JPH10308284A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a low-resistant and high-transparent opposing electrode, and to form a transparent conductive film, through which moisture and oxygen are hard to intrude, so as to improve durability by forming a positive electrode of a positive hole filling electrode layer and a non-crystal transparent conductive film, and making the positive hole filling electrode layer contact with an organic layer interposed between a negative electrode and a positive electrode. SOLUTION: An organic layer 3, which contains an organic light emitting layer, is interposed between a negative electrode (lower electrode) 2 and a positive electrode as an opposing electrode formed on a glass board 1. The positive electrode as the opposing electrode is formed of a positive hole filling electrode layer 4 and a non-crystal transparent conductive film 5, and the positive filling electrode layer 4 is made to contact with the organic layer 3 so as to form an organic electroluminescent element. As a non-crystal transparent conductive film 5, In-Za-O base oxide film is desirably used. As a positive hole filling electrode layer 4, Pt, Ni, Pd, Os are sued, and film thickness is formed at about 1-20 nm. With this structure, an EL element is filled with electron from the negative electrode 2, and while the EL element is excellently charged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly durable organic electroluminescent device capable of extracting light from both sides of the device.

[0002]

2. Description of the Related Art Electroluminescent devices utilizing electroluminescence (hereinafter abbreviated as EL devices) have high visibility due to self-emission and are excellent in shock resistance because they are completely solid devices. Therefore, utilization as a light emitting element in various display devices has been attracting attention.

[0003] An 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 them, the organic EL element can easily be miniaturized because the applied voltage can be greatly reduced, and therefore, research on its practical use as a next-generation display element has been actively conducted. The configuration of the organic EL element is basically based on the configuration of a lower electrode / a light emitting layer / a counter electrode, and a configuration in which a lower electrode is provided on a substrate using a glass plate or the like is usually adopted. In this case, light emission is extracted to the substrate side.

In recent years, attempts have been made to make the opposing electrode transparent and extract light emission to the opposing electrode side for the following reasons. (A) If the lower electrode is made transparent, a transparent light emitting element can be obtained. (A) An arbitrary color can be adopted as the background color of the transparent light emitting element, and a colorful display can be obtained even when light is not emitted, so that decorativeness is improved. When black is used as the background color, the contrast at the time of light emission is improved.

(C) When a color filter or a color conversion layer is used, these can be placed on the light emitting element.
Therefore, the device can be manufactured without considering these layers. As an advantage, for example, the substrate temperature can be increased when the lower electrode is formed, thereby lowering the resistance value of the lower electrode. Since the above-mentioned advantages can be obtained by making the counter electrode transparent, attempts have been made to produce an organic EL device using a transparent counter electrode.

Japanese Patent Application Laid-Open No. 8-185988 discloses a transparent organic material provided with a lower electrode made of a transparent conductive layer and a counter electrode made of an ultra-thin electron injection metal layer and a transparent conductive layer formed thereon. An EL device is disclosed. The publication discloses that the materials constituting these transparent conductive layers include IT
O (indium tin oxide) and SnO ₂ are disclosed. However, they cannot reduce the crystallinity to such an extent that the X-ray diffraction peak disappears, and are essentially crystalline. For this reason, when laminating on a substrate via an organic layer, the substrate temperature should be between room temperature and 1 to prevent damage to the organic layer.
When vapor deposition is performed at a temperature close to 00 ° C., a transparent conductive layer having a high specific resistance is formed (in ITO, 1 × 10 ⁻³ Ω · c).
m or more). In such an organic EL element, a voltage drop occurs in the wiring line of the transparent conductive layer, and non-uniformity of light emission occurs. Therefore, improvement such as lowering a specific resistance value is required. Besides, ITO or SnO
_{Since 2} is crystalline in nature, moisture and oxygen easily penetrate from the crystal grain boundaries. For this reason, the adjacently injected electron injection metal layers are susceptible to deterioration, and as a result, a light emission defect occurs or light emission stops, and the durability is not sufficient, and further improvement is required. I have.

As another technique, there is a case where an oxide film as a transparent conductive layer is directly formed on an organic layer by sputtering to form a counter electrode. However, in this method,
There is a problem that the organic layer is damaged by oxygen plasma generated at the time of sputtering and good performance cannot be exhibited.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an organic EL device having a low-resistance and highly transparent counter electrode. Further, the present invention provides an organic EL element having an anode having a structure in which moisture and oxygen hardly penetrate from a transparent conductive film constituting a counter electrode, have excellent durability, and have a structure in which an organic layer is not damaged during formation of the transparent conductive film. It is in.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by adopting an amorphous transparent conductive film as a transparent conductive film constituting a counter electrode. It was found that the above-mentioned problems were solved.
The present invention has been completed based on such findings.

That is, the gist of the present invention is as follows. (1) An organic electroluminescence device in which an organic layer including an organic light emitting layer is interposed between a cathode serving as a lower electrode and an anode serving as an opposite electrode of the cathode, wherein the anode is a hole injection electrode layer And an amorphous transparent conductive film, wherein the hole injection electrode layer is in contact with the organic layer.

(2) The hole injecting electrode layer is selected from a hole injecting metal, alloy, conductive polymer and carbon.
The organic electroluminescent device according to the above (1), wherein the organic electroluminescent device is formed in an ultra-thin film using at least two kinds of species. (3) The hole injecting electrode layer is a mixed layer of one or more kinds of hole injecting metals, alloys, conductive polymers and carbon and a hole transporting organic material. The organic electroluminescence device according to the above (1).

(4) The organic electroluminescent device according to the above (1), wherein the hole injection electrode layer comprises an island-shaped hole injection region. (5) The above (1) to (4), wherein the amorphous transparent conductive film is formed using an oxide made of indium (In), zinc (Zn), and oxygen (O). The organic electroluminescent device according to any one of the above.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the organic EL device of the present invention, an organic layer including an organic light emitting layer is interposed between the lower electrode and the counter electrode, and the counter electrode is constituted by a hole injection electrode layer and an amorphous transparent conductive film. In addition, the hole injection electrode layer is in contact with the organic layer. This configuration can be schematically represented by, for example, FIG. Hereinafter, these configurations will be described.

<Amorphous Transparent Conductive Film> First, the amorphous transparent conductive film constituting the counter electrode in the organic EL device of the present invention will be described. The amorphous transparent conductive film used in the present invention may be any as long as it is amorphous and has transparency, but as described above, in order to eliminate the non-uniformity of the voltage drop and the light emission caused by the voltage drop, Specific resistance value is 5 × 10 ^-4 Ω · c
m or less.

The material is preferably an In-Zn-O-based oxide film. Here, the In-Zn-O-based oxide film is a transparent conductive film including an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements. Atomic ratio of In [In / (In + Z
n)] is preferably from 0.45 to 0.90. because,
If the content is outside this range, the conductivity may be low. The atomic ratio [In / (In + Zn)] of In is particularly preferably from 0.50 to 0.90 from the viewpoint of conductivity.
70-0.85 is more preferred.

The above-mentioned amorphous oxide may contain substantially only In and Zn as main cation elements, or may contain one or more third cations having a valence of at least trivalent.
It may contain an element. Specific examples of the third element include tin (Sn), aluminum (Al),
Examples thereof include antimony (Sb), gallium (Ga), germanium (Ge), and titanium (Ti). From the viewpoint of improving conductivity, a material containing Sn is particularly preferable. Also, the content of the third element is determined by the atomic ratio of the total amount [(all third elements) / [In + Zn + (all third elements)]].
Is preferably 0.2 or less. If the atomic ratio of the total amount of the third elements exceeds 0.2, the conductivity may decrease due to ion scattering. A particularly preferred atomic ratio of the total amount of the third element is 0.1 or less. Even if the composition is the same, the crystallized one is inferior in conductivity to the amorphous one. Therefore, it is necessary to use an amorphous transparent conductive film also from this point.

The above-mentioned amorphous oxide can be used as a transparent conductive film by forming it into a thin film. It is preferable that the film thickness at this time is approximately 3 to 3000 nm. because,
If the thickness is less than 3 nm, the conductivity tends to be insufficient, and 3000 n
When m exceeds m, the light transmittance is reduced, and cracks and the like are easily generated in the transparent conductive film when the organic EL element is intentionally or inevitably deformed during or after the manufacturing of the organic EL element. . The particularly preferred thickness of this transparent conductive film is 5 to 1000 nm, and the more preferred thickness is 1
0 to 800 nm.

In the organic EL device of the present invention, when a counter electrode is formed on a substrate via a lower electrode and an organic layer, an amorphous transparent conductive film (oxide film) is formed on the hole injection electrode layer.
Is formed. As a method of forming the amorphous transparent conductive film,
In addition to the sputtering method, a chemical vapor deposition method, a sol-gel method, an ion plating method, or the like can be employed. However, the sputtering method is preferred from the viewpoint of less thermal influence on the organic layer and simplicity. In this case, care must be taken so that the organic layer is not damaged by plasma generated during sputtering. Further, since the heat resistance of the organic layer is low, the temperature of the substrate is preferably set to 200 ° C. or lower.

The sputtering method is RF or D
C magnetron sputtering or reactive sputtering may be used, and the composition of the sputtering target to be used and sputtering conditions are appropriately selected according to the composition of the transparent conductive film to be formed. RF or D
In-Zn-O by C magnetron sputtering etc.
When forming a transparent transparent conductive film, the following (i):
It is preferable to use the sputtering target of (ii).

(I) A sintered target composed of a composition of indium oxide and zinc oxide, wherein the indium atomic ratio is predetermined. Here, “the atomic ratio of indium is predetermined” means that the atomic ratio of In in the finally obtained film [In / (In + Zn)] is a desired value in the range of 0.45 to 0.90. It means that the atomic ratio in the sintered target is approximately 0.50 to 0.90. The sintered target may be a sintered body comprising a mixture of indium oxide and zinc oxide, an In ₂
A sintered body substantially consisting of one or more hexagonal layered compounds represented by O ₃ (ZnO) _m (m = 2 to 20) may be used, or In ₂ O ₃ (ZnO) _m (m = 2 to 20) and at least one of the hexagonal layered compounds represented by In ₂ O ₃ and / or
Alternatively, it may be a sintered body substantially composed of ZnO.
In the above formula representing a hexagonal layered compound, m is 2 to 2
The reason for limiting to 0 is that if m is outside the above range, it will not be a hexagonal layered compound.

(Ii) A sputtering target comprising an oxide-based disk and one or more oxide-based tablets disposed on the disk. The oxide-based disk may be substantially composed of indium oxide or zinc oxide, or one of hexagonal layered compounds represented by In ₂ O ₃ (ZnO) _m (m = 2 to 20). From the above, a sintered body substantially consisting of In ₂ O ₃ (ZnO) _m (m
= 2 to 20), and may be a sintered body substantially composed of one or more of the hexagonal layered compounds represented by In ₂ O ₃ and / or ZnO. As the oxide-based tablet, the same one as the above-mentioned oxide-based disk can be used. The composition and the use ratio of the oxide-based disk and the oxide-based tablet have a desired value such that the atomic ratio [In / (In + Zn)] of In in the finally obtained film is in the range of 0.45 to 0.80. As appropriate.

It is preferable that the purity of each of the sputtering targets (i) and (ii) is 98% or more. When the purity of the sputtering target is less than 98%, the moisture-heat resistance (durability) of the obtained film may be reduced, the conductivity may be reduced, or the light transmittance may be reduced due to the presence of impurities. More preferred purity is 99%
The purity is more preferably 99.9% or more.

When a sintered target is used, the relative density of the target is preferably 70% or more. If the relative density is less than 70%, the film forming rate and the film quality are likely to be reduced. A more preferable relative density is 85% or more, and further preferably 90% or more. The sputtering conditions for providing a transparent conductive film by the direct sputtering method vary depending on the method of the direct sputtering, the composition of the sputtering target, the characteristics of the apparatus to be used, and the like. In the case of the sputtering method, for example, it is preferable to set as follows.

Degree of vacuum during sputtering and target
Preferably, the applied voltage is set as follows. That is,
The degree of vacuum during sputtering is 1.3 × 10^-2~ 6.7 ×
10 ⁰About Pa, more preferably 1.7 × 10^-2~ 1.
3 × 10⁰About Pa, more preferably 4.0 × 10^-2~
6.7 × 10^-1It is about Pa. Also, target application
The voltage is preferably 200 to 500V. During sputtering
Vacuum degree of 1.3 × 10^-2Less than Pa (1.3 × 1
0^-2Pressure is lower than Pa), the plasma stability is poor
6.7 × 10⁰Higher than Pa (6.7 × 10⁰P
pressure is higher than a).
The applied voltage cannot be increased. Also, target
When the applied voltage is less than 200 V, it is difficult to obtain a good quality thin film.
It may be difficult or the deposition rate may be limited.

As the atmosphere gas, a mixed gas of an inert gas such as an argon gas and an oxygen gas is preferable. When an argon gas is used as the inert gas, the mixing ratio (volume ratio) of the argon gas and the oxygen gas is approximately 1: 1 to 99.
99: 0.01, preferably 9: 1 to 99.9: 0.1
And Outside this range, a film having low resistance and high light transmittance may not be obtained.

The substrate temperature is appropriately selected in accordance with the heat resistance of the organic layer within a temperature range at which the organic layer does not deform or deteriorate due to heat. If the substrate temperature is lower than room temperature, a separate cooling device is required, which increases the manufacturing cost.
In addition, when the substrate is heated to a high temperature, a separate heat treatment apparatus is required, which increases the manufacturing cost.
For this reason, the substrate temperature is preferably between room temperature and 200 ° C.

The target transparent conductive film can be provided on the organic layer by performing direct sputtering under the conditions described above using the sputtering targets (i) and (ii) described above.

<Hole Injection Electrode Layer> Next, the hole injection electrode layer will be described. The hole injection electrode layer is a layer of an electrode that can well inject holes into the organic layer including the light emitting layer, and preferably has a light transmittance of 50% or more to obtain a transparent light emitting element. In order to achieve this, the film thickness must be set at 0.
It is desirable to form an ultrathin film of about 5 to 20 nm.

The hole injecting electrode layer is made of, for example, a metal having a work function of 4.8 eV or more (a metal having a hole injecting property), for example, Pt, Ni, Pd, Os or the like, and has a film thickness of 1-2.
A layer having a thickness of 0 nm can be given. In this case, a configuration that provides a light transmittance of 50% or more, particularly 60% or more, is preferable. As another preferable example, a hole injection electrode layer using an alloy (an alloy having a hole injection property) of the above-mentioned metal having a work function of 4.8 eV or more (or a plurality of kinds thereof) and another metal may be mentioned. it can. As such an alloy, any alloy capable of forming a hole injection electrode layer is sufficient. For example, a gold-indium alloy, a gold-aluminum alloy, an indium-platinum alloy, a lead-gold alloy, a bismuth-gold alloy ,
Examples include a tin-gold alloy, an aluminum-platinum alloy, an aluminum-nickel alloy, and an aluminum-palladium alloy. Also in this case, the film thickness is 1 to 20.
nm, and preferably a layer giving a light transmittance of 50% or more, particularly 60% or more.

When the hole injection electrode layer is formed using the above metal or alloy, a resistance heating evaporation method or an electron beam evaporation method is preferably used. In this case, the substrate temperature is set to 10 to 1
The temperature is set between 00 ° C. and the deposition rate is set to 0.05 to 20 nm /
It is preferable to set it in seconds. In particular, when vapor-depositing an alloy, it is possible to vapor-deposit the two kinds of metals by individually setting the vapor-deposition rate using a binary vapor deposition method. In this case, P
The deposition rate of t, Ni, Pd, Au or the like is set to 0.01 to 0.1.
nm / sec, and the vapor deposition rate of another metal such as In may be set at 1 to 10 nm / sec to perform simultaneous vapor deposition. In the case of depositing an alloy, a one-source deposition method can be used. In this case, a vapor-deposited pellet or granular material in which a hole-injecting metal is charged in a base metal at a desired ratio in advance is placed on a resistance heating boat or filament,
Heat deposition.

Still another preferred embodiment is a thin-film-like hole-injecting carbon having a thickness of 0.1 to 20 nm.
m ultra-thin film. Preferred examples of the carbon include graphite and amorphous carbon. As a method of forming the carbon layer, a method of depositing carbon by an arc discharge deposition method can be adopted.

The hole injecting electrode layer can be formed by using not only one kind but also two or more kinds of the metal, alloy and carbon having the hole injecting property described above. As still another preferred example, the hole injection electrode layer may be a hole injection metal, alloy, or a mixed layer of carbon and a hole transfer compound. Metal, alloy,
Examples of the carbon include the metals, alloys, and carbons described above. In addition, not only one kind but also two or more kinds can be used. On the other hand, the hole-transporting compound may be any compound that transmits holes, and a compound containing a kind of hole-transporting aromatic tertiary amine is preferable. The aromatic tertiary amine is a compound having at least one trivalent nitrogen atom bonded only to carbon atoms, one of which is a ring member of an aromatic ring. In one embodiment, the aromatic tertiary amine includes an arylamine such as a monoarylamine, a diarylamine, a triarylamine, or a polymer arylamine. Small triarylamines are disclosed in Klupfel et al., US Pat. No. 3,180,7.
No. 30 discloses this. Other suitable triarylamines substituted with vinyl or vinylene radicals and / or containing at least one hydrogen-containing group are described in U.S. Pat. No. 3,567,450 to Brantley et. Al. And U.S. Pat.
No. 8,520 discloses this. A preferred class of aromatic tertiary amines are those containing at least two amine components. Such compounds include the following structural formula
And those represented by [I].

[0033]

Embedded image

In the formula, Q ¹ and Q ² are independently aromatic tertiary amine components, and G represents an arylene group, a cycloalkylene group, an alkylene group, or a carbon-carbon bond. A particularly preferred type of triarylamine that satisfies structural formula [I] and contains two triaryl components is one that satisfies the following structural formula [II].

[0035]

Embedded image

In the formula, R ¹ and R ² each independently represent a hydrogen atom, an aryl group or an alkyl group;
¹ and R ² represent a group wherein a cycloalkyl group is completed by bonding, and R ³ and R ⁴ each independently represent the following structural formula [I
II] represents an aryl group substituted with a diaryl-substituted amino group.

[0037]

Embedded image

Wherein R ⁵ and R ⁶ are each independently selected aryl groups. Another preferred type of aromatic tertiary amine includes tetraaryldiamine. This tetraaryldiamine has two diaryl groups represented by the structural formula [III] bonded through an arylene group.
It is preferable to include these. Preferred tetraarylenediamines include those represented by the following structural formula [IV].

[0039]

Embedded image

Wherein Are is an arylene group, n is an integer from 1 to 4, and Ar, R ⁷ , R ⁸ and R ⁹ are independently selected aryl groups. The above structural formula [I],
The various alkyl, alkylene, aryl and arylene components of [II], [III], and [IV] may each be substituted. Typical substituents include, for example, alkyl, alkoxy, aryl, aryloxy groups and halogens such as fluorine, chlorine and bromine. The various alkyl and alkylene components typically have about 1 to 6 carbon atoms. The cycloalkyl component has about 3 to 10 carbon atoms, but typically contains 5, 6, or 7 ring carbon atoms and has, for example, a cyclopentyl, cyclohexyl, and cycloheptyl ring structure. Things. The aryl and arylene components preferably have phenyl and phenylene structures.

The mixing ratio (weight ratio) of the hole-injecting metal, alloy, or carbon to the hole-transporting compound is 100:
It is preferable to set it as 1-1: 100. The mixed layer of a hole-injecting metal, an alloy, and an electron-transporting compound is preferably formed by a binary simultaneous evaporation method. The substrate temperature at that time may be set between 10 and 100 ° C.

As still another preferred example, there is a configuration in which the hole injection electrode layer is an island-shaped hole injection region. Here, the island shape means that a hole injecting compound layer is formed discontinuously as shown in FIG. 2, for example, and this layer does not cover the surface of the organic layer. The island-shaped hole injection region is formed by discontinuously forming a metal, oxide, alloy, carbon, or the like having a high work function of 4.8 eV or more in an island shape. There is no particular limitation, but in the form of fine particles or crystals,
Those having a size of about 0.5 nm to 5 μm are preferred.

Further, this hole injection region does not indicate a thin film shape, nor does it indicate a state of isolated atom dispersion. This refers to a state in which the metal or compound having the high work function is dispersed in the form of particles on the conductive thin film or in the organic compound layer. Due to such dispersion, the area in contact with the organic compound layer increases, and the hole injecting property increases. As the metal and alloy having a high work function constituting the island-shaped hole injection region, those having a work function of 4.8 eV or more are preferable, and examples thereof include the metals and alloys described above. or,
As the oxide having a high work function, nickel oxide and manganese oxide are preferable.

As a method for forming the island-shaped hole injection region, a resistance heating evaporation method or an electron beam evaporation method can be employed. In the latter case, oxide or carbon having a high melting point is formed discontinuously in an island shape by electron beam evaporation. In the organic EL device of the present invention, since the anode serving as the counter electrode is composed of the hole injection electrode layer and the amorphous transparent conductive film, the organic layer is damaged when the amorphous transparent conductive film is formed. This protects the hole injection electrode layer. As a result, a good organic EL device can be manufactured.

When the hole injection electrode layer is in contact with the organic layer, holes are injected into the organic layer. Thereby, the charge is well injected into the EL element in combination with the electron injection from the cathode side, which is the lower electrode. In the organic EL device of the present invention, usually, a cathode serving as a lower electrode is laminated on a substrate,
A configuration in which an organic layer is laminated thereon is adopted. In this case, a hole injection electrode layer is formed on the organic layer including the organic light emitting layer. The formation method is as described above, and there is a sputtering method as another preferable method. In using this method, care must be taken so that the organic layer is not damaged by plasma.

As another preferable hole injecting electrode layer, a conductive polymer such as an all-conjugated polymer such as polyarylenevinylene, polythiophene, polychenylenevinylene, or polyaniline can be used.

<Organic Layer> In the organic EL device of the present invention, the organic layer interposed between the anode and the cathode includes at least a light emitting layer. The organic layer may be a layer composed of only the light emitting layer, or may have a multilayer structure in which a hole injection transport layer and the like are laminated together with the light emitting layer.

In this organic EL device, the light emitting layer has the following functions: (1) a function of injecting holes by an anode or a hole transport layer and applying an electron from an electron injection layer when an electric field is applied; 2) a transport function of moving the injected charges (electrons and holes) by the force of an electric field; and (3) a light-emitting function of providing a field for recombination of electrons and holes inside the light-emitting layer and connecting it to light emission. Have. There is no particular limitation on the type of light emitting material used in the light emitting layer, and any known organic EL element can be used.

The hole injecting and transporting 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 light emitting layer and the light emitting layer, many holes are injected into the light emitting layer at a lower electric field. In addition, the electrons injected from the electron injection layer into the light emitting layer cause the luminous efficiency of the EL element accumulated near the interface in the light emitting layer due to the electron barrier existing at the interface between the light emitting layer and the hole injection transport layer. Is improved, and as a result, an EL element having excellent light emission performance is obtained. There is no particular limitation on the hole transporting compound used in the hole injecting and transporting layer, and it has been conventionally used in organic EL devices.
Known hole transport compounds can be used. The hole injecting and transporting layer can be not only a single layer but also a multilayer.

<Cathode> Next, the cathode will be described. The cathode is a layer of an electrode capable of satisfactorily injecting electrons into an organic layer including a light-emitting layer. In order to obtain a transparent light-emitting element, the light transmittance is preferably 50% or more. It is desirable to form an ultrathin film having a thickness of about 0.5 to 20 nm.

As the cathode, for example, a work function of 3.8 e
V or less metal (electron injecting metal), for example, Mg, C
a, Ba, Sr, Li, Yb, Eu, Y, Sc, or the like; In this case, when it is desirable to provide a structure that gives a light transmittance of 50% or more, particularly 60% or more, the film thickness is preferably 1 to 1.
It needs to be 20 nm.

Another preferred example is electron injection using an alloy (an electron-injecting alloy) of the above-mentioned metal having a work function of 3.8 eV or less (or a plurality of kinds) and a metal having a work function of 4.0 eV or more. An electrode layer can be mentioned. As such an alloy, any alloy capable of forming an electron injection electrode layer is sufficient. For example, aluminum-lithium alloy, magnesium-aluminum alloy, indium-lithium alloy, lead-lithium alloy, bismuth-lithium alloy, Examples include a tin-lithium alloy, an aluminum-calcium alloy, an aluminum-barium alloy, and an aluminum-scandium alloy. Also in this case, by setting the film thickness to 1 to 20 nm, 50% or more,
In particular, the layer can provide a light transmittance of 60% or more.

When a cathode is formed using the above metal or alloy, a resistance heating evaporation method is preferably used. In this case, it is preferable to set the substrate temperature between 10 and 100 ° C. and set the deposition rate between 0.05 and 20 nm / sec. In particular, in the case of depositing an alloy, it is possible to perform deposition by separately setting the deposition rates of the two metals by using a binary deposition method. In this case, Li, Ba, Ca, Sc,
It is possible to adopt a technique in which the deposition rate of Mg or the like is set between 0.01 and 0.1 nm / sec, and the deposition rate of the base metal such as Al is set between 1 and 10 nm / sec and the deposition is performed simultaneously. In the case of depositing an alloy, a one-source deposition method can be used. In this case, a vapor-deposited pellet or granular material in which a metal having an electron-injecting property is previously charged into a base metal at a desired ratio is placed on a resistance heating boat or a filament and heated and vapor-deposited.

Still another preferred embodiment is a thin film electron-injecting alkaline earth metal oxide, alkali oxide or alkali fluoride having a film thickness of 0.1 to 10 nm.
m ultra-thin film. Examples of the alkaline earth metal oxide include BaO, SrO, CaO, and Ba _x Sr _1-x O (0 <x <1) in which these are mixed.
Alternatively, Ba _x Ca _1-x O (0 <x <1) can be mentioned as a preferable example. Examples of the alkali oxide or alkali fluoride include LiF, Li ₂ O, and NaF.

As a method of forming the alkaline earth metal oxide layer, oxygen is introduced into the vacuum chamber while the alkaline earth metal is being deposited by the resistance heating evaporation method to reduce the degree of vacuum to 10 ^-3 to 1.
A method in which the pressure is set to 0 ^-4 Pa and vapor deposition is performed while reacting oxygen and an alkaline earth metal is preferable. Further, a method of forming a film of an alkaline earth metal oxide by an electron beam evaporation method can be employed.

As a method for forming an alkali oxide, a method similar to the above-described method for forming an alkaline earth metal oxide can be used. Examples of the method for forming the alkali fluoride include an electron beam evaporation method and a resistance heating evaporation method. In addition, the metal, alloy,
As for the alkaline earth metal oxide, not only one kind but also two kinds
The electron injection electrode layer can be formed using more than one kind.

More preferred examples include Al ₂ O ₃ or AlO _X (1 <x ≦ 3/2). Examples of the manufacturing method include natural oxidation of Al and oxidation by plasma. As another manufacturing method, a method of electron beam evaporation of Al ₂ O ₃ , introduction of oxygen into a vacuum chamber to a degree of vacuum of 10 ⁻³ to 10 ⁻⁴ Pa, and vapor deposition while reacting oxygen and Al. The method is preferred.

Further, a more preferable method is an anodic oxidation method in which Al is used as an anode in an electrolyte solution and is energized and oxidized. The detailed conditions of the anodic oxidation method are as follows. In a dilute solution of citric acid, phosphoric acid, ammonium borate, and ammonium tartrate, a voltage of 5 to 300 V is set using the aforementioned Al as an anode and a noble metal such as platinum as a cathode. Energize with current. At this time, if it is manufactured by adjusting the pH and maintaining the pH in the range of 6 to 8, dense AlO _x (1 <x ≦ 3 /
2) can be done.

<Structure of Organic EL Element> Organic EL Element of the Present Invention
In the device, an organic layer including an organic light emitting layer is interposed between an anode and a cathode, and the anode is composed of a hole injection electrode layer and an amorphous transparent conductive film. The object of the present invention can be achieved by providing a structure in contact with a layer, but various functions can be provided by further adding another structure. Hereinafter, a configuration using the organic EL device of the present invention will be exemplified.

Transparent cathode / organic layer / hole injection electrode layer /
Amorphous transparent electrode Cathode / organic layer / hole injection electrode layer / amorphous transparent electrode /
Color filter cathode / organic layer / hole injection electrode layer / amorphous transparent electrode /
Color conversion layer Transparent cathode / organic layer / hole injection electrode layer / amorphous transparent electrode / black light absorbing layer Transparent cathode / organic layer / hole injection electrode layer / amorphous transparent electrode / background color forming layer Black light absorption Layer / transparent cathode / organic layer / hole injecting electrode layer / amorphous transparent electrode Background color forming layer / transparent cathode / organic layer / hole injecting electrode layer / amorphous transparent electrode Is transparent, so that a transparent display element is formed.

In the case of the above configuration, the cathode is formed on the support substrate, and light emission can be taken out in the direction opposite to the support substrate. Therefore, it is not necessary to form an anode on a color filter or a color conversion layer. Therefore, it is possible to adopt a process in which the substrate temperature becomes 150 ° C. or higher when forming the cathode. Depending on the cathode to be formed, it may be limited to the use of a high-temperature process or in terms of lowering the resistance value of the cathode. There are great benefits. Further, since the color filter and the color conversion layer are formed after the formation of the cathode, there is no need to worry about deterioration due to the adoption of the high temperature process. FIG. 3 illustrates the above configuration. Here, it is preferable that the color conversion layer is made of a transparent polymer containing a fluorescent dye, and converts the EL emission color to another color by fluorescence.

In the embodiment in which a large number of pixels are formed in the above configuration, an auxiliary wiring and a TFT (Thin Film Transister) other than the anode are formed on the substrate.
When light is extracted in the direction of the substrate, the auxiliary wiring and the TFT block the light, and the aperture ratio for extracting light is reduced. As a result, there is a disadvantage that the brightness of the display is reduced and the image quality is reduced. Therefore, by using the present invention, light can be extracted in the direction opposite to the direction of the substrate. In this case, there is an effect that light is not blocked and the aperture ratio of light extraction does not decrease.

[0063]

[Example 1]

<Preparation of Organic EL Element> A 100-nm thick ITO film (manufactured by Geomatics Co., Ltd.) was formed on a 25 mm × 75 mm × 1 mm glass substrate, and a conductive thin film was formed on the substrate. Used as one. Next, this was immersed in isopropyl alcohol and subjected to ultrasonic cleaning.
Washing was carried out for 30 minutes using UV light and ozone in combination with 300.

Next, Al was deposited to a thickness of 15 nm by a vacuum deposition apparatus. Then, a 0.1 mol / L aqueous solution of ammonium tartrate and ethylene glycol were mixed at a volume ratio of 1: 9, and a small amount of an aqueous solution of ammonium was added thereto to prepare a solution prepared by adding the above-mentioned glass substrate on which Al was formed. It was immersed and used as an anode for anodic oxidation. In the anodization, the voltage was set to 4 to 6 V so that the thickness of the oxide film to be formed was 3 nm. As a result, a cathode of Al / aluminum oxide was formed on the ITO.

Next, this substrate was immersed in isopropyl alcohol and subjected to ultrasonic cleaning, and then washed for 5 minutes using the same ultraviolet irradiator UV-300 (manufactured by Samco International) using both ultraviolet and ozone. did. The substrate was mounted on a substrate holder of a vacuum evaporation apparatus, and 8-quinolinol aluminum complex (hereinafter abbreviated as Alq) was added to the substrate holder.
0 nm was deposited. Next, N, N'-bis (3-methylphenyl) -N, N'-diphenyl- (1,1'-biphenyl) -4,4'-diamine (hereinafter abbreviated as TPD)
Was deposited to a thickness of 20 nm. Next, 4,4′-bis- (N, N
-Di-m-tolylamino) -4 ″ -phenyl-triphenylamine (hereinafter abbreviated as TPD74) was deposited to a thickness of 80 nm. Here, Alq, TPD, and TPD74 were each
It functions as a light emitting layer, a hole transport layer, and a hole injection layer. Next, carbon was deposited to a thickness of 10 nm by arc discharge deposition. This carbon functions as a hole injection electrode layer.

Next, the substrate was transferred and set to a substrate holder in another vacuum chamber connected to the above-mentioned vacuum deposition apparatus.
During this time, the degree of vacuum is maintained. The other vacuum chamber is In-Z by DC magnetron sputtering.
Equipment is provided to form an n-O-based oxide film.
The target for forming the In—Zn—O-based oxide film is a sintered body composed of In ₂ O ₃ and ZnO.
The atomic ratio [In / (In + Zn)] of n is 0.67. A mixed gas of argon gas and oxygen gas (volume ratio: 1000: 2.8) in this vacuum chamber was introduced until the pressure became 3 × 10 ⁻¹ Pa, the sputtering output was set to 100 W, the substrate temperature was set to room temperature, and the film thickness was set. A 200 nm amorphous transparent conductive film was formed. Note that the fact that the In—Zn—O-based oxide film was amorphous was confirmed by X-ray diffraction using a glass substrate on which an ITO thin film had not been deposited by forming a laminate in the same manner as described above. .

Next, the organic EL device was evaluated. First, the amorphous transparent conductive film was examined for sheet resistance by a four-probe method using Loresta FP manufactured by Mitsubishi Yuka Co., Ltd.
It was 23 Ω / □. And since the film thickness was 200 nm, it was confirmed that the specific resistance value was as low as 4.6 × 10 ⁻⁴ Ω · cm. Next, a voltage of 7 V was applied using ITO / Al / aluminum oxide as a cathode and the carbon layer / In—Zn—O transparent conductive film as an anode.
The current density became mA / cm ² , and when observed from the side of the amorphous transparent conductive film, light emission with a luminance of 70 Cd / m ² was observed. This light emission was green light emitted from Alq.

Further, when this device was left in an atmosphere of 70% RH (relative humidity) in the air for 500 hours, no light emitting point was visually observed, and the light emitting performance of the device was maintained. The transparent anode of the present invention was found to be resistant to moisture and oxygen in the air.

Comparative Example 1 An organic EL device was manufactured in the same manner as in Example 1. However, instead of forming an In-Zn-O-based oxide film, an In-Sn-O-based oxide (ITO) was formed as a crystalline transparent conductive film by DC magnetron sputtering.

Thereafter, the performance of the organic EL device was evaluated in the same manner as in Example 1, and the sheet resistance was found to be 300 Ω.
/ □ showed a large value. Then, since the film thickness was 200 nm, it was confirmed that the specific resistance value was as high as 6 × 10 ⁻³ Ω · cm. Next, when a voltage of 8 V was applied to the organic EL device using ITO / Al / aluminum oxide as a cathode and the carbon layer / In—Sn—O transparent conductive film as an anode, a current density of 2.4 mA / cm ² was obtained. When observed from the side of the amorphous transparent conductive film, the luminance was 60 Cd /
There was emission of m ² . This light emission was green light emitted from Alq.

When this device was allowed to stand in an atmosphere of 70% RH (relative humidity) in the air for 500 hours, a large number of non-emission points (3,000 pieces / cm ² or more) were visually observed, and it was confirmed that there were many light emission defects. Was done. Further, it was found that when the substrate temperature was room temperature, the crystalline ITO substrate exhibited a high resistance value, and when the substrate was thinned to about 1 mm or less to emit light, the luminance became non-uniform.

Comparative Example 2 An organic EL device was manufactured in the same manner as in Example 1. However, an In—Zn—O transparent conductive film was formed directly on the TPD 74 without forming carbon (hole injection electrode layer).

An organic EL device was prepared in the same manner as in Example 1.
When the performance of the amorphous transparent conductive film was evaluated,
Was about 25 Ω / □, which was almost the same as that in Example 1.
And since the film thickness is 200 nm, in terms of the specific resistance value,
Is 4 × 10^-FourΩ · cm and excellent
Was. Next, using ITO / Al / aluminum oxide as the cathode
By using the In-Zn-O transparent conductive film as an anode,
A voltage of 7 V was applied to the organic EL device, but the current density was 0.1 V.
2mA / cm^TwoAnd a lower value than Example 1.
When observed from the side of the amorphous transparent conductive film, the luminance was 70%.
Cd / m^TwoIs 4.0 mA / cm. ^TwoAnd large
And the efficiency dropped significantly. This is because In-Z
During the DC magnetron sputtering of n-O,
It is thought that the TPD74 has been damaged by the
You. The hole injection electrode layer is damaged by plasma (especially oxygen
Is assumed to be necessary to prevent
Was.

Example 2 An organic EL device was manufactured in the same manner as in Example 1. However, carbon (hole injection electrode layer) was not formed, and instead of this, as a hole injection electrode layer, an Au thin film (thickness: 5 n) formed by resistance heating evaporation was used.
m) was used. When this Au thin film was observed with a scanning electron microscope, Au was formed in an island shape. And A
An In-Zn-O transparent conductive film was formed on the u thin film.

When the performance of the organic EL device was evaluated in the same manner as in Example 1, the sheet resistance of the Au / In—Zn—O laminated body was 8 Ω / □. From this result, it was found that an electrode in which a metal thin film / amorphous transparent conductive film having a high work function was laminated was useful as a counter electrode having a low resistance value. Therefore, this small value is useful when light emission is performed using a thinned counter electrode.

Next, when a voltage of 7 V was applied to the organic EL device using ITO / Al / aluminum oxide as a cathode and an Au thin film / In-Zn-O transparent conductive film as an anode, the current density was 2.3 mA / cm. ² and the luminance was 50 Cd / m ² when observed from the side of the amorphous transparent conductive film. This light emission was green light emitted from Alq. Further, a standing test in the air was performed in the same manner as in Example 1. However, no light emitting point was visually observed, and light emitting performance was maintained.

Example 3 An organic EL device was manufactured in the same manner as in Example 1. However, as a hole injection electrode layer, an Au: In alloy thin film was formed using a binary deposition method,
The thickness of the Au: In alloy thin film was 7 nm.

The performance of the organic EL device was evaluated in the same manner as in Example 1. Au: In / In—Zn—O
The sheet resistance of the counter electrode, which was a laminate, was as low as 8 Ω / □. From this result, it was found that an electrode in which a metal thin film / amorphous transparent conductive film having a high work function was laminated was useful as a counter electrode having a low resistance value. Therefore, this small value is useful when light emission is performed using a thinned counter electrode.

Next, when a voltage of 7 V was applied to the organic EL device using ITO / Al / aluminum oxide as a cathode and an Au: In alloy thin film / In—Zn—O transparent conductive film as an anode, the current density was 3 0.0 mA / cm ² , and the luminance was 40 Cd / m ² . Further, a standing test in the air was performed in the same manner as in Example 1. However, no light emitting point was visually observed, and light emitting performance was maintained.

Example 4 T which is a hole-transporting compound
An organic EL device was manufactured in the same manner as in Example 1, except that PD74 and carbon were mixed at a weight ratio of 1: 1 by vapor deposition to form a hole injection electrode layer.

The organic EL device was evaluated in the same manner as in Example 1. That is, using ITO / Al / aluminum oxide as a cathode, a mixed layer of carbon and TPD74 / In-Z
When a voltage of 7 V was applied using the n-O transparent conductive film as an anode, the current density was 2.1 mA / cm ² , and the luminance was 78 Cd /
m ² . The sheet resistance of the counter electrode is 21Ω /
It was □.

Further, a standing test in the air was carried out in the same manner as in Example 1. However, no light emitting point was visually observed, and light emitting performance was maintained. Next, a mixed layer of carbon and TPD74 / In-
When a voltage of 8 V was applied using the Zn—O transparent conductive film as an anode, a current density of 3.8 mA / cm ² was obtained. When observed from the side of the amorphous transparent conductive film, a luminance of 65
There was light emission of Cd / m ² . This light emission was green light emitted from Alq.

Further, when this device was left in an atmosphere of 70% RH in the air for 500 hours, no light emitting point was visually observed, the luminous efficiency of the device did not decrease, and the luminous performance was maintained.

[0084]

Since the organic EL device of the present invention has a low-resistance and highly transparent anode, light can be efficiently extracted from both sides of the device. Also, it has excellent durability. For this reason, the organic EL element of the present invention is suitably used, for example, for displays of information equipment.

[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 an example of a configuration in which an island-shaped hole injection region is present at an interface between an amorphous transparent conductive film and an organic layer in the organic EL device of the present invention.

FIG. 3 is a simplified cross-sectional view showing an example of a use mode of the organic EL element of the present invention, showing a configuration in which a color filter is added outside an amorphous transparent conductive film.

FIG. 4 is a simplified cross-sectional view showing an example of a use mode of the organic EL element of the present invention, showing a configuration in which a black absorbing layer is provided outside an amorphous transparent conductive film.

FIG. 5 is a simplified cross-sectional view of an example of a use mode of the organic EL element of the present invention, showing a configuration in which a background color forming layer is provided outside a transparent cathode.

[Explanation of symbols]

 1: substrate 2: cathode (lower electrode) 3: organic layer 4: hole injection electrode layer 5: amorphous transparent conductive film 6: island-like injection region 7: color filter 8: black light absorption layer 9: background color formation layer

Claims (5)

[Claims] 1. An organic electroluminescent device comprising an organic layer including an organic light emitting layer interposed between a cathode serving as a lower electrode and an anode serving as a counter electrode of the cathode,
An organic electroluminescence device, wherein the anode comprises a hole injection electrode layer and an amorphous transparent conductive film, and the hole injection electrode layer is in contact with the organic layer. 2. The method according to claim 1, wherein the hole injecting electrode layer comprises a hole injecting metal,
The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device is formed in an ultra-thin film using one or more selected from alloys, conductive polymers, and carbon. 3. The method according to claim 1, wherein the hole injecting electrode layer comprises a hole injecting metal,
The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device is a mixed layer of one or more selected from an alloy, a conductive polymer, and carbon and a hole-transporting organic substance. 4. The organic electroluminescent device according to claim 1, wherein the hole injecting electrode layer comprises an island-like hole injecting region. 5. An amorphous transparent conductive film is made of indium (I)
The organic electroluminescence device according to any one of claims 1 to 4, wherein the organic electroluminescence device is formed using an oxide composed of n), zinc (Zn), and oxygen (O).