JP2011040437A - Organic electroluminescence element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescence element which has small light emission unevenness, high efficiency, and a long life. <P>SOLUTION: The organic electroluminescence element has a light emitting layer 5 provided between an anode 2 and a cathode 7. A mixture layer 9 composed of a hole transport material and a metal oxide material is formed, on a surface of the anode 2 on the side of the light emitting layer 5, by laminating a first hole transport layer 3a, a metal oxide layer 4, and a second hole transport layer 3b in this order on the surface of the anode 2 on the side of the light emitting layer 5. Cations and dications can be efficiently generated in the mixture layer 9. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence element that can be used for a flat panel display, a backlight for a liquid crystal display, an illumination light source, and the like, and more specifically, an organic electroluminescence formed by providing an organic light emitting layer between two electrodes. In the element, a hole transport material layer, a metal oxide layer, and a hole transport material layer are laminated in this order on the surface of the anode on the light emitting layer side or on a part of the intermediate layer. The present invention relates to an organic electroluminescence device that controls the oxidation reaction of a hole transport material at an interface and does not use a co-evaporation method, has no light emission unevenness, and has a high efficiency and a long lifetime.

  Organic electroluminescence devices are capable of emitting high-luminance surface light at a low voltage of about several volts, and capable of emitting light in an arbitrary color tone by selecting a light-emitting substance. It attracts attention as a next-generation light source that can be used as a backlight for display devices and as a light source for illumination, and energetic basic research is being conducted and development aimed at practical use is being carried out. In recent years, in particular, it has been noted that it is excellent in stability in the atmosphere and the material is very inexpensive, and organic devices using metal oxides or metal oxide mixed layers have been actively developed. ing.

  For example, in Patent Document 1, a low driving voltage of the light emitting element is achieved by using a metal oxide having a high work function such as molybdenum oxide for the anode. Furthermore, the effect with respect to lifetime improvement is also acquired. However, although the hole injection property is improved, it cannot be said that only the means disclosed in Patent Document 1 is sufficient for improving the hole transport property, and it is necessary to develop a technology for achieving higher efficiency. It was. Further, this configuration is very susceptible to the surface condition of ITO or a metal oxide having a high work function, and it is necessary to develop a technique for improving uneven light emission.

  In Patent Document 2, a mixed layer of molybdenum oxide and aromatic amine is inserted between the electrodes to achieve a low driving voltage and a long lifetime of the light emitting element. However, when a mixed film of molybdenum oxide and aromatic amine is used for an organic electroluminescence element, carrier transportability and absorption spectrum change due to a slight difference in reaction amount, so that a stable device can be manufactured. However, it is necessary to strictly manage the film forming conditions. In recent years, high-rate film formation technology has been actively developed for the purpose of shortening the film formation time. However, when a mixed film of molybdenum oxide and aromatic amine is used for an organic electroluminescence device, the reaction amount is reduced. It is necessary to manage the deposition rate for the purpose of control, and it is difficult to use the high-rate deposition method by the same means as the deposition of other layers. In recent years, there has been a vapor deposition method that achieves high material use efficiency by maintaining the inner wall of the vapor deposition tank at a temperature as high as the sublimation temperature of the vapor deposition material and preventing the material from adhering to the inner wall for the purpose of increasing the efficiency of high material use. Proposed. However, when a mixed film of molybdenum oxide and aromatic amine is used for an organic electroluminescence device, the sublimation temperatures of molybdenum oxide and aromatic amine are extremely different. Cannot be used.

  In Patent Document 3, an electron-accepting material is present at the interface of a hole transport layer formed of a different material that is not in contact with the anode electrode, thereby reducing a hole movement barrier and reducing power consumption. It has been shown that it can. When this method is used, it is effective for reducing the hole transfer barrier between different organic materials. However, in the organic electroluminescence device using a single hole transport layer, the hole transfer barrier at the interface of the hole transport layer is originally. Since it does not exist, reduction in power consumption cannot be expected. In addition, with only the means shown in Patent Document 3, the electron-accepting substance is present at a position that is not in contact with the anode electrode, so that the hole injection property cannot be improved, and as a result, the hole injection property is improved. Describes a method using a hole injection layer at the same time, which complicates the manufacturing process of the organic electroluminescence element.

Japanese Patent No. 2824411 Japanese Patent No. 3748110 Japanese Patent No. 4300196

  The present invention has been made in view of the above points, and uses a high-rate vapor deposition technique and a high-material-use-efficient vapor deposition technique, resulting in less uneven emission, higher efficiency, and longer life than conventional organic electroluminescence elements. An object of the present invention is to provide an electroluminescence element.

  The organic electroluminescent device according to claim 1 of the present invention is the organic electroluminescent device in which the light emitting layer 5 is provided between the anode 2 and the cathode 7, and the first hole is formed on the surface of the anode 2 on the light emitting layer 5 side. The transport layer 3a, the metal oxide layer 4, and the second hole transport layer 3b are laminated in this order, whereby a mixture of a hole transport material and a metal oxide material is formed on the surface of the anode 2 on the light emitting layer 5 side. The layer 9 is formed.

  The organic electroluminescence device according to claim 2 of the present invention is characterized in that, in claim 1, the thickness of the metal oxide layer 4 is 1 to 20 nm.

  The organic electroluminescence device according to claim 3 of the present invention is the organic electroluminescent device according to claim 1 or 2, wherein the thickness of the first hole transport layer 3a formed in contact with the surface of the anode 2 on the light emitting layer 5 side is 1 to 10 nm. It is characterized by being.

  The organic electroluminescence device according to claim 4 of the present invention is an organic electroluminescence device in which two light emitting layers 5 are laminated between an anode 2 and a cathode 7 with an intermediate layer 10 interposed therebetween. A plurality of layers are stacked, and the first hole transport layer 3a, the metal oxide layer 4, and the second hole transport layer 3b are included in this order, thereby including holes in the intermediate layer 10. A mixed layer 9 made of a transport material and a metal oxide material is formed.

  The organic electroluminescence element according to claim 5 of the present invention is characterized in that, in claim 4, the metal oxide layer 4 has a thickness of 1 to 20 nm.

  According to the first aspect of the present invention, cations and dications can be efficiently generated in the mixed layer 9, there is little unevenness in light emission, and high efficiency and long life can be achieved.

  In the invention of claim 2, the oxidation reaction of the hole transport material can be carried out efficiently and uniformly in the light emitting surface, and it is difficult to increase the voltage and the life characteristics, thereby increasing the efficiency and lengthening. It is possible to reliably obtain a long life.

  In the invention of claim 3, the oxidation reaction of the hole transport material can be carried out efficiently and uniformly in the light emitting surface, and it is difficult for the high voltage and the life characteristics to be deteriorated. It is possible to reliably obtain a long life.

  According to the fourth aspect of the present invention, cations and dications can be efficiently generated in the mixed layer 9, there is little unevenness in light emission, and high efficiency and long life can be achieved.

  In the invention of claim 5, the oxidation reaction of the hole transport material can be carried out efficiently and uniformly in the light emitting surface, and it is difficult to increase the voltage and the life characteristics, thereby increasing the efficiency and lengthening. It is possible to reliably obtain a long life.

It is a schematic sectional drawing which shows an example of embodiment of this invention. It is a schematic sectional drawing which shows an example of other embodiment of this invention. It is a schematic sectional drawing which shows an example of other embodiment of this invention. 5 is a graph showing a 532 nm excitation Raman spectrum of an α-NPD / MoO ₃ laminated film. It is a graph which shows a 633 nm excitation Raman spectrum of the α-NPD / MoO ₃ laminated film. It is a graph showing the 532nm excitation Raman spectra of MoO ₃ / α-NPD film stack. It is a graph showing the 633nm excitation Raman spectra of MoO ₃ / α-NPD film stack.

  Hereinafter, modes for carrying out the present invention will be described.

  FIG. 1 shows an example of the organic electroluminescence element of the present invention. In this organic electroluminescence element, an anode 2 made of a transparent conductive film is formed on the surface of a substrate 1, and a first hole transport layer 3 a, a metal oxide layer 4, and a second hole transport layer are formed on the surface of the anode 2. 3b is laminated in this order, and the light emitting layer 5, the electron transport layer 6, and the cathode 7 are further laminated in this order. And the mixed layer 9 is formed in the surface of the anode 2 by mixing the hole transport material which comprises the 1st hole transport layer 3a, and the metal oxide which comprises the metal oxide layer 4. FIG. . The organic electroluminescence device of the present invention is characterized by achieving high efficiency and long life by effectively oxidizing the hole transport material with a metal oxide in the mixed layer 9. It is important to pull out electrons from the hole transport material and advance the oxidation reaction of the hole transport material into a cation and a dication.

  The substrate 1 has optical transparency when light is emitted, and may be slightly colored or ground glass in addition to being colorless and transparent. For example, a transparent glass plate such as soda lime glass or non-alkali glass, a plastic film or a plastic plate produced by an arbitrary method from a resin such as polyester, polyolefin, polyamide, or epoxy, or a fluorine resin can be used. . Furthermore, it is possible to use a substrate that contains particles, powder, bubbles, or the like having a refractive index different from that of the substrate matrix in the substrate 1 or has a light diffusion effect by imparting a shape to the surface. Further, when light is emitted without passing through the substrate 1, the substrate 1 does not necessarily have to be light transmissive, and an arbitrary substrate 1 is used as long as the light emission characteristics, life characteristics, etc. of the element are not impaired. be able to. In particular, the substrate 1 having high thermal conductivity can be used in order to reduce a temperature rise due to heat generation of the element during energization.

The anode 2 is an electrode for injecting holes into the light emitting layer 5, and an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function is preferably used. It is preferable to use a voltage of 4 eV or more. Examples of the material of the anode 2 include metals such as gold, CuI, ITO (indium-tin oxide), SnO ₂ , ZnO, IZO (indium-zinc oxide), and conductive materials such as PEDOT and polyaniline. Examples thereof include a conductive polymer doped with a polymer and an optional acceptor, and a conductive light-transmitting material such as a carbon nanotube. The anode 2 can be produced, for example, by forming these electrode materials into a thin film on the surface of the substrate 1 by a method such as vacuum deposition, sputtering, or coating. In order to transmit light emitted from the light emitting layer 5 through the anode 2 and irradiate the light to the outside, the light transmittance of the anode 1 is preferably set to 70% or more. Furthermore, the sheet resistance of the anode 2 is preferably several hundred Ω / □ or less, particularly preferably 100 Ω / □ or less. Here, the film thickness of the anode 2 varies depending on the material in order to control the light transmittance, sheet resistance, and other characteristics of the anode 2 as described above, but is set to a range of 500 nm or less, preferably 10 to 200 nm. It is good.

The cathode 7 is an electrode for injecting electrons into the light emitting layer 5, and it is preferable to use an electrode material made of a metal, an alloy, an electrically conductive compound and a mixture thereof having a small work function, and the work function is It is preferably 5 eV or less. Examples of the electrode material of the cathode 7 include alkali metals, alkali metal halides, alkali metal oxides, alkaline earth metals and the like, and alloys thereof with other metals such as sodium, sodium-potassium alloys, Examples include lithium, magnesium, a magnesium-silver mixture, a magnesium-indium mixture, an aluminum-lithium alloy, and an Al / LiF mixture. Aluminum, Al / Al ₂ O ₃ mixture, etc. can also be used. Furthermore, an alkali metal oxide, an alkali metal halide, or a metal oxide may be used as the base of the cathode 7, and one or more conductive materials such as metals may be stacked and used. For example, an alkali metal / Al laminate, an alkali metal halide / alkaline earth metal / Al laminate, an alkali metal oxide / Al laminate, and the like can be given as examples. Moreover, it is good also as a structure which takes out light from the cathode 7 side using the transparent electrode represented by ITO, IZO, etc. FIG. The organic layer at the interface of the cathode 7 may be doped with an alkali metal such as lithium, sodium, cesium, or calcium, or an alkaline earth metal.

  Moreover, the said cathode 7 can be produced by forming these electrode materials in a thin film by methods, such as a vacuum evaporation method and sputtering method, for example. When light emission in the light emitting layer 4 is taken out from the anode 2 side, the light transmittance of the cathode 7 is preferably 10% or less. Conversely, when light is extracted from the cathode 7 side using the transparent electrode as the cathode 7 (including the case where light is extracted from both the anode 2 and the cathode 7), the light transmittance of the cathode 7 is set to 70% or more. It is preferable. In this case, the thickness of the cathode 7 varies depending on the material in order to control characteristics such as the light transmittance of the cathode 7, but is usually 500 nm or less, preferably 100 to 200 nm.

  As a material that can be used for the light emitting layer 5, any material known as a material for an organic electroluminescence element can be used. For example, anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline, bisstyryl, cyclopentadiene, quinoline metal complex, tris (8-hydroxyxyl) Norinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzoquinoline metal complex, tri- (p-terphenyl- 4-yl) amine, 1-aryl-2,5-di (2-thienyl) pyrrole derivative, pyran, quinacridone, rubrene, distyrylbenzene derivative, distyrylarylene derivative, distili Amine derivatives and various fluorescent dyes, but include those including a material system and its derivatives of the foregoing, the present invention is not limited to these. Moreover, it is also preferable to mix and use the light emitting material selected from these compounds suitably. Further, not only a compound that emits fluorescence, typified by the above-described compound, but also a material system that emits light from a spin multiplet, for example, a phosphorescent material that emits phosphorescence, and a part thereof are included in a part of the molecule. A compound can also be used suitably. The light emitting layer (organic layer) 5 made of these materials may be formed by a dry process such as vapor deposition or transfer, or by a wet process such as spin coating, spray coating, die coating, or gravure printing. May be.

  The hole transport material used for the first and second hole transport layers 3a and 3b may be any material that reacts with a so-called electron accepting material and generates an oxidation state such as a cation or a dication. , N'-bis (3-methylphenyl)-(1,1'-biphenyl) -4,4'diamine (TPD) and 4,4'-bis [N- (naphthyl) -N-phenyl-amino] biphenyl Aromatic diamine compounds such as (α-NPD), stilbene derivatives, pyrazoline derivatives, polyarylalkanes, 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m -MTDATA) and polymer materials such as polyvinyl carbazole, but are not limited thereto.

  The metal oxide material used for the metal oxide layer 4 has a deposition temperature higher than that of the hole transport material and efficiently transports the hole transport as an electron-accepting dopant in order to promote the reaction with the hole transport material efficiently at the interface. Mention may be made of those having the property of being able to oxidize the material Lewisally. Specific examples include metal oxides such as vanadium oxide, molybdenum oxide, rhenium oxide, tungsten oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, titanium oxide, and aluminum oxide, but are not limited thereto. is not.

  Examples of film forming methods of the hole transport layers 3a and 3b and the metal oxide layer 4 include, for example, vapor deposition, sputtering, coating, casting, spraying, CVD, transfer, and the like. Selected. In the case of vapor deposition, a film forming method by co-evaporation using a heat vapor deposition method or an EB vapor deposition method using a metal oxide, an insulator, a metal, or the like as an evaporating substance is given as an example. In addition, it is possible to oxidize some substances as needed by controlling the atmosphere. In the case of sputtering, a metal oxide may be used as a target. For example, the material may be formed by reactive sputtering in an oxygen-containing atmosphere using a metal as a target. The method is not particularly limited as long as it is not a method that causes fatal damage to the organic layer such as the light emitting layer 5, and any method for obtaining necessary film characteristics can be arbitrarily used. In the case of wet film formation such as casting or coating, a material system that does not adversely affect the surrounding layers may be selected. Regarding the transfer, a transfer method that does not adversely affect the surrounding layers may be selected, and the means is not particularly limited. In the present invention, it is preferable to use a high rate vapor deposition technique or a high material use efficiency vapor deposition technique.

  The electron transport material constituting the electron transport layer 6 has the ability to transport electrons, has the effect of injecting electrons from the cathode 7, and has an excellent effect of injecting electrons into the light emitting layer 5. The compound which prevents the movement to the electron carrying layer 6, and was excellent in the thin film formation ability can be mentioned. Specifically, fluorene, bathophenanthroline, bathocuproine, anthraquinodimethane, diphenoquinone, oxazole, oxadiazole, triazole, imidazole, anthraquinodimethane, 4,4′-N, N′-dicarbazole biphenyl (CBP) And their compounds, metal complex compounds, and nitrogen-containing five-membered ring derivatives. Specific examples of the metal complex compound include tris (8-hydroxyquinolinate) aluminum, tri (2-methyl-8-hydroxyquinolinate) aluminum, tris (8-hydroxyquinolinato) gallium, Bis (10-hydroxybenzo [h] quinolinato) beryllium, bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8) -Quinolinato) (1-naphtholato) aluminum, bis (2-methyl-8-quinolinato) -4-phenylphenolate, and the like, but are not limited thereto. The nitrogen-containing five-membered ring derivative is preferably an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative. Specifically, 2,5-bis (1-phenyl) -1,3,4-oxazole, 2,5-bis (1-phenyl) -1,3,4-thiazole, 2,5-bis (1 -Phenyl) -1,3,4-oxadiazole, 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) 1,3,4-oxadiazole, 2,5-bis ( 1-naphthyl) -1,3,4-oxadiazole, 1,4-bis [2- (5-phenylthiadiazolyl)] benzene, 2,5-bis (1-naphthyl) -1,3,4 -Triazole, 3- (4-biphenylyl) -4-phenyl-5- (4-t-butylphenyl) -1,2,4-triazole, and the like, but is not limited thereto. Polymer materials used in polymer organic light emitting devices can also be used For example, polyparaphenylene and derivatives thereof, fluorene and derivatives thereof, etc. The thickness of the electron transport layer 6 is not particularly limited, but may be, for example, 10 to 300 nm. The film can be formed by any method.

  And in manufacturing the organic electroluminescent element of this invention, the anode 2, the 1st hole transport layer 3a, the metal oxide layer 4, the 2nd hole transport layer 3b, and the light emitting layer 5 in order on the surface of the board | substrate 1. The electron transport layer 6 and the cathode 7 are laminated. Then, the first hole transport layer 3a, the metal oxide layer 4, and the second hole transport layer 3b are laminated in this order, whereby the first hole transport layer is formed on the surface of the anode 2 on the light emitting layer 5 side. A mixed layer 9 composed of the hole transport material of the layer 3a and the metal oxide material of the metal oxide layer 4 is formed. This mixed layer 9 is formed when the first hole transport layer 3a and the metal oxide layer 4 are entirely mixed, or at the interface between the first hole transport layer 3a and the metal oxide layer 4. In some cases, the thickness of the mixed layer 9 may be greater than 0 nm and 30 nm or less.

  Here, the thickness of the metal oxide layer 4 is preferably 1 to 20 nm. In the mixed layer 9, in order to efficiently oxidize the hole transport material efficiently and uniformly in the light emitting surface, the metal oxide layer 4 needs to be 1 nm or more. Further, when the thickness of the metal oxide layer 4 is 20 nm or more, the amount of the metal oxide that does not contribute to the reaction at the interface increases. As a result, the injection from the first hole transport layer 3 to the metal oxide layer 4 is performed. Since the barrier increases and the voltage increases and the life characteristics deteriorate, it is important for the metal oxide layer 4 to have a film thickness of 1 nm to 20 nm for high efficiency and long life.

  Moreover, it is preferable that the thickness of the 1st hole transport layer 3a formed in contact with the surface at the side of the light emitting layer 5 of the anode 2 is 1-10 nm. In order to perform the first hole transport material in contact with the anode 2 efficiently and uniformly in a plane, the hole transport material in the portion in contact with the anode 2 needs to have a thickness of 1 nm or more. Moreover, when the thickness of the hole transport material in contact with the anode 2 is 10 nm or more, the amount of the hole transport material that does not contribute to the reaction at the interface with the metal oxide layer 4 increases. Since the hole injection barrier to the hole transport layer 3a is increased, resulting in a higher voltage and a decrease in life characteristics, the film thickness of the first hole transport layer 3a in contact with the anode 2 is 1 nm to 10 nm. It is important for high efficiency and long life.

In the mixed layer 9, as a method for controlling the reaction amount and reaction depth (thickness of the mixed layer 9) of the hole transport material and the metal oxide material, the film thickness of the first hole transport layer 3a, the film of the metal oxide layer 4 Adjustment is possible by changing the thickness. In addition, the means for controlling the reaction amount and reaction depth between the hole transport material and the metal oxide material is not limited to the above-described film thickness adjustment, and the film formation rate (particularly, the film formation rate of the metal oxide layer 4), It can also be adjusted by the substrate temperature at the time of film formation and the energy selection at the time of film formation (selection of the film formation method). When the film formation rate is used as the control means, the state of molecules during the deposition of the hole transport material and the metal oxide material changes depending on the film formation rate. For example, the metal oxide material is MO ₃ . In this case, the reaction rate between the hole transport material and the metal oxide material tends to increase as the deposition rate of the metal oxide layer 4 decreases. In addition, when the substrate temperature at the time of film formation or the energy selection at the time of film formation is used as a control means, the reaction tends to progress as the energy at the time of vapor deposition of the hole transport material and the metal oxide material increases. When the energy increases during film formation or when the film is formed, the reaction amount between the hole transport material and the metal oxide material tends to increase. Moreover, it is also possible to control the reaction amount and reaction depth of the hole transport material and the metal oxide material by heating for a certain time after laminating all the layers as described above. Heating tends to increase the amount of reaction between the hole transport material and the metal oxide material.

  In the case where the metal oxide layer is laminated on the hole transport material layer and the case where the hole transport material layer is laminated on the metal oxide layer, the present inventors have a reaction state at the interface. By clarifying this difference and actively using this feature, we achieved higher efficiency and longer life of the organic electroluminescence device. As shown in Japanese Patent Application No. 2007-274235, the present inventors have realized evaluation of a reactive mixed layer inside an organic electroluminescence element by nondestructive measurement by using Raman spectroscopy.

Using this technique, a sample in which MoO ₃ that is a metal oxide is laminated on α-NPD that is a hole transport material, and α-NPD that is a hole transport material is formed on MoO ₃ that is a metal oxide. The reaction state of the sample laminated with was evaluated. By selecting two types of excitation wavelengths of 532 nm and 633 nm, the production state of α-NPD cation (α-NPD +) and α-NPD dication (α-NPD ++) at the interface was evaluated. FIG. 4 shows a 532 nm excitation Raman spectrum and FIG. 5 shows a 633 nm excitation Raman spectrum of a sample obtained by laminating MoO ₃ which is a metal oxide on α-NPD. Further, FIG. 6 shows a 532 nm excitation Raman spectrum and FIG. 7 shows a 633 nm excitation Raman spectrum of a sample in which α-NPD as a hole transport material is laminated on MoO ₃ as a metal oxide. A resonance Raman spectrum of the cation of α-NPD is possible with 532 nm excitation, and a resonance Raman spectrum of the dication of α-NPD is possible with 633 nm excitation. 4 and 6, in the laminated film of α-NPD and MoO ₃ , the Raman spectrum attributed to the cation of α-NPD is obtained regardless of the lamination order, and the generation of cation of α-NPD at the interface of the laminated film is obtained. Revealed. Further, from FIG. 5 and FIG. 7, the multilayer film interface of alpha-NPD and MoO _3, the Raman spectrum attributed to dications alpha-NPD is obtained, the laminated film interface than this result, alpha-NPD and MoO ₃ Then, it was clarified that a cation and a dication of α-NPD were formed simultaneously. It should be noted that in FIG. 5 and FIG. 7, there is a large difference in the Raman scattering intensity of the dication of α-NPD, as is apparent from the ratio of the background and Raman spectral intensity. The amount of dication generation of α-NPD in a sample in which MoO ₃ as a metal oxide is laminated on α-NPD as a material is determined as α-NPD as a hole transport material on MoO ₃ as a metal oxide. Compared with the amount of dication produced in the sample laminated with, it was clarified that a large amount was produced. The generation of these cations and dications is effective for improving the efficiency and extending the life of organic electroluminescence devices. In order to generate cations and dications more efficiently, a metal oxide is formed on the hole transport material. It has been found that laminating is effective.

  From the above results, in the present invention, the first hole transport layer 3a, the metal oxide layer 4, and the second hole transport layer 3b are laminated in this order in the most efficient manner inside the organic electroluminescence element. Cations and dications can be generated. By using this method, the organic electroluminescence device can be highly efficient and have a long life.

  FIG. 2 shows another example of the organic electroluminescence element of the present invention. In this case, in the same manner as described above, the anode 2 made of a transparent conductive film is formed on the surface of the substrate 1, and the first hole transport layer 3 a, the metal oxide layer 4, and the second hole are formed on the surface of the anode 2. The transport layer 3b is laminated in this order. Further, for the purpose of adjusting driving voltage and carrier balance, a metal oxide layer 4 and a third hole transport layer 3c are laminated thereon, and a layer made of a hole transport material / a layer made of a metal oxide material / hole transport. A combination of layers made of materials is repeated twice, and a light emitting layer 5, an electron transport layer 6, and a cathode 7 are further laminated thereon in the same manner as described above. In this way, the first hole transport layer 3a and the metal oxide layer 4 are formed by repeatedly laminating the combination of the layer composed of the hole transport material / the layer composed of the metal oxide material / the layer composed of the hole transport material. The mixed layer 9 and the mixed layer 9 composed of the metal oxide layer 4 and the second hole transport layer 3b can be formed, and the oxidation reaction of the hole transport material can be effectively advanced. The third hole transport layer 3c can be formed in the same manner as the first and second hole transport layers 3a and 3b.

  FIG. 3 shows another example of the organic electroluminescence element of the present invention. This is an organic electroluminescence element of a multi-unit element in which two light emitting layers 5 and 5 are laminated via an intermediate layer 10. The intermediate layer 10 is formed by stacking a plurality of layers, and includes a portion in which the first hole transport layer 3a, the metal oxide layer 4, and the second hole transport layer 3b are stacked in this order. The mixed hole 9 is formed by the first hole transport layer 3a and the metal oxide layer 4 in FIG. In this case, in the same manner as described above, the anode 2 made of a transparent conductive film is formed on the surface of the substrate 1, and the first hole transport layer 3 a, the metal oxide layer 4, and the second hole are formed on the surface of the anode 2. The transport layer 3b is laminated in this order. A light emitting layer 5 and an electron transport layer 6 were laminated thereon, and an alkali metal layer / transparent electrode layer was further laminated thereon as a partial layer 8 of the intermediate layer 10. Next, a first hole transport layer 3a, a metal oxide layer 4 and a second hole transport layer 3b different from the above are laminated in this order on the cathode 7 side of a part of the layer 8 of the intermediate layer 10, The light emitting layer 5, the electron carrying layer 6, and the cathode 7 are laminated | stacked as 2nd unit. Thus, by using a stacked layer of the hole transport layer 3a, the metal oxide layer 4, and the hole transport layer 3b as a part of the intermediate layer 10, a multi-unit element can be manufactured without using a mixed layer by a co-evaporation method. Is possible. In addition, the first hole transport layer 3a used for the intermediate layer 10 is oxidized by the metal oxide layer 4 laminated thereon to generate cations and dications, thereby enabling higher efficiency and longer life. It becomes. In the metal oxide layer 4 in the intermediate layer 10, the absorption and refractive index of the metal oxide layer 4 greatly affect the light extraction efficiency. When the metal oxide layer 4 is 20 nm or more, the amount of light emission absorbed by the metal oxide layer 4 is increased, and the refractive index of the metal oxide layer 4 is different from that of the hole transport material. Occurs, and the light extraction efficiency decreases. In order to prevent these problems, the thickness of the metal oxide layer 4 in the intermediate layer 10 is important to be 1 nm to 20 nm for high efficiency and long life.

  And, in the present invention, without the mixed layer by the co-evaporation method, it is possible to reduce the light emission unevenness, increase the efficiency and extend the life, and produce the organic electroluminescence device with high stability, high material use efficiency and high yield. Is possible.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
A 150 nm ITO film is formed as a transparent electrode layer (anode 2) on a glass substrate (substrate 1), and an amine compound α-NPD (manufactured by Nippon Steel Chemical Co., Ltd.) is formed as a first hole transport layer 3a by a vacuum deposition method. ) 3 nm, a metal oxide layer 4 thereon, molybdenum trioxide (manufactured by Furuuchi Chemical Co., Ltd .; hereinafter referred to as MoO ₃ ) 3 nm, and an α-NPD 44 nm as a second hole transport layer 3b thereon. Filmed. In this case, the mixed layer 9 is formed when the metal oxide layer 4 is formed on the first hole transport layer 3a. Next, 50 nm of an aluminum metal complex Alq3 (manufactured by Nippon Steel Chemical Co., Ltd.) is formed as the electron transport layer 6 and the light emitting layer 5 on the second hole transport layer 3 b, and LiF is 1 nm as the cathode 7. , Al was deposited to a thickness of 80 nm to produce an organic electroluminescence element. Then, the organic electroluminescence element was sealed under a nitrogen atmosphere, and voltage-current-luminance characteristics and life characteristics were evaluated.

(Example 2)
The same procedure as in Example 1 was performed except that the thickness of the metal oxide layer 4 was changed to 0.5 nm.

(Example 3)
The same procedure as in Example 1 was performed except that the thickness of the metal oxide layer 4 was 25 nm.

Example 4
Example 1 was performed except that the thickness of the first hole transport layer 3a was changed to 0.5 nm.

(Example 5)
Example 1 was performed except that the thickness of the first hole transport layer 3a was changed to 15 nm.
(Comparative Example 1)
ITO is deposited as a transparent electrode layer (anode 2) on a glass substrate (substrate 1) with a thickness of 150 nm, α-NPD is deposited as a hole transport material layer with a thickness of 50 nm, an electron transport layer 6 and a light emitting layer 5 by vacuum deposition. An Alq3 film having a thickness of 50 nm was formed, and a LiF film having a thickness of 1 nm and an Al film having a thickness of 80 nm were formed as the cathode 7 to produce an organic electroluminescence element. In the same manner as in Example 1, sealing was performed in a nitrogen atmosphere and evaluation was performed.
(Comparative Example 2)
ITO is deposited on a glass substrate (substrate 1) as a transparent electrode layer (anode 2) with a thickness of 150 nm, and by vacuum deposition, a MoO ₃ layer is 3 nm, a hole transport material layer is α-NPD at 47 nm, and an electron transport layer 6 and 50 nm of Alq3 was formed as the light-emitting layer 5, and 1 nm of LiF and 80 nm of Al were formed as the cathode 7 to produce an organic electroluminescence element. In the same manner as in Example 1, sealing was performed in a nitrogen atmosphere and evaluation was performed.

The element of each example and comparative example was energized at a current density of 10 mA / cm ² , and the luminance and driving voltage at that time were measured. In addition, regarding the life characteristics, energization was performed at a current density of 50 mA / cm ² , and the time when the luminance reached 90% of the initial luminance (LT90) and the time when the luminance reached 80% (LT80) were measured. In each of Examples 1 to 5, Comparative Example 1, and Comparative Example 2, the initial luminance at the time of life measurement is about 3000 cd / m ² . The measurement results are shown in Table 1.

表１に示したように、比較例１では、陽極であるＩＴＯからホール輸送層であるα‐ＮＰＤへのホール注入障壁、比較例２では、陽極であるＩＴＯからＭｏＯ_３、ＭｏＯ_３からホール輸送材料の層であるα‐ＮＰＤへのホール注入障壁の影響と思われる高電圧化が観測された。また、実施例１と比較例１、２では寿命特性に大きな違いがあり、本発明の実施例１は比較例１に対し約５０倍、比較例２に対し約５倍と、長寿命化していることがわかる。また、実施例１と実施例２〜５の対比から、第一のホール輸送層３ａの厚みや金属酸化物層４の厚みが好適な範囲から逸脱すると、駆動電圧や寿命の性能が低下することがわかる。また、実施例１では比較例１、２に比べて発光ムラが少なかった。
（実施例６）
ガラス基板（基板１）上に透明電極層（陽極２）としてＩＴＯを１５０ｎｍ成膜し、真空蒸着法により、第一のホール輸送層３ａとして、α-ＮＰＤを３ｎｍ、金属酸化物層４としてＭｏＯ_３を３ｎｍ、さらにその上に第二のホール輸送層３ｂとして、α‐ＮＰＤを４４ｎｍ成膜した。この場合、第一のホール輸送層３ａの上に金属酸化物層４を成膜した時に混合層９が形成される。次に、第二のホール輸送層３ｂの上に、電子輸送層６で且つ発光層５としてアルミ金属錯体Ａｌｑ３を５０ｎｍ成膜した。その上に中間層１０としてＬｉを２ｎｍ、ＩＴＯを５ｎｍ成膜し、さらに、第一のホール輸送材料３ａとして、α-ＮＰＤを３ｎｍ、金属酸化物層４としてＭｏＯ_３を３ｎｍ、さらにその上に第二のホール輸送材料３ｂとして、α-ＮＰＤを４４ｎｍ成膜し、中間層１０を形成した。この場合、第一のホール輸送層３ａの上に金属酸化物層４を成膜した時に混合層９が形成される。次に、中間層１０の上に第二の発光層５としてＡｌｑ３を５０ｎｍ成膜し、陰極７として、ＬｉＦを１ｎｍ、Ａｌを８０ｎｍ成膜し、中間層１０の一部にホール輸送材料の層／金属酸化物材料の層／ホール輸送材料の層が積層された部分を含む有機エレクトロルミネッセンス素子を作製した。作製した有機エレクトロルミネッセンス素子の発光面積は５ｃｍ□であり、面内での輝度分布測定より、発光ムラの評価を行った。

As shown in Table 1, in Comparative Example 1, the hole injection barrier from ITO serving as the anode to α-NPD serving as the hole transporting layer was used. In Comparative Example 2, hole transporting from the ITO serving as the anode to MoO ₃ and MoO ₃ was performed. High voltage, which is considered to be the effect of the hole injection barrier on α-NPD, which is the material layer, was observed. Further, there is a great difference in life characteristics between Example 1 and Comparative Examples 1 and 2, and Example 1 of the present invention has a long life of about 50 times that of Comparative Example 1 and about 5 times that of Comparative Example 2. I understand that. Moreover, when the thickness of the 1st hole transport layer 3a and the thickness of the metal oxide layer 4 deviate from a suitable range from contrast of Example 1 and Examples 2-5, the performance of a drive voltage or a lifetime will fall. I understand. Further, in Example 1, light emission unevenness was smaller than those in Comparative Examples 1 and 2.
(Example 6)
An ITO film having a thickness of 150 nm is formed on a glass substrate (substrate 1) as a transparent electrode layer (anode 2), and α-NPD is 3 nm as a first hole transport layer 3a and MoO as a metal oxide layer 4 by vacuum deposition. _{As a} second hole transport layer 3b, α-NPD was deposited in a thickness of 44 nm. In this case, the mixed layer 9 is formed when the metal oxide layer 4 is formed on the first hole transport layer 3a. Next, an aluminum metal complex Alq3 having a thickness of 50 nm was formed as the electron transport layer 6 and the light emitting layer 5 on the second hole transport layer 3b. A Li layer of 2 nm and an ITO layer of 5 nm are formed thereon as an intermediate layer 10, and α-NPD is 3 nm as a first hole transport material 3 a, MoO ₃ is 3 nm as a metal oxide layer 4, and further thereon. As the second hole transport material 3b, α-NPD was deposited to a thickness of 44 nm, and the intermediate layer 10 was formed. In this case, the mixed layer 9 is formed when the metal oxide layer 4 is formed on the first hole transport layer 3a. Next, 50 nm of Alq3 is formed as the second light-emitting layer 5 on the intermediate layer 10, 1 nm of LiF and 80 nm of Al are formed as the cathode 7, and a hole transport material layer is formed on a part of the intermediate layer 10. An organic electroluminescence device including a part where a layer of / metal oxide material layer / hole transport material layer was laminated was produced. The light emitting area of the produced organic electroluminescent element is 5 cm □, and the unevenness of light emission was evaluated by measuring the luminance distribution in the surface.

(Example 7)
An ITO film having a thickness of 150 nm is formed on a glass substrate (substrate 1) as a transparent electrode layer (anode 2), and α-NPD is 3 nm as a first hole transport layer 3a and MoO as a metal oxide layer 4 by vacuum deposition. _{As a} second hole transport layer 3a, an α-NPD film having a thickness of 44 nm was formed thereon. In this case, the mixed layer 9 is formed when the metal oxide layer 4 is formed on the first hole transport layer 3a. Next, an aluminum metal complex Alq3 having a thickness of 50 nm was formed as the electron transport layer 6 and the light emitting layer 5 on the second hole transport layer 3b. On top of that, Li was deposited in a thickness of 2 nm, ITO was deposited in a thickness of 5 nm, MoO ₃ was deposited in a thickness of 3 nm as a metal oxide material layer, and α-NPD was deposited in a thickness of 50 nm as a hole transport material layer thereon. An intermediate layer 10 was formed. Next, 50 nm of Alq3 was formed as the second light-emitting layer 5 on the intermediate layer 10, and 1 nm of LiF and 80 nm of Al were formed as the cathode 7 to produce an organic electroluminescence element. Sealing was performed under a nitrogen atmosphere, and using the same method as in Example 6, the emission unevenness was evaluated.

(Example 8)
The same procedure as in Example 6 was performed except that the thickness of the metal oxide layer 4 in the intermediate layer 10 was changed to 0.5 nm.

Example 9
The same procedure as in Example 6 was performed except that the thickness of the metal oxide layer 4 in the intermediate layer 10 was set to 25 nm.

Energized at a current density of 10 mA / cm ² to the device of Example 6-9, the average luminance of the light emitting surface to obtain the luminance distribution. The measurement results are shown in Table 2.

表２に示したように、実施例６では中間層１０の陰極７側に用いた、ホール輸送材料の層／金属酸化物材料の層／ホール輸送材料の層の積層により面内に均一に混合層（反応層）９を形成することができており、輝度分布を抑えることができた。一方、実施例７では、中間層１０の陰極７側にＭｏＯ_３層のみを用いており、効果的な混合層（反応層）９の形成が出来ておらず、平均輝度、輝度分布ともに、実施例６に比べて低い性能であることがわかる。また、実施例８、９のように、中間層１０における金属酸化物層４の厚みが好適な範囲から逸脱すると、平均輝度や輝度分布の性能が低下することがわかる。

As shown in Table 2, in Example 6, uniform mixing was performed in-plane by laminating the hole transport material layer / metal oxide material layer / hole transport material layer used on the cathode 7 side of the intermediate layer 10. The layer (reaction layer) 9 could be formed, and the luminance distribution could be suppressed. On the other hand, in Example 7, only the MoO ₃ layer was used on the cathode 7 side of the intermediate layer 10 and an effective mixed layer (reaction layer) 9 was not formed, and both the average luminance and the luminance distribution were carried out. It can be seen that the performance is lower than that of Example 6. Further, as in Examples 8 and 9, it can be seen that when the thickness of the metal oxide layer 4 in the intermediate layer 10 departs from a suitable range, the performance of average luminance and luminance distribution deteriorates.

2 Anode 3a First hole transport layer 3b Second hole transport layer 4 Metal oxide layer 5 Light emitting layer 7 Cathode 9 Mixed layer 10 Intermediate layer

Claims (5)

  In the organic electroluminescence device in which the light emitting layer is provided between the anode and the cathode, the first hole transport layer, the metal oxide layer, and the second hole transport layer are arranged in this order on the surface of the anode on the light emitting layer side. An organic electroluminescence device comprising: a mixed layer comprising a hole transport material and a metal oxide material formed on the surface of the anode on the light emitting layer side.   The thickness of a metal oxide layer is 1-20 nm, The organic electroluminescent element of Claim 1 characterized by the above-mentioned.   The organic electroluminescence device according to claim 1 or 2, wherein the thickness of the first hole transport layer formed in contact with the surface of the anode on the light emitting layer side is 1 to 10 nm.   In an organic electroluminescence device in which two light emitting layers are laminated via an intermediate layer between an anode and a cathode, the intermediate layer is formed by laminating a plurality of layers, and the first hole transport layer and the metal An organic layer characterized in that a mixed layer composed of a hole transport material and a metal oxide material is formed in the intermediate layer by including a portion in which the oxide layer and the second hole transport layer are laminated in this order. Electroluminescence element. The thickness of a metal oxide layer is 1-20 nm, The organic electroluminescent element of Claim 4 characterized by the above-mentioned.

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