JP2000215984A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element capable of continuously and stably emitting light for hours with a high luminance. SOLUTION: This organic electroluminescent element 1 comprises an anode 6, a positive hole transport layer 5, a luminescent layer 4, an electron transport layer 3 and a cathode 2. The electron transport layer 3 contains an n-type inorganic compound semiconductor. Because an electron injection efficiency from the cathode 2 to the luminescent layer 4 can be improved, the organic electroluminescent element 1 has a high luminance and allows improvement of a long-time driving characteristic in time of light emission with a high luminance.

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 used for various display devices, a light source of the display device, a backlight, or a light emitting device used for an optical communication device.

[0002]

2. Description of the Related Art An electroluminescent device is a light emitting device utilizing the electroluminescence of a fixed phosphor substance also called an electroluminescent device or an EL device. At present, an inorganic electroluminescent device using an inorganic material as a luminescent material is practically used. Some applications have been developed for backlights of liquid crystal displays and flat panel displays.
However, an inorganic electroluminescent element requires a voltage of 10 to emit light.
0 V or higher, and it is difficult to emit blue light.
It was difficult to achieve full color by three primary colors.

On the other hand, research on organic electroluminescent devices using an organic material as a luminous body has been attracting attention for a long time, and various studies have been made. Did not reach.

However, in 1987, Kodak C.E.
W. Tang et al. Proposed an organic electroluminescence having a function-separated layered structure in which an organic material was divided into two layers, a hole transport layer and a light-emitting layer.
It was found that a high emission luminance of 000 cd / m ² or more was obtained. Since then, organic electroluminescent devices have begun to attract attention, and active research has been conducted.

As a result of such research and development, the organic electroluminescent device has a low voltage of about 10 V,
Surface emission with a high luminance of about 0000 cd / m ² was made possible, and emission from blue to red was made possible by selecting the type of fluorescent substance.

[0006]

However, the conventional organic electroluminescent device developed as described above has a problem that the light emission life at the time of high luminance light emission is short, and the storage durability and reliability are low. Was. The reason is that in the development of the organic electroluminescent device, a hole transporting material that can be applied to the hole transporting layer has been developed, which has an excellent hole injection efficiency from the anode to the light emitting layer. Even if an attempt was made to arrange an electron transport layer to improve the electron injection efficiency, there were few materials having excellent electron transport properties in the organic compounds, and the electron injection efficiency from the cathode to the light emitting layer was low. This hinders high brightness and low voltage driving, leading to deterioration of life characteristics.

The present invention has been made in view of the above points, and has as its object to provide an organic electroluminescent device capable of emitting light stably and continuously for a long time with high light emission luminance.

[0008]

An organic electroluminescent device 1 according to a first aspect of the present invention comprises an anode 6, a hole transport layer 5, a light emitting layer 4, an electron transport layer 3, and a cathode 2. The transport layer 3 is made of a material containing an n-type inorganic compound semiconductor.

The organic electroluminescent device 1 according to a second aspect of the present invention, in addition to the configuration of the first aspect, further comprises at least one of cadmium sulfide, zinc sulfide, and zinc oxide as the n-type inorganic compound semiconductor. It is characterized by using one of the following.

According to a third aspect of the present invention, there is provided an organic electroluminescent device according to the third aspect of the present invention, in addition to the first or the second aspect, wherein the electron transport layer is formed of only an n-type inorganic compound semiconductor. It is a feature.

According to a fourth aspect of the present invention, in the organic electroluminescent device 1 according to the first or second aspect, the electron transport layer 3 is made of an n-type inorganic compound semiconductor and another electron transport material. It is characterized by being constituted as a laminated structure or a mixed layer.

An organic electroluminescent device 1 according to a fifth aspect of the present invention has the structure according to any one of the first to fourth aspects,
It is characterized in that the content of the n-type inorganic compound semiconductor in the electron transport layer 3 is 0.5 to 500 nm in terms of film thickness.

According to a sixth aspect of the present invention, in the organic electroluminescent device 1 according to the first or second aspect, the electron transport layer 3 is formed by dispersing an n-type inorganic compound semiconductor in a polymer compound. Characterized by being formed as a dispersed layer.

According to a seventh aspect of the present invention, in the organic electroluminescent device 1 according to the sixth aspect, the content of the n-type inorganic compound semiconductor in the electron transport layer 3 is 15 to 70% by weight.
It is characterized by comprising.

[0015]

Embodiments of the present invention will be described below.

The organic electroluminescent device 1 according to the present invention is shown in FIG.
As shown in FIG. 1, the anode 6, the hole transport layer 5, the light emitting layer 4, the electron transport layer 3, and the cathode 2 are sequentially laminated. A positive voltage is applied to the anode 6, and a negative voltage is applied to the cathode 2. Is applied, the electrons injected into the light emitting layer 4 through the electron transport layer 3 and the holes injected into the light emitting layer 4 through the hole transport layer 5 recombine in the light emitting layer 4. Light emission occurs.

As the anode 6, which is an electrode for injecting holes into the device, it is preferable to use an electrode material made of a metal, an alloy, an electrically conductive compound or a mixture thereof having a large work function. Here, as these electrode materials, those having a work function of 4 eV or more are preferably used. Specific examples of such an electrode material include metals such as gold, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. The anode 6 is made of, for example, these electrode materials,
It can be manufactured by forming a thin film on the glass substrate 7 by a method such as a vacuum evaporation method or a sputtering method.

When the light emitted from the light emitting layer 4 is irradiated to the outside through the anode 6, the light transmittance of the anode 6 is preferably set to 10% or more. The sheet resistance of the anode 6 is preferably several hundred Ω / □ or less, particularly preferably 100 Ω / □ or less. The lower the sheet resistance is, the better, but the practical lower limit is 10 Ω / □ at present.

The thickness of the anode 6 depends on the material in order to control the light transmittance, sheet resistance and other characteristics of the anode 6 as described above.
Hereinafter, it is preferably in the range of 10 to 200 μm.

On the other hand, for the cathode 2, which is an electrode for injecting electrons into the device, it is preferable to use an electrode material made of a metal, an alloy, an electrically conductive compound or a mixture thereof having a small work function. Here, as these electrode materials, those having a work function of 5 eV or less are preferably used. Such electrode material, specifically, for example, sodium, sodium - potassium alloy, lithium, magnesium, aluminum, magnesium - silver mixture, a magnesium - indium mixture, an aluminum - lithium alloy, Al / Al ₂ O ₃ mixture, Al / LiF
Mixtures and the like can be mentioned. The cathode 2 can be produced, for example, by forming these electrode materials into a thin film by a method such as a vacuum evaporation method or a sputtering method.

When light emitted from the light emitting layer 4 is transmitted through the cathode 2 and radiated to the outside, the cathode 2 preferably has a light transmittance of 10% or more.

Here, the thickness of the cathode 2 varies depending on the material in order to control the characteristics such as the light transmittance of the cathode 2 as described above, but is usually 500 μm or less, preferably 10 to 200 μm. Range.

The light emitting material or doping material usable for the light emitting layer 4 includes anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline , Bisstyryl, cyclopentadiene, quinoline metal complex, aminoquinoline metal complex, benzoquinoline metal complex, pyran, quinacridone, rubrene, and fluorescent dye, but are not limited thereto. The light emitting layer 4 can be composed only of a light emitting material selected from these compounds. The light emitting material selected from these compounds is 90 to 9
It is also preferable to include 9.5 parts by weight and 0.5 to 10 parts by weight of the doping material. The thickness of the light-emitting layer 4 is equal to 0.1.
The thickness is 5 to 500 nm, more preferably 0.5 to 200 nm.

The hole transporting material constituting the hole transporting layer 5 has the ability to transport holes, has the effect of injecting holes from the anode 6, and is superior to the light emitting layer 4 or the light emitting material. Compounds that have a hole injection effect, prevent electrons generated in the light emitting layer 4 from moving to the hole transport layer 5, and have an excellent thin film forming ability. Specifically, phthalocyanine derivative, naphthalocyanine derivative, porphyrin derivative, oxazole, oxadiazole, triazole, imidazole, imidazolone, pyrazoline, tetrahydroimidazole, polyarylalkane, butadiene, benzidine triphenylamine, styrylamine triphenylamine And polymeric materials such as diamine-type triphenylamine and derivatives thereof, polyvinylcarbazole, polysilane, and conductive polymers, but are not limited thereto.

In particular, when the hole transport layer 5 is composed of an organic compound having a high glass transition temperature and hardly causing crystallization,
The organic electroluminescent device 1 having a long life and excellent heat resistance can be obtained.

For the purpose of reducing the hole injection barrier between the anode 6 and the hole transport layer 5, as a hole transport material, a phthalocyanine derivative or 4,4 ′, 4 ″ -tris (3-methylphenyl) is used. Phenylamino) triphenylamine (m
-MTDATA) or the like,
The effect of reducing the driving voltage is increased.

Further, when an electron accepting substance is added to the hole transporting material, the carrier density in the hole transporting layer 5 is increased, the hole transporting property is improved, and the light emission luminance can be improved.

In the present invention, the electron transporting layer 3 contains an n-type inorganic compound semiconductor. By doing so, the efficiency of electron injection from the cathode 2 to the light emitting layer 4 can be improved, and the organic electroluminescent element 1
In addition to achieving high luminance, it is possible to improve long-time drivability during high-luminance light emission. The n-type inorganic compound semiconductor is not particularly limited,
It is preferable to use cadmium sulfide, zinc sulfide, or zinc oxide, or a mixture of two or more of these. These compounds have a high electron affinity and a high electron transport ability, and can be easily formed into a film by a vacuum evaporation method, a sputtering method, or the like.

The electron transport layer 3 can be formed only of the above-mentioned n-type inorganic compound semiconductor.
In this case, the film thickness is preferably formed to be 0.5 to 500 nm. If the film thickness is less than 0.5 nm, the effect of improving the efficiency of electron injection from the cathode 2 to the light emitting layer 4 is small, and
If it exceeds 00 nm, problems such as an increase in applied voltage and a decrease in luminous efficiency may occur.

Further, the electron transport layer 3 can be made of an n-type inorganic compound semiconductor and another electron transport material.

Other electron transporting materials have the ability to transport electrons, have the effect of injecting electrons from the cathode 2, and have an excellent electron transporting effect on the light emitting layer 4 or the light emitting material. Compounds that prevent holes generated in the light emitting layer 4 from moving to the electron transporting layer 3 and have excellent thin film forming ability may be used. Specific examples include, but are not limited to, fluorene, anthraquinodimethane, diphenoquinone, oxazole, oxadiazole, triazole, imidazole, anthraquinodimethane, and derivatives thereof.

In the organic electroluminescent device 1 of the present invention, examples of other more effective electron transporting materials include a metal complex compound and a nitrogen-containing five-membered derivative. Specifically, as the metal complex compound, tris (8-hydroxyquinolinato) aluminum, tris (2-methyl-8-hydroxyquinolinato) aluminum, tris (8-hydroxyquinolinato) gallium, bis ( 10
-Hydroxybenzo [h] quinolinato) beryllium,
Bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8-quinolinato) (1-naphtholate) aluminum, and the like. However, the present invention is not limited to these. As the nitrogen-containing five-membered derivative, an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative is preferable, and specifically, 2,5-bis (1-phenyl) -1,3,4-oxazole, ,
5-bis (1-phenyl) -1,3,4-thiazole,
2,5-bis (1-phenyl) -1,3,4-oxadiazole, 2- (4′-tert-butylphenyl)-
5- (4 "-biphenyl) -1,3,4-oxadiazole, 2,5-bis (1-naphthyl) -1,3,4-oxadiazole, 1,4-bis [2- (5 -Phenylthiadiazolyl)] benzene, 2,5-bis (1-naphthyl) -1,3,4-triazole, 3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl ) -1,2,4-triazole and the like, but are not limited thereto.

It is also preferable to add an electron-donating substance to the above-mentioned other electron-transporting materials. In this case, the electron density in the electron-transporting layer 3 is improved, so that the electron-transporting property is improved. And the light emission luminance can be improved.

When the electron transporting layer 3 is composed of the n-type inorganic compound semiconductor and another electron transporting material as described above, the electron transporting layer 3 is composed of a layer made of the n-type inorganic compound semiconductor, It can be formed to have a laminated structure with a layer made of another electron transporting material, or it can be formed as a mixed layer formed by mixing an n-type inorganic compound semiconductor and another electron transporting material.

In the case where the electron transport layer 3 is formed in a laminated structure, a layer made of an n-type inorganic compound semiconductor and a layer made of another electron transport material are preferably connected to the cathode 2 side with a higher electron affinity. In this case, the efficiency of injecting electrons from the cathode 2 into the electron transport layer 3 can be improved, and the electron transportability can be improved.
At this time, the thickness of the layer made of the n-type inorganic compound semiconductor is 0.5 to 500 nm, and the thickness of the entire electron transport layer 3 is 0.5
It is preferable that the thickness be formed to about 800 nm. n
If the thickness of the layer made of the inorganic compound semiconductor of the type is less than 0.5 nm, the effect of improving the efficiency of electron injection from the cathode 2 to the light emitting layer 4 is small. There is a possibility that problems such as a decrease in efficiency may occur.

When the electron transport layer 3 is formed as a mixed layer, the amount of the n-type inorganic compound semiconductor contained in the mixed layer is preferably 0.5 to 500 nm in terms of film thickness. The total thickness of the mixed layer is 0.5 to 800 nm.
Is preferable. Here, the film thickness conversion means that the n-type inorganic compound semiconductor contained in the mixed layer forms a layer made of the n-type inorganic compound semiconductor in the electron transport layer 3 having a laminated structure. It is the amount converted to the thickness of the layer made of the inorganic compound semiconductor. n
If the compounding amount in terms of the film thickness of the layer made of the inorganic compound semiconductor of the type is less than 0.5 nm, the effect of improving the electron injection efficiency from the cathode 2 to the light emitting layer 4 is small. There is a possibility that problems such as an increase in light emission and a decrease in light emission efficiency may occur.

The electron transport layer 3 can be formed as a dispersion layer in which the above-mentioned n-type inorganic compound semiconductor is dispersed in a polymer compound. Polymer compounds that can be used at this time include polystyrene, polycarbonate, polyarylate, polyester, polyamide, polyurethane,
Insulating polymer compounds such as polysulfone, polymethyl methacrylate, polymethyl acrylate, and cellulose;
Examples thereof include photoconductive resins such as poly-N-vinylcarbazole and polysilane, and conductive polymers such as polythiophene and polypyrrole.

In forming the electron transport layer 3 as a dispersion layer, an n-type inorganic compound semiconductor is dispersed in a polymer compound, and then chloroform, 1,2-dichloroethane,
A dispersion can be prepared by adding an appropriate solvent such as tetrahydrofuran or dioxane, and can be formed by, for example, a wet film formation method such as a spin coating method or a dipping method.

The compounding amount of the n-type inorganic compound semiconductor in the electron transport layer 3 formed as the dispersion layer is 15 to 70
If the amount is less than 15% by weight, the electron transport performance from the cathode 2 to the light emitting layer 4 cannot be sufficiently obtained. It becomes too high and it is difficult to obtain a uniform thin film. The thickness of the electron transporting layer 3 formed as a dispersion layer is preferably 5 to 1000 nm, more preferably 5 to 500 nm.

In manufacturing the organic electroluminescent device 1 of the present invention using the above materials, for example, an anode 6 is formed on a glass substrate 7 by a sputtering method or a vacuum evaporation method, and then the hole transport is further performed. The layer 5 and the light emitting layer 4 are sequentially formed by a vacuum evaporation method, a sputtering method, or the like. When the electron transport layer 3 is formed as a single layer of an n-type inorganic compound, the electron transport layer is formed by a method such as a vacuum evaporation method or a sputtering method using an n-type inorganic compound semiconductor following the formation of the light-emitting layer 4. 3 is formed. When the electron transport layer 3 is formed in a laminated structure, one of the n-type inorganic compound semiconductor layer and the other electron transport material layer is formed following the formation of the light emitting layer 4 by a vacuum evaporation method or the like. After being formed by a sputtering method or the like, the other is formed by a vacuum evaporation method, a sputtering method, or the like. When the electron transport layer 3 is formed as a mixed layer, the n-type inorganic compound semiconductor and another electron transport material are simultaneously formed with the electron transport layer 3 by a vacuum evaporation method, a sputtering method, or the like, following the formation of the light emitting layer 4. Form.
After the formation of the electron transport layer 3, the cathode 2 can be formed by a method such as a vacuum evaporation method or a sputtering method. When the electron transporting layer 3 is formed as a single layer of an n-type inorganic compound semiconductor, or as a laminate or a mixture, a plurality of layers constituting the organic electroluminescent element 1 are formed by a vacuum evaporation method, a sputtering method, or the like. According to the method described above, they can be formed continuously in the same vacuum vessel or the like, and the production efficiency is good.

When the electron transport layer 3 is formed as a dispersion layer, the electron transport layer 3 is formed by a wet film forming method such as a spin coating method or a dipping method after forming the light emitting layer 4. After the formation of the electron transport layer 3, the cathode 2
Can be formed by a method such as a vacuum evaporation method or a sputtering method. Thus, the electron transport layer 3
Is formed as a dispersion layer, whereby the electron transport layer 3 containing an n-type inorganic compound semiconductor can be formed by a coating process such as a wet film formation method. In this case, the hole transporting layer 5, the light emitting layer 4, and the electron transporting layer 3 can all be formed by a wet film forming method such as a spin coating method or a dipping method.

After forming the anode 6, the hole transport layer 5, the light emitting layer 4, the electron transport layer 3, and the cathode 2 in this manner, in order to improve stability against temperature, humidity, atmosphere and the like, After coating and curing a resin composition prepared by compounding a filler such as silica gel powder with a silicone-based adhesive on the element surface and providing a protective layer, if necessary, a glass substrate It is also possible to protect the element by bonding together using a method such as, or by enclosing silicon oil or the like between the glass substrate and the element in a state where the glass substrate is disposed on the outer surface of the element.

The organic electroluminescent device 1 configured as described above can achieve high emission luminance, obtain a practically usable luminance at a low driving voltage, and deteriorate during long-term driving. Can also be significantly reduced. The organic electroluminescent device 1 according to the present invention is considered to be applied to a flat panel display such as a wall-mounted television, a light source such as a copying machine or a printer as a flat illuminant, a light source of a liquid crystal display or an instrument, a display board, a sign, and the like. It has a very high industrial value.

[0044]

Hereinafter, the present invention will be described in detail with reference to Examples.
The present invention is not limited to the following examples.

As a hole transport material, N, N'-bis (3-methylphenyl)-(1-1'-biphenyl)-
4,4′-diamine (hereinafter abbreviated as TPD) [manufactured by Tokyo Chemical Industry Co., Ltd.] and (8-hydroxyquinolinone) aluminum (hereinafter abbreviated as Alq3) as a luminescent material [(stock) ) Dojin Chemical Laboratory). In addition, as the electron transporting material, cadmium sulfide [manufactured by Kojundo Chemical Laboratory], zinc sulfide [manufactured by Kojundo Chemical Laboratory] as an n-type inorganic compound semiconductor having the composition shown in Table 1,
Zinc oxide [manufactured by Kojundo Chemical Laboratory Co., Ltd.] was used, and as other electron transporting materials, 3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -1,
2,4-triazole (hereinafter abbreviated as TAZ)
As a polymer compound, polycarbonate [manufactured by Teijin Chemicals Ltd., trade name Panlite K-1300] was used.

(Example 1) An ITO glass electrode (made by Matsunami Glass), in which ITO was vacuum-deposited on a glass substrate 7 having a thickness of 1 mm to form an anode 6 having a sheet resistance of 50 Ω / □, was washed with a neutral detergent and pure water. After ultrasonic cleaning with water, acetone and ethanol for 20 minutes, it was dried. This ITO glass electrode was fixed to a substrate holder of a commercially available vacuum evaporation apparatus [manufactured by TOKUDA]. On the other hand, three molybdenum resistance heating boats were prepared, TPD, Alq3, and 100 mg of cadmium sulfide, which is an n-type inorganic compound semiconductor, were placed in each boat, and the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁵ Torr. Then, the resistance heating board containing the TPD is heated first, and the resistance heating board is monitored with a quartz crystal film thickness meter.
The film was formed to a thickness of 50 nm at a deposition rate of 2 nm / s.
Subsequently, the resistance heating boat containing Alq3 was heated to form a film having a thickness of 50 nm under the same conditions. Further, the resistance heating boat containing cadmium sulfide was heated to form a film having a thickness of 5 nm under the same conditions. This was taken out of the vacuum chamber, provided with a stainless steel mask, and attached again to the substrate holder. On the other hand, 1 g of an Al—Li alloy having a Li content of 1% by weight was put in a tungsten filament, and the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁵ Torr. Then, the tungsten filament was heated, a film was formed at a deposition rate of 1 nm / s to a thickness of 150 nm, a cathode 2 was formed, and an organic electroluminescent device 1 was manufactured.

(Example 2) An organic electroluminescent device 1 was produced in the same manner as in Example 1 except that zinc sulfide was used instead of cadmium sulfide as the n-type inorganic compound semiconductor.

Example 3 An organic electroluminescent device 1 was produced in the same manner as in Example 1 except that zinc oxide was used instead of cadmium sulfide as an n-type inorganic compound semiconductor.

Example 4 The thickness of the electron transport layer 3 was set to 80 n.
An organic electroluminescent element 1 was produced in the same manner as in Example 1 except that the organic electroluminescent device 1 was formed in m.

(Example 5) Cadmium sulfide was used as an n-type inorganic compound semiconductor and TAZ was used as another electron transporting material. Each of them was placed on a molybdenum resistance heating board, and together with a hole transporting material and a luminescent material, Placed in a vacuum chamber. In forming the electron transport layer 3,
First, the resistance heating board containing TAZ is heated to form a layer made of TAZ to a thickness of 5 nm at a deposition rate of 0.2 nm / s by a vacuum deposition method, and then the resistance heating board containing cadmium sulfide is heated. Then, a layer made of cadmium sulfide was formed at a deposition rate of 0.2 nm / s to a thickness of 5 nm by vacuum deposition, thereby forming an electron transport layer 3 having a laminated structure. Other than that, it carried out similarly to Example 1 and produced the organic electroluminescent element 1.

(Example 6) Cadmium sulfide was used as an n-type inorganic compound semiconductor and TAZ was used as another electron transporting material. Each of these was placed on a molybdenum resistance heating board, and together with a hole transporting material and a luminescent material, Placed in a vacuum chamber. In forming the electron transport layer 3,
The resistance heating board containing cadmium sulfide and the heating board containing TAZ are simultaneously heated and vacuum-deposited simultaneously at a deposition rate of 0.2 nm / s, and the total film thickness is 10 nm, including cadmium sulfide 5 nm in terms of film thickness. The electron transport layer 3 of the mixed layer was formed. Otherwise, the procedure was the same as in Example 1,
Organic electroluminescent device 1 was produced.

(Example 7) The anode 6 up to the formation of the light emitting layer 4 was taken out of the vacuum chamber and fixed on a spin coater. On the other hand, cadmium sulfide, which is an n-type inorganic compound semiconductor, is dispersed in a polycarbonate (manufactured by Teijin Chemicals Ltd., trade name: Panlite K-1300) at a ratio of 20% by weight. ,
2-dispersed in dichloromethane, spin-coated on the surface of the light emitting layer 4 under the condition of 1500 rpm,
An electron transport layer 3 having a thickness of 70 nm was formed. Other than that, it carried out similarly to Example 1 and produced the organic electroluminescent element 1.

(Example 8) The anode 6 to which the light-emitting layer 4 was formed was taken out of the vacuum chamber and fixed on a spin coater. On the other hand, cadmium sulfide, which is an n-type inorganic compound semiconductor, is dispersed at a ratio of 50% by weight in a high-molecular compound polycarbonate [manufactured by Teijin Chemicals Ltd., trade name: Panlite K-1300]. ,
2-dispersed in dichloromethane, spin-coated on the surface of the light emitting layer 4 under the condition of 1500 rpm,
An electron transport layer 3 having a thickness of 80 nm was formed. Other than that, it carried out similarly to Example 1 and produced the organic electroluminescent element 1. (Comparative Example 1) The same procedure as in Example 1 was carried out except that the electron transport layer 3 was not formed and the light emitting layer 4 was also used as the electron transport layer 3.
Organic electroluminescent device 1 was produced.

(Evaluation Test) A positive voltage was applied to the ITO glass electrode as the anode 6 under the dry nitrogen atmosphere under the organic electroluminescent device 1 of each of Examples and Comparative Examples manufactured as described above.
A negative voltage was applied to the electrode made of an Al—Li alloy as the cathode 2, and the emission luminance of light emitted to the outside through the glass substrate 7 at an applied voltage of 8 V was measured.

The maximum luminance was measured when the voltage applied to the organic electroluminescent device 1 was continuously increased in a dry nitrogen atmosphere.

Further, a constant current is applied to the organic electroluminescent device 1 under a condition of a current density of 10 mA / cm ^{2 in} a dry nitrogen atmosphere, and the organic electroluminescent device 1 is continuously driven in a direct current at an initial luminance of 100 cd / m ² .
The time required for the emission luminance to decrease to 50% of the initial emission luminance (luminance half-life) was measured to evaluate the continuous driveability.

Here, the measurement of the luminance is performed by using a luminance meter [TOPCON
And product number BM-7].

Table 1 shows the above results.

[0059]

[Table 1]

As is clear from Table 1, in Examples 1 to 8, the emission luminance at 8 V was higher and the maximum luminance was higher than Comparative Example 1 in which the electron transport layer 3 containing the n-type inorganic compound semiconductor was not formed. Was also high, and it was confirmed that the continuous driving property was also high.

[0061]

As described above, the organic electroluminescent device according to the first aspect of the present invention comprises an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode. It uses an inorganic compound semiconductor that can improve the efficiency of electron injection from the cathode to the light-emitting layer, achieves high luminance of the organic electroluminescent device, and operates for a long time during high-luminance light emission. It is possible to improve the performance.

According to a second aspect of the present invention, there is provided the organic electroluminescent device according to the first aspect, wherein at least one of cadmium sulfide, zinc sulfide, and zinc oxide is used as the n-type inorganic compound semiconductor. These compounds have a high electron affinity and a high electron transport ability, so that the efficiency of electron injection from the cathode to the light emitting layer can be improved. Thus, it is possible to easily form a film.

According to a third aspect of the present invention, there is provided the organic electroluminescent device according to the first or second aspect, wherein the electron transporting layer comprises only an n-type inorganic compound semiconductor. The efficiency of electron injection from the cathode to the light-emitting layer can be improved by the electron transport layer composed of only the inorganic compound semiconductor of the above, and the high brightness of the organic electroluminescent element is achieved, Drivability can be improved.

According to a fourth aspect of the present invention, in the organic electroluminescent device according to the first or second aspect, in addition to the constitution of the first or second aspect, the electron transport layer has a laminated structure comprising an n-type inorganic compound semiconductor and another electron transport material. Or as a mixed layer, n
Injection efficiency from the cathode to the light-emitting layer can be improved by the electron transport layer composed of the inorganic compound semiconductor of the type and another electron transport layer, achieving high brightness of the organic electroluminescent device and high brightness. It is possible to improve long-time drivability during light emission.

According to a fifth aspect of the present invention, in the organic electroluminescent device according to the fifth aspect, in addition to any one of the first to fourth aspects, the content of the n-type inorganic compound semiconductor in the electron transport layer is calculated by converting the content into a film thickness. In this case, the effect of improving the efficiency of electron injection from the cathode into the light emitting layer and the effect of suppressing an increase in applied voltage and a decrease in light emitting efficiency can be obtained in a well-balanced manner.

According to a sixth aspect of the present invention, in the organic electroluminescent device according to the first or second aspect, the electron transport layer is formed by dispersing an n-type inorganic compound semiconductor in a polymer compound. The electron transport layer can be formed by a wet film formation method.

According to a seventh aspect of the present invention, there is provided the organic electroluminescent device according to the sixth aspect, wherein the content of the n-type inorganic compound semiconductor in the electron transport layer is 15 to 70% by weight. In addition to providing sufficient electron transport performance from the cathode to the light-emitting layer, and suppressing the viscosity of the dispersion during film formation from becoming too high, a uniform thin film is formed by a wet film formation method. Is what you can do.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing an example of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic electroluminescent element 2 Cathode 3 Electron transport layer 4 Light emitting layer 5 Hole transport layer 6 Anode

Claims (7)

[Claims] 1. An organic electric field comprising an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode, wherein the electron transport layer comprises an n-type inorganic compound semiconductor. Light emitting element. 2. The organic electroluminescent device according to claim 1, wherein at least one of cadmium sulfide, zinc sulfide, and zinc oxide is used as the n-type inorganic compound semiconductor. 3. The organic electroluminescent device according to claim 1, wherein the electron transporting layer is composed of only an n-type inorganic compound semiconductor. 4. The organic electroluminescence according to claim 1, wherein the electron transporting layer is formed as a laminated structure or a mixed layer comprising an n-type inorganic compound semiconductor and another electron transporting material. element. 5. The organic electroluminescence according to claim 1, wherein the content of the n-type inorganic compound semiconductor in the electron transport layer is 0.5 to 500 nm in terms of film thickness. element. 6. The organic electroluminescent device according to claim 1, wherein the electron transport layer is formed as a dispersion layer in which an n-type inorganic compound semiconductor is dispersed in a polymer compound. 7. The organic electroluminescent device according to claim 6, wherein the content of the n-type inorganic compound semiconductor in the electron transport layer is 15 to 70% by weight.