JPH053080A - Organic electroluminescence element - Google Patents

Abstract

PURPOSE:To improve the breakdown voltage property and to realize an even luminous property by inserting a metal oxide with an insulating property of 4.0eV or higher of energy gap between a luminous layer and a cathode. CONSTITUTION:By inserting a metallic oxide with the insulating property having the energy gap Eg 4.0eV or higher between a luminous layer and a cathode, the breakdown voltage property can be improved. In this case, the ionizing energy is also increased because of the wide energy gap, it functions as a hole barrier layer, and the luminous efficiency can be improved effectively. And the metallic oxide has a high breakdown voltage property as well as a good insulation, and the surface temperature when the membrane is produced can be suppressed at a low value. The voltage breakdown property is improved regardless of the position where the metal oxide is inserted, but the effect is larger when it is inserted between the luminous layer and the cathode, and furthermore, the attaching efficiency of the cathode and the luminous layer can be also improved. Consequently, an even luminous property is realized, the recombining property of the electrons and holes is improved, and a high efficiency of organic EL element can be obtained without dropping the luminous efficiency.

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, and more particularly to an organic electroluminescence device having excellent withstand voltage, good electrode adhesion, and high luminous efficiency.

[0002]

2. Description of the Related Art An organic electroluminescence device (hereinafter, referred to as an organic EL device) is composed of an organic luminescent material sandwiched between counter electrodes, and electrons are emitted from one of the electrodes. Then, holes are injected from the other electrode. Light emission occurs when the injected electrons and holes recombine in the light emitting layer. For example, a single crystal substance is used as a light emitting body in such an element, but the single crystal substance is expensive to manufacture and has many problems in terms of mechanical strength. Furthermore, it is not easy to reduce the thickness of the light emitter, and light emission is weak with a light emitter having a thickness of about 1 mm, and a drive voltage of 100 V or more may be required. Had not reached.

Then, for example, an attempt to obtain a film of anthracene having a thickness of 1 μm or less is carried out by a vapor deposition method (Thin Solid Film).
s, 94,171,1982) and the Langmuir-Blodgett method (L
Method B: Thin Solid Films, 99, 283, 1983). However, in order to obtain sufficient performance, it was necessary to form a thin film having a thickness of several thousand angstroms under strictly controlled film forming conditions. In addition, although the light-emitting layer is formed as a highly accurate thin film, since the probability of excitation of functional molecules due to movement or recombination of electrons or holes is low, efficient light emission cannot be obtained, and power consumption and brightness are particularly high. Is not satisfactory in terms of. Further, a hole injection layer is provided between the anode and the light emitting layer,
It is known that high luminous efficiency can be obtained by increasing the hole density (Japanese Patent Application Laid-Open No. 57-51781).
(See JP 59-194393 A). However, there is a problem that the device is broken when a high electric field is applied to obtain high brightness.

Further, as the insulating layer, an organic material layer (especially one formed by using an LB film) or an organic EL element in which SiO ₂ is used and inserted between the organic layer and the electrode is disclosed (Japanese Patent Laid-Open Publication No. 2000-242242). 61-37873, 61-3
No. 7882, No. 61-37883, No. 61-
(See Japanese Patent No. 37884). However, when the organic material is used as the insulating layer, the adhesiveness to the Mg electrode is poor, and there is a problem that the interface between the organic material and the Mg electrode is destroyed when the organic EL element is driven for a long time. Moreover, uniform light emission could not be obtained. When SiO ₂ is inserted between the organic layer and the electrode, it is necessary to use a relatively high energy method (high temperature, accelerated particles) such as sputtering or CVD (chemical vapor deposition method) as a film forming method. When this method is used, there is a problem that the performance of the organic substance is deteriorated by melting or crystallizing the organic substance used in the light emitting layer or the hole injecting layer which constitutes the organic EL element. In addition, there is a problem that sputtered particles attack an organic substance and change the interface to lose the injection characteristics of electrons and holes. Indeed, in the invention using SiO ₂ as the insulating layer, SiO ₂ is not deposited only on ITO. By the way, Kodak's Tang et al.
er, Volume 51, No. 12, P913. “Organic electroluminescent
In "diodes", by using an 8-hydroxyquinoline derivative, which is an electron-transporting compound, as the light-emitting layer and a diamine derivative as the hole-injecting layer, an organic EL device with a high electron and hole barrier property can be realized. Point out that it is important in. However, no satisfactory material has been found to achieve this. Further, for the purpose of preventing pinholes, it has been attempted to separate the functions of light emission and electron injecting substance, use a microcrystalline light emitting layer, and provide an electron injecting layer between the light emitting layer and the cathode (Japanease Jour.
nal of Applied Physics, 27,2, L269,1988 and 27,4, L71
3,1988), but the luminous efficiency is not improved. For the purpose of improving the light emission efficiency, a device in which a hole blocking layer having a larger ionization energy than that of the light emitting layer is provided instead of the electron injecting layer has also been studied (JP-A-2-195683). However, the hole barrier property is insufficient because only organic substances are used as the hole barrier layer. Further, there is also mentioned a technique of providing an electron injection layer or a hole blocking layer between the cathode and the light emitting layer in order to enhance the adhesion between the cathode and the light emitting layer for the purpose of uniform light emission (JP-A-2-195683). JP-A-2-255
788). However, there are problems in practical use such as the life of the device and fine processing. Therefore, the present inventors have conducted extensive studies to solve the above problems.

[0005]

As a result, the present inventors have found that an organic EL element having an insulating (4.0 eV or more) metal oxide layer inserted between a light emitting layer and a cathode has a high withstand voltage. To improve the adhesion of the metal used for the cathode to enable uniform light emission, and to further enhance the recombination of electrons and holes with the hole barrier property due to the effect of the wide energy gap (4.0 eV or more). It was found that the luminous efficiency is high without lowering the luminous efficiency. The present invention has been completed based on such findings.

That is, in the present invention, the energy gap (hereinafter referred to as Eg) between the light emitting layer and the cathode is 4.0.
Organic EL with insulating metal oxide of eV or more inserted
It provides an element.

As described above, the organic EL device of the present invention has an insulating metal oxide having an Eg of 4.0 eV or more inserted between the light emitting layer and the cathode. In order to improve the withstand voltage, this metal oxide may be inserted at any position in the usual device structure, and particularly when this metal oxide is inserted between the light emitting layer and the cathode, a wide Eg causes ionization. The energy also becomes large, and it acts as a hole blocking layer, so that the luminous efficiency can be effectively improved. Also, the adhesion between the cathode and the light emitting layer can be improved. By the way, as the insulating material, other than metal oxides, for example, organic materials,
Examples thereof include SiO ₂ . However, organic substances are inferior in withstand voltage as compared with metal oxides, and SiO ₂ is unsuitable as a constituent element of an organic EL device because the surface temperature rises when a thin film is formed. On the other hand, metal oxides have high withstand voltage and can suppress the surface temperature at the time of forming a thin film to a low level, and can be effectively used in the present invention. Here, the metal oxide used in the present invention has an Eg of 4.0 eV or more, preferably 4.5 eV or more. Eg is 4.0
When it is less than eV, it becomes a semiconductor, which is not preferable in terms of insulation properties, and has insufficient voltage resistance.

The metal oxide having an Eg of 4.0 eV or more used in the present invention includes, for example, MgO, BaO, CaO,
NiO etc. are mentioned. The application range of these metal oxides is limited as compared with semiconductors, and there are few examples in which Eg was measured in detail. E of the above metal oxide investigated by the present inventors
g is shown below. MgO: 4.5 eV or more (optical absorption spectrum was measured and the obtained results were extrapolated.) BaO: 4.2 eV or more (RHBube, "Photoconductivity
of Solids ".. P233, John Wiley & Sons, Inc. (1960)). CaO: 7.03 eV or more (Phys. Rev. P1380, 1969) NiO: 4.0 eV (American Institute of Physics Ha
ndbook (McGraw-Hill, 1972) 3rd.9-19)

The metal oxide in the organic EL device of the present invention can be prepared by using the above compound, for example, vacuum deposition method (resistance heating method, electron beam deposition method, high frequency induction heating method, reactive deposition method, molecular beam etapicy method, hot wall method). Vapor deposition method, ion plating method, cluster ion beam method, ion assisted vapor deposition method, etc., sputtering method (two pole sputtering method, two pole magnetron sputtering method, three pole and four pole plasma sputtering method, reactive sputtering method, ion beam sputtering) Law etc.),
CVD (thermal CVD, plasma CVD, laser CVD,
It can be formed by a known thinning method such as metal organic CVD (MOCVD). Among these, the electron beam vapor deposition method and the reactive vapor deposition method, which are less likely to adversely affect the organic substance of the base, are preferable.
The thickness of the metal oxide layer is not particularly limited, but is usually 1 nm to 500 nm, preferably 2 nm to 25 nm.
Is. If the film thickness is less than 1 nm, a uniform thin film cannot be obtained, and if it exceeds 500 nm, power consumption increases.

The film formation conditions for the metal oxide differ depending on the vapor deposition method and metal oxide used for film formation. For example, when MgO is used as the metal oxide and electron beam vapor deposition is used as the vapor deposition method, the degree of vacuum before vapor deposition in the vacuum chamber is 1 × 10 5.
^-2 Pa or less, preferably 6 × 10 ^-3 Pa or less, and a vapor deposition rate of 50 nm / sec or less, preferably 1 nm / sec or less, and electron beam (accelerated at about 4 kV) to MgO as a vapor deposition material.
And heat to 2600 ° C. or higher to blow off steam to form a film. The substrate temperature at this time is 200 ° C. or lower, preferably 100 ° C. or lower. Further, as the metal oxide, MgO,
When the reactive vapor deposition method is used as the vapor deposition method, the degree of vacuum in the vacuum chamber before vapor deposition is set to 1 × 10 ⁻² Pa or less, preferably 6 × 10 ⁻³ Pa or less, and oxygen and / or water vapor is contained in the vacuum chamber. To introduce. At that time, the pressure in the vacuum chamber is 7 × 10 ⁻³ Pa or more, preferably 1 × 10 ⁻²
After adjusting the pressure to Pa or higher, the metal Mg as the vapor deposition raw material is changed to 1000
C. or lower, preferably 800.degree. C. or lower, and the vapor deposition rate is 50 nm / sec or lower, preferably 1 nm / sec or lower. The substrate temperature at this time is 200 ° C. or lower, preferably 100 ° C.
It is below ℃.

The organic EL device of the present invention has the above Eg of 4.
It is characterized by inserting an insulating metal oxide of 0 eV or more between the light emitting layer and the cathode, and the configuration, shape, size, etc. of other elements are not limited as long as they function as an organic EL element.

There are various organic materials for the organic EL element used in the present invention. For example, the organic compound that can be used as the light emitting material is not particularly limited, but a brightening agent such as benzothiazole-based, benzimidazole-based, benzoxazole-based, a metal chelated oxinoid compound, a styrylbenzene-based compound, or the like can be used. Can be mentioned. Specific examples of the compound name include those described in JP-A-59-194393. A typical example thereof 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-
[4- (5-Methyl-2-benzoxazolyl) phenyl] vinyl] benzoxazolyl; 2- [2- (4
-Chlorophenyl) vinyl] naphtho [1,2-d] oxazole and other benzoxazoles, 2,2 '-(p
-Phenylenedivinylene) -benzothiazoles such as bisbenzothiazole, 2- [2- [4- (2-benzimidazolyl) phenyl] vinyl] benzimidazole; 2- [2- (4-carboxyphenyl) vinyl] benzimidazole Fluorescent brighteners such as benzimidazole-based. Still another useful compound is Chemistry of Synthetic Soybean 1971,
Listed on pages 628-637 and 640. As the metal chelated oxinoid compound, for example, those described in JP-A-63-295695 can be used. Typical examples are tris (8-quinolinol) aluminum; bis (8-quinolinol) Mg;
Bis (benzo [f] -8-quinolinol) zinc; Bis (2-methyl-8-quinolinolate) aluminum oxide; Tris (8-quinolinol) In; Tris (5-
Methyl-8-quinolinol) aluminum; 8-quinolinol lithium; tris (5-chloro-8-quinolinol) gallium; bis (5-chloro-8-quinolinol)
Calcium; 8-hydroxyquinoline-based metal complexes such as poly [zinc (II) -bis (8-hydroxy-5-quinolinonyl) methane] and dilithium epindridione.

As the styrylbenzene compound, those described in, for example, European Patent No. 0319881 and European Patent No. 0373582 can be used. Typical examples thereof are 1,4-bis (2-methylstyryl) benzene; 1,4- (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.

Further, the distyrylpyrazine derivative described in JP-A-2-252793 can be used as a light emitting material. A typical example is 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- (4-biphenyl) vinyl] pyrazine; 2,5-bis [2- (1-pyrenyl) vinyl] pyrazine and the like. As other substances, for example, the polyphenyl compounds described in European Patent No. 0387715 can also be used as the light emitting material.

In addition to the above compounds, for example, 12-
Phthaloperinone (J.Appl.Phys., Volume 27, L713
(1988)); 1,4-diphenyl-1,3-butadiene; 1,1,4,4-tetraphenyl-1,3-butadiene (Appl. Phys. Lett., Volume 56, L799 (1990).
Year)); naphthalimide derivative (Japanese Patent Laid-Open No. 30588/1993)
6); perylene derivative (JP-A-2-189890)
); Oxadiazole derivative (JP-A-2-216)
No. 791, and the oxadiazole derivative disclosed by Hamada et al. At the 38th Joint Federation of Applied Physics);
Aldazine derivative (JP-A-2-220393);
Pyrazillin derivative (JP-A-2-220394);
Cyclopentadiene derivative (JP-A-2-289675); Pyrrolopyrrole derivative (JP-A-2-29689)
No. 1); styrylamine derivatives (Appl.Phys.Lett.,
Volume 56, L799 (1990)) or coumarin-based compounds (Japanese Patent Laid-Open No. 2-191694) can be used. Further, as a light emitting material, Japanese Patent Application No. 2-24
The dimer compound shown by 8749 specification and Japanese Patent Application No. 2-279304 specification is also mentioned. Further, as the light emitting material, there are international patent WO90 / 13148 and Appl.P.
Polymer compounds such as those described in hys. Lett., vol 58, 18, P1982 (1991) are also preferable. In the present invention, an aromatic dimethylidyne compound (European Patent Application No.
Those described in the specification of No. 388768) are preferably used. As a specific example, 1,4-phenylene dimethylidene; 4,4'-phenylene dimethylidene; 2,5
-Xylylene dimethylidene; 2,6-naphthylene dimethylidene; 1,4-biphenylene dimethylidene;
1,4-p-Telephenylenedimethyridin; 9,10
-Acetracenediyl dimethylidin and the like and their derivatives.

As a method of forming a light emitting layer using the above light emitting material, for example, a vapor deposition method, a spin coating method, a casting method,
It can be formed by thinning it by a known method such as the LB method, but a molecular deposition film is particularly preferable. Here, the molecular deposition film is a thin film formed by depositing the compound from the gas phase state, or a film formed by solidifying from the solution state or liquid phase state of the compound, and usually this molecular deposition film. Can be distinguished from the thin film (molecular cumulative film) formed by the LB method by the difference in the aggregation structure, the higher order structure, and the functional difference caused by the difference. Further, the light emitting layer is prepared by dissolving a binder such as a resin and the compound in a solvent to form a solution, as disclosed in JP-A-57-51781, and then spin coating the solution. Can be formed into a thin film.
The thickness of the light emitting layer thus formed is not particularly limited and may be appropriately selected depending on the circumstances, but is usually preferably in the range of 5 nm to 5 μm.

The light emitting layer in the organic EL device of the present invention is
When an electric field is applied, holes can be injected from the anode or the hole injection layer, and electrons can be injected from the cathode or the electron injection layer, injected charges (electrons and holes)
It has a transport function of moving the electrons by the force of the 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 of injecting holes and the ease of injecting electrons. The transport function represented by the mobilities of holes and electrons may have different sizes, but it is preferable to move one of them.

As the anode in this organic EL device,
A material having a high work function (4 eV or more), an alloy, an electrically conductive compound, or a mixture thereof as an electrode material is preferably used. Specific examples of such electrode materials include metals such as Au and dielectric transparent materials such as CuI, ITO, SnO ₂ and ZnO. The anode can be prepared by forming a thin film of these electrode substances by a method such as vapor deposition or sputtering. When the emitted light is taken out from this electrode, it is desirable that the transmittance is higher than 10%, and the sheet resistance as an electrode is preferably several hundred Ω / □ or less. Further, the film thickness depends on the material, but is usually 10 nm to 1 μm, preferably 10 to 2
It is selected in the range of 00 nm.

On the other hand, as the cathode, a material having a low work function (4 eV or less), an alloy, an electrically conductive compound or a mixture thereof as an electrode material is used. Specific examples of such an electrode material include Na, Na-K alloy,
Examples include Mg, Li, a mixture of Mg / Cu, a mixture of Al / Al ₂ O ₃ and In. The cathode can be produced by forming a thin film of these electrode substances by a method such as vapor deposition or sputtering. The sheet resistance as an electrode is preferably several hundred Ω / □ or less, and the film thickness is usually 10 to 500 nm, preferably 50 to 200 n.
It is selected in the range of m. In this organic EL element, it is convenient that either the anode or the cathode is transparent or semi-transparent to allow the emitted light to pass therethrough, so that the emission efficiency of the emitted light is good.

In the present invention, the hole injecting layer and the electron injecting layer are not particularly necessary constituent elements of the organic EL element, and may or may not be used. Here, the compound that can be used as the hole injection material is not particularly limited, but any compound having the above-described preferable properties can be used, and conventionally, it is conventionally used as the hole injection material in the optical transmission material. Any known material used for the hole injection layer of the organic EL element can be selected and used. This hole injection material has either hole injection or electron barrier properties, and may be either an organic substance or an inorganic substance. Examples of the hole injection material include triazole derivatives (see US Pat. No. 3,112,197), oxadiazole derivatives (see US Pat. No. 3,189,447), imidazole derivatives (JP-B-37-16096). ), Polyarylalkane derivative (US Pat. Nos. 3,615,402, 3,820,989, and 3,54).
No. 2,544, Japanese Patent Publication No. 45-555, No. 51-
10983, JP-A-51-93224, JP-A-55-17105, JP-A-56-4148, JP-A-55-108667, JP-A-55-156953, and JP-A-56-36656). , Pyrazoline derivatives and pyrazolone derivatives (US Pat. Nos. 3,180,729 and 4,278,746, JP-A-55-88064).
No. 55-88065 and No. 49-1055.
37, 55-51086, 56-80.
No. 051, No. 56-88141, No. 57-4.
No. 5545, No. 54-112637, No. 55.
No. 74546, etc.), phenylenediamine derivatives (US Pat. No. 3,615,404, JP-B-51-10).
No. 105, No. 46-3712, No. 47-25.
336, JP-A-54-53435, 54
No. 110536, No. 54-119925, etc.), arylamine derivatives (US Pat. No. 3,567,450).
No. 3,180,703, No. 3,240,597, No. 3,658,520, No. 4,232,103, No.
4,175,961 specification, 4,012,376 specification, Japanese Patent Publication No. 4
9-35702, 39-27577, JP-A-55-144250, 56-119132.
No. 56-22437, West German Patent No. 1,110,
518 etc.), amino-substituted chalcone derivatives (see US Pat. No. 3,526,501 etc.), oxazole derivatives (described in US Pat. No. 3,257,203 etc.), styrylanthracene derivatives (JP-A-56- 46
234, etc.), fluorenone derivatives (Japanese Patent Application Laid-Open No. Sho 5
4-110837, etc.), hydrazone derivatives (US Pat. No. 3,717,462, JP-A-54-591).
43, 55-52063, 55-52.
064, 55-46760, 55-8.
No. 5495, No. 57-11350, No. 57-
148749, Japanese Patent Laid-Open No. 2-311591, etc.), Stilbene derivatives (Japanese Patent Laid-Open No. 61-210363)
No. 61-228451 and No. 61-146.
42, 61-72255, 62-47.
No. 646, No. 62-36674, No. 62-1
No. 0652, No. 62-30255, No. 60-
No. 93445, No. 60-94462, No. 60
-174749, 60-175052, etc.) and the like. Further, as a hole injecting and transporting material, a silazane derivative (US Pat.
950), polysilane type (JP-A-2-2049).
96), aniline-based copolymer (JP-A-2-282)
No. 263), and conductive polymer oligomers described in Japanese Patent Application No. 1-211399, particularly thiophene oligomers.

In the present invention, these compounds can be used as a hole injecting material, and the following porphyrin compounds (described in JP-A No. 63-295965) and aromatic tertiary compounds. Amine compounds and styrylamine compounds (US Pat. No. 4,127,412,
JP-A-53-27033, JP-A-54-58445, JP-A-54-149634, and JP-A-54-6429.
No. 9, gazette 55-79450, gazette 55-144.
No. 250, No. 56-119132, No. 61-
No. 295558, No. 61-98353, No. 6
3-295695, etc.), and it is particularly preferable to use the aromatic tertiary amine compound.

Representative examples of the porphyrin compound include:
Porphine; 1,10,15,20-tetraphenyl-
21H, 23H-porphine copper (II); 1,10,1
5,20-Tetraphenyl 21H, 23H-porphine cuprous (II); 5,10,15,20-Tetrakis (pentafluorophenyl) -21H, 23H-porphine;
Silicon phthalocyanine oxide; Aluminum phthalocyanine chloride; Phthalocyanine (no metal); Dilithium phthalocyanine; Copper tetramethylphthalocyanine;
Copper phthalocyanine; chromium phthalocyanine; zinc phthalocyanine; lead phthalocyanine; titanium phthalocyanine oxide; Mg phthalocyanine; copper octamethylphthalocyanine and the like. Further, as typical examples of the aromatic tertiary amine compound and the styrylamine compound, N, N, N ′, N′-tetraphenyl-4,4′-
Diaminophenyl; N, N'-diphenyl-N, N'-
Di (3-methylphenyl) -4,4'-diaminobiphenyl (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) styryl] stilbene; 4-N, N-diphenylamino- (2-diphenylvinyl) benzene; 3-methoxy-4'-N, N-diphenylaminostilbenzene; N-phenyl Examples include carbazole. Further, the above-mentioned aromatic dimethylidyne compounds shown as the light emitting material can also be used.

The hole injecting layer in the organic EL device of the present invention can be formed by forming the above compound into a film by a known thinning method such as a vacuum vapor deposition method, a spin coating method, a casting method and an LB method. it can. The thickness of the hole injection layer is not particularly limited, but is usually 5 nm to 5 μm.
This hole injection layer may be composed of a single layer made of one or more of these hole injection transport materials, or a hole injection layer made of a compound different from the hole injection layer is laminated. It may be one.

The compound usable as the electron injection material has a function of transmitting the electrons injected from the cathode to the light emitting layer. Such an electron injection material is not particularly limited, and any one of conventionally known compounds can be selected and used. For example, nitro-substituted fluorenone derivatives, JP-A-57-149259 and 58-58.
-55450, 63-104061 and the like, anthraquinodimethane derivative, Polymer Prep
rints, Japan Vol. 37, No. 3 (1988), p.681 etc., diphenylquinone derivative, thiopyran dioxide derivative, naphthalene perylene, etc. heterocyclic tetracarboxylic acid anhydride, carbodiimide, Japanease Journal of Appl
ied Physics, 27, L 269 (1988), JP-A-60-6965.
No. 7, No. 61-143764, No. 61-148159.
Fluorenylidene methane derivatives described in JP-A Nos. 61-225151 and 61-23375.
Anthraquinodimethane derivatives and anthrone derivatives described in Japanese Patent Publication No. 0, etc., Appl. Phys. Lett., 55, 15, 1
489 and the oxadiazole derivatives disclosed by Hamada et al. At the 38th Applied Physics Association Lecture, and the series of electron-transporting compounds described in JP-A-59-194393. In this publication, the substance is disclosed as a material for forming a light emitting layer, but as a result of studies, we found that it can be used as a material for forming the electron injection layer of the present invention.

The metal complexes of 8-quinolinol derivatives, specifically the following compounds, namely, tris (8-quinolinol) aluminum, tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,5). 7-
Dibromo-8-quinolinol) aluminum, tris (2-methyl-8-quinolinol) aluminum, and Mg, Cu, Ga, S other than aluminum and In.
There are n, Pb complexes and the like. Metal-free or metal phthalocyanine, or those whose terminal is substituted with an alkyl group, a sulfonic acid group or the like is also desirable. Further, the distyrylpyrazine derivative shown as the light emitting material can also be mentioned as the electron injecting material.

The organic compound usable as the electron injection layer can be formed by forming the above compound into a film by a known thin film forming 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.
The electron injection layer may be composed of a single layer made of one or more of these electron injection materials, or may be a stack of electron injection layers made of a compound different from the above layers. Good. Furthermore, p-type Si, p which is an inorganic substance
A hole injecting / transporting material of type-SiC and an electron injecting / transporting material of n-type-Si, n-type-SiC can be used as the electron injecting / transporting material. For example, International Publication WO9
Inorganic semiconductors and the like disclosed in 0/05998 are mentioned.

Next, a suitable example of producing an organic EL device by the method of the present invention will be described. The device structure of the present invention includes anode / light emitting layer / MgO layer / cathode, anode / hole injection layer / light emitting layer / MgO layer / cathode, anode / light emitting layer / electron injection layer / MgO layer / cathode, anode / light emitting. Layer / MgO layer / electron injection layer / cathode, anode / hole injection layer / light emitting layer / electron injection layer /
Examples include MgO layer / cathode, anode / hole injection layer / light emitting layer / MgO layer / electron injection layer / cathode, and here, for example, anode / hole injection layer / light emitting layer / MgO layer / cathode. A method for manufacturing the organic EL element will be described. Note that Mg
Other metal oxides instead of O, such as BaO, CaO, N
It is also possible to use iO or the like. First, 1 μm of a thin film made of a desired electrode material, for example, an anode material, on a suitable substrate.
The anode is formed by a method such as vapor deposition or sputtering so as to have a film thickness of m or less, preferably 10 to 200 nm. Next, a thin film made of a hole injecting and transporting material is formed on this to provide a hole injecting layer. As a method for thinning the hole injecting and transporting material, there are spin coating method, casting method, vapor deposition method and the like as described above, but it is easy to obtain a uniform film and it is difficult to generate pinholes. The vacuum deposition method is preferred. When this vapor deposition method is used for thinning the hole injection material, the vapor deposition conditions vary depending on the type of compound used, the target crystal structure of the molecular deposited film, the recombination structure, etc. 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 3
It is desirable to appropriately select in the range of 00 ° C. and the film thickness of 5 nm to 5 μm. Next, after forming the light emitting layer, the above-mentioned MgO layer is formed, and a thin film of the cathode material is formed on the MgO layer by 10 to 500
A desired organic EL device can be obtained by forming a film having a thickness of 50 to 200 nm, preferably by a method such as vapor deposition or sputtering, and providing a cathode. In the production of this organic EL element, the production order may be reversed, and the cathode, the MgO layer, the light emitting layer, the hole injection layer and the anode may be produced in this order. When a direct current voltage is applied to the organic EL device thus obtained, the positive electrode has a positive polarity and the negative electrode has a negative polarity.
When a voltage of about 40V is applied, light emission can be observed. 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 achieved only when the anode is in the + state and the cathode is in the − state. The waveform of the alternating current applied may be arbitrary.

[0028]

EXAMPLES Next, the present invention will be described in more detail by way of examples. Example 1 A transparent electrode substrate was prepared by forming an ITO electrode with a thickness of 100 nm on a white plate glass substrate having a size of 25 mm × 75 mm × 1.1 mm. This substrate was ultrasonically cleaned with isopropyl alcohol for 30 minutes, ultrasonically cleaned with pure water for 30 minutes, and further ultrasonically cleaned with isopropyl alcohol for 30 minutes. This transparent electrode substrate was fixed to a substrate holder of a commercially available vapor deposition device (manufactured by Nippon Vacuum Technology Co., Ltd.), and was placed in a resistance heating boat made of molybdenum, N, N'-diphenyl-N, N'-.
200 mg of bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPDA) was put into another molybdenum boat and 4,4 '-(2,4'-(2
200 mg of 2'-diphenylvinyl) biphenyl (DPVBi) was added, and the vacuum layer was depressurized to 1 x 10 ^-4 Pa. After that, the TPDA-containing boat is set to 215-22.
The film was heated to 0 ° C. and vapor-deposited on the transparent electrode substrate at a vapor deposition rate of 0.1 to 0.3 nm / sec to form a hole injection layer having a film thickness of 60 nm. The substrate temperature at this time was room temperature. Without taking this out from the vacuum layer, DPVBi as a light emitting layer was laminated and vapor-deposited by 60 nm on the hole injection layer from another boat. As for the vapor deposition conditions, the boat temperature is 250 ° C and the vapor deposition rate is 0.
The substrate temperature was room temperature, 1 to 0.2 nm / sec. Next, 1 g of Mg ribbon was put in a resistance heating boat made of molybdenum, and indium (I) was put in another resistance heating boat made of molybdenum.
n) 500 mg was attached. Then, the vacuum layer is 2 × 10.
^After decompressing to ^-4 Pa, ^add 8x1 oxygen gas into the vacuum chamber.
It was introduced so as to have a pressure of 0 ^-2 Pa, a boat containing Mg was heated to generate Mg vapor, and vapor was vapor-deposited on the light emitting layer at a vapor deposition rate of 0.05 nm / sec to form an oxide layer with a thickness of 10 nm. Filmed Further, the vacuum layer was decompressed to 2 × 10 ⁻⁴ Pa again, and then the boat containing In was heated to 500 ° C.
n is vapor-deposited at a vapor deposition rate of 0.03 to 0.08 nm / sec, and at the same time, the boat containing Mg is heated from the other boat to 800 ° C. by a resistance heating method to deposit Mg at a vapor deposition rate of 1.7.
Deposited at ~ 2.8 nm / sec. Under the above conditions, In and Mg
The mixed metal electrode of was laminated and vapor-deposited on the light emitting layer by 150 nm to form a counter electrode. The ITO of the obtained organic EL device is used as an anode and M
Using the g / In mixed electrode as a cathode, uniform blue light emission with a brightness of 3000 cd / m ² was observed at an applied voltage of 30 V and a current density of 300 mA / cm ² . Further, this organic EL device was destroyed by an applied voltage of 32.5V.

Example 2 An organic EL device was manufactured in the same manner as in Example 1 except that 2,5-bis- (2,2'-diparatolylvinyl) xylene was used for the light emitting layer and the MgO film thickness was 20 nm. It was created. Using ITO of this organic EL element as an anode and a Mg / In mixed electrode as a cathode, an applied voltage of 35 V and a current density of 360 mA / c
It was observed even blue-green light emission luminance of 1722cd / m ² in m ^2. Further, this organic EL element was destroyed by an applied voltage of 40V.

Example 3 Tris (8-quinolinol) aluminum (A
Organic E was prepared in the same manner as in Example 1 except that 1q ₃ ) was used.
An L element was created. ITO of this organic EL element is used as an anode,
Using the Mg / In mixed electrode as a cathode, uniform blue-green light emission with a luminance of 5000 cd / m ² was observed at an applied voltage of 30 V and a current density of 400 mA / cm ² . Further, this organic EL element was destroyed by an applied voltage of 35V.

Example 4 A light emitting layer was prepared in the same manner as in Example 1, and MgO pellets were attached to an electron beam vapor deposition device in the same vacuum chamber.
Electrons are applied to the MgO pellets at an acceleration voltage of kV to heat the surface, and vapor deposition is performed at a vapor deposition rate of 0.05 nm / sec.
nm oxide layer was formed. ITO of this organic EL element
As the anode and the Mg / In mixed electrode as the cathode, and the applied voltage 3
2000 cd / m at 0 V and current density of 300 mA / cm ^2.
A uniform blue emission with a brightness of ² was observed. Further, this organic EL element was destroyed by an applied voltage of 35V.

Example 5 An organic EL device was prepared in the same manner as in Example 1 except that barium (Ba) was used instead of Mg. That is, Mg
BaO was inserted instead of O between the cathode and the light emitting layer.
This BaO was obtained by heating a molybdenum boat at 800 ° C. and vapor-depositing it at a vapor deposition rate of 0.05 nm / sec. The film thickness was 10 nm. With the ITO of this organic EL element as an anode and the Mg / In mixed electrode as a cathode, an applied voltage of 30
V, at a current density of 250mA / cm ² 1200cd / m ²
A blue light emission with uniform brightness was observed. Also, this organic E
The L element was destroyed at an applied voltage of 32.5V.

Comparative Example 1 An organic EL device was prepared in the same manner as in Example 1 except that the MgO film was not provided. With the ITO of this organic EL element as an anode and the Mg / In mixed electrode as a cathode, an applied voltage of 12.
1500 cd / at 5 V and current density of 1500 mA / cm ^2.
Ring-shaped blue light emission with a brightness of m ² and a diameter of about 100 μm was observed. Moreover, this organic EL element was destroyed at an applied voltage of 15V.

Reference Example (Confirmation of MgO Film Formation) Oxygen was introduced into the vacuum chamber under the same conditions as in Example 1 to produce metallic Mg.
By resistance heating to evaporate and oxidize in the chamber.
(In order to avoid measurement confusion between the oxygen of MgO and the oxygen of the glass substrate, Au was deposited between the glass substrate and the oxide layer).
Inserted. ) A film having a thickness of 30 nm was formed by vapor deposition on a glass substrate. As a result of XPS (X-ray photoelectron spectroscopy) analysis of this film, it was confirmed that this film was MgO from the peak shift of Mg and the ratio of the amounts of Mg and oxygen in the film.

[0035]

As described above, according to the present invention, an organic EL element having an insulating (4.0 eV or more) metal oxide layer inserted between a light emitting layer and a cathode has improved withstand voltage. To improve the adhesion of the metal used for the cathode and enable uniform light emission,
Due to the effect of a wider energy gap (4.0 eV or more), it has a hole barrier property, enhances the recombination property of electrons and holes, and a highly efficient organic EL device can be obtained without lowering the light emission efficiency. Therefore, the present invention can be expected to be effectively used in the chemical industry, particularly in the field of display devices.

Claims (3)

[Claims] 1. An organic electroluminescence device comprising an insulating metal oxide having an energy gap of 4.0 eV or more inserted between a light emitting layer and a cathode. 2. The organic electroluminescence device according to claim 1, wherein the metal oxide is MgO. 3. The organic electroluminescent device according to claim 1, wherein the light emitting layer is an aromatic methylidin compound.