JPH06243968A - Organic EL element - Google Patents

Abstract

(57) [Summary] [Object] To provide a new organic EL device having a cathode with high chemical stability and having improved power conversion efficiency. [Structure] An organic EL device comprising a vapor deposition film containing Bi and a metal having a work function of 4.2 eV or less as a cathode.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art An organic EL device is constructed by interposing at least a thin film (light emitting layer) of an organic light emitting body between a pair of electrodes facing each other. In this organic EL device, the electrons injected from the cathode directly into the light emitting layer via the electron injection layer and the holes injected from the anode directly into the light emitting layer via the hole injection layer are in the light emitting layer. Light is emitted by recombination at.

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 cathode material generally aims to improve the emission characteristics by increasing the efficiency of electron injection into the light emitting layer. 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 cathode materials.

For example, US Pat. Nos. 3,173,050 and 3,382,394 disclose organic EL devices using an alkali metal such as Na--K alloy for the cathode. There is. The organic EL devices disclosed in these specifications have high quantum efficiency (RCA Review vol.30,
P322) is preferable, 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 cathode by using a metal other than the alkali metal. For example,
In US Pat. No. 4,539,507, In is used for the cathode.
There is disclosed an organic EL device using the method described in Japanese Patent Laid-Open No. 3-2.
Japanese Patent No. 31970 discloses an organic EL element using a Mg-In alloy as a cathode. Also, European Patent No. 027
No. 8757 describes a cathode composed of a layer containing a plurality of metals other than alkali metals, and a layer having a work function of at least one of these metals of 4 eV or less (specifically, , Mg-Ag electrode, like Mg
And an Mg-based electrode composed of Ag, In, Sn, Sb, Te, or Mn).

Furthermore, Li, Na, Ca, which have a good electron injection property, are added to relatively stable metals such as Mg, Al, In and Sn.
Various organic EL elements in which a metal such as Sr is mixed at 11 at.% Or more to form a cathode have been announced at the forum for polymer discussion 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 cathode.

[0007]

As described above, various proposals have been made for forming a cathode using an electron-injecting metal, but these cathodes have low chemical stability over time,
The power conversion efficiency of the obtained organic EL element was still insufficient. Therefore, an object of the present invention is to provide a new organic E having a cathode with high chemical stability over time and having improved power conversion efficiency.
It is to provide an L element.

[0008]

The organic EL device of the present invention which achieves the above object is characterized in that a vapor deposition film containing Bi and a metal having a work function of 4.2 eV or less is provided as a cathode. .

The present invention will be described in detail below. As described above, the cathode in the organic EL device of the present invention is composed of a vapor deposition film containing Bi and a metal having a work function of 4.2 eV or less. Here, specific examples of the metal having a work function of 4.2 eV or less include In, Cd, Mn, Ti, Ta, Zr, La,
Examples thereof include Ca, Li, Ba, Na, Mg, Cd, K, Y and Yb. From the viewpoint of improving the electron injection property, a metal having a work function of 4.0 eV or less is particularly preferable, and specific examples thereof include La, Ca, Li, Ba, Na, and the like listed above.
Examples thereof include Mg, Gd, K, Y, Yb. The deposition method of the vapor deposition film containing Bi and the above-mentioned metal having a work function of 4.2 eV or less (hereinafter, this metal may be referred to as a second metal) is not particularly limited, but as a specific example, Is resistance heating evaporation method, electron beam evaporation method, high frequency induction heating method, molecular beam epitaxy method, hot wall evaporation method,
Ion plating method, cluster ion beam method,
Examples include a direct electrodeposition method of alloys and a multi-source simultaneous evaporation method using a method such as a two-electrode sputtering method, a two-electrode magnetron sputtering method, a three-electrode and four-electrode plasma sputtering method, an ion beam sputtering method. From the viewpoint of efficiently producing a cathode having a desired composition, it is particularly preferable to apply the multi-source simultaneous vapor deposition method.

The cathode formed as described above is made of Bi.
In addition to the above, at least one second metal may be contained, but the ratio of Bi in the cathode is 90 to 99.999 at.
% Is preferable. The reason is that the ratio of Bi is 9
This is because when it is 0 to 99.999 at.%, Bi serves as a base material of the cathode and the chemical stability of the cathode over time is improved.
A particularly preferable Bi ratio is 95 to 99.99 at.%.

The composition of the cathode can be controlled by appropriately setting the ratio of the vapor deposition rate of Bi and the vapor deposition rate of the second metal when the film is formed by the multi-source simultaneous vapor deposition method, for example. Preferred deposition rate is 2 nm / sec for Bi
Or more, especially 4 nm / sec or more, and in the case of the second metal,
It is 0.5 nm / sec or less, particularly 0.2 nm / sec or less. By making the vapor deposition rate of Bi higher than the vapor deposition rate of the second metal in this way, a vapor deposition film composed of a large proportion of Bi and a small proportion of the second metal can be obtained. By thus combining Bi and at least one kind of the second metal, a cathode having an excellent electron injecting property can be obtained. The film thickness of the cathode thus obtained is not particularly limited as long as there is conduction in the film, but is preferably 10 to 400 nm, and particularly preferably 15 to 300 nm.

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, the structure of the organic EL element is as follows: anode / light emitting layer / cathode, anode / hole injection layer / light emitting layer / cathode, anode /
Light emitting layer / electron injection layer / cathode, anode / hole injection layer / light emitting layer / electron injection layer / cathode, etc.
The L element may have any configuration. Further, when the organic EL device of the present invention is manufactured, the material other than the cathode 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 thereof 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 the like, 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. As typical examples thereof, 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 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., Volume 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. At the 38th Joint Lecture on Applied Physics), aldazine derivative (JP-A-2-220393), pyrazirine derivative (JP-A-2-220394), Cyclopentadiene derivative (JP-A-2-289675), 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 Appl. Phys. Lett., Vol 58, 18, P1982 (1991) and the like can also be used as a material for 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
-Phenylenedimethylidene, 4,4'-Phenylenedimethylidene, 2,5-Xylylenedimethylidene,
2,6-naphthylene dimethylidene, 1,4-biphenylene dimethylidene, 1,4-p-terephenylene dimethylidene, 9,10-anthracene diyldimethylidene, 4,4′-bis (2,2) 2-di-t-butylphenylvinyl) biphenyl (hereinafter abbreviated as DTBPVBi), 4,4′-bis (2,2-diphenylvinyl) biphenyl (hereinafter abbreviated as DPVBi), and the like, and derivatives thereof. Can be mentioned.

Examples of the method for forming a light emitting layer using the above materials include vapor deposition, spin coating, casting,
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 refers to 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, and usually this molecular deposition film. Can be distinguished from the thin film (molecular cumulative film) formed by the LB method based on the difference in agglomeration structure and higher-order structure, and the functional difference resulting therefrom. In addition, JP-A-57
As disclosed in JP-A-51781 and the like, a light emitting layer can also be obtained 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 cathode or the electron injection layer when an electric field is applied, and the injected charge ( It provides a transport function to move (electrons and holes) by the force of the electric field, a field for recombination of electrons and holes,
It has a light-emitting function that connects this to light emission. In addition,
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 or a mixture thereof having a large work function (4 eV or more) is preferably used. As a specific example,
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 hundred 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 hole injection materials for optical transmission materials and used for hole injection layers for organic EL devices are known. Any one can be selected and used from the things. The material of 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 derivative (US Pat. No. 3,189,44
No. 7, etc.), imidazole derivatives (Japanese Patent Publication No. 37)
-16096, etc.), polyarylalkane derivatives (U.S. 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-
17105, 56-4148, 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. No. 3,567,450).
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. No. 3,717,462, JP-A-54-59143, 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 (JP-A-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 for the hole injecting layer, the above 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 above 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.

Representative 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 TPD), 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) styryl] stilbene, 4-N, N-diphenylamino- (2-diphenylvinyl) benzene, 3-methoxy-4'-N, N-diphenylamino Stillebenzene,
Examples thereof include N-phenylcarbazole. Further, 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 injection layer can be formed by forming the above compound into a thin film 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 provided as required may have a function of transmitting the electrons injected from the cathode to the light-emitting layer, and its material may be any known compound. It 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 derivatives 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, and JP-A-61-114815.
9 and the like, fluorenylidene methane derivatives, JP-A-61-225151 and 61-23.
Anthraquinodimethane derivatives and anthrone derivatives disclosed in Japanese Patent No. 3750, Appl. Phys. Lett., 5
5,15,1489 and the oxadiazole derivative 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 electron-transporting compound is disclosed as a material for the light-emitting layer in Japanese Patent Laid-Open No. 194393, the inventors of the present invention have found that it can be used as a material for the electron-injecting layer.

Metal complexes of 8-quinolinol derivatives, 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 in which the terminal thereof is substituted with an alkyl group, a sulfone group or the like is also desirable. Further, 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 forming the above compound into a thin film 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 for 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 negative electrode is formed by the method described above. The organic EL device of the present invention that can be formed may have any structure as described above, but the following will be described below on the substrate: anode / hole injection layer / light-emitting layer /
An example of manufacturing an organic EL device having a structure in which a cathode is 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, and 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, a light emitting layer is provided on the hole injection layer. The light emitting layer can also be formed by thinning the organic light emitting material using a desired organic light emitting material by a method such as a vacuum deposition method, a spin coating method, or a casting method, but a uniform film is easily obtained, and It is preferable to form the pinball by the vacuum deposition method because it is difficult to generate the pinball.
When the light emitting layer is formed by the vacuum vapor deposition method, the vapor deposition conditions can be selected from the same range of conditions as those for the hole injection layer, although the vapor deposition conditions vary depending on the compound used.

Next, after forming the light emitting layer, Bi and at least one second metal are vapor-deposited simultaneously on the light emitting layer to form a cathode. As a result, the target organic EL device is obtained. The vapor deposition conditions for forming a cathode by simultaneous vapor deposition of Bi and at least one second metal together by a vacuum vapor deposition method vary depending on the type of the second metal used, but generally the vapor deposition source temperature is 100 to 5,000. ℃, vacuum degree 1
It is preferable to appropriately select in the range of × 10 ^-2 Pa or less and the substrate temperature of -200 to 500 ° C. As described above, the vapor deposition rate is such that Bi is 2 nm / sec or more, particularly 4 nm / sec or more, and the second metal is 0.5 nm / sec or less, particularly 0.2 nm.
/ Sec or less. The thickness of the cathode is 10-4 as described above.
It is preferably 00 nm, particularly preferably 150 to 300 nm. In the production of this organic EL element, it is also possible to reverse the production order and produce negative electrode / light emitting layer / hole injection layer / anode in this order on the substrate.

The thus-obtained organic EL device of the present invention provided with the deposited film containing Bi and at least one kind of second metal as a cathode has a power conversion efficiency higher than that of conventional organic EL devices. Organic E using Mg-based cathode which is considered to be high
The power conversion efficiency is equal to or higher than that of the L element.
Also, the chemical stability of the cathode over time is high. 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 anode having a positive polarity and the cathode 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 cathode 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 was ultrasonically cleaned with isopropyl alcohol for 5 minutes, then with pure water for 5 minutes, and finally again with isopropyl alcohol for 5 minutes. The transparent supporting substrate after cleaning was fixed to a substrate holder of a commercially available vacuum evaporation system [manufactured by Nippon Vacuum Technology Co., Ltd.], and N, N'-diphenyl-N, N'-bis- (3 -Methylphenyl)-(1,
1'-biphenyl) -4,4'-diamine (hereinafter TP
200 mg of D) and 200 g of 4,4'-bis (2,2-diphenylvinyl) biphenyl (hereinafter referred to as DPVBi) in another molybdenum resistance heating boat.
After adding mg, the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa.

Next, the resistance heating boat containing TPD is heated to 215 to 220 ° C. to deposit TPD on the ITO film of the transparent support substrate at a 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 taking this out of the vacuum chamber, the molybdenum resistance heating boat containing DPVBi was heated to 220 ° C.
VBi 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 thickness of 40 nm. The substrate temperature at this time was also room temperature.

As described above, the substrate on which the anode, the hole injection layer and the light emitting layer were sequentially formed was taken out from the vacuum chamber,
A stainless steel mask was placed on the light emitting layer and fixed again on the substrate holder. Next, 200 mg of tris (8-quinolinol) aluminum (Alq.) Was put into a resistance heating boat made of molybdenum and mounted in a vacuum chamber. Further, 8 g of Bi ingot was placed in an alumina-coated tungsten basket, and 1 g of Mg (work function 3.68 eV) ribbon was placed in another molybdenum boat.

After that, the inside of the vacuum chamber was 2 × 10 ⁻⁴ Pa.
Depressurize to Alq. 280 ℃ boat containing
To the Alq. Was evaporated at a deposition rate of 0.3 nm / sec for 20 nm to form an electron injection layer.

Next, Bi was co-evaporated at a vapor deposition rate of 9 nm / sec and Mg at a vapor deposition rate of 0.04 nm / sec to obtain a cathode made of a Bi-Mg vapor deposited film having a film thickness of 200 nm. In this way, an organic EL device was obtained by providing the anode, hole injection layer, light emitting layer, electron injection layer and cathode on the glass substrate.

The composition ratio of Bi and Mg of the cathode is calculated by the following equation from the ratio of vapor deposition rates.

[Equation 1] It was calculated by As a result, the composition of Bi was 99.3%, M
The composition of g was 0.7%.

When the cathode of the obtained organic EL device was made negative and the anode (ITO film) was made positive, a DC voltage of 7 V (current density: 2.6 mA / cm ² ) was applied. A uniform blue light emission of 45 cd / m ² was observed. The power conversion efficiency at this time is 0.78 as shown in Table 1.
The efficiency was as high as lm / W. When the state of the cathode after being left in air for 6 months was examined, there was no change as shown in Table 1 and it was excellent in chemical stability over time.

Example 2 Ca (work function 2.9) was used as the second metal, and this was deposited at a deposition rate of 0.2 nm / s, and Bi was deposited at a deposition rate of 8.8 nm / sec. An organic EL device was obtained in exactly the same manner as in Example 1. When the composition of the cathode in the obtained organic EL device was calculated, B in this negative electrode was calculated.
The composition of i is 98.1 at.%, and the composition of Ca is 1.9.
%Met. Further, when a cathode of the obtained organic EL device had a negative polarity and an anode (ITO film) had a positive polarity and a DC voltage of 7 V (current density: 2.2 mA / cm ² ) was applied, it was 50 cd / m 2. A uniform blue emission of ² was observed. The power conversion efficiency at this time is 1.00 as shown in Table 1.
The efficiency was as high as lm / W. Further, as shown in Table 1, the cathode was excellent in chemical stability over time.

Example 3 Li (work function 2.93) was used as the second metal, this was deposited at a deposition rate of 0.05 nm / s, and Bi was deposited at a deposition rate of 10 nm / sec. An organic EL device was obtained in exactly the same manner as in 1. When the composition of the cathode in the obtained organic EL device was calculated, B in this cathode was calculated.
The composition of i was 99.2 at.%, and the composition of Li was 0.8.
was at.%. In addition, 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.
When a DC voltage of V (current density: 5.0 mA / cm ² ) was applied, blue uniform light emission of 100 cd / m ² was observed. The power conversion efficiency at this time was as high as 0.90 lm / W as shown in Table 1. Further, as shown in Table 1, the cathode was excellent in chemical stability over time.

Example 4 Except for Example 1 except that Mg (work function 3.68) was used as the second metal, the vapor deposition rate of Mg was 0.2 nm / sec, and the vapor deposition rate of Bi was 5 nm / sec. Similarly,
An organic EL device was obtained. When the composition of the cathode in the obtained organic EL device was calculated, the composition of Bi in this cathode was 94.2 at.% And the composition of Mg was 5.8 at.%. Further, when a cathode of the obtained organic EL device had a negative polarity and an anode (ITO film) had a positive polarity and a DC voltage of 7 V (current density: 1.4 mA / cm ² ) was applied,
A uniform blue light emission of 22 cd / m ² was observed. The power conversion efficiency at this time is 0.71 lm / W as shown in Table 1.
And was highly efficient. Further, as shown in Table 1, the cathode was excellent in chemical stability over time.

Comparative Example 1 Example in which Au (work function 5.1) was used as the second metal, this was deposited at a deposition rate of 0.05 nm / s, and Bi was deposited at a deposition rate of 10 nm / sec. An organic EL device was obtained in exactly the same manner as in 1. When the composition of the cathode in the obtained organic EL device was calculated, Bi in this cathode was calculated.
Has a composition of 99.0 at.% And Au has a composition of 1.0a.
It was t.%. In addition, the cathode of the obtained organic EL element has a negative polarity, and the anode (ITO film) has a positive polarity of 13 V.
Then, a direct current voltage (current density: 7.0 mA / cm ² ) was applied to observe light emission. At this time, the power conversion efficiency was 0.017 lm / W, which was extremely low as shown in Table 1.

Comparative Example 2 Ni (work function 5.15) was used as the second metal, and this was deposited at a deposition rate of 0.04 nm / s and Bi was deposited at a deposition rate of 8.5 nm / sec. An organic EL device was obtained in exactly the same manner as in Example 1. When the composition of the cathode in the obtained organic EL device was calculated, the composition of Bi in this cathode was 98.5 at.% And the composition of Ni was 1.
It was 5 at.%. In addition, the cathode of the obtained organic EL device is set to a negative polarity, and the anode (ITO film) is set to a positive polarity.
Light emission was observed by applying a DC voltage of V (current density: 50 mA / cm ² ). At this time, the power conversion efficiency was 0.0046 lm / W, which was extremely low as shown in Table 1.

Comparative Example 3 An organic EL device was obtained in the same manner as in Example 1 except that the second metal was not used and only Bi was deposited at a deposition rate of 13 nm / sec. Light emission was observed by applying a DC voltage of 15 V (current density: 16 mA / cm ² ) with the cathode of the obtained organic EL device having a negative polarity and the anode (ITO film) having a positive polarity. The power conversion efficiency at this time is 0.0 as shown in Table 1.
It was extremely low at 1 lm / W.

Comparative Example 4 Example except that Mg was used in place of Bi, In was used as the second metal, and Mg deposition rate was 8 nm / sec and In deposition rate was 0.06 nm / sec. An organic EL device was obtained in the same manner as in 1. When the composition of the cathode in the obtained organic EL device was calculated, M in this cathode was calculated.
The composition of g is 99.3 at.%, and the composition of In is 0.7.
It was at.

Further, the cathode of the obtained organic EL device was made to have a negative polarity and the anode (ITO film) was made to have a positive polarity, and a DC voltage of 7 V (current density: 10 mA / cm ² ) was applied to observe light emission. did. The power conversion efficiency at this time was 0.45 lm / W as shown in Table 1. As shown in Table 1, this organic EL device was left in the air for 6 months, and the cathode became oxidized and became transparent. Therefore, it was confirmed that the cathode was inferior in chemical stability over time.

[0054]

[Table 1]

[0055]

As described above, the organic EL device of the present invention
The power conversion efficiency of the device is high. Also, the chemical stability of the cathode over time is 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 over time and having improved power conversion efficiency.

Claims (3)

[Claims] 1. An organic E comprising a vapor-deposited film containing Bi and a metal having a work function of 4.2 eV or less as a cathode.
L element. 2. The ratio of Bi in the cathode is 90 to 99.
The organic EL device according to claim 1, wherein the organic EL device is 999 at.%. 3. A vapor-deposited film constituting a cathode has Bi of 2 nm /
The organic EL device according to claim 1, which is obtained by performing multi-source simultaneous vapor deposition of a metal having a work function of 4.2 eV or less at a vapor deposition rate of sec or more at a vapor deposition rate of 0.5 nm / sec or less.