JP3279014B2 - Organic electroluminescent device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly to a thin film device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn, which is a group II-VI compound semiconductor of an inorganic material, is used.
In general, S, CaS, SrS, and the like are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, or the like) which is a luminescence center. However, EL devices manufactured from the above inorganic materials include: 1) AC drive is required (50-1000 Hz), 2) High drive voltage (up to 200 V), 3) It is difficult to achieve full color (especially blue), 4) Cost of peripheral drive circuit is high. ing.

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has been started. In particular, the electrode type was optimized for the purpose of improving the efficiency of carrier injection from the electrode in order to increase the luminous efficiency, and the organic luminescent layer composed of an organic hole transport layer composed of an aromatic diamine and the aluminum complex of 8-hydroxyquinoline was used. Of an organic electroluminescent device provided with a layer (Appl. Phy
s. Lett. , 51, 913, 1987)
As a result, the luminous efficiency is greatly improved as compared with a conventional electroluminescent device using a single crystal such as anthracene or the like, and practical characteristics are approached.

[0004] In addition to the above materials, poly (p-phenylenevinylene) (Natur
e, 347, 539, 1990; Appl. Ph
ys. Lett. 61, p. 2793 (1992)), poly [2-methoxy, 5- (2'-ethylhexoxy) -1,4-phenylenevinylene] (Appl. P.
hys. Lett. 58, 1982, 1991.
Year, Thin Solid Films, 216, 96
1992, Nature, 357, 477,
1992), poly (3-alkylthiophene)
(Jpn. J. Appl. Phys, 30, L193
8, 1991, J. Mol. Appl. Phys. , 72
Vol., P. 564, 1992) and a device in which a light emitting material and an electron transfer material are mixed with a polymer such as polyvinyl carbazole (Applied Physics, Vol. 61, 104).
4, 1992).

[0005]

The biggest problem of the organic electroluminescent device is the life during driving. Although there are several factors that shorten the life of the device, deterioration of the thin film shape of the organic layer is dominant. It is considered that the deterioration of the thin film shape is caused by crystallization (or aggregation) of the organic amorphous film due to heat generated during element driving. This low heat resistance results from the low glass transition temperature (Tg) and low melting point of the material.
Compounds of low molecular weight (molecular weight of about 400 to 600),
In particular, many hole transport materials have low melting points and low Tg. Representative aromatic diamine compounds that have been used as hole transport materials in organic electroluminescent devices have been described below.

[0006]

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[0007]

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Aromatic diamine (D1), N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'
-Biphenyl-4,4'-diamine (usually called TPD) has a melting point of 167 ° C and Tg of 60 ° C, and aromatic diamine (D2) has a melting point of 183 ° C and Tg of 78 ° C (J. Phys. Chem., 97, 6240,
1993). For other aromatic diamine compounds, -23 to 82 ° C (see U.S. Pat. No. 4,127,412) and 39 to 78 ° C (the 51st JSAP, 28a).
-PB-3, 1990). Generally, there is a correlation between the melting point and Tg, and a material having a high Tg has a high melting point, and most of the aromatic diamine compounds which have been reported so far have a melting point of 250 ° C. or less and a high Tg. Was not expected, and as a result, heat resistance could not be expected.

[0010] Many of the organic amorphous thin films formed from the compounds described above are accelerated in crystallization by a rise in temperature, and as a result, often exhibit an island-like aggregated structure. When such crystallization occurs, phenomena such as a decrease in luminous efficiency, the generation of a non-light-emitting portion called a dark spot, a short circuit, etc. appear as deterioration of the light-emitting characteristics of the device, and eventually lead to a reduction in drive life. Even when the element is not driven, the temperature is expected to rise in the steps of vapor deposition, baking (annealing), wiring, sealing, and the like during the production of the element. Therefore, the melting point may be 250 ° C. or more and the Tg may be 100 ° C. or more. desirable. For the purpose of increasing the melting point and Tg, studies have been made to make the molecular structure rigid, and the following aromatic diamine compounds (D3, D4) have been synthesized (The 65th Annual Meeting of the Chemical Society of Japan, 3C6). , 43, 1993).

[0010]

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[0011]

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The melting point of D3 is 283 ° C., and the melting point of D4 is 32
Although it is as high as 0 ° C., the ionization potential is 5.
It is 86 eV, 5.45 eV, which is higher than 5.15 eV of TPD (D1) which has been used so far, resulting in a higher driving voltage, which is not preferable as a hole transport material of an organic electroluminescent device. . On the other hand, attempts have been made to use a polymer material as an organic hole transport layer of an organic electroluminescent device instead of a low molecular weight compound. Polyvinylcarbazole (IEICE Technical Report, OME90
-38, 1990), polysilanes (Appl.
hys. Lett. 59, p. 2760, 1991), and polyphosphazene (see the 42nd Annual Meeting of the Society of Polymer Science, I-8-07 and I-8-08, 1993). Polyvinylcarbazole has a high Tg of 200 ° C., but has problems such as trapping and has low durability. Polysilane has a short driving life of several seconds due to photodegradation, and polyphosphazene has a high ionization potential and surpasses conventional aromatic diamines. Properties are not shown. In addition, a hole transport layer in which an aromatic diamine compound is dispersed in a polycarbonate or polymethyl methacrylate (PMMA) in an amount of 30 to 80% by weight has been studied (Jpn. J. Appl. Phys., Vol. 31, L96).
0, 1992), a low molecular compound acts as a plasticizer to lower Tg, and the device characteristics are also lower than those of aromatic diamine compounds.

For the reasons described above, the organic electroluminescent device has a serious problem in the driving life of the device for practical use.

[0014]

Means for Solving the Problems In view of the above situation, the present inventors have conducted intensive studies with the aim of providing an organic electroluminescent device exhibiting long-term stable light emitting characteristics. It has been found that it is preferable to use the aromatic diamine of the present invention, and the present invention has been completed.

That is, the gist of the present invention is an organic electroluminescent device including at least an organic hole transport layer and an organic light emitting layer sandwiched between an anode and a cathode on a substrate, wherein the organic hole transport layer comprises: An organic electroluminescent device comprising an aromatic diamine represented by the following general formula (I).

[0016]

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(Wherein R ^{1 to} R ¹⁶ are each independently
A hydrogen atom, a halogen atom, a hydroxyl group, a saturated or unsaturated aliphatic hydrocarbon group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, Represents an optionally substituted alkoxy group, an optionally substituted aryloxy group, an optionally substituted dialkylamino group, or an optionally substituted diarylamino group. Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an example of the structure of the organic electroluminescent device of the present invention, wherein 1 is a substrate, 2a and 2b are conductive layers, 3 is an organic hole transport layer, and 4 is an organic light emitting layer. Express.

The substrate 1 serves as a support for the organic electroluminescent device of the present invention, and may be a quartz or glass plate, a metal plate or a metal foil, a plastic film or a sheet, or the like. And a transparent synthetic resin substrate such as polymethacrylate, polycarbonate, and polysulfone. A conductive layer 2a is provided on the substrate 1. The conductive layer 2a is usually made of aluminum,
Metals such as gold, silver, nickel, palladium and tellurium, metal oxides such as oxides of indium and / or tin, copper iodide, carbon black, and conductive polymers such as poly (3-methylthiophene) It consists of. The formation of the conductive layer is usually performed by a sputtering method, a vacuum evaporation method, or the like, but metal fine particles such as silver or copper iodide, carbon black, conductive metal oxide fine particles, conductive polymer fine powder, etc. In the case of (1), it can also be formed by dispersing in an appropriate binder resin solution and applying it on a substrate. Further, in the case of a conductive polymer, a thin film can be formed directly on a substrate by electrolytic polymerization or can be formed by coating on a substrate (Appl. Phys. L).
ett. 60, 2711, 1992). The above conductive layers can be stacked with different materials.
The thickness of the conductive layer 2a varies depending on the required transparency. If transparency is required, the visible light transmittance is 6%.
It is desirable that the transmittance is 0% or more, preferably 80% or more. In this case, the thickness is usually about 5 to 1000 nm, preferably about 10 to 500 nm. If opaque, the conductive layer 2a may be the same as the substrate 1.

In the example shown in FIG. 1, the conductive layer 2a functions as an anode (anode) for injecting holes. on the other hand,
The conductive layer 2b serves as a cathode (cathode) to inject electrons into the organic light emitting layer 4. As the material used for the conductive layer 2b, the material for the conductive layer 2a can be used. However, for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium, indium, aluminum, A suitable metal such as silver or an alloy thereof is used. The thickness of the conductive layer 2b is usually the same as that of the conductive layer 2a. Although not shown in FIG. 1, a substrate similar to the substrate 1 can be further provided on the conductive layer 2b. However, it is necessary for the EL element that at least one of the conductive layers 2a and 2b has good transparency. For this reason, one of the conductive layers 2a and 2b preferably has a thickness of 10 to 500 nm, and is desired to have good transparency.

An organic hole transporting layer 3 is provided on the conductive layer 2a. The hole transporting material has a high melting point or a high Tg from the viewpoint of heat resistance.
It is necessary that the material has a high hole injection efficiency from a and can efficiently transport the injected holes. For that, the ionization potential is small,
In addition, it is required that the hole mobility is high, the stability is excellent, and impurities serving as traps are hardly generated during production or use. The organic electroluminescent device of the present invention is characterized by containing one or a mixture of two or more compounds selected from the compounds represented by the formula (I) as the organic hole transporting material.

In the general formula (I), preferably,
R ^{1 to} R ¹⁶ each independently represent a hydrogen atom; a halogen atom; a hydroxyl group; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an α-haloalkyl group; an alkenyl group such as a vinyl group; , An aromatic hydrocarbon group such as a biphenyl group; an alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; a methoxy group;
An alkoxy group having 1 to 6 carbon atoms such as an ethoxy group; an aryloxy group such as a phenoxy group and a benzyloxy group; a dialkylamino group such as a diethylamino group and a diisopropylamino group; a diarylamino group such as a dibenzylamino group and a diphenylamino group The saturated or unsaturated aliphatic hydrocarbon group, aromatic hydrocarbon group, alkoxy group, aryloxy group, dialkylamino group, and diarylamino group may have a substituent.

The compound represented by the general formula (I) is usually
It is synthesized by the following route. The following general formula (II)

[0023]

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An iodide of a biphenyl derivative represented by the following general formula (III)

[0025]

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The phenoxazine derivative represented by
mann reaction (Organic Synthesis,
1, p. 544) and produced by the following general formula (IV)

[0027]

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After separating the monosubstituted compound represented by the formula (I) with a column, the following general formula (V)

[0029]

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Ullmann reaction is carried out in the same manner as in the phenoxazine derivative represented by the formula (1) to obtain the desired aromatic diamine compound represented by the formula (I). The above synthesis example is a synthesis example of an asymmetric aromatic diamine. In the case of a symmetric aromatic diamine, a phenoxazine derivative (II
Only the reaction with (I) is required to proceed to the final disubstituted product. In the present invention, the melting point can be set to 250 ° C. or more and the ionization potential can be set to 5.3 eV or less by the molecular structure represented by the general formula (I).

Preferable specific examples of the aromatic diamine represented by the general formula (I) are shown in Tables 1 and 2, but are not limited thereto.

[0032]

[Table 1]

[0033]

[Table 2]

The organic hole transporting layer 3 of the general formula (I) is formed by laminating on the conductive layer 2a by a coating method or a vacuum evaporation method. In the case of the coating method, one or more of the above organic hole transporting compounds and a binder resin which does not trap holes as required, and an additive such as a coating property improving agent such as a leveling agent are added and dissolved. The solution is prepared, and the conductive layer 2 is formed by a method such as spin coating.
a, and dried to form an organic hole transport layer 3.
Examples of the binder resin include polycarbonate, polyarylate, and polyester. Since a large amount of the binder resin decreases the hole mobility, a small amount is desirable, and the amount is preferably 50% by weight or less.

In the case of the vacuum deposition method, the organic hole transporting material is put into a crucible provided in a vacuum vessel, and the inside of the vacuum vessel is evacuated to 10 ^-6 Torr by a suitable vacuum pump.
The crucible is heated to evaporate the hole transport material and form a layer on the substrate placed opposite the crucible. In the case of forming an organic hole transporting layer, a metal complex and / or a metal salt of an aromatic carboxylic acid is further used as an acceptor (Japanese Unexamined Patent Publication No.
No. 320484), benzophenone derivatives and thiobenzophenone derivatives (see Japanese Patent Application No. 4-106977) and fullerenes (see Japanese Patent Application No. 4-144479) at a concentration of 10 ^-3 to 10% by weight. By generating holes as free carriers, low-voltage driving can be performed.

The thickness of the organic hole transport layer 3 formed as described above is usually 10 to 300 nm, preferably 3 to 300 nm.
0-100 nm. An organic light emitting layer 4 is provided on the organic hole transporting layer 3, and the organic light emitting layer 4 efficiently transports electrons from the cathode toward the organic hole transporting layer between electrodes to which an electric field is applied. Formed from compounds that can The compound used for the organic light emitting layer 4 needs to be a compound having high electron injection efficiency from the conductive layer 2b and capable of efficiently transporting the injected electrons. For this purpose, it is required that the compound has a high electron affinity, a high electron mobility, a high stability, and an impurity which becomes a trap and hardly occurs during production or use. Further, a role of emitting light at the time of recombination of holes and electrons is also required. Furthermore, providing a uniform thin film shape is also important in terms of device stability.

As the material of the organic light emitting layer, aromatic compounds such as tetraphenylbutadiene (Japanese Patent Laid-Open No. 57-5178)
No. 1) and metal complexes such as aluminum complexes of 8-hydroxyquinoline (JP-A-59-194393, U.S. Pat. No. 5,151,629, U.S. Pat.
141, 671), cyclopentadiene derivatives (see JP-A-2-289675), perinone derivatives (see JP-A-2-289676), oxadiazole derivatives (see JP-A-2-216791),
Bisstyrylbenzene derivatives (JP-A 1-245087)
JP-A-2-222484), perylene derivatives (JP-A-2-189890, JP-A-3-21890).
No. 791), coumarin compounds (JP-A No. 2-19)
1694, JP-A-3-792), rare-earth complexes (see JP-A-1-256584), distyrylpyrazine derivatives (see JP-A-2-252793), and p-phenylene compounds (see JP-A-3-252793). No. 33183), thiadiazolopyridine derivatives (Japanese Unexamined Patent Publication No.
37292), pyrrolopyridine derivatives (see JP-A-3-37293), naphthyridine derivatives (see JP-A-3-203982) and the like. These compounds may be used alone, or may be used as a mixture as necessary.

The thickness of the organic light emitting layer 4 is usually 10 to 20.
0 nm, preferably 30-100 nm. For the purpose of improving the luminous efficiency of the device and changing the luminescent color, for example, doping a fluorescent dye for laser such as coumarin using 8-hydroxyquinoline aluminum complex as a host material (J. Appl. Phys., Vol. 65) , 36
10, 1989). Also in the present invention, the organic light emitting layer 4 is further doped with an organic phosphor such as a laser dye by 10 ⁻³ to 10 mol%,
The light emitting characteristics of the element can be further improved. Examples of the structure of the organic electroluminescent device of the present invention include those having the following layer configuration.

[0039]

TABLE 3 Anode / organic hole transport layer / organic light emitting layer / cathode Anode / organic hole transport layer / organic light emitting layer / electron transport layer / cathode anode / organic hole transport layer / organic light emitting layer / interface layer / cathode Anode / organic hole transport layer / organic light emitting layer / electron transport layer / interface layer / cathode In the above layer configuration, the electron transport layer is for further improving the efficiency of the device, and is laminated on the organic light emitting layer. Is done.
The compound used in the electron transport layer is required to be capable of easily injecting electrons from the cathode and having a higher electron transport ability. As such an electron transport material,

[0040]

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[0041]

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Oxadiazole derivatives such as (Appl.
Phys. Lett. 55, 1489, 1989.
Year; Jpn. J. Appl. Phys. , 31 volumes, 18
12, 1992) and a system in which they are dispersed in a resin such as PMMA (Appl. Phys. Lett., Vol. 61,
2793, 1992) or n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide and the like. The thickness of the electron transport layer is usually 5 to 200 nm,
Preferably it is 10 to 100 nm. Similarly, in the above-described layer structure, the interface layer is for improving the contact between the cathode and the organic layer, and is composed of an aromatic diamine compound (see Japanese Patent Application No. 5-48075) and a quinacridone compound (see Japanese Patent Application No. 5-58075). -116204), naphthacene derivatives (see Japanese Patent Application No. 5-116205), organic silicon compounds (see Japanese Patent Application No. 5-116206), and organic phosphorus compounds (see Japanese Patent Application No. 5-116207). . The thickness of the interface layer is usually 2 to 100 nm, preferably 5 to 30 n.
m. Instead of providing the interface layer, the above-mentioned interface layer material is added at 50 mol% in the vicinity of the cathode interface between the organic light emitting layer and the electron transport layer.
A region including the above may be provided.

In the present invention, by forming the organic hole transporting layer with a specific aromatic diamine, a device having heat resistance and exhibiting stable luminescence characteristics even for long-term driving can be obtained. In addition, it is also possible to stack the conductive layer 2b, the organic light emitting layer 4, the organic hole transporting layer 3, and the conductive layer 2a in this order on the substrate, that is, at least as described above. It is also possible to provide the organic electroluminescent device of the present invention between two substrates, one of which is highly transparent. Similarly, it is also possible to laminate in a structure opposite to the above-mentioned respective layer constitutions.

[0044]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist. Production Example of Aromatic Diamine (No. (1) in Table 1) 5.0 g of 4,4′-diiodobiphenyl, 4.97 g of phenoxazine, 2.51 g of potassium carbonate, and 0.1 g of copper iodide.
23 g was added to 50 ml of nitrobenzene,
The reaction was performed at 00 ° C. for 24 hours. The precipitated yellow reaction product was filtered, washed twice with demineralized water, and then washed with toluene.
After washing with acetone and drying, 2.53 g of a white powder was obtained. The yield was 40%. 1.0 g of this product
Was purified by sublimation and the melting point was measured. The molecular weight was 516 by mass spectrometry, and it was further confirmed by an IR spectrum and an NMR spectrum that the compound was an aromatic diamine represented by the following structural formula (1).

[0045]

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Example 1 A glass substrate was subjected to ultrasonic cleaning with acetone, water cleaning with pure water, ultrasonic cleaning with isopropyl alcohol, and drying with dry nitrogen. ×
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the pressure became 10 ⁻⁶ Torr or less. The aromatic diamine compound represented by the structural formula (1) placed in the ceramic crucible placed in the above apparatus was heated by a tantalum wire heater around the crucible to perform vapor deposition. At this time, the temperature of the crucible was controlled in the range of 160 to 170 ° C. The degree of vacuum at the time of vapor deposition was 2 × 10 ⁻⁶ Torr, and a thin film having a thickness of 110 nm was obtained in a vapor deposition time of 7 minutes. The ionization potential of this thin film sample was measured using an ultraviolet electron analyzer (AC-1) manufactured by Riken Keiki Co., Ltd., and showed a low value of 5.28 eV. Even when this thin film sample was stored in the air for 70 days, the shape of the film was stable and stable.

Comparative Example 1 A thin film was formed on a glass substrate in the same manner as in Example 1 except that an aromatic diamine (D3) was used as a deposition material. The thin film sample was crystallized after being stored in the air for 3 days, and the uniform thin film shape was lost.

Example 2 A laminated film of an organic hole transport layer and an organic light emitting layer was produced by the following method. Indium tin oxide (IT
O) A transparent conductive film deposited to a thickness of 120 nm was subjected to ultrasonic cleaning with acetone, water cleaning with pure water, ultrasonic cleaning with isopropyl alcohol, drying with dry nitrogen, and UV / ozone cleaning. An organic hole transport layer comprising an aromatic diamine compound represented by the structural formula (1) is
m. Further, as a material for the organic light emitting layer, 8-hydroxyquinoline complex of aluminum represented by the following structural formula; Al (C ₉ H ₆ NO) ₃ was evaporated from another ceramic crucible in the same manner as the organic hole transport layer. .

[0049]

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At this time, the temperature of the crucible was 290 to 310 ° C.
And the degree of vacuum at the time of vapor deposition is 2 × 10 ⁻⁶ Torr.
r, evaporation time was 3 minutes and 30 seconds. In this way,
An organic light emitting layer having a thickness of 75 nm was laminated on the organic hole transport layer. After the above-mentioned laminated film on the ITO glass substrate was vapor-deposited, the film was taken out of the vacuum vapor deposition apparatus and observed by an electron microscope (SEM) (20,000 times). As a result, the film was excellent in uniformity and free from defects. Put this laminated film in a vacuum electric furnace,
After heating at 83 ° C. for 1 hour at a degree of vacuum of 10 ⁻⁴ Torr, SEM observation was performed again, but there was no change in the uniform and defect-free film structure.

Comparative Example 2 An aromatic diamine (D1) was formed as a material for the organic hole transport layer to a thickness of 60 nm by a vacuum evaporation method, except that
In the same manner as in Example 2, a laminated film composed of an organic hole transport layer / organic light emitting layer was formed on an ITO glass substrate.

When the laminated film was observed by SEM (magnification: 20,000), void-like defects having a size of about 100 nm were observed at a density of 15 pieces per 84 μm ² .
The laminated film was formed in a vacuum electric furnace in the same manner as in Example 2.
When heated at 1 ° C. for 1 hour, the film became cloudy and violently agglomerated to such an extent that it was clearly visible.

Example 3 An organic electroluminescent device having the structure shown in FIG. 1 was produced by the following method. A transparent conductive film of indium tin oxide (ITO) 120 nm deposited on a glass substrate is subjected to ultrasonic cleaning with acetone, water cleaning with pure water, ultrasonic cleaning with isopropyl alcohol, drying with dry nitrogen, and UV / ozone cleaning. After that, the apparatus was set in a vacuum evaporation apparatus, and evacuated using an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less. After forming an organic hole transporting layer (thickness: 60 nm) comprising an aromatic diamine (1) in the same manner as in Example 2, the aluminum complex (E
An organic light emitting layer (thickness: 75 nm) composed of 1) was laminated.

Finally, as a cathode, an alloy electrode of magnesium and silver was deposited to a thickness of 150 nm by a binary simultaneous vapor deposition method. Vapor deposition was performed using a molybdenum boat and the degree of vacuum was 4
A glossy film was obtained at × 10 ⁻⁶ Torr and a deposition time of 4 minutes and 20 seconds. The atomic ratio of magnesium to silver is 10: 1.
It was 5. When a positive DC voltage is applied to the ITO electrode (anode) and a negative DC voltage is applied to the magnesium / silver alloy electrode (cathode) of the organic electroluminescent device thus manufactured,
This device exhibited uniform green light emission, and the peak wavelength of light emission was 530 nm. Table 3 shows the light emission characteristics of this device.

Comparative Example 3 An organic electroluminescent device was produced in the same manner as in Example 3, except that an aromatic diamine (D4) was used as the organic hole transporting layer. Table 3 shows the light emission characteristics of this device.

[0056]

[Table 4]

[0057]

According to the organic electroluminescent device of the present invention, since the organic hole transporting layer is made of a specific aromatic diamine, a device having a thermally stable thin film structure and exhibiting excellent light emitting characteristics can be obtained. Obtainable. Accordingly, the organic electroluminescent device according to the present invention can be used as a flat panel display (for example, for an OA computer or a wall-mounted television) or a light source utilizing the characteristics of a surface light emitter (for example, a light source of a copier, a backlight of a liquid crystal display or an instrument). It can be applied to light sources, display boards, and marker lights, and its technical value is great.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescent device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2a, 2b Conductive layer 3 Organic hole transport layer 4 Organic light emitting layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-90256 (JP, A) JP-A-6-312981 (JP, A) JP-A-6-220447 (JP, A) JP-A-2- 220396 (JP, A) JP-A-59-194393 (JP, A) JP-A-6-124784 (JP, A) JP-A-5-32625 (JP, A) JP-A-6-312982 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 33/22 C09K 11/06 G03G 5/06 CA (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. An organic electroluminescent device comprising at least an organic hole transport layer and an organic light emitting layer sandwiched between an anode and a cathode on a substrate, wherein the organic hole transport layer has the following general formula (I) An organic electroluminescent device comprising an aromatic diamine represented by the formula: Embedded image (Wherein, R ^{1 to} R ¹⁶ each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a saturated or unsaturated aliphatic hydrocarbon group which may have a substituent, or a substituent. An aromatic hydrocarbon group which may be substituted, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a dialkylamino group which may have a substituent or a substituent. Represents a diarylamino group which may be present.)