JP2931229B2 - Organic electroluminescence 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 electroluminescence (hereinafter abbreviated as EL) device, and more particularly, to providing an organic light emitting layer and a light absorption / diffusion layer between a pair of electrodes, or a pair of electrodes. The present invention relates to an organic EL device in which one of them has a light absorbing and diffusing property to prevent reflection of external light and significantly improve contrast.

[0002]

2. Description of the Related Art An EL element utilizing electroluminescence is highly visible due to self-emission and is a completely solid state element.
Due to its characteristics such as excellent impact resistance, attention has been paid to its use as a light emitting element in various display devices. This EL element includes an inorganic EL element using an inorganic compound as a light-emitting material and an organic EL element using an organic compound. Among these, the organic EL element can greatly reduce the applied voltage. Practical research on the practical application of the device as a next-generation display device has been actively conducted. The organic EL element includes an organic compound layer including at least a light emitting layer and a pair of electrodes sandwiching the organic compound layer. Specifically, the organic EL element has a basic structure of anode / light emitting layer / cathode. And a hole injection layer or an electron injection layer appropriately provided thereon,
For example, those having a configuration of anode / hole injection layer / light-emitting layer / cathode and anode / hole injection layer / light-emitting layer / electron injection layer / cathode are known. The hole injection layer has a function of transmitting holes injected from the anode to the light emitting layer, and the electron injection layer has a function of transmitting electrons injected from the cathode to the light emitting layer. By interposing the hole injection layer between the light emitting layer and the anode, many holes were injected into the light emitting layer at a lower electric field, and further injected into the light emitting layer from the cathode or the electron injection layer. It is known that electrons accumulate at the interface between the hole injection layer and the light emitting layer because the hole injection layer does not transport the electrons, and the luminous efficiency increases.

In an organic EL device having such a structure, when a voltage is applied between a pair of electrodes, excitons are generated in a light emitting layer by recombination of electrons injected from a cathode and holes injected from an anode. This exciton emits light in the process of radiation deactivation. At least one of the pair of electrodes is translucent, and light is emitted outside through the transparent or translucent electrode. However, in the conventional organic EL element, as described above, by applying a voltage to an organic functional layer including an organic light emitting layer and an optional hole injection layer, an electron injection layer, and the like,
Since the light was emitted and the light was extracted from the transparent substrate side, there was a problem that the contrast was significantly reduced due to, for example, reflection of external light from a metal-based cathode. In addition, the inorganic EL element has a similar problem. In order to solve such a problem, for example, an organic EL device having a light absorption / diffusion layer outside an electrode has been proposed (Japanese Patent Application Laid-Open No. Hei 6-1994).
No. 5367). However, in this EL device, it is necessary to make the metal-based electrode thin so as to be translucent, and as a result, there is a problem that the injectability of charges from the electrode is inevitably reduced. On the other hand, an inorganic EL device having a light absorbing layer or a light absorbing electrode has been disclosed (International Patent Publication Nos. 94-14298 and 94-142).
No. 99), since this inorganic EL device has a structure in which a light emitting layer is sandwiched between insulating layers, the material disclosed therein is applied to a device such as an organic EL device which emits light by charge injection. Can not do it.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic EL device in which the drawbacks of the conventional organic EL device are improved, the reflection of external light is prevented, and the contrast is significantly improved. It is the purpose.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to develop an organic EL device with improved contrast. As a result, at least one of a pair of transparent or translucent electrodes is formed. Along with the organic light emitting layer, one provided with a charge injection light absorption / diffusion layer, or one of a pair of electrodes being transparent or translucent, and the other having light absorption / diffusion, can be suitable for the purpose. Was found. The present invention
It has been completed based on such knowledge. That is,
A first object of the present invention is to provide an organic EL device having an organic light emitting layer and a charge injection light absorption / diffusion layer sandwiched between a pair of electrodes, at least one of which is transparent or translucent. The second object is that in an organic EL device having an organic light emitting layer sandwiched between a pair of electrodes, one of the electrodes is transparent or translucent, and the other has light absorption and diffusion properties. An object of the present invention is to provide an organic EL device characterized by the following. The organic EL device according to the first invention has an organic light-emitting layer and a charge-injecting light-absorbing diffusion layer sandwiched between a pair of electrodes as essential constituent layers. In this device, at least one of the pair of electrodes needs to be transparent or translucent, and the organic EL device is usually formed by stacking electrodes and respective layers on a substrate made of glass or plastic. Therefore, when only the electrode in contact with the substrate is transparent or translucent, the substrate also needs to be transparent or translucent. The charge injection light absorption / diffusion layer,
It has both light absorption and diffusion properties and charge injection properties. Here, light absorption and diffusion properties refer to the action of absorbing or diffusing visible light, while charge injection properties refer to electrons or holes. Is received from the electrode or the charge injection layer and transferred to the charge injection layer or the light emitting layer in contact with the light absorption / diffusion layer.
In organic EL devices, holes from the anode are injected into the light-emitting layer through an optional hole injection layer, while electrons from the cathode are injected into the light-emitting layer through an optional electron injection layer. Here, since light emission is caused by the recombination of electrons and holes, the light absorption / diffusion layer provided between both electrodes also needs to have charge injection properties. That is, in the case where a light absorption / diffusion layer is provided between the cathode and the light emitting layer, the light absorption / diffusion layer needs to have at least an electron injecting property among the charge injecting properties. When a light absorption / diffusion layer is provided between the light-emitting layer and the light-emitting layer, the light absorption / diffusion layer needs to have at least the hole injection property among the charge injection properties.

The organic EL device of the first invention has various aspects. For example, (1) a conventional organic EL layer having an organic light-emitting layer as an essential constituent layer between a pair of electrodes; An organic EL element in which a charge-injecting light-absorbing diffusion layer is further provided between a pair of electrodes; and (2) an organic light-emitting layer, a hole-injecting layer, and / or an electron-injecting layer between the pair of electrodes Conventional organic EL sandwiching an organic functional layer including
In the device, a preferable embodiment is one in which the hole injection layer and / or the electron injection layer has a function of absorbing and diffusing light. Organic E in the above embodiment (1)
The configuration of the L element is not particularly limited as long as the organic light emitting layer and the charge injection light absorption / diffusion layer are sandwiched between the pair of electrodes as essential constituent layers. Preferred examples include those in which (a) an organic light emitting layer, (b) a hole injection layer and / or an electron injection layer, and (c) a charge injection light absorption / diffusion layer are sandwiched between electrodes. Specific examples of such a material are: anode / organic light emitting layer / cathode, anode / hole injection layer / organic light emitting layer / cathode, anode / organic light emitting layer / electron injection layer / cathode, anode / hole injection layer / organic Light emitting layer / electron injection layer / cathode,
And the like, in which a charge injection light absorption / diffusion layer is provided at an appropriate position between an anode and a cathode. These are usually laminated on a substrate made of glass or plastic, but there is no particular limitation on the lamination order on the substrate, and they may be laminated from the anode or from the cathode.

Among the organic EL devices having these configurations, particularly preferred are (a) anode / hole injection layer / light absorption / diffusion layer / organic light emitting layer / cathode, and (b) anode / hole injection layer /
Light absorption / diffusion layer / organic light emitting layer / electron injection layer / cathode, (c)
Anode / light absorption / diffusion layer / hole injection layer / organic light emitting layer / cathode,
(D) anode / light absorption / diffusion layer / hole injection layer / organic light emitting layer /
Electron injection layer / cathode, (e) anode / hole injection layer / organic light emitting layer / light absorption / diffusion layer / cathode, (f) anode / hole injection layer / organic light emission layer / electron injection layer / light absorption / diffusion layer / Cathode or (g) anode / hole injection layer / organic light emitting layer / light absorption / diffusion layer /
An electron injection layer / cathode configuration can be given.
In the organic EL device having the above-described device configuration, when the anode is a transparent or translucent electrode and the cathode is a metal-based electrode, the above configurations (e), (f), and (g) are advantageous. The reason is that in the configurations (e), (f), and (g), the light absorption / diffusion layer absorbs and scatters only external light, and the light emission of the organic EL element is directly observed from the transparent electrode. Conversely, when the cathode is transparent or translucent and light is extracted from the cathode side, the above configurations (a), (b), (c) or (d) are advantageous. Further, as described later, the hole injection layer and the electron injection layer may themselves be composed of a plurality of layers. Therefore, it may be inserted between the charge injection layers such as the anode / first hole injection layer / light absorption / diffusion layer / second hole injection layer. FIG. 1 is a cross-sectional view showing an example of a device configuration in which an anode is a transparent or translucent electrode and a cathode is a metal electrode in the organic EL device of the present invention. A transparent anode 2, a hole injection layer 3, an organic light emitting layer 4, a light absorption / diffusion layer 5, and a cathode 6 composed of a metal-based electrode are sequentially laminated.

Next, the organic EL device according to the above mode (2) is used.
The device has a hole injection layer and / or an electron injection layer provided with a function of light absorption and diffusion. The hole injection layer has both functions of hole injection and light absorption and diffusion. The injection layer has both functions of electron injection and light absorption and diffusion. There are various configurations of such an organic EL device. For example, (h) anode / light-absorbing / diffusing hole-injecting layer / organic light-emitting layer / cathode; Injection layer / organic light emitting layer / electron injection layer / cathode, (d) anode / organic light emitting layer / light absorbing / diffusing electron injection layer / cathode, (l) anode / hole injection layer / organic light emitting layer / light absorbing / diffusing property An electron injection layer / a cathode can be exemplified. When the anode is a transparent or translucent electrode and the cathode is a metal-based electrode in the organic EL device having the above-described device configuration, the above configurations (nu) and (lu) are advantageous for the same reason as described above. On the other hand, when the cathode is transparent or translucent and light is extracted from the cathode side, the above configurations (H) and (H) are advantageous. The light-absorbing and diffusing hole-injecting layer and the light-absorbing and diffusing electron-injecting layer can be manufactured by including a light-absorbing and diffusing substance in the hole-injecting layer and the electron-injecting layer.

In the organic EL device of the present invention, the substance having both functions of charge injection and light absorption / diffusion forming the charge injection / light absorption / diffusion layer is such that the light absorption / diffusion layer is more negative than the organic light emitting layer. In the case where it is provided on the side, for example, n-SiC or graphite, a metal oxide and a work function of 4.0 eV
A mixture of the following metals, a mixture of a metal oxide and an organic compound preferably used for an electron injection layer described below, and a mixture of a metal having a work function of 4.2 eV or less and an organic compound preferably used for an electron injection layer described below ( Specific examples thereof include a mixture of aluminum and tris (8-hydroxyquinoline) aluminum, and ultrafine metal particles having a work function of 4.0 eV or less (average particle diameter of about 100 μm or less). Furthermore, the general formula (I)

[0010]

Embedded image

Wherein R is an alkyl group, M is an alkali metal such as sodium or potassium, or an alkaline earth metal such as calcium, and n is a valence of M. (Which may contain water of crystallization), and a vacuum-deposited film of this compound is disclosed in JP-A-64-1784.
No. 9 absorbs visible light. These substances may be used in combination of two or more. Among the compounds having both functions of charge injection and light absorption and diffusion, a mixture of a metal oxide and an organic compound used for an electron injection layer and a metal having a work function of 4.2 eV or less and an electron injection layer are used. The mixture with the organic compound obtained can also be used for the formation of the light-absorbing and diffusive electron injection layer in the embodiment (2). On the other hand, when the light absorption / diffusion layer is provided on the anode side of the organic light emitting layer, the material having both functions of charge injection and light absorption / diffusion includes, for example, graphite, a metal oxide and a work function described below. A mixture of a metal having 0 eV or more, a mixture of a metal oxide and an organic compound preferably used for a hole injection layer described later, and a metal having a work function of 4.2 eV or more and an organic compound preferably used for a hole injection layer described later. , An ultrafine metal particle having a work function of 4.0 eV or more (average particle size of about 100 μm or less), or a compound having absorption to visible light such as polyacetylene.
These substances may be used in combination of two or more. Among the compounds having both functions of charge injection and light absorption / diffusion, a mixture of a metal oxide and an organic compound used for a hole injection layer and a metal having a work function of 4.2 eV or more and a hole injection layer The mixture with the organic compound used for (1) can also be used for forming the light-absorbing and diffusive hole injection layer in the mode (2).

The method of forming the light absorption / diffusion layer in the organic EL device of the present invention is not particularly limited, and can be appropriately selected from spin coating, casting, vapor deposition and the like depending on the substance to be used. Particularly, a vacuum deposition method is preferable. This is because it is easy to obtain a uniform film, and it is desirable that the organic light emitting layer, the hole injection layer, and the electron injection layer are formed by a vacuum deposition method as described later. This is because the film can be formed, the production time and labor can be saved, and the mixing of impurities can be prevented. In the case of employing this vacuum deposition method, the deposition conditions vary depending on the type of the substance used for the light absorption / diffusion layer.
500 ° C., degree of vacuum is 10 ⁻⁶ to 10 ⁻³ Pa, deposition rate is 0.
It can be appropriately selected within the range of 01 to 50 nm / sec and the substrate temperature of 50 to 300 ° C. On the other hand, in the case of inorganic substances such as metals, metal oxides, and graphite, the heating temperature is usually 500 to 4,
000 ° C. Among the inorganic substances, those having a high melting point such as graphite are preferably a sputtering method, an electron beam evaporation method, and an arc evaporation method which can form a film having a high melting point among the evaporation methods. There is no particular limitation on the film thickness of the light absorption / diffusion layer thus obtained.
A range of 100 μm is preferable, and a range of 10 nm to 1 μm is particularly preferable.

Next, in the organic EL device of the second invention, an organic light-emitting layer is sandwiched between a pair of electrodes as an essential constituent layer, and one of the electrodes is transparent or translucent, and the other is light-emitting. It is made of an absorbing and diffusing substance and is in contact with the organic functional layer. In order to make the electrode have light absorption and diffusion properties, for example, in the case of a cathode, a material having light absorption and diffusion properties and a work function of 4.0 e
The electrode may be made of a mixture with a metal of V or less. Here, as a metal having a work function of 4.0 eV or less, for example, C
a, Li, Yb, Na, Y, Gd, Ba, Cs, Sr,
Rare earth metals such as Mg, alkali metals, and alkaline earth metals are exemplified. Specific examples of such a cathode include a mixed electrode of graphite and Li and a mixed electrode of metal oxide and Ca. On the other hand, in the case of the anode, the electrode may be made of a mixture of a substance having a light absorption and diffusion property and a metal having a work function of 4.0 eV or more. Examples of the metal having a work function of 4.0 eV or more include Au, Ni, Ag, Pt, and C.
u and the like. Examples of the configuration of the organic EL device of the second invention include the same ones as exemplified above.

FIG. 2 shows an organic EL device of the present invention.
FIG. 2 is a cross-sectional view showing an example of a configuration in which a cathode has light absorption and diffusion properties, in which a transparent or translucent anode 2, a hole injection layer 3, an organic light emitting layer 4, and a light absorption and diffusion property are provided on a transparent substrate 1. Cathodes 6 'are sequentially stacked. Next, in the organic EL device of the present invention, each layer other than those described above will be described. First, the anode has a large work function (4e
V or more) Those using a metal, an alloy, an electrically conductive compound, a mixture thereof or the like as an electrode material are preferably used.
Specific examples of such an electrode material include metals such as Au, CuI, indium tin oxide (hereinafter abbreviated as ITO), and dielectric transparent materials such as SnO ₂ and ZnO. The anode can be produced by forming a thin film from these electrode substances by a method such as vapor deposition or sputtering. When light is extracted from this electrode, the transmittance is desirably greater than 10%, and the sheet resistance of the electrode is several hundred Ω / □.
The following is preferred. Further, although the film thickness depends on the material, it is usually 1
The range is preferably from 0 nm to 1 μm, particularly preferably from 10 to 200 nm.

On the other hand, as the cathode, those using a metal, an alloy, an electrically conductive compound, a mixture thereof or the like having a low work function (4 eV or less) as an electrode material are used. Specific examples of such an electrode material include sodium, sodium-potassium alloy, magnesium, lithium, magnesium-silver alloy, Al / AlO ₂ , indium, and rare earth metals. The cathode can be manufactured by forming a thin film of these electrode substances by a method such as evaporation or sputtering. Further, the sheet resistance as an electrode is preferably several hundreds Ω / □ or less, and the film thickness is usually 10 nm to 1 μm, particularly preferably 50 to 200 nm. In the organic EL device of the first invention, it is necessary that at least one of the anode and the cathode is transparent or translucent.
In the L element, one of the anode and the cathode needs to be transparent or translucent, and the rest need to have light absorption and diffusion as described above.

Further, the organic light emitting layer is (1) when an electric field is applied,
Holes can be injected by the anode or the hole injection layer,
In addition, an injection function capable of injecting electrons from the cathode or the electron injection layer, (2) a transport function of moving injected charges (electrons and holes) by the force of an electric field, and (3) a recombination of electrons and holes. A field is provided inside the light-emitting layer, and the light-emitting layer has a light-emitting function and the like for connecting this to light emission. There is no particular limitation on the type of light emitting material used for the light emitting layer, and a known organic light emitting material in an organic EL element can be used. Specific examples of such organic light-emitting materials include benzothiazole-based, benzimidazole-based, benzoxazole-based fluorescent whitening agents, metal-chelated oxinoid compounds, styrylbenzene-based compounds, distyrylpyrazine derivatives, and aromatic dimethylidene. And the like. The organic light-emitting layer may be formed of a mixture of the organic light-emitting material, a hole transport material, and / or an electron injection material, in addition to the organic light-emitting material alone. Specific examples of the material of the organic light emitting layer in this case include polymethyl methacrylate, bisphenol A, polycarbonate (P
C) or a polymer in which a small amount of an organic luminescent material such as coumarin is dispersed in a polymer such as C), a polymer in which a distyrylbenzene derivative is introduced into a polycarbonate skeleton, or a polyphenylene vinyl (PPV) derivative or a polyalkylthiophene Electron-injecting oxadiene in conjugated polymers such as (PAT) derivative systems, polyalkylfluorene (PAF) derivative systems, polyphenylene (PP) derivative systems, and polyarylene (PA) derivative systems, and in hole-transporting polyvinylcarbazole Examples include a system in which an azole derivative is dispersed.

Next, the hole injection layer is a layer made of a hole transporting compound, and has a function of transmitting holes injected from the anode to the light emitting layer. By interposing between the layers, more holes are injected into the light emitting layer at a lower electric field. In addition, electrons injected into the light emitting layer by the cathode or the electron injection layer are accumulated near the interface between the light emitting layer and the hole injection layer due to the electron barrier existing at the interface between the light emitting layer and the hole injection layer, and the luminous efficiency of the EL element is increased. And an EL device having excellent light emitting performance. There is no particular limitation on the hole transporting compound used in the hole injecting layer, and a conventionally known hole transporting compound in an organic EL device can be used. Specific examples of such a hole transport compound include a triazole derivative, an oxadiazole derivative, an imidazole derivative, a polyarylalkane derivative, a pyrazoline derivative, a pyrazolone derivative, a phenylenediamine derivative, an arylamine derivative, an amino-substituted chalcone derivative, and an oxazole derivative. , Styryl anthracene derivatives, fluorenone derivatives, hydrazone derivatives,
Specific conductive polymer oligomers such as stilbene derivatives, silazane derivatives, polysilane compounds, aniline polymers, and thiophene oligomers are exemplified.

Further, the electron injection layer has a function of transmitting electrons injected from the cathode to the organic light emitting layer. There is no particular limitation on the electron transfer compound used in the electron injection layer, and a known electron transfer compound in an organic EL device can be used. Specific examples of such an electron transfer compound include nitro-substituted fluorenone derivatives, anthraquinodimethane derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, heterocyclic tetracarboxylic anhydrides such as naphthaleneperylene, carbodiimide, and fluorenylidene. Methane derivatives, anthrone derivatives, oxadiazole derivatives, and metal complexes of 8-quinolinol or its derivatives, for example, tris (8
-Quinolinol) aluminum, bis (8-quinolinol) magnesium, bis (benzo-8-quinolinol)
Zinc, bis (2-methyl-8-quinolinolate) aluminum oxide, tris (8-quinolinol) indium, tris (5-methyl-8-quinolinol) aluminum, lithium 8-quinolinol, tris (5-chloro-8-quinolinol) Gallium, bis (5-chloro-8
-Quinolinol) calcium, tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7
-Dibromo-8-quinolinol) aluminum, bis (8-quinolinol) beryllium, bis (2-methyl-
8-quinolinol) beryllium, bis (8-quinolinol) zinc, bis (2-methyl-8-quinolinol) zinc, bis (8-quinolinol) tin, tris (7-propyl-8-quinolinol) aluminum, and the like. The organic light-emitting layer, the hole injection layer, and the electron injection layer may be composed of one or more layers of each material, or two or more layers of different materials laminated. It may be.

Next, a preferred method of fabricating the organic EL device of the present invention will be described with reference to a device having a constitution of anode / hole injection layer / organic light emitting layer / electron injection layer / light absorption / diffusion layer / cathode as an example. explain. First, on a suitable substrate, the desired electrode material,
For example, a thin film made of a material for an anode is formed by a method such as evaporation or sputtering so as to have a thickness of 1 μm or less, preferably in the range of 10 to 200 nm, to produce an anode. Next, a thin film made of a material for a hole injection layer, an organic light emitting layer, an electron injection layer, and a light absorption / diffusion layer, which are element materials, is sequentially formed thereon. Although the fabrication of the light absorption / diffusion layer has already been described, other fabrication methods of the thin film include a spin coating method, a casting method, and a vapor deposition method. However, a vacuum deposition method is preferable because a uniform film is easily obtained and a pinhole is hardly generated. In this thinning,
When this vapor deposition method is employed, the vapor deposition conditions vary depending on the type of the compound used, the target crystal structure of the molecular deposition film, the association structure, and the like.
500 ° C., degree of vacuum 10 ⁻⁶ to 10 ⁻³ Pa, deposition rate 0.01
~ 50nm / sec, substrate temperature -50 ~ 300 ° C, film thickness 5n
It is desirable to select an appropriate value in the range of m to 5 μm. After the formation of these layers, a thin film made of a material for a cathode is
m and preferably in the range of 50 to 200 nm, for example, by a method such as vapor deposition or sputtering, and providing a cathode to obtain a desired EL element. In the production of this EL device, the production order can be reversed, and the cathode, the light absorption / diffusion layer, the electron injection layer, the organic light emitting layer, the hole injection layer, and the anode can be produced in this order.

A method for fabricating an element comprising an anode / mixed layer / light absorption / diffusion layer / cathode sandwiching a hole injection layer, an organic light emitting layer, and an electron injection layer between a pair of electrodes in a mixed manner includes: For example, a thin film made of a material for an anode is formed on an appropriate substrate, and is made of a hole injection material, a light emitting material, an electron injection material, a binder such as polyvinyl carbazole, polycarbonate, polyarylate, polyester, polyether, and the like. There is a method in which a thin film is formed by applying a solution or a dip coating method from the solution to form a mixed layer, a light absorption / diffusion layer is formed thereon, and a thin film made of a cathode material is formed. When a DC voltage is applied to the organic EL device thus obtained, the anode is + and the cathode is-.
When a voltage of about 5 to 40 V is applied as a polarity, light emission can be observed. Also, even if a voltage is applied with the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the positive electrode becomes + and the negative electrode becomes-. The waveform of the applied alternating current may be arbitrary.

[0021]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 A transparent support substrate was formed by forming ITO electrodes to a thickness of 100 nm on a glass substrate having a size of 25 mm x 75 mm x 1.1 mm. This with isopropyl alcohol
After ultrasonic cleaning for 0 minutes, the substrate was washed with pure water for 30 minutes and finally again with isopropyl alcohol for 30 minutes. Next, this transparent support substrate was fixed to a substrate holder of a commercially available vacuum evaporation apparatus (manufactured by Nippon Vacuum Technology Co., Ltd.), and N, N'-diphenyl- was added to a molybdenum resistance heating boat.
N, N'-bis- (3-methylphenyl)-[1,1 '
-Biphenyl] -4,4'-diamine (TPD) 200
mg of tris (8-hydroxyquinoline) aluminum complex (Al) into another molybdenum resistance heating boat.
q) 200 mg was added. Further, graphite was set in an arc evaporation apparatus. After the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa, the boat containing TPD was heated to deposit TPD on the substrate to form a 60-nm-thick hole injection layer. Then, from another boat, Alq was deposited in a thickness of 60 nm as a light emitting layer by vapor deposition. Graphite was deposited thereon by an arc evaporation method to a thickness of 30 nm to provide a light-absorbing diffusion layer.

Next, this was taken out of the vacuum chamber, a stainless steel mask was placed on the light emitting layer, and fixed again to the substrate holder. 0.5 g of silver wire is put in a tungsten basket, and 1 g of magnesium ribbon is put in another molybdenum boat.
The pressure was reduced to 10 ^-4 Pa, and the atomic ratio of magnesium and silver was 1
A negative electrode was prepared by vapor deposition at 0: 1. The contrast of the device thus obtained was determined by the following method, and was found to be 80. <Method of Measuring Contrast> First, an element was placed on a predetermined table under a fluorescent lamp in a normal laboratory with the light-emitting surface facing upward, and an incandescent lamp (100 W) was placed at a distance of about 50 cm diagonally above the element. Was placed. Then, a 9 V voltage is applied to the element while the incandescent lamp is turned on, and the luminance when the element emits light and the luminance when no voltage is applied to the element are measured by a colorimeter (Minolta camera). CS-1
00), and the contrast was calculated from the equation: contrast = [brightness when voltage is applied (during light emission)] / [brightness when no voltage is applied (during no light emission)]. Note that the optical environment at the time of measuring the luminance simulates a typical optical environment when the organic EL element is actually used.

Example 2 An Alq layer was deposited in the same manner as in Example 1 except that no graphite layer was provided. Next, lithium was put into a molybdenum boat, graphite was set in an arc evaporator, the pressure was reduced to a degree of vacuum of 1 × 10 ⁻⁴ Pa, and lithium and graphite were co-deposited so that the atomic ratio became 1:99. A mixed electrode of graphite and graphite (negative electrode having a Li concentration of 1 atomic% and light absorption and diffusion) was provided on the Alq layer. When the contrast of the device thus obtained was determined in the same manner as in Example 1, it was 78.

Comparative Example 1 An organic EL device was prepared in the same manner as in Example 1 except that the light absorption / diffusion layer (graphite layer) was not provided, and the contrast was determined. The result was significantly lower than the devices obtained in Example 1 and Example 2.

[0025]

According to the organic EL device of the present invention, a light absorbing / diffusing layer is provided between a pair of electrodes together with an organic light emitting layer, or one of the pair of electrodes has a light absorbing / diffusing property. Thus, reflection of external light is prevented, and the contrast is significantly improved. The organic EL device of the present invention is suitably used as a light emitting device in various display devices.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an example of an organic EL device of the present invention.

FIG. 2 is a cross-sectional view illustrating the configuration of another example of the organic EL device of the present invention.

[Explanation of symbols]

 1: transparent substrate 2: transparent or translucent anode 3: hole injection layer 4: organic light emitting layer 5: light absorbing and diffusing layer 6: cathode 6 ': light absorbing and diffusing cathode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-211994 (JP, A) JP-A-6-151063 (JP, A) JP-A-1-298680 (JP, A) JP-A-6-106 5367 (JP, A) JP-A-8-8665 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 33/22 H05B 33/28

Claims (6)

(57) [Claims] 1. An organic electroluminescent device comprising an organic light emitting layer and a charge injection light absorption / diffusion layer sandwiched between a pair of transparent or translucent electrodes. 2. A method comprising: (a) an organic light emitting layer, (b) a hole injection layer and / or an electron injection layer, and (c) a charge injection light absorption / diffusion layer sandwiched between a pair of electrodes. Item 2. The organic electroluminescent device according to Item 1. 3. The device configuration is as follows: (a) anode / hole injection layer / light absorption / diffusion layer / organic light emitting layer /
Cathode, (b) anode / hole injection layer / light absorption / diffusion layer / organic light emitting layer /
(C) anode / light absorption / diffusion layer / hole injection layer / organic light emitting layer /
Cathode, (d) anode / light absorption / diffusion layer / hole injection layer / organic light emitting layer /
Electron injection layer / cathode, (e) anode / hole injection layer / organic light emitting layer / light absorption / diffusion layer /
Cathode, (f) anode / hole injection layer / organic light emitting layer / electron injection layer / light absorption / diffusion layer / cathode, or (g) anode / hole injection layer / organic light emission layer / light absorption / diffusion layer / electron injection layer 3. The organic electroluminescence device according to claim 2, wherein the organic electroluminescence device is a negative electrode. 4. An element structure in which an organic light emitting layer and a hole injection layer and / or an electron injection layer are sandwiched between a pair of electrodes, wherein the hole injection layer and / or the electron injection layer has a light absorbing / diffusing property. The organic electroluminescence device according to claim 1, comprising: 5. An organic electroluminescence device having an organic light-emitting layer sandwiched between a pair of electrodes, wherein one of the electrodes is transparent or translucent and the other is made of a light-absorbing and diffusing substance. An organic electroluminescent device, which is in contact with a layer . 6. An electrode comprising a light-absorbing and diffusive substance is an anode
In the case of containing a metal having a work function of 4.0 eV or more,
In the case of, contain a metal whose work function is 4.0 eV or less
The organic electroluminescent device according to claim 5, wherein
Sensing element.