JPH05251185A - Organic electroluminescence element - Google Patents

Abstract

PURPOSE:To provide an element provided with a cathode having high chemical stability and having high electric power converting efficiency by forming this cathode of a deposition film including Zn, alkaline earth metal having a work function of 3eV or less and/or rare earth metal having a work function of 3eV or less. CONSTITUTION:A cathode is formed of a deposition film including Zn, alkaline earth metal having a work function of 3eV or less and/or rare earth metal having a work function of 3eV or less. Ca, Sr or Ba is used as alkaline earth metal having a work function of 3eV or less, and Ce, Sm, Eu, Er, Yb or the like is used as a rare earth metal having a work function of 3eV or less. A composition ratio of Zn in the cathode is preferably 30-96at% and, more preferably, 90-94at%. A deposition speed for Zn and second metal is 50nm/sec and, more preferably, 1.2-10nm/sec. Although a film forming method is not specifically limited, a resistance heating deposition method, an electron beam deposition method, a high frequency induction heating method, a molecular beam epitaxy method, a hot wall deposition method, an ion plating method and the like can be adopted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device (hereinafter abbreviated as an organic EL device) used as a display device, a light emitting device or the like.

[0002]

2. Description of the Related Art An organic EL element is constructed by interposing at least a thin film (light emitting layer) of an organic light emitting element between a pair of electrodes facing each other. In this organic EL device, electrons injected from the negative electrode directly into the light emitting layer via the electron injection layer and holes injected directly from the positive electrode into the light emitting layer via the hole injection layer emit light. Recombination within the layer causes emission of light.

As means for improving the light emitting characteristics of an organic EL device based on such a light emitting mechanism, selection or improvement of organic light emitting material, improvement of film quality of light emitting layer, selection or improvement of cathode material, etc. are known. Has been. Among these, the selection or improvement of the negative electrode material is generally intended to enhance the efficiency of electron injection into the light emitting layer to improve the light emitting characteristics. For this reason, it has been attempted to use various electrically conductive metals, alloys, intermetallic compounds, and the like having a low work function as negative electrode materials.

For example, in US Pat. Nos. 3,173,050 and 3,382,394, an organic EL using an alkali metal, for example, a Na--K alloy as a negative electrode is disclosed.
A device is disclosed. The organic EL devices disclosed in these specifications have high quantum efficiency (RCA Review vol.3
0, P322), but alkali metals and alloys of alkali metals are not practical because they are highly active and chemically unstable.

Therefore, various proposals have been made to form the negative electrode by using a metal other than the alkali metal. For example, U.S. Pat. No. 4,539,507 discloses an organic EL element using In for a negative electrode, and JP-A-3-231970 discloses a Mg-In alloy for a negative electrode. An organic EL device is disclosed. Further, European Patent No. 0278757 describes a negative electrode having a layer containing a plurality of metals other than alkali metals and having a work function of at least one metal of these metals of 4 eV or less. An organic EL element provided with an electrode (specifically, a Mg-based electrode made of Mg and any of Ag, In, Sn, Sb, Te, and Mn, such as a Mg-Ag electrode) is disclosed. ..

Furthermore, Li, Na, Ca, which have a good electron injection property, can be added to relatively stable metals such as Mg, Al, In and Sn.
Various organic ELs with negative electrodes formed by mixing metals such as Sr
The device was presented at the polymer debate in the fall of 1991 (Proceedings of the Polymer Society, Vol. 40, No. 10, P. 3582).
However, the efficiency (power conversion efficiency) of the organic EL element announced here was not as high as that of the organic EL element provided with the Mg-Ag electrode as the negative electrode.

[0007]

As described above, various proposals have been made for forming a negative electrode by using an electron injecting metal, but the power conversion efficiency of these organic EL elements is still insufficient. there were.

Therefore, an object of the present invention is to provide a new organic EL element having a negative electrode having high chemical stability and having improved power conversion efficiency.

[0009]

An organic EL device of the present invention which achieves the above object is a vapor deposition film containing Zn and an alkaline earth metal having a work function of 3 eV or less and / or a rare earth metal having a work function of 3 eV or less. It is characterized by being provided as a negative electrode.

The present invention will be described in detail below. As described above, the negative electrode in the organic EL element of the present invention is Zn
And an alkaline earth metal having a work function of 3 eV or less and / or a rare earth metal having a work function of 3 eV or less. Here, specific examples of the alkaline earth metal having a work function of 3 eV or less include Ca, Sr, and Ba. Further, specific examples of the rare earth metal having a work function of 3 eV or less include Ce, Sm, Eu, Er, Yb and the like.

A method for forming a vapor deposition film containing Zn and the above-mentioned alkaline earth metal and / or rare earth metal (hereinafter, these alkaline earth metal and rare earth metal may be collectively referred to as a second metal) is described below. Specific examples thereof include, but are not limited to, resistance heating vapor deposition method, electron beam vapor deposition method, high frequency induction heating method, molecular beam epitaxy method, hot wall vapor deposition method, ion plating method, cluster ion beam method, and 2 Examples thereof include a direct vapor deposition method for alloys and a multi-source simultaneous vapor deposition method using methods such as a polar sputtering method, a bipolar magnetron sputtering method, a tripolar and quadrupole plasma sputtering method, and an ion beam sputtering method. From the viewpoint of efficiently producing a negative electrode having a desired composition, it is particularly preferable to apply the multi-source simultaneous vapor deposition method.

The negative electrode formed as described above is Z
It suffices that at least one second metal is contained in addition to n, but the composition ratio of Zn in the negative electrode is 30 to 96 at.%.
Is preferred. More preferably 90 to 94
at.%. The composition of the negative electrode can be controlled by appropriately setting the ratio between the vapor deposition rate of Zn and the vapor deposition rate of the second metal when the film is formed by the multi-source simultaneous vapor deposition method, for example. A preferable vapor deposition rate is 50 nm / sec for both Zn and the second metal. More preferably, 1.
2 to 10 nm / sec. In this way Zn and the second
By combining at least one kind of metal, a negative electrode excellent in electron injection property can be obtained.

The structure of the organic EL device of the present invention is not particularly limited except that the above-mentioned negative electrode is provided.
For example, as the constitution of the organic EL element, anode / light emitting layer / negative electrode, anode / hole injection layer / light emitting layer / negative electrode, anode / light emitting layer / electron injection layer / negative electrode, anode / hole injection layer / Although there are a light emitting layer / electron injection layer / cathode, etc., the organic EL element of the present invention may have any configuration. Also,
When manufacturing the organic EL element of the present invention, the material other than the negative electrode is not particularly limited, and it can be formed by various methods using various materials.

For example, the organic compound that can be used as the material of the light emitting layer is not particularly limited, but a fluorescent brightening agent such as a benzothiazole type, a benzimidazole type, a benzoxazole type, a metal chelated oxinoid compound, or a styrylbenzene is used. Examples thereof include system compounds.

Specific examples of the compound name include those disclosed in JP-A-59-194393. A typical example is 2,5-bis (5,7
-Di-t-pentyl-2-benzoxazolyl) -1,
3,4-thiadiazole, 4,4'-bis (5,7-t
-Pentyl-2-benzoxazolyl) stilbene,
4,4'-bis [5,7-di- (2-methyl-2-butyl) -2-benzoxazolyl] stilbene, 2,5-
Bis (5,7-di-t-pentyl-2-benzoxazolyl) thiophene, 2,5-bis [5-α, α-dimethylbenzyl-2-benzoxazolyl] thiophene,
2,5-bis [5,7-di- (2-methyl-2-butyl) -2-benzoxazolyl] -3,4-diphenylthiophene, 2,5-bis (5-methyl-2-benzo) Oxazolyl) thiophene, 4,4'-bis (2-benzoxazolyl) biphenyl, 5-methyl-2- [2-
Benzoxazole-based compounds such as [4- (5-methyl-2-benzoxazolyl) phenyl] vinyl] benzoxazole and 2- [2- (4-chlorophenyl) vinyl] naphtho [1,2-d] oxazole, 2 , 2 '-(p-phenylenedivinylene) -bisbenzothiazole and other benzothiazoles, 2- [2- [4- (2-benzimidazolyl) phenyl] vinyl] benzimidazole, 2-
Examples include fluorescent whitening agents such as benzimidazole series such as [2- (4-carboxyphenyl) vinyl] benzimidazole. In addition, other useful compounds are Chemistry of Synthetic Soybean 1971, 628-6.
They are listed on pages 37 and 640.

As the chelated oxinoid compound, for example, those disclosed in JP-A-63-295695 can be used. Typical examples are tris (8-quinolinol) aluminum, bis (8-quinolinol) magnesium, bis (benzo [f] -8-quinolinol) zinc, bis (2-methyl-).
8-quinolinolate) aluminum oxide, tris (8-quinolinol) indium, tris (5-methyl-8-quinolinol) aluminum, 8-quinolinol lithium, tris (5-chloro-8-quinolinol)
Gallium, bis (5-chloro-8-quinolinol) calcium, poly [zinc (II) -bis (8-hydroxy-5)
-Quinolinonyl) methane] and other 8-hydroxyquinoline-based metal complexes, dilithium epinetridione, and the like.

As the styrylbenzene compound, for example, those disclosed in European Patent No. 0319881 and European Patent No. 0373582 can be used. Typical examples thereof are 1,4-bis (2-methylstyryl) benzene and 1,4-bis (3
-Methylstyryl) benzene, 1,4-bis (4-methylstyryl) benzene, distyrylbenzene, 1,4-
Bis (2-ethylstyryl) benzene, 1,4-bis (3-ethylstyryl) benzene, 1,4-bis (2-
Methylstyryl) -2-methylbenzene, 1,4-bis (2-methylstyryl) -2-ethylbenzene and the like can be mentioned.

The distyrylpyrazine derivative disclosed in JP-A-2-252793 can also be used as a material for the light emitting layer. Typical examples are 2,
5-bis (4-methylstyryl) pyrazine, 2,5-bis (4-ethylstyryl) pyrazine, 2,5-bis [2
-(1-naphthyl) vinyl] pyrazine, 2,5-bis (4-methoxystyryl) pyrazine, 2,5-bis [2
Examples thereof include-(4-biphenyl) vinyl] pyrazine and 2,5-bis [2- (1-pyrenyl) vinyl] pyrazine. Others include, for example, European Patent No. 03877.
The polyphenyl compound disclosed in Japanese Patent No. 15 can also be used as a material for the light emitting layer.

Further, in addition to the above-mentioned optical brightener, metal chelated oxinoid compound, styrylbenzene compound, etc., for example, 12-phthaloperinone (J.Appl.P).
hys., 27, L713 (1988)), 1,4-
Diphenyl-1,3-butadiene, 1,1,4,4-tetraphenyl-1,3-butadiene (above, Appl. Phys.
Lett., Vol. 56, L799 (1990)), naphthalimide derivative (JP-A-2-305886), perylene derivative (JP-A-2-189890), oxadiazole derivative (JP-A-2-216791). Publication, or the oxadiazole derivative disclosed by Hamada et al. In the 38th Joint Lecture on Applied Physics), the aldazine derivative (JP-A-2-220393), the pyrazine derivative (JP-A-2-220394), A cyclopentadiene derivative (JP-A-2-289675), a pyrrolopyrrole derivative (JP-A-2-296891),
Styrylamine derivatives (Appl. Phys. Lett., Volume 56, L
799 (1990)), coumarin-based compounds (JP-A-2
-191694), International Publication WO90 / 13.
148 and polymer compounds such as those described in Appl. Phys. Lett., Vol 58, 18, P1982 (1991) can also be used as the material of the light emitting layer.

In the present invention, an aromatic dimethylidyne compound (European Patent No. 0388876) is used as a material for the light emitting layer.
No. 8 and those disclosed in JP-A-3-231970) are preferably used. As a specific example, 1,4
-Phenylenedimethytilidine, 4,4'-Phenylenedimethylidene, 2,5-Xylylenedimethylidene,
2,6-naphthylene dimethylidene, 1,4-biphenylene dimethylidene, 1,4-p-terephenylene dimethylidene, 9,10-anthracene diyl dimethylidene, 4,4 ′-(2,2 -Di-t-butylphenylvinyl) biphenyl (hereinafter abbreviated as DTBPVBi), 4,4 '-(2,2-diphenylvinyl) biphenyl (hereinafter abbreviated as DPVBi), and the like, and derivatives thereof. ..

As a method for forming a light emitting layer using the above materials, for example, a vapor deposition method, a spin coating method, a casting method,
A known method such as the LB method can be applied. The light emitting layer is preferably a molecular deposition film. Here, the molecular deposition film is a thin film formed by depositing a material compound in a vapor phase state, or a film formed by solidifying a material compound in a solution state or a liquid phase state. Can be distinguished from the thin film (molecular cumulative film) formed by the LB method based on the difference in the aggregation structure and the higher order structure and the functional difference caused by the difference. In addition, JP-A-57
As disclosed in Japanese Patent No. 51781, etc., a light emitting layer can also be formed by dissolving a binder such as a resin and a material compound in a solvent to form a solution, and then thinning the solution by a spin coating method or the like. Can be formed.

The thickness of the light emitting layer thus formed is not particularly limited and may be appropriately selected depending on the situation, but is usually preferably in the range of 5 nm to 5 μm.
The light emitting layer in the organic EL device has an injection function capable of injecting holes from the anode or the hole injection layer and electrons from the negative electrode or the electron injection layer when an electric field is applied. It has a transport function of moving (electrons and holes) by the force of an electric field, a field of recombination of electrons and holes, and a light emitting function of connecting this to light emission. Note that there may be a difference between the ease with which holes are injected and the ease with which electrons are injected. The transport function represented by the mobilities of holes and electrons may have different sizes, but it is preferable to move at least one of them.

As the material of the anode, a metal, an alloy, an electrically conductive compound having a large work function (4 eV or more) or a mixture thereof is preferably used. As a specific example, A
Examples thereof include metals such as u and dielectric transparent materials such as CuI, ITO, SnO ₂ , and ZnO. The anode can be manufactured by forming a thin film of the above material by a method such as a vapor deposition method or a sputtering method. When the light emitted from the light emitting layer is taken out from the anode, the transmittance of the anode is preferably higher than 10%. The sheet resistance of the anode is preferably several hundreds Ω / □ or less. The thickness of the anode depends on the material, but is usually 10 nm to 1 μm.
m, preferably in the range of 10 to 200 nm.

As a material for the hole injection layer provided as necessary, known materials conventionally used as a hole injection material for an optical transmission material or used for a hole injection layer for an organic EL element are known. Any one can be selected and used from the things. The material for the hole injection layer has either hole injection or electron barrier properties, and may be either an organic substance or an inorganic substance.

Specific examples include, for example, triazole derivatives (see US Pat. No. 3,112,197),
Oxadiazole derivatives (US Pat. No. 3,189,44
No. 7, etc.), imidazole derivatives (Japanese Patent Publication No. 37)
-16096, etc.), polyarylalkane derivatives (US Pat. Nos. 3,615,402, 3,820,989, and 3,542,544).
Specification, Japanese Patent Publication No. 45-555, 51-109
83, JP-A-51-93224, 55-
No. 17105, No. 56-4148, No. 55-
108667, 55-156953, 56-36656, etc.), pyrazoline derivatives and pyrazolone derivatives (US Pat. No. 3,180,729).
No. 4,278,746, JP-A-5
No. 5-88064, No. 55-88065, No. 49-105537, No. 55-51086, No. 56-80051, No. 56-88141, No. 57-45545, No. 54. -11263
No. 7, JP-A-55-74546, etc.), phenylenediamine derivatives (US Pat. No. 3,615,404, JP-B-51-10105, JP-A-46-37).
12, JP-A-47-25336, JP-A-54-
No. 53435, No. 54-110536, No. 5
No. 4,119,925), arylamine derivatives (U.S. Pat. No. 3,567,450, U.S. Pat.
180,703, 3,240,597, 3,658,520, 4,23.
2,103, 4,175,961, 4,012,376, and JP-B-49-3.
5702, 39-27577 and JP-A-5
No. 5-144250, No. 56-119132, No. 56-22437, West German Patent No. 1,11.
0518, etc.), amino-substituted chalcone derivatives (see US Pat. No. 3,526,501, etc.),
Oxazole derivatives (disclosed in US Pat. No. 3,257,203, etc.), styrylanthracene derivatives (see JP-A-56-46234, etc.), fluorenone derivatives (see JP-A-54-110837, etc.) ),
Hydrazone derivatives (U.S. Pat. Nos. 3,717,462, JP-A-54-59143 and JP-A-55-520)
63, 55-52064, 55-46.
No. 760, No. 55-85495, No. 57-1.
No. 1350, No. 57-148749, and Japanese Unexamined Patent Publication No. 2-311591, and stilbene derivatives (Japanese Unexamined Patent Publication Nos. 61-210363 and 61-2284).
No. 51, No. 61-14642, No. 61-72
No. 255, No. 62-47646, No. 62-3.
6674, 62-10652, and 62-
No. 30255, No. 60-93445, No. 60
-94462, 60-174749, 60-175052, etc.), silazane derivatives (U.S. Pat. No. 4,950,950), polysilanes (Japanese Patent Laid-Open No. 2-204996), Aniline-based copolymer (JP-A-2-28263), JP-A-1-
Examples thereof include conductive polymer oligomers (particularly thiophene oligomers) disclosed in Japanese Patent Publication No. 211399.

As the material of the hole injection layer, the above-mentioned materials can be used.
No. 3,295,965), aromatic tertiary amine compounds and styrylamine compounds (US Pat. No. 4,127,412, JP-A-53-270).
No. 33, No. 54-58445, No. 54-14
No. 9634, No. 54-64299, No. 55-
79450, 55-144250, and 5
6-119132, 61-295558, 61-98353, 63-295695.
It is preferable to use aromatic tertiary amine compounds.

Typical examples of the porphyrin compound include porphine, 1,10,15,20-tetraphenyl-21H, 23H-porphine copper (II), 1,10,
15,20-Tetraphenyl-21H, 23H-porphine zinc (II), 5,10,15,20-tetrakis (pentafluorophenyl) -21H, 23H-porphine, silicon phthalocyanine oxide, aluminum phthalocyanine chloride, phthalocyanine (metal free) ),
Examples thereof include dilithium phthalocyanine, copper tetramethylphthalocyanine, copper phthalocyanine, chromium phthalocyanine, zinc phthalocyanine, lead phthalocyanine, titanium phthalocyanine oxide, Mg phthalocyanine and copper octamethylphthalocyanine.

Typical examples of the aromatic tertiary amine compound and the styrylamine compound are N, N,
N ', N'-tetraphenyl-4,4'-diaminophenyl, N, N'-diphenyl-N, N'-bis- (3-
Methylphenyl)-[1,1'-biphenyl] -4,
4'-diamine (hereinafter abbreviated as TPDA), 2,2
-Bis (4-di-p-tolylaminophenyl) propane, 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane, N, N, N ', N'-tetra-p
-Tolyl-4,4'-diaminobiphenyl, 1,1-bis (4-di-p-tolylaminophenyl) -4-phenylcyclohexane, bis (4-dimethylamino-2-methylphenyl) phenylmethane, bis ( 4-di-p-tolylaminophenyl) phenylmethane, N, N'-diphenyl-N, N'-di (4-methoxyphenyl) -4,
4'-diaminobiphenyl, N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether,
4,4'-bis (diphenylamino) quadriphenyl, N, N, N-tri (p-tolyl) amine, 4- (di-p-tolylamino) -4 '-[4 (di-p-tolylamino) Examples include styryl] stilbene, 4-N, N-diphenylamino- (2-diphenylvinyl) benzene, 3-methoxy-4′-N, N-diphenylaminostilbenzene, N-phenylcarbazole and the like. Also,
The above-mentioned aromatic dimethylidyne compound shown as the material for the light emitting layer can also be used as the material for the hole injection layer.

The hole injecting layer can be formed by thinning the above compound by a known method such as a vacuum vapor deposition method, a spin coating method, a casting method and an LB method. The thickness of the hole injection layer is not particularly limited, but is usually 5 nm to 5 μm. This hole injection layer is
It may have a single-layer structure composed of one or more of the above-mentioned materials, or may have a multi-layer structure composed of a plurality of layers having the same composition or different compositions.

The electron-injection layer, which is provided as necessary, may have a function of transmitting the electrons injected from the negative electrode to the light-emitting layer, and its material is any one of the conventionally known compounds. Can be selected and used.

Specific examples include nitro-substituted fluorenone derivatives, JP-A-57-149259 and JP-A-58-5.
5450, 63-104061 and the like, anthraquinodimethane derivative disclosed in Polymer Prep
rints, Japan Vol.37, No. 3 (1988) p.681 etc., diphenylquinone derivative, thiopyran dioxide derivative, heterocyclic tetracarboxylic acid anhydride such as naphthaleneperylene, carbodiimide, Japanese Journal of Applied
Physics, 27, L 269 (1988), JP-A-60-69657, JP-A-61-143764, JP-A-61-114815.
Fluorenylidene methane derivatives disclosed in, for example, JP-A-61-225151 and JP-A-61-23.
Anthraquinodimethane derivatives and anthrone derivatives disclosed in Japanese Patent No. 3750, Appl. Phys. Lett., 5
5,15,1489 and oxadiazole derivatives disclosed by Hamada et al. At the 38th Joint Lecture Meeting on Applied Physics,
A series of electron-transporting compounds disclosed in JP-A-59-194393 can be mentioned. Incidentally, JP-A-59
Although the above-mentioned electron-transporting compound is disclosed as a material for the light-emitting layer in Japanese Patent Laid-Open No. 194393, it has been clarified by the study by the present inventors that it can be used as a material for the electron-injecting layer.

A metal complex of an 8-quinolinol derivative, specifically, tris (8-quinolinol) aluminum, tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol). ) Aluminum, tris (2-methyl-8-quinolinol) aluminum, and the like, and metal complexes in which the central metal of these metal complexes is replaced with In, Mg, Cu, Ca, Sn, or Pb, etc. are also materials for the electron injection layer. Can be used as In addition, metal-free or metal phthalocyanine, or those whose terminal is substituted with an alkyl group, a sulfone group or the like is also desirable. In addition, the distyrylpyrazine derivatives exemplified as the material for the light emitting layer are also
It can be used as a material for the electron injection layer.

The electron injection layer can be formed by thinning the above compound by a known method such as a vacuum vapor deposition method, a spin coating method, a casting method and an LB method. The thickness of the electron injection layer is not particularly limited, but is usually 5 nm to 5 μm. This electron injection layer is
It may have a single-layer structure composed of one or more of the above-mentioned materials, or may have a multi-layer structure composed of a plurality of layers having the same composition or different compositions.

The material of the hole injection layer is p-type-S.
A hole injecting and transporting material composed of an inorganic compound such as i, p-type-SiC can also be used, and as a material for the electron injecting layer,
An electron injecting and transporting material made of an inorganic compound such as n-type-Si or n-type-SiC can also be used. Specific examples of the inorganic material for the hole injection layer and the inorganic material for the electron injection layer include the inorganic semiconductors disclosed in International Publication WO90 / 05998.

A light emitting layer, an anode, a hole injecting layer if necessary, and an electron injecting layer if necessary are formed by the materials and methods exemplified above, and a cathode is formed by the method described above. The organic EL device of the present invention which can be formed may have any structure as described above. The following will be described below on the substrate: anode / hole injection layer / light emitting layer /
An example of manufacturing an organic EL element having a structure in which negative electrodes are sequentially provided will be briefly described.

First, a thin film made of an anode material is formed on a suitable substrate by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably 10 to 200 nm, to prepare an anode. Next, a hole injection layer is provided on this anode. The hole injection layer can be formed by a method such as a vacuum deposition method, a spin coating method, a casting method, an LB method as described above, but a uniform film is easily obtained and pinholes are not easily generated. From the viewpoints of the above, it is preferable to form by the vacuum deposition method. When the hole injection layer is formed by a vacuum deposition method, the deposition conditions vary depending on the compound used (the material of the hole injection layer), the crystal structure or recombination structure of the target hole injection layer, etc. Deposition source temperature 50 to 450 ° C., vacuum degree 10 ⁻⁵ to 10 ⁻³ Pa, deposition rate 0.01 to 50 nm / sec, substrate temperature −50 to 30.
It is preferable to select appropriately in the range of 0 ° C. and the film thickness of 5 nm to 5 μm.

Next, after forming a light emitting layer, Zn and at least one second metal are vapor-deposited on the light emitting layer to form a negative electrode. As a result, the target organic EL device is obtained. The vapor deposition conditions in the case of forming a negative electrode by multi-source vapor deposition of Zn and at least one second metal together by a vacuum vapor deposition method vary depending on the type of the second metal used, etc.
Generally, the vapor deposition source temperature is 100 to 5000 ° C, and the degree of vacuum is 1 x 10
It is preferable to appropriately select ⁻² Pa or less, a deposition rate of 0.001 to 100 nm / sec, and a substrate temperature of −200 to 500 ° C. In the production of this organic EL element,
It is also possible to reverse the manufacturing order and manufacture on the substrate in the order of negative electrode / light emitting layer / hole injection layer / anode.

The power conversion efficiency of the organic EL element of the present invention obtained in this manner is as high as that of a conventional organic EL element because it is provided with a deposited film containing Zn and at least one second metal as a negative electrode. This is higher than the power conversion efficiency of the EL element. Moreover, the chemical stability of the negative electrode is also high. In addition,
When a direct current voltage is applied to the organic EL device of the present invention, light emission can be observed by applying a voltage of 5 to 40 V with the positive electrode having a positive polarity and the negative electrode having a negative polarity. Moreover, even if a voltage is applied with the opposite polarity, no current flows and no light emission occurs. Furthermore, when an AC voltage is applied, uniform light emission is observed only when the anode has a positive polarity and the negative electrode has a negative polarity.
The waveform of the alternating current applied may be arbitrary.

[0039]

EXAMPLES Examples of the present invention will be described below. Example 1 IT on a glass substrate having a size of 25 × 75 × 1.1 mm
A 100-nm thick O film (corresponding to the anode) was used as a transparent support substrate. The transparent support substrate is ultrasonically cleaned with isopropyl alcohol for 30 minutes, and then with pure water.
Wash for 30 minutes, and then again with isopropyl alcohol for 30 minutes.
Ultrasonic cleaning was performed for a minute. The transparent supporting substrate after cleaning was fixed to a substrate holder of a commercially available vacuum deposition apparatus [manufactured by Nippon Vacuum Technology Co., Ltd.], and N, N'-diphenyl-N, N'-bis- (3 -Methylphenyl)-
200 mg of (1,1′-biphenyl) -4,4′-diamine (hereinafter referred to as TPDA) was put, and tris- (8-quinolinol) aluminum (hereinafter referred to as Alq.) Was placed in another molybdenum resistance heating boat. 200m
Then, the inside of the vacuum chamber was depressurized to 1 × 10 ⁻⁴ Pa.

Next, the resistance heating boat containing TPDA is heated to 215 to 220 ° C. to deposit TPDA on the ITO film of the transparent support substrate at a vapor deposition rate of 0.1 to 0.3 nm / sec. A hole injection layer having a film thickness of 60 nm was formed. The substrate temperature at this time was room temperature. Without removing this from the vacuum chamber, Alq. The molybdenum resistance heating boat containing the above is heated to 315 ° C.
lq. Was deposited on the hole injection layer at a vapor deposition rate of 0.1 to 0.2 nm / sec to form a light emitting layer having a film thickness of 60 nm. The substrate temperature at this time was also room temperature.

After that, a negative electrode was formed by the following procedure.
First, 1 g of Zn was put in a resistance heating boat made of molybdenum, and 1 g of Ca as a second metal was put in another resistance heating boat made of molybdenum, and the inside of the vacuum chamber was set to 2 × 10 ⁻⁴ P.
The pressure was reduced to a. After depressurization, the molybdenum resistance heating boat containing Ca was heated to deposit Ca on the light emitting layer at a deposition rate of 3.2 nm / sec, and at the same time, the molybdenum resistance heating boat containing Zn was heated to 800 ° C. And then 3.2n
Zn is deposited on the light emitting layer at a deposition rate of m / sec to give Z.
A 150 nm-thick negative electrode made of a mixed metal of n and Ca was formed. By providing the ITO film (positive electrode), the hole injection layer, the light emitting layer, and the negative electrode on the glass substrate as described above, an organic EL device was obtained.

When the composition of the negative electrode in the thus obtained organic EL device was analyzed by X-ray photoelectron spectroscopy (XPS), the composition of Ca in the negative electrode was 25.
It was confirmed that the composition of Zn was 75 at.%. The composition ratio of Zn and Ca can be calculated by the following equation from the ratio of vapor deposition rates.

[Equation 1] It agreed with the value calculated by.

Further, the negative electrode of the obtained organic EL device was
When a direct current voltage (current density: 8.0 mA / cm ² ) of 5 V was applied with the positive electrode (ITO film) having a positive polarity, the uniform green emission of 190 cd / m ² was observed. As shown in Table 1, the power conversion efficiency at this time is 1.
The efficiency was as high as 5 lm / W.

Example 2 An organic EL device was obtained in exactly the same manner as in Example 1 except that the vapor deposition rate of Ca was 0.8 nm / sec. When the composition of the negative electrode in the obtained organic EL device was analyzed in the same manner as in Example 1, the composition of Ca in the negative electrode was 8
It was confirmed that the composition of Zn was 92 at.%. The composition ratio was in agreement with the value calculated from the ratio of vapor deposition rates. Further, when a negative electrode of the obtained organic EL device was made to have a negative polarity and a positive electrode (ITO film) was made to have a positive polarity and a DC voltage of 5 V (current density: 6.0 mA / cm ² ) was applied, 180 cd was obtained. A uniform green emission of / m ² was observed. The power conversion efficiency at this time was as high as 1.9 lm / W as shown in Table 1.

Example 3 Ba was used as the second metal, and the deposition rate of Ba was set to 0.
Except for 8 nm / sec, the same procedure as in Example 1 was performed.
An organic EL device was obtained. When the composition of the negative electrode in the obtained organic EL device was analyzed in the same manner as in Example 1, the composition of Ba in this negative electrode was 5.5 at.
It was confirmed that the composition of n was 94.5 at.%. The composition ratio was in agreement with the value calculated from the ratio of vapor deposition rates. Further, when a negative electrode of the obtained organic EL device was made to have a negative polarity and a positive electrode (ITO film) was made to have a positive polarity and a DC voltage of 5 V (current density: 4.0 mA / cm ² ) was applied, it was 200 cd. A uniform green emission of / m ² was observed.
The power conversion efficiency at this time is 1.3 lm as shown in Table 1.
The efficiency was as high as / W.

Example 4 Yb was used as the second metal, and the deposition rate of Yb was 1 n.
An organic EL device was obtained in exactly the same manner as in Example 1 except that m / sec was set. When the composition of the negative electrode in the obtained organic EL device was analyzed in the same manner as in Example 1, it was confirmed that the composition of Yb in this negative electrode was 26 at.% And the composition of Zn was 74 at.%. Was done. The composition ratio was in agreement with the value calculated from the ratio of vapor deposition rates. Further, when the negative electrode of the obtained organic EL device was made to have a negative polarity and the positive electrode (ITO film) was made to have a positive polarity and a DC voltage of 5 V (current density: 4.9 mA / cm ² ) was applied, 180
A uniform green emission of cd / m ² was observed. The power conversion efficiency at this time was as high as 2.3 lm / W.

Example 5 An organic EL device was obtained in exactly the same manner as in Example 1 except that the deposition rate of Yb was 1 nm / sec and the deposition rate of Zn was 0.5 nm / sec. When the composition of the negative electrode in the obtained organic EL device was analyzed in the same manner as in Example 1, it was confirmed that the composition of Yb in this negative electrode was 58 at.% And the composition of Zn was 42 at.%. Was done.
The composition ratio was in agreement with the value calculated from the ratio of vapor deposition rates. Further, when a negative electrode of the obtained organic EL device was made to have a negative polarity and a positive electrode (ITO film) was made to have a positive polarity and a DC voltage of 5 V (current density: 8.0 mA / cm ² ) was applied, 260 cd was obtained. A uniform green emission of / m ² was observed.
The power conversion efficiency at this time was as high as 2.0 lm / W.

Example 6 Eu was used as the second metal, and the deposition rate of Eu was 1.
Except for 2 nm / sec, the same procedure as in Example 1 was performed.
An organic EL device was obtained. When the composition of the negative electrode in the obtained organic EL device was analyzed in the same manner as in Example 1, the composition of Eu in this negative electrode was 10.6 at.
It was confirmed that the composition of Zn was 89.4 at.%.
The composition ratio was in agreement with the value calculated from the ratio of vapor deposition rates. Further, when a negative electrode of the obtained organic EL device was made to have a negative polarity and a positive electrode (ITO film) was made to have a positive polarity and a DC voltage of 5 V (current density: 5.3 mA / cm ² ) was applied, 160 cd was obtained. A uniform green emission of / m ² was observed.
The power conversion efficiency at this time was as high as 1.9 lm / W.

Comparative Examples 1 to 15 The metals shown in Table 1 were used as the negative electrode materials, and the respective materials were listed in Table 1.
Organic EL devices were obtained in the same manner as in Example 1 except that the vapor deposition was performed at the vapor deposition rate shown in. For each organic EL device, the negative electrode was made to have a negative polarity, the positive electrode (ITO film) was made to have a positive polarity, and a DC voltage having a value shown in Table 1 was applied to observe light emission. Table 1 shows the current density, luminance, and power conversion efficiency of Kotoki.

[0050]

[Table 1]

As is clear from Table 1, the power conversion efficiencies of the organic EL elements obtained in Examples 1 to 6 were higher than those of any of the comparative organic EL elements.

[0052]

As described above, the organic EL device of the present invention
The power conversion efficiency of the device is high. Moreover, the chemical stability of the negative electrode is also high. Therefore, according to the present invention, it is possible to provide a new organic EL element including a negative electrode having high chemical stability and having improved power conversion efficiency.

Claims (1)

[Claims] 1. An organic EL device comprising a vapor deposition film containing Zn and an alkaline earth metal having a work function of 3 eV or less and / or a rare earth metal having a work function of 3 eV or less as a negative electrode.