substance constituting the mixed layer contains a hexaazatriphenylene derivative. Since the hexaazatriphenylene derivative has a deep electron affinity, if it is used, a sufficient carrier density can be generated more reliably, and the efficiency of charge injection into the light emitting layer can be increased more reliably, and the driving voltage can be reduced. The increase can be suppressed.

In the organic EL device of the present invention, it is preferable that the metal constituting the mixed layer contains a metal element belonging to Group 3 to Group 13. If this is used, voltage loss in the intermediate layer can be greatly reduced, and an increase in drive voltage can be suppressed.

In the organic EL element of the present invention, the mixed layer is a co-deposition layer of the organic material and the metal, even if the mixed layer is formed of a laminate of the organic material layer and the metal layer. It may be configured. That is, the mixed layer may be a laminate formed by sequentially laminating an organic layer and a metal layer, or a co-deposited layer formed by co-evaporating an organic layer and a metal. . According to this, an intermediate layer having high reproducibility and more reliable charge injection efficiency can be obtained, and an increase in drive voltage can be suppressed.

Here, the characteristic feature of the present invention is “a mixture of an insulating organic layer provided in a portion that serves as a barrier against charge transfer to the light emitting unit, and an organic material and a metal provided adjacent to the insulating organic layer. The intermediate layer including the layers will be described. The role of this intermediate layer is to inject the same amount of electrons into the light emitting unit adjacent to the unit on the anode side of the intermediate layer and holes into the unit on the cathode side. By maintaining this balance of injection, each light emitting unit is equivalently connected in series, and the operation expected as a stacked element can be obtained.

The intermediate layer in the organic EL device of the present invention acts as a so-called “charge generation layer” in the layer or at one interface (more precisely, acts as a carrier generation layer or a carrier generation interface), and is generated at the other interface. It has a function of injecting the thus-prepared carrier into the light emitting unit in contact with the interface. Specifically, a layer including a material having a deep electron affinity or a layer composed of the material is converted into a hole transport layer having a shallow ionization potential (for example, a layer composed of NPB or other triphenylamine derivatives). Next, by applying an electric field, holes can be generated on the hole transport layer side, and at the same time, electrons can be generated on the intermediate layer side.

Conventionally, in various literatures, a layer having such a function is referred to as a “charge generation layer”, and it has been described that a special configuration or an effect is generated, but this phenomenon itself is an organic EL. There is nothing special in the technical field of the element, and it is well known to those skilled in the art. For example, it is a well-known fact that ITO that has been used for the anode of an organic EL element can inject holes into an amine-based hole transport layer. In addition, ITO is an n-type semiconductor, and the fact that its “work function” is the energy level of the conduction band, that is, the electron affinity, if there is an interface having such an energy level relationship, on the amine side. It is immediately understood that holes can be injected. Therefore, conventionally, in various literatures, there are many misunderstandings regarding the so-called “charge generation layer” that a combination of an electron-accepting compound and an electron-donating compound or the generation of a charge transfer complex is necessary. There are many descriptions of whether this has been achieved by construction, but this property is determined purely by the energy relationship.

Next, as described above, the deep electron affinity of the organic material constituting the mixed layer and a layer adjacent to the side of the mixed layer opposite to the insulating organic layer side (for example, a hole transport layer in a light emitting unit) ) Is not more than 1.4 eV, preferably not more than 0.8 eV, and it is preferable because carriers can be generated more reliably. In the case of ITO and an amine-based hole transport material, it is known that the work function of ITO, that is, the electron affinity, varies depending on the surface treatment with oxygen and the like, and is generally in the range of 4.7 eV to 5.3 eV. . Further, for example, D.I. J. Millylon, I.D. G. Hill, C.I. Shen, A. Kahn, J.M. Schwartz, J.M. Appl. Phys. Vol. 87 (2000) and 572 are obtained from about 4.1 eV to 4.5 eV, indicating that hole injection is possible even when the difference from the ionization potential of the hole transport layer is 1.34 eV. Has been.

The electron affinity of the amine hole transport material is 5.4 eV for 4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (NPB) and 5 for triphenylenediamine (TPD). .5 eV, starburst amine derivatives are known to be about 5.0 eV to 5.2 eV. Therefore, if the difference between the electron affinity of the layer having a deep electron affinity and the ionization potential of the hole transport layer is 1.4 eV or less, carrier generation is sufficiently possible.

The value of 1.4 eV can be found theoretically from the energy level distribution of the organic layer. For example, in the case of an amorphous thin film, a distribution occurs in polarization energy with respect to electric charge due to non-uniformity of intermolecular distance and molecular orientation distribution. Therefore, the electron affinity and ionization potential have a spatial distribution, and the deviation is 0.2. This produces a Gaussian distribution of ~ 0.3 eV. For this reason, the difference of 1.4 eV gives an overlap at the base of this distribution, and the overlap width is located at 2.33-3.5σ from the center of the distribution, and erfc (2. 33) It has a density of states of 2 to erfc (3.5) 2 This corresponds to a state density of 10 ¹⁵ to 10 ¹⁸ / cm ³ when the total state density is 10 ^ 22, and a carrier density of 10 ¹⁴ to 10 ¹⁷ / cm ³ required for organic EL light emission. From this, it can be seen that a sufficient carrier density can be generated within 1.4 eV.

Here, in the case where the above configuration is reversed, holes are generated on the intermediate layer side, and electrons are generated in the light emitting unit on the adjacent anode side, the layer formed of a material having a shallow ionization potential on the intermediate layer side Alternatively, a layer containing the material is arranged, and a layer made of an insulating organic compound is arranged at the interface with the light emitting unit on the cathode side. In this case, if the difference in electron affinity between the shallow ionization potential layer and the layer in contact with the light emitting unit on the anode side is 1.4 eV or less, carriers can be generated, which is preferable.

Also, when the difference between the deep electron affinity of the organic material constituting the mixed layer and the ionization potential of the layer adjacent to the side opposite to the insulating organic layer side of the mixed layer becomes negative (for example, has a deep electron affinity) When the electron affinity of the layer becomes larger than the ionization potential of the hole transport layer), carriers are generated at the interface without applying an electric field. From the definition of electron affinity, ie “(neutral molecule energy) − (anion molecule energy)” and the definition of ionization potential, ie “(cation molecule energy) − (neutral molecule energy)”, both molecules Since anion and cation have lower energy than is neutral, carrier generation occurs spontaneously in a thermal equilibrium state. Therefore, even when the difference is negative as described above, the carrier generation effect is obtained, and thus the layer having the energy level relationship as described above can be used as the intermediate layer.

It is sometimes misunderstood that this carrier is generated and both carriers are present as “a charge transfer complex is generated.” However, the charge transfer complex has binding energy to form a complex. Therefore, it is a well-known fact that this binding energy is larger than the difference between the electron affinity of the acceptor and the ionization potential of the donor, and it is clear from the above discussion. When this charge transfer complex is generated, in order to generate electrons and holes as free carriers from the charge transfer complex, it is necessary to give energy exceeding the binding energy. This is equivalent to giving a potential difference corresponding to the energy to a single molecule, and causes an increase in the applied voltage of the potential difference even when all the complexes are arranged at the interface. In the case of a mixed layer, when the charge transfer complex is distributed in the layer, the voltage rise is several times the molecular layer, and even a film thickness of about several nanometers has a potential difference of several volts or more. It becomes difficult to make it function.

The important point as an intermediate layer is that in the case of the configuration of this example, electrons generated on the layer side having a deep electron affinity must be injected beyond the high barrier to the light emitting unit located on the anode side. It is to be realized by such a method. In the above-mentioned patent document 11, the present inventors can inject electrons into an electron transport layer having a shallow electron affinity rather than a deep electron affinity layer by disposing a thin layer of an insulating organic compound at this interface. It was found that series operation is possible equivalently. Furthermore, the present inventors have made extensive studies, and when a metal is dosed to a layer made of an organic material having a deep electron affinity adjacent to the insulating organic material layer, or adjacent to the insulating organic material layer. However, when a metal layer is laminated on a layer made of an organic substance having a deep electron affinity, a voltage loss in the intermediate layer made up of the insulating organic layer and the mixed layer is greatly reduced and lower. It has been found that it operates with a driving voltage, and has reached the present invention.

As the organic substance having a deep electron affinity, a hexaazatriphenylene derivative (for example, HAT-CN6) is a preferred compound, but the organic substance used is not limited to this example. Organic substances having a deep electron affinity and metal elements tend to cause strong coordination bonds. Since the organic coordinated metal molecule functions as a molecule different from the original organic compound, different functions and physical properties can be realized by dosing the metal.

Here, FIG. 4 shows the measurement results of the conductivity of a film in which Al is coordinated to HAT-CN6 by co-evaporation. The measurement element was measured by arranging two parallel ITO electrodes with a spacing of 0.2 mm and forming a 100 nm thick film by vacuum deposition. In this example, when the dose amount or stacking amount starts to exceed 3 in terms of molar ratio, the conductivity rapidly increases, and ohmic changes from the original semiconductor characteristics of HAT-CN6. The reason why the electron injection efficiency through the insulating layer is improved by increasing the conductivity is unknown exactly, but probably the carriers generated by the improvement in conductivity do not stay near the generation interface layer. The electric potential created by the holes that reach the interface between the insulating layers and reach the insulating layer and are contained and stored on the light-emitting unit side, and the electric potential created by the electrons in this intermediate layer effectively act on the insulating layer to apply an electric field, thereby injecting electrons. It is thought that it promotes. For this reason, an insulating layer and / or an electron transporting layer that is a sufficient hole barrier from which invalid hole current does not flow into the intermediate layer from the light emitting unit side is required.

When the conductivity of the intermediate layer is low, that is, in the case of an insulator or the like in which no thermal equilibrium carrier exists, the generated carrier causes “band bending” in a state where it stays at the generation interface due to the space charge generated by each charge. Is easy to understand. In order to solve this bending and move electrons and holes, it is necessary to further increase the applied voltage.

As the metal to be dosed, that is, the metal contained in the mixed layer, Al, Ga, and In of group 13 are preferable, but transition metal elements of groups 3 to 12 can also be used because they provide the same effect. The reason why the Group 13 metal is preferable is that the outermost orbital electrons are deeply involved, although the exact place is unknown. The group 13 metal has a structure sandwiched between two nitrogen atoms and is coordinated in bidentate to HAT-CN6, etc., so there is one more lone electron, which induces electron transfer between molecules. It is thought that. Moreover, since the group 13 metal is coordinated as an electron pair to the aromatic ring or CC double bond, it is considered that one excess electron exists and the same effect can be obtained.

The reason why the transition metals of Groups 3 to 12 are effective is not clear, but the arrangement of the outermost electrons is probably changed during coordination, and some s electrons move to the d orbital and coordinate. One electron is deficient at this time, which is considered to cause a state opposite to that of the 13th group. As such transition metals, for example, Ag has an arrangement of 4d ¹⁰ 3s ¹ , and there are many such as s ¹ that are Cu, Cr, Rh, Ru, Au, Pt and the like. In consideration of the case of coordinating with organic molecules and changing, it can be said that all transition metal elements can be used as the metal in the present invention. Of course, the transition metal of group 3 to group 12 changes its electron configuration by coordination with an organic molecule, so whether or not the effect is exerted depends on the combination.

The insulating organic material layer in the organic EL device of the present invention may be a single film made of only an insulating organic material, and may be an insulating organic material and an electron transporting organic material and / or an intermediate layer used for an electron transporting layer. A mixed film containing an organic substance having a deep electron affinity to be used may be used.

According to the present invention, while avoiding the use of reducing substances such as alkali metals, which are essential for the structure of the conventional stack type organic EL device, the manufacturing process is greatly simplified, while the performance is almost the same as the conventional one. It is possible to realize a stack type organic EL element having a low driving voltage.

It is a schematic sectional drawing which shows the typical structure of the organic EL element of this invention. It is the schematic of the energy diagram which shows the typical structure of the organic EL element of this invention. 6 is a graph plotting voltage (V) −luminance (cd / m ² ) for the organic EL devices fabricated in Example 1 and Comparative Example 1. FIG. 6 is a graph plotting current density (mA / cm ² ) -current efficiency (cd / A) for the organic EL devices fabricated in Example 2 and Comparative Example 2. 5 is a graph plotting voltage (V) −luminance (cd / m ² ) for the organic EL devices fabricated in Example 2 and Comparative Example 2. FIG.

The organic EL device of the present invention includes an anode, a cathode, a plurality of light emitting units including a light emitting layer located between the anode and the cathode, an intermediate layer located between the plurality of light emitting units, An insulating organic layer provided at a site that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit, and an organic material provided adjacent to the insulating organic layer; And a mixed layer made of a metal. Hereinafter, preferred embodiments of the organic EL device of the present invention will be described in detail. In the following description, overlapping description may be omitted.

FIG. 1 is a schematic cross-sectional view showing a configuration of the organic EL element of the present embodiment, and FIG. 2 is a schematic diagram of an energy diagram showing a typical configuration of the organic EL element of the present invention. As shown in FIG. 1, the organic EL element 1 of the present embodiment includes n light emitting units (n is an integer of 2 or more), for example, an anode 4 formed in order on a glass substrate 2; A first intermediate layer 9-1 including a first insulating organic layer 8-1 and a first mixed layer (mixed layer made of an organic substance and a metal) 10-1. The second light emitting unit 6-2; the second intermediate layer 9-2 including the second insulating organic material layer 8-2 and the second mixed layer 10-2; and the (n-1) insulating organic material. An (n-1) th intermediate layer 9- (n-1) including a layer 8- (n-1) and an (n-1) th mixed layer 10- (n-1); and an nth light emitting unit 6-n; and cathode 14;

Hereinafter, the first light-emitting unit 6-1, the second light-emitting unit 6-2, and the n-th light-emitting unit 6-n are collectively referred to as “light-emitting unit 6”, and the first insulating organic material layer 8-1. The second insulating organic material layer 8-2 and the (n-1) th insulating organic material layer 8- (n-1) may be collectively referred to as "insulating organic material layer 8". Further, the first intermediate layer 9-1, the second intermediate layer 9-2, and the (n-1) th intermediate layer 9- (n-1) may be collectively referred to as "intermediate layer 9". The first mixed layer, the second mixed layer 10-2, and the (n-1) th mixed layer 10- (n-1) may be collectively referred to as "mixed layer 10".

As described above, the organic EL element 1 of the present embodiment does not include any strong electron donating substance such as an alkali metal that quenches the luminescent organic substance contained in the light emitting unit 6. Further, in order to efficiently supply electronic charges into the light emitting unit 6, a low dielectric constant insulating organic material layer 8 is provided between the mixed layer 10 and the light emitting unit 6.

As described above, the insulating organic material layer 8 in the organic EL element 1 of the present invention may be composed of an insulating organic material having a low relative dielectric constant, and various organic compounds are used as the insulating organic material. It is expected. Among them, for example, the following formula:

And metal complexes having β-diketone type ligands such as Ca (dpm) ₂ (bis-di-pivaloyl-methanate-calcium) represented by

Further, for example, when the insulating organic material layer 8 is provided at a site where electronic charges move, it may be any layer that functions as an insulating layer with respect to the transport of electronic charges. ) A hole transporting organic material layer formed of a transporting organic material may be used.

The organic substance constituting the mixed layer 10 in the present embodiment may be any substance that can form a site for generating electrons and holes at the interface with an adjacent layer (for example, a hole transport layer) as described above. For example, the mixed layer 10 is composed of an organic substance having a deep electron affinity (for example, HAT-CN6) and a group 3 to group 13 element (for example, Al), and a hole transport layer (for example, NPB) adjacent to the cathode 14 side. For example, when a voltage is applied, carriers of electrons and holes are generated at the interface, and good carrier injection can be performed to the light emitting unit 6 through the insulating organic material layer 8.

The mixed layer 10 is composed of an organic substance having a deep electron affinity (for example, HAT-CN6) and a group 3 to group 13 element (for example, Al), and further, a deep electron adjacent to the cathode side. A layer composed only of an organic substance having affinity may be laminated. That is, it is preferable to adopt such a two-layer structure when electron and hole carrier generation at the interface with the adjacent hole transport layer is inhibited by the presence of elements of Group 3 to Group 13 instead. .

As a material constituting the cathode 14, generally, a metal having a small work function, an alloy containing them, a metal oxide, or the like is used. Specifically, an alkali metal such as Li, an alkaline earth metal such as Mg or Ca, a rare earth metal such as Eu, or an alloy of these metals with Al, Ag, In, or the like can be given. It is done.

In addition, when adopting a configuration in which a metal-doped organic layer is used at the interface between the cathode 14 and the organic layer (see, for example, Japanese Patent Laid-Open Nos. 10-270171 and 2001-102175), the cathode is electrically conductive. If it is a material, its properties such as work function are not limited.

For example, using the techniques disclosed in Japanese Patent Application Laid-Open Nos. 11-233262 and 2000-182774, an organic layer (organic layer in the light-emitting unit 6) in contact with the cathode 14 is formed with an alkali metal ion or an alkaline earth metal. When constituted by an organometallic complex compound containing at least one of ions and rare earth metal ions, a metal capable of reducing metal ions contained in the organometallic complex compound to a metal in a vacuum, for example, Al, A (thermally reducible) metal such as Zr, Ti, or Si, or an alloy containing these metals can also be used as the cathode material. Of these, Al, which is generally widely used as a wiring electrode, is preferable from the viewpoints of easiness of vapor deposition, high light reflectance, chemical stability, and the like.

The material constituting the anode 4 is not particularly limited. For example, a transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide) can be used. For example, when the ITO film is formed by a sputtering method that does not damage the organic film using the technique described in Japanese Patent Application Laid-Open No. 2002-332567, as in the case of the cathode 14, Japanese Patent Application Laid-Open No. 10-270171. If the metal-doped organic layer described in the publication is used for the electron injection layer, the transparent conductive material such as ITO or IZO described above can also be used for the cathode 14.

Therefore, if both the cathode 14 and the anode 4 are transparent, the light emitting unit including the organic layer and the intermediate layer are transparent as well, so that a transparent organic EL element can be produced. Contrary to the case of a general organic EL element, the anode 4 is made of metal and the cathode 14 is a transparent electrode, so that light is extracted from the cathode 14 side instead of the glass substrate 2 side. The organic EL element 1 can also be used. Further, regarding the order of forming each layer, it is not always necessary to start with the formation (film formation) of the anode 14, and the formation may be started from the cathode 4.

The light emitting unit 6 in the present embodiment can take various structures as in the case of a conventionally known organic EL element, and is composed of, for example, a combination of a light emitting layer and a hole transport layer and / or an electron transport layer. Various modes may be adopted as the combination.

The “light emitting layer” included in the light emitting unit 6 may be a conventional light emitting layer used in a conventional organic EL element, and the light emitting material constituting the light emitting layer is not particularly limited, and various fluorescent materials or phosphorescences are used. Any known material can be used. For example, the following formula:

And tris (8-quinolinolato) aluminum complex (Alq3) and the like.

The “hole transport layer” may be formed using a hole transport material that constitutes the hole transport layer of the conventional organic EL device, and is not particularly limited. For example, the ionization potential is smaller than 5.7 eV, and the hole transport property is That is, an organic compound having an electron donating property (electron donating substance) can be used. In general, it is desirable that the ionization potential is smaller than 5.7 eV in order for an organic compound having an electron donating property to easily enter a radical cation state.

For example, the general formula (I):

(In formula (I), Ar ₁ , Ar ₂ and Ar ₃ each independently represents an aromatic hydrocarbon group which may have a substituent) are preferably arylamine compounds. Of these, 4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (NPB) is preferable.

In addition to the arylamine compound, a pigment-based organic material containing a phthalocyanine compound that has been conventionally used as a hole injection material for organic EL elements may be used for the “hole transport layer”. Any material that can be generated can be appropriately selected and used.

The “electron transport layer” may be formed using an electron transport material constituting the electron transport layer of the conventional organic EL device, and is not particularly limited. Generally, the electron transport material used in this embodiment is Among the electron transport materials used in the organic EL element, those having a relatively deep ionization potential are preferable. Specifically, it is preferable to use an electron transporting material having an ionization potential of at least about 6.0 eV. When an electron transporting material having a deep ionization potential is used as described above, the hole charge is difficult to move toward the electron transporting material, and the electron charge generated in the intermediate layer 9 is electrically neutralized as described above. The light emitting material can be surely excited to emit light without being summed.

In addition, the electron affinity of the electron transporting substance used in the present embodiment is the electron affinity of the (strong) electron accepting substance used in the intermediate layer 9 and the electron affinity of the luminescent organic substance contained in the light emitting unit 6. It is preferably located between.

In addition, as an electron transport substance (organic substance), for example, KLET02 manufactured by Chemipro Kasei Co., Ltd. can be used. The physical properties of the electron transport material (organic substance) manufactured by Chemipro Kasei Co., Ltd. are shown below (from Chemipro Kasei Co., Ltd. HP. Http://www.chemipro.co.jp/Yuki# EL / Products.html).

Here, as an organic substance used for the mixed layer 10 which comprises the intermediate | middle layer 9 in this embodiment, following formula:

And a hexaazatriphenylene derivative (HAT-CN6) represented by the formula:

As mentioned above, although the embodiment having a typical laminated structure (unit) of the organic EL element of the present invention has been described, the present invention can be modified in various ways within the scope of the technical idea of the present invention. Naturally, the invention whose design has been changed is also included in the present invention.

<Deformation mode>
For example, when the electron transport layer is adjacent to the insulating organic material layer in the organic EL element of the present invention, the electron transporting organic material constituting the electron transporting layer may be mixed in the insulating organic material layer. That is, the organic EL device of the present invention may have an insulating organic substance / electron transporting substance mixed layer instead of the insulating organic substance layer.

In the organic EL device of the present invention, when the strong electron accepting material layer is adjacent to the insulating organic material layer, the strong organic accepting material constituting the strong electron accepting material layer is mixed in the insulating organic material layer. It may be. That is, the organic EL element of the present invention may have an insulating organic substance / strong electron accepting substance mixed layer instead of the insulating organic substance layer. Even in such a configuration, an undesirable interaction between the electron transporting substance and the strong electron accepting substance may be avoided, and this can be confirmed by experiments as appropriate.

In general, the light emitting layer in the light emitting unit is often composed of a host material and a light emitting material dispersed in the host material, and the host material is an electron transporting material. May be the same material. Therefore, in the organic EL device of the present invention, when the electron transport layer is adjacent to the light emitting layer, the light emitting layer and the electron transport layer are configured as a single layer integrally formed using the same material. May be.

In the organic EL device of the present invention, when the hole transport layer is adjacent to the light emitting layer, the hole transport material may emit light or function as a host material for the light emitting layer. The layer and the hole transport layer may be formed as a single layer formed integrally. Furthermore, in this case, the luminescent material may be dispersed and mixed only in the hole transport layer near the cathode.

More specifically, the organic EL element of the present invention can have, for example, the following laminated structure.
a) Anode b) Organic layer with deep electron affinity c) Hole transport layer d) Light emitting layer e) Electron transport layer f) Insulating organic layer g) Mixed layer containing organic matter and metal h) Above b) to g) above Repeat -------------------------------
i) Cathode

The organic EL device of the present invention may have a laminated structure having a mixed layer of an organic substance having a deep electron affinity and a hole transporting substance in the laminated structure as described below. As described above, the mixed layer can be formed by separately heating a plurality of vapor deposition sources to form a laminated film, or can be formed as a mixed film by simultaneously heating a plurality of vapor deposition sources ( Co-deposition), the latter is common, but is not limited thereto.

Moreover, the organic EL element of this invention can also take the following laminated structures, for example.
a) anode b) organic material layer / hole transport material mixed layer having deep electron affinity c) hole transport layer d) light emitting layer e) electron transport layer f) insulating organic material layer g) mixed layer containing organic material and metal h) above b) to repeat g) above ------------------------------
i) Cathode

Further, in the above laminated structure, a laminated constitution part (“electron transport layer / insulating organic layer”) in which the electron transport layer and the insulating organic layer are adjacent to each other is divided into an electron transport layer and an electron transporting organic material / insulating organic material mixed layer. May be changed to an adjacent laminated component (“electron transport layer / electron transport organic compound / insulating organic compound mixed layer”). That is, the electron transporting organic material constituting the electron transporting layer may be mixed with the insulating organic material layer and used.

Furthermore, the entire electron transport layer portion may be replaced in advance with an “electron transport organic compound / insulating organic compound mixed layer”, and the “electron transport organic compound / insulating organic compound mixed layer / insulating organic compound layer” Thus, the insulating organic material layer may be laminated adjacent to the mixed layer.

Moreover, in the above laminated structure, the laminated component (“electron transport layer / insulating organic layer”) in which the electron transport layer and the insulating organic layer are adjacent to each other is mixed with the electron transport layer and the insulating organic / strong electron accepting substance mixture. The layer may be changed to a laminated component (“electron transport layer / insulating organic substance / strong electron accepting substance mixed layer”) adjacent to the layer. That is, the strong electron accepting material constituting the strong electron accepting material layer may be used by mixing with the insulating organic material layer. Even in such a configuration, an undesirable interaction between the electron-transporting organic substance and the strong electron-accepting substance may be avoided, and these can be confirmed by experiments as appropriate.

In general, in a light emitting layer, a light emitting substance is often dispersed in a host material, and the host material may be the same as an electron transporting substance. Therefore, in the organic EL device of the present invention, the stacked constituent portion where the light emitting layer and the electron transport layer are adjacent may be a single layer made of the same material.

The hole transport material having the above laminated structure may constitute a light emitting layer or may function as a host material of the light emitting layer. In these cases, the “hole transport layer / light emitting layer / electron transport layer” laminated structure The part may be changed to a stacked constituent part of “hole transport layer (light emitting layer) / electron transport layer”. When the light-emitting substance is dispersed and mixed only in the portion near the cathode of the hole transport layer, the “hole transport layer / light-emitting layer / electron transport layer” layered structure is “hole transport layer / hole transport material / light-emitting material”. It may be changed to a layered configuration portion of “mixed layer / electron transport layer”.

That is, in an organic EL element including an anode, a cathode, a plurality of light emitting units including a light emitting layer positioned between the anode and the cathode, and an intermediate layer positioned between the plurality of light emitting units, the intermediate layer to the light emitting layer An organic EL element including a laminated structure in which an insulating organic layer is provided in a portion that serves as a barrier against the transfer of electric charge to the insulating layer, and a mixed layer of an organic substance and a metal is formed adjacent to the insulating organic layer. However, it is basically included in the technical scope of the organic EL device of the present invention.

Although the structure of the basic unit of the organic EL element of the present invention has been described above, the organic EL element of the present invention may have a structure in which a plurality of these basic units are stacked. The organic EL element of the present invention as described above can be produced by a conventionally known method using a vacuum vapor deposition apparatus. In particular, when obtaining an organic EL device having a structure in which each layer other than the anode and the cathode is formed of an organic compound, the production can be easily carried out without making the process complicated.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1
As an organic EL element of Example 1, layers of materials and thicknesses shown in Table 1 below were laminated in order on a glass substrate to produce an organic EL element 1 including the structure shown in FIG. For the formation of each layer, a vacuum deposition machine manufactured by Eiko Co., Ltd. was used. The thickness of each layer is measured using a stylus type surface shape measuring instrument (DEKTAK3030), and for the characteristic evaluation of the obtained organic EL element, a source meter 2400 manufactured by Keithley Instruments Co., Ltd. and Topcon Co., Ltd. are used. Luminometer BM-7.

≪Comparative example 1≫
As an organic EL element of Comparative Example 1, in the same manner as in Example 1, layers of materials and thicknesses shown in Table 2 below were sequentially laminated on a glass substrate to produce Comparative Organic EL Element 1.

[Evaluation test]
The direct current voltage was 0.1 V / 2 seconds or 0.5 V between the anode and the cathode of the organic EL device 1 (Example 1) and the comparative organic EL device 1 (Comparative Example 1) produced as described above. The voltage was applied stepwise at a rate of / 2 seconds, and the luminance (green light emission from the light emitting layer) and current value after 1 second of voltage increase were measured. FIG. 3 shows a graph plotting voltage (V) -luminance (cd / m ² ). As shown in FIG. 3, the voltage of Example 1 is significantly lower than that of Comparative Example 1.

<< Example 2 and Comparative Example 2 >>
As organic EL elements of Example 2 and Comparative Example 2, two types of organic EL elements (green phosphorescent light emitting elements) 2 and comparative organic EL elements 2 having a structure composed of materials shown in Tables 3 and 4 respectively. Was made. The comparative organic EL element 2 is an element having a single light emitting unit, and the organic EL element 2 is an element having a configuration in which three light emitting units are connected by an intermediate layer having the configuration of the present invention.

The compounds used here were as follows.
1) HT04 (trade name): Hall transport material manufactured by Chemipro Kasei Co., Ltd.

2) Ir (ppy) ₃ :

Tris (2-phenylpyridine) iridium having the structure

3) Mg (acac) ₂ : following formula:

Magnesium acetylacetonate dehydrate with the structure

4) TCTA: The following formula:

4,4 ′, 4 ″ -Tris (carbazol-9-yl) -triphenylamine having the structure

5) NS60 (trade name): a light emitting layer host material manufactured by Nippon Steel Chemical Co., Ltd.

The results of Example 2 and Comparative Example 2 are shown in FIGS. As shown in the graph of FIG. 4, the organic EL element (element having the structure shown in Table 4) 2 having three light emitting units connected by the intermediate layer of the present invention is a comparative example having a single light emitting unit. Compared with the organic EL element (element having the structure of Table 3) 2, the current efficiency was approximately tripled (˜60 cd / A → ˜180 cd / A). Furthermore, as shown in the graph of FIG. 5, the drive voltage is also approximately three times, so that it was proved that the connection was ideally connected in series.

From the above, it can be said that the organic EL device of the present invention can be used in a wide range of product fields that require light generation, such as various light sources and image display devices that are required to have low energy consumption.

Claims

The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units,
The intermediate layer is composed of an insulating organic layer provided at a site that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit, and an organic material and a metal provided adjacent to the insulating organic layer. A mixed layer,
Organic electroluminescent element characterized by the above.
The difference between the electron affinity of the organic material constituting the mixed layer and the ionization potential of the layer adjacent to the side of the mixed layer opposite to the insulating organic layer side is 1.4 eV or less,
The organic electroluminescent element according to claim 1.
The organic substance constituting the mixed layer contains a hexaazatriphenylene derivative;
The organic electroluminescent element according to claim 1 or 2.
The metal constituting the mixed layer contains a metal element belonging to Group 3 to Group 13,
The organic electroluminescent device according to any one of claims 1 to 3, wherein:
The mixed layer is composed of a laminate of the organic layer and the metal layer;
The organic electroluminescent device according to any one of claims 1 to 4, wherein:
The organic electroluminescent device according to any one of claims 1 to 4, wherein the mixed layer is composed of a co-evaporated layer of the organic substance and the metal.