JP2012234737A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element of double-sided emission type having improved drive voltage and luminous efficiency, which emits light from a cathode side or emits light from both anode and cathode sides.SOLUTION: The organic electroluminescent element includes a unit 10 composed of the layers laminated in the order mentioned: a first layer 11 in thickness of 0.1 to 30 nm and containing metal having an extinction coefficient of 5.0 or less at 550 nm; a second layer 12 consisting of alkali metal nobler than -3 Vvs.SHE in standard electrode potential, a compound of the alkali metal, or alkali earth metal or a compound of the alkali earth metal; a third layer 13 consisting of an organic electron transport material containing alkali metal nobler than -3 Vvs.SHE in standard electrode potential, a compound of the alkali metal, or alkali earth metal or a compound of the alkali earth metal; and a fourth layer 14 consisting of only an organic electron transport material.

Description

  The present invention relates to an organic electroluminescence element applied to various displays, display devices, illumination, and the like.

Surface light emitters used as backlights for various displays, display boards such as signboards and emergency lights, and light sources for lighting, etc. have attracted attention in recent years because they have many excellent features such as high brightness, high luminous efficiency, thinness, and light weight. Has been. Among such surface light emitters, an organic electroluminescence element (hereinafter also referred to as an organic EL element) that emits light by using electric energy from positive and negative electrodes using an organic material has a low voltage of about several volts to several tens of volts. In particular, it has been attracting attention in recent years because it is a thin-film type complete solid-state device and saves space.
Furthermore, various lighting fixtures have been proposed that utilize the characteristic of thin surface emission. In general, one of the electrodes is generally a reflective electrode, but recently, a material using a transmissive material for both electrodes has been proposed.

A metal oxide typified by indium tin oxide (ITO) is preferably used as an anode on the hole injection side because of its high work function, but its characteristics as electron injection are extremely low. Therefore, when a metal oxide is used as the cathode, it is necessary to increase the electron injecting property. In addition, there is a method of thinning a metal such as aluminum which is usually used as a cathode. However, it is difficult to achieve both suppression of light absorption and electron injection, and a device with high transparency has a large driving voltage. It was accompanied by a rise. This is because if the metal layer is thinned to reduce light absorption, metal atoms will be scattered in islands, resulting in inability to secure conductivity on the surface, and in the islands. This is probably because the area functioning as the electron injection layer is reduced.
When dealing with the interaction between light and matter, the amount of absorption per vibration of the electromagnetic field of light is the standard. For this reason, the extinction coefficient κ is defined as an amount that defines the light absorption of the substance. In general, the larger the value of κ, the larger the light absorption. Therefore, selecting a material having a small value of κ is important for producing an organic electroluminescence device with low light absorption.

Patent Document 1 proposes a cathode containing 50% or more of magnesium and 0.1% or more of a metal having a work function of 4 eV or more. Although it is excellent in sheet resistance as long as it is a certain film thickness or more, it was found that the transmittance is not sufficient as a light-emitting element having high see-through property, and there is a problem in the stability of the element.
In Patent Document 2, a first cathode of alkali metal or alkaline earth metal, an electron transporting protective layer containing alkali metal or alkaline earth metal, and a second cathode of inorganic oxide or inorganic nitride are laminated. Thus, a cathode structure has been proposed that has optical transparency and excellent electron injection and transport properties. However, this technique has a problem that the alkali metal or alkaline earth metal used for the second cathode diffuses into the organic light emitting layer over time, and the efficiency and life of the device are lowered.
In Patent Document 3, a cathode buffer layer made of an electron transporting organic material having a film thickness of 5 to 10 nm is provided between the cathode and an electron injection layer made of alkali metal or alkaline earth metal. A technique for exhibiting the effect of injecting the tunnel is disclosed.
However, the technique of Patent Document 3 significantly reduces the drive life due to problems such as the cathode buffer layer being unable to alleviate the damage caused by sputtering when the ITO film is formed by sputtering, and the cathode and anode are short-circuited. It was.
Patent Document 4 discloses a technique for suppressing diffusion of lithium by providing a layer having a ligand capable of binding to lithium and forming a metal complex between an electron injection layer made of lithium and an organic light emitting layer. Is disclosed.

Japanese Patent No. 2723242 JP 2004-127740 A JP 2009-295822 A JP 2010-10333 A

However, in the method of Patent Document 4, it has been clarified that the reaction between the ligand and the alkali metal or alkaline earth metal in the film hardly occurs, and the decrease in electron injection property can hardly be suppressed. As a result, it has been found that the driving voltage increases with time, and it is not possible to suppress a decrease in luminous efficiency and a decrease in lifetime.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an organic electroluminescence device that emits light from the cathode side, or emits light from both the anode side and the cathode side, with improved driving voltage and luminous efficiency. Is to provide.

In order to solve the above-mentioned problem, the invention of claim 1 includes a first layer containing a metal having a thickness of 0.1 to 30 nm and an extinction coefficient at 550 nm of 5.0 or less,
Standard electrode potential is −3 V vs. A second layer of an alkali metal or the alkali metal compound that is noble than SHE, or an alkaline earth metal or the alkaline earth metal compound;
Standard electrode potential is −3 V vs. A third layer made of an organic electron transport material containing an alkali metal that is noble than SHE or the alkali metal compound, or an alkaline earth metal or alkaline earth metal compound;
A fourth layer made of only an organic electron transport material has a unit laminated in this order.

The invention of claim 2 is the organic electroluminescence device according to claim 1,
The surface roughness Ra of the first layer opposite to the surface in contact with the second layer is 1 nm or more and 10 nm or less.

The invention of claim 3 is the organic electroluminescence device according to claim 1 or 2, wherein
An auxiliary electrode is laminated on a surface of the first layer opposite to the second layer.

Invention of Claim 4 is set in the organic electroluminescent element of Claim 1 or 2,
An organic layer made of an organic material or an inorganic layer made of an inorganic material is laminated on the surface of the first layer opposite to the second layer,
A transparent conductive layer is laminated on the surface of the organic layer or inorganic layer opposite to the second layer.
The invention of claim 5 is the organic electroluminescence device according to claim 4,
The organic layer and the inorganic layer have a certain pattern shape.

The invention of claim 6 provides the organic electroluminescent device according to claim 4 or 5,
An auxiliary electrode is laminated on the surface of the transparent conductive layer opposite to the organic layer or the inorganic layer.

Invention of Claim 7 is set in the organic electroluminescent element as described in any one of the said Claims 1-6,
The alkali metal or alkali metal compound of the second layer, or the alkaline earth metal or alkaline earth metal compound, and the alkali metal or alkali metal compound contained in the third layer, or the alkaline earth metal or alkaline earth It is characterized in that the same metal compound is the same.

  ADVANTAGE OF THE INVENTION According to this invention, the drive voltage and luminous efficiency can be improved, and the double-sided organic electroluminescent element which light-emits from the cathode side or emits light from both the anode side and the cathode side can be provided.

It is the schematic sectional drawing which showed a part of layer structure of the organic electroluminescent element of this invention.

Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.
FIG. 1 is a schematic cross-sectional view showing a part of the layer configuration of the organic electroluminescence element of the present invention.
As shown in FIG. 1, the organic electroluminescence element of the present invention (hereinafter simply referred to as an organic EL element) is made of a metal having a thickness of 0.1 to 30 nm and an extinction coefficient at 550 nm of 5.0 or less. A first layer containing (hereinafter referred to as a metal layer 11) and a standard electrode potential of −3 Vvs. A second layer 12 made of an alkali metal or the alkali metal compound, or an alkaline earth metal or the alkaline earth metal compound, which is noble than SHE, and a standard electrode potential of −3 Vvs. A third layer 13 made of an organic electron transport material containing an alkali metal or alkali metal compound that is noble than SHE, or an alkaline earth metal or alkaline earth metal compound, and a fourth layer made only of an organic transport material. And the unit 10 stacked in this order.
Furthermore, the surface roughness of the surface of the metal layer 11 opposite to the surface in contact with the second layer is 1 nm or more and 10 nm or less, and the surface of the metal layer 11 opposite to the second layer 12 is formed with an organic material. An organic layer made of or an inorganic layer 15 made of an inorganic material, and a transparent conductive layer 16 is laminated on the surface of the organic layer or inorganic layer 15 opposite to the second layer 12, and the organic layer The inorganic layer 15 has a certain pattern, and the auxiliary electrode 17 is laminated on the surface of the transparent conductive layer 16 opposite to the organic layer or the inorganic layer 15.

Hereinafter, the organic EL element of the present invention will be described.
[Organic EL device]
First, embodiments of the organic EL device of the present invention, which is an example of a surface light emitter, will be described in detail. The contents described below are representative examples of embodiments of the present invention, and the present invention exceeds the gist thereof. As long as there is no, it is not limited to these contents.
First, the preferable specific example of the layer structure of an organic EL element is shown below.
(I) Anode / light-emitting layer / electron transport layer (fourth layer) / alkali metal, alkali metal compound, alkaline earth metal, electron transport layer containing alkaline earth metal (third layer) / alkali metal, Electron injection layer (second layer) made of any one of an alkali metal compound, alkaline earth metal, and alkaline earth metal / a metal layer having a thickness of 0.1 to 30 nm with an extinction coefficient of 5.0 or less (first layer).
(Ii) Anode / hole transport layer / light emitting layer / electron transport layer (fourth layer) / electron transport layer (second layer) containing alkali metal, alkali metal compound, alkaline earth metal, alkaline earth metal ) / Electron injection layer (third layer) made of any one of alkali metal, alkali metal compound, alkaline earth metal, and alkaline earth metal / metal having a thickness of 0.1 to 30 nm with an extinction coefficient of 5.0 or less Layer (fourth layer).
(Iii) Anode / hole transport layer / light emitting layer / electron transport layer (fourth layer) / electron transport layer (third layer) containing alkali metal, alkali metal compound, alkaline earth metal, alkaline earth metal ) / Electron injection layer (second layer) made of any one of alkali metal, alkali metal compound, alkaline earth metal, and alkaline earth metal / metal having a thickness of 0.1 to 30 nm with an extinction coefficient of 5.0 or less Layer (first layer) / organic layer / transparent conductive layer (iv) anode / hole transport layer / light emitting layer / electron transport layer (fourth layer) / alkali metal, alkali metal compound, alkaline earth metal, Electron transport layer (third layer) containing alkaline earth metal / electron injection layer (second layer) / extinction composed of any of alkali metal, alkali metal compound, alkaline earth metal, and alkaline earth metal Metal layer having a thickness of 0.1 to 30 nm with a coefficient of 5.0 or less (First layer) / inorganic layer / transparent conductive layer (v) anode / hole transport layer / light emitting layer / electron transport layer (fourth layer) / alkali metal, alkali metal compound, alkaline earth metal, alkaline earth Electron transport layer (third layer) containing an alkali metal / electron injection layer (second layer) made of any one of alkali metal, alkali metal compound, alkaline earth metal, and alkaline earth metal / extinction coefficient 5 0.1 to 30 nm thick metal layer (first layer) / organic layer / transparent conductive layer / auxiliary electrode (vi) anode / hole transport layer / light emitting layer / electron transport layer (fourth Layer) / electron transport layer containing alkali metal, alkali metal compound, alkaline earth metal, alkaline earth metal (third layer) / alkaline metal, alkali metal compound, alkaline earth metal, alkaline earth metal Electron injection layer (second layer) consisting of either / extinction factor Metal layer (first layer) having a thickness of several tens or less of 0.1 to 30 nm / inorganic layer / transparent conductive layer / auxiliary electrode

The organic EL device of the present invention is characterized in that the cathode is transparent, and the opposing electrode can be selected either transparent or opaque depending on the application.
The organic EL device of the present invention preferably has a top emission type or double side emission type configuration.
The light emitting layer preferably contains at least two kinds of light emitting materials having different emission colors, and a single layer or a light emitting layer unit composed of a plurality of light emitting layers may be formed. The hole transport layer also includes a hole injection layer and an electron blocking layer.

《Electron injection cathode》
The electron injection cathode of the present invention is a metal layer having an extinction coefficient of 5.0 or less at 550 nm and a thickness of 0.1 to 30 nm.
Furthermore, on the opposite side from the light emitting layer, an organic layer made of an organic material or an inorganic layer made of an inorganic material, a transparent conductive layer, and even an auxiliary electrode may function as a cathode.

Hereinafter, each layer will be described.
<< Metal layer (first layer 11) >>
As a material constituting the metal layer of the present invention, the extinction coefficient κ at 550 nm is 5.0 or less.
Examples of the metal material having an extinction coefficient at 550 nm of 5.0 or less include the following. For example, silver (Ag: extinction coefficient 3.32), gold (Au: extinction coefficient 2.32), copper (Cu: extinction coefficient 2.86), palladium (Pd: extinction coefficient 3.85), Nickel (Ni: extinction coefficient 3.32), rhodium (Rh: extinction coefficient 5.02), platinum (Pt: extinction coefficient 3.71), tantalum (Ta: extinction coefficient 1.83), titanium ( Ti: extinction coefficient 3.34), iron (Fe: extinction coefficient 3.35), chromium (Cr: extinction coefficient 4.42), tungsten (W: extinction coefficient 2.49), molybdenum (Mo: An extinction coefficient 3.51) etc., or a mixture thereof is mentioned.
More preferably, it is 4.0 or less as an extinction coefficient in 550 nm, More preferably, it is 3.5 or less, Gold, silver, copper, etc. are preferable.
For the purpose of adjusting the work function, the metal layer can be used by mixing different kinds of metals or metal oxides as necessary. For example, in the case of silver, it is preferable to mix magnesium, calcium, barium, strontium, indium, zinc, tin, molybdenum oxide, zinc oxide, yttrium oxide, tungsten oxide, indium trioxide, and the like.

The metal layer of the present invention is preferably thinner in order to effectively extract light emitted from the light emitting layer without absorbing it when passing through the metal layer. The thickness of the metal layer is preferably 0.1 to 30 nm, more preferably 0.1 to 10 nm.
When a metal becomes a thin film, it may be observed as an aggregate of grains instead of a film. When the grains are not dense but sparse depending on the film forming method and conditions, the surface of the metal film is observed coarsely, and the conductivity and electron injecting properties are greatly reduced. Therefore, the surface roughness Ra of the surface opposite to the surface in contact with the second layer of the metal layer of the present invention is preferably 1 nm or more and 10 nm or less, more preferably 6 nm or less. The reason why the surface roughness Ra of the metal layer is 1 nm or more and 10 nm or less is that if the distance is between 1 nm and less than 1 nm, the distance between the particles constituting the metal thin film tends to approach or the surface is in contact. This is because it becomes easy to take a so-called island structure in which individual particles exist alone.
Here, the surface roughness (arithmetic mean roughness) Ra is measured with an atomic force microscope. The surface of the sample is scanned with a fine probe, the nanoscale unevenness is measured three-dimensionally, the value within the reference length is extracted from the roughness curve, and the distance from the average value of this value to the actual curve Is defined as the average of the absolute values of

<< Standard electrode potential is -3 Vvs. Layer made of alkali metal or alkaline earth metal noble than SHE or a compound thereof: electron injection layer (second layer 12) >>
The alkali metal or alkaline earth metal according to the present invention has a metal ion (Mn +) / metal (M) standard electrode potential of −3 Vvs. It is characterized by being an alkali metal or alkaline earth metal or a compound thereof more noble than SHE.
Here, the standard electrode potential E ° of the Mn + / M system according to the present invention is an electrode potential with respect to a standard hydrogen electrode in an aqueous solution having a temperature of 25 ° C. and an solute activity of all 1. For example, “Revised Third Edition You can refer to the values in Tables 12 and 46, page II-474 of “Chemical Handbook II” (The Chemical Society of Japan).
According to the present invention, the standard electrode potential of an alkali metal or alkaline earth metal ion (Mn +) / metal (M) system is −3 Vvs. Specific examples of the alkali metal or alkaline earth metal more precious than SHE or the metal constituting these compounds include potassium (-2.925 (V)), calcium (-2.840 (V)). , Sodium (-2.714 (V)), magnesium (-2.356 (V)), rubidium (-2.924 (V)), barium (-2.92 (V)), strontium (-2. 89 (V)).
The alkali metal or alkaline earth metal of the present invention or the metal constituting these compounds is preferably potassium. Elements whose standard electrode potential is lower than -3V, such as cesium (-3.027 (V)) and lithium (-3.045 (V)), have the effect of enhancing the electron injection property, but themselves Since it is easily oxidized, it has a defect of low production compatibility.

<< Standard electrode potential is -3 Vvs. Organic Electron Transport Layer Containing Alkali Metal or Alkaline Earth Metal Noble from SHE, or These Compounds: Electron Transport Layer (Third Layer 13 ) >>
According to the present invention, the standard electrode potential is −3 Vvs. As an organic electron transporting material constituting an organic electron transporting layer containing an alkali metal or alkaline earth metal noble from SHE or a compound thereof, it has a function of transmitting electrons injected from the cathode to the light emitting layer. Any material can be selected and used from conventionally known compounds. Examples include nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, oxadiazole derivatives, phenylpyridine derivatives, and the like.
Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as an electron transport material. Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

In addition, metal complexes of 8-quinolinol derivatives such as tris (8-quinolinol) aluminum (Alq ₃ ), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol) Aluminum, tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), etc., and the central metal of these metal complexes are In, Cu Metal complexes replaced with Sn, Ga or Pb can also be used as the electron transport material. In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transporting material. Further, the distyrylpyrazine derivatives exemplified as the material of the light emitting layer can also be used as the electron transport material, and inorganic semiconductors such as n-type-Si and n-type-SiC can be used as well as the hole injection layer and the hole transport layer. It can be used as an electron transport material.

The electron transport layer can be formed by thinning the electron transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, a printing method including an ink jet method, or an LB method. . Although there is no restriction | limiting in particular about the film thickness of an electron carrying layer, Usually, 5 nm-about 5 micrometers, Preferably it is 5-200 nm. The electron transport layer may have a single layer structure composed of one or more of the above materials.
Preferable examples of the organic electron transporting material include phenylpyridine derivatives.
The standard electrode potential contained in the organic electron transport layer is −3 Vvs. The addition amount of alkali metal or alkaline earth metal, or a compound thereof more noble than SHE is preferably 5 to 50% by volume, particularly preferably 10 to 30% by volume of the whole organic electron transport layer. It is preferable.

<< Organic Electron Transport Layer Containing Only Organic Electron Transport Material (Fourth Layer 14) >>
The organic electron transport layer made of only the organic electron transport material has a standard electrode potential of −3 Vvs. Alkali metals or alkaline earth metals that are noble from SHE, or the same organic electron transporting material that constitutes the organic electron transporting layer containing these compounds can be used.
The organic electron transport layer material consisting only of the organic electron transport material is the same as the organic electron transport material constituting the organic electron transport layer containing an alkali metal or alkaline earth metal, or a compound thereof, which is noble from SHE. More preferably.
Moreover, the film thickness of the organic electron transport layer made of only the organic electron transport material can be adjusted as necessary because recombination of holes and electrons is efficiently performed in the light emitting layer.

<< Organic layer or inorganic layer 15 laminated on the side opposite to the organic electron transport layer as viewed from the metal layer >>
According to the present invention, an organic layer made of an organic material or an inorganic layer made of an inorganic material, which is laminated on the outside of the metal layer (opposite side of the electron transport layer) as needed, is further transparently laminated on the outside thereof. There is no particular limitation as long as it is a material and a film thickness that can alleviate damage from the metal layer to the light emitting layer, which occurs when the conductive layer is formed.
In particular, when ITO is formed by a sputtering method, metal oxide is particularly preferable in that it has a function of absorbing the implantation of ITO particles from the target and suppressing the penetration from the metal layer. In addition, metal complexes represented by tris (8-quinolinol) aluminum (Alq ₃ ), organic electron transporting monomers, polymers, and the like can also be used.
Further, the organic layer and the inorganic layer can be formed by providing a certain pattern according to the electron injecting property and conductivity of the metal layer. Depending on the light emitting area, if the electrical conductivity in the plane direction of the metal layer is insufficient, a very fine through-hole is provided in the organic layer or inorganic layer, and contact is made directly from the transparent conductive layer described later. It is possible to ensure the properties and substantially eliminate the damage during the film formation.
Examples of the certain pattern include stripes, lattices, and dot patterns.

<< Transparent conductive layer 16 >>
Since the metal layer of the present invention is extremely thin, chemical and physical destruction may occur due to various external factors such as when a flexible plastic is used instead of hard glass as a substrate.
Moreover, as mentioned above, when ensuring a required light emission area, the necessity for supplementing the electroconductivity of a metal layer arises. In such a case, a transparent conductive layer is further formed, the conductivity is ensured by directly contacting the metal layer, and a stronger film is laminated on the outside of the thin film metal layer to obtain physical strength. Is also preferable.
As the transparent conductive layer, for example, ITO formed by sputtering is preferably used.

<< Auxiliary electrode 17 >>
In the organic EL device of the present invention, an auxiliary electrode can be provided on the metal layer or the transparent conductive layer for the purpose of reducing the sheet resistance of the metal layer or the transparent conductive film.
As a material for forming the auxiliary electrode, a metal having low resistance such as gold, platinum, silver, copper, and aluminum is preferable.
Examples of the method for forming the auxiliary electrode include a vapor deposition method, a sputtering method, a printing method, an ink jet method, and an aerosol jet method.
The pattern is not particularly limited, such as a lattice, stripe, or honeycomb, and the line width of the auxiliary electrode of the present invention is preferably 50 μm or less from the viewpoint of the aperture ratio of the transparent conductive layer, and the pitch is 500 μm or more. The thickness of the auxiliary electrode is preferably 1 μm or more from the viewpoint of conductivity.

<Light emitting layer>
The light emitting layer of the present invention is characterized by containing a phosphorescent compound as a light emitting material.
The light-emitting layer is a layer that emits light by recombination of electrons and holes injected from the electrode, the electron transport layer, or the hole transport layer. It may be an interface with an adjacent layer.
As a light emitting layer, if the light emitting material contained satisfies the light emission requirement, there will be no restriction | limiting in particular in the structure. Moreover, there may be a plurality of layers having the same emission spectrum and emission maximum wavelength. Moreover, it is preferable to have a non-light emitting intermediate | middle layer between each light emitting layer.

The total thickness of the light emitting layers is preferably in the range of 1 to 100 nm, and more preferably 1 nm or more and 30 nm or less because a lower driving voltage can be obtained. Note that the total film thickness of the light emitting layer is a film thickness including the intermediate layer when a non-light emitting intermediate layer exists between the light emitting layers.
The thickness of each light emitting layer is preferably adjusted to a range of 1 to 50 nm, more preferably adjusted to a range of 1 to 20 nm. There is no particular limitation on the relationship between the film thicknesses of the blue, green and red light emitting layers.

For the production of the light-emitting layer, a light-emitting material or a host compound, which will be described later, is formed by forming a film by a known thin film forming method such as a vacuum deposition method, a spin coating method, a casting method, an LB method, or an inkjet method. it can.
Each light emitting layer may be a mixture of a plurality of light emitting materials, or a phosphorescent light emitting material and a fluorescent light emitting material may be mixed and used in the same light emitting layer.
As a structure of the light emitting layer, it is preferable to contain a host compound and a light emitting material (also referred to as a light emitting dopant compound) and emit light from the light emitting material.

<Host compound>
As the host compound contained in the light emitting layer of the organic EL device, a compound having a phosphorescence quantum yield of phosphorescence emission at room temperature (25 ° C.) of less than 0.1 is preferable. More preferably, the phosphorescence quantum yield is less than 0.01. Moreover, it is preferable that the volume ratio in the layer is 50% or more among the compounds contained in a light emitting layer.
As the host compound, known host compounds may be used alone or in combination of two or more. By using a plurality of types of host compounds, it is possible to adjust the movement of charges, and the organic EL element can be made highly efficient. In addition, by using a plurality of kinds of light emitting materials described later, it is possible to mix different light emission, thereby obtaining an arbitrary light emission color.
The host compound used may be a conventionally known low molecular compound, a high molecular compound having a repeating unit, or a low molecular compound having a polymerizable group such as a vinyl group or an epoxy group (evaporation polymerizable light emitting host). .
As the known host compound, a compound having a hole transporting ability and an electron transporting ability, preventing an increase in emission wavelength, and having a high Tg (glass transition temperature) compound is preferable. The glass transition point (Tg) here is a value obtained by a method based on JIS-K-7121 using DSC (Differential Scanning Colorimetry).

  Specific examples of known host compounds include compounds described in the following documents. For example, Japanese Patent Application Laid-Open Nos. 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357777, 2002-334786, 2002-8860 Gazette, 2002-334787 gazette, 2002-15871 gazette, 2002-334788 gazette, 2002-43056 gazette, 2002-334789 gazette, 2002-75645 gazette, 2002-338579 gazette. No. 2002-105445, No. 2002-343568, No. 2002-141173, No. 2002-352957, No. 2002-203683, No. 2002-363227, No. 2002-231453. No. 2003-3165, No. 2002-234888, No. 2003-27048, No. 2002-255934, No. 2002-286061, No. 2002-280183, No. 2002-299060. 2002-302516, 2002-305083, 2002-305084, 2002-308837, and the like.

<Light emitting material>
Next, the light emitting material will be described.
As the light-emitting material, a phosphorescent material (also referred to as a phosphorescent compound or a phosphorescent compound) can be used.
A phosphorescent material is a compound in which light emission from an excited triplet is observed. Specifically, it is a compound that emits phosphorescence at room temperature (25 ° C.), and the phosphorescence quantum yield is 0.01 or more at 25 ° C. However, the preferable phosphorescence quantum yield is 0.1 or more.
The phosphorescence quantum yield can be measured by the method described in Spectroscopic II, page 398 (1992 edition, Maruzen) of the Fourth Edition Experimental Chemistry Course 7. The phosphorescence quantum yield in a solution can be measured using various solvents. However, when a phosphorescent material is used in the present invention, the phosphorescence quantum yield (0.01 or more) is achieved in any solvent. Just do it.
There are two types of light emission principles of phosphorescent materials. One is the recombination of carriers on the host compound to which carriers are transported, generating an excited state of the host compound, and this energy is transferred to the phosphorescent material. The energy transfer type is to obtain light emission from the phosphorescent light emitting material, and the other is that the phosphorescent light emitting material becomes a carrier trap, and carrier recombination occurs on the phosphorescent light emitting material, and light emission from the phosphorescent light emitting material is obtained. In any case, the excited state energy of the phosphorescent light emitting material is required to be lower than the excited state energy of the host compound.
The phosphorescent light-emitting material can be appropriately selected from known materials used for the light-emitting layer of the organic EL element, and is preferably a complex compound containing a group 8-10 metal in the periodic table of elements. More preferably, an iridium compound, an osmium compound, or a platinum compound (platinum complex compound), or a rare earth complex, and most preferably an iridium compound.

《Hole injection layer》
The details of the hole injection layer are described in JP-A-9-45479, JP-A-9-260062, JP-A-8-288069, and the like. As a specific example, a phthalocyanine layer represented by copper phthalocyanine And an oxide layer typified by vanadium oxide, an amorphous carbon layer, and a polymer layer using a conductive polymer such as polyaniline (emeraldine) or polythiophene.

<Blocking layer: hole blocking layer, electron blocking layer>
The blocking layer is provided as necessary in addition to the basic constituent layer of the organic compound thin film as described above. For example, they are described in JP-A Nos. 11-204258 and 11-204359, and “Organic EL elements and their forefront of industrialization” (issued on November 30, 1998 by NTS Corporation). There is a hole blocking (hole blocking) layer.
In a broad sense, the hole blocking layer has a function of an electron transport layer and is composed of a hole blocking material having a function of transporting electrons and having a remarkably small ability to transport holes, while transporting electrons. By blocking holes, the recombination probability of electrons and holes can be improved. Moreover, the structure of the electron carrying layer mentioned later can be used as a hole-blocking layer concerning this invention as needed. The hole blocking layer is preferably provided adjacent to the light emitting layer.
On the other hand, the electron blocking layer, in a broad sense, has a function of a hole transport layer, and is made of a material having a function of transporting holes while having a remarkably small ability to transport electrons, while transporting holes. By blocking electrons, the probability of recombination of electrons and holes can be improved. Moreover, the structure of the positive hole transport layer mentioned later can be used as an electron blocking layer as needed. The thickness of the hole blocking layer according to the present invention is preferably 3 to 100 nm, and more preferably 5 to 30 nm.

《Hole transport layer》
The hole transport layer is made of a hole transport material having a function of transporting holes, and in a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. The hole transport layer can be provided as a single layer or a plurality of layers.
The hole transport material has any one of hole injection or transport and electron barrier properties, and may be either organic or inorganic. For example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, Examples thereof include stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, particularly thiophene oligomers.
The above-mentioned materials can be used as the hole transport material, but it is preferable to use a porphyrin compound, an aromatic tertiary amine compound and a styrylamine compound, particularly an aromatic tertiary amine compound.

  Representative examples of aromatic tertiary amine compounds and styrylamine compounds include N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl; N, N′-diphenyl-N, N′— Bis (3-methylphenyl)-[1,1′-biphenyl] -4,4′-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl; 1,1-bis (4-di-p-tolyl) Aminophenyl) -4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N'-diphenyl-N, N ' Di (4-methoxyphenyl) -4,4'-diaminobiphenyl; N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis (diphenylamino) quadriphenyl N, N, N-tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 '-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenylamino -(2-diphenylvinyl) benzene; 3-methoxy-4'-N, N-diphenylaminostilbenzene; N-phenylcarbazole, and also two described in US Pat. No. 5,061,569 Having a condensed aromatic ring of, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-308 4,4 ', 4 "-tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units described in Japanese Patent No. 88 are linked in a starburst type ( MTDATA) and the like.

Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used. In addition, inorganic compounds such as p-type-Si and p-type-SiC can also be used as the hole injection material and the hole transport material.
JP-A-11-251067, J. Org. Huang et. al. A so-called p-type hole transport material described in a book (Applied Physics Letters 80 (2002), p. 139) can also be used. In the present invention, it is preferable to use these materials because a light-emitting element with higher efficiency can be obtained.

The hole transport layer is formed by thinning the hole transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, a printing method including an ink jet method, or an LB method. Can do. Although there is no restriction | limiting in particular about the film thickness of a positive hole transport layer, Usually, 5 nm-about 5 micrometers, Preferably it is 5-200 nm. The hole transport layer may have a single layer structure composed of one or more of the above materials.
Alternatively, a hole transport layer having a high p property doped with impurities can be used. Examples thereof include JP-A-4-297076, JP-A-2000-196140, 2001-102175, J.A. Appl. Phys. 95, 5773 (2004), and the like.
It is preferable to use such a hole transport layer having a high p property because an element with lower power consumption can be manufactured.

"anode"
As the anode, the above-described material constituting the transparent conductivity may be used, or an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof may be used.
Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like.
The anode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering.
The sheet resistance as the anode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 nm to 200 nm.

[Usage]
The organic EL element of the present invention can be used as a display device, a display, and various light emission sources. Examples of light sources include home lighting, interior lighting, clock and liquid crystal backlights, billboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processors, and light sources for optical sensors. Although it is not limited to this, it can be effectively used for a backlight of a liquid crystal display device combined with a color filter and a light source for illumination.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "%" is used in an Example, unless otherwise indicated, "volume%" is represented.

Example 1
[Production of bottom emission type organic EL element]
The organic EL elements 101 to 111 were prepared so that the light emission area was 5 cm × 5 cm.
<Preparation of organic EL element 101>
(Formation of anode)
ITO was formed and patterned on a transparent glass substrate by a sputtering method under a condition of a thickness of 100 nm to form an anode made of an ITO layer. Next, the substrate provided with the ITO layer was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.
(Formation of hole injection layer to electron transport layer)
The substrate provided with this ITO layer is fixed to a substrate holder of a commercially available vacuum deposition apparatus, α-NPD (Bis [N- (1-naphthyl) -N-pheny] benzidine), shown below, on a tantalum resistance heating board. Host compound H4, dopant compound Ir-4 shown below, BAlq (Bis (2-methyl-8-quinolinolato-N1, O8)-(1,1′-Biphenyl-4-olato) aluminum), Alq ₃ , fluoride Potassium was added and attached to the first vacuum chamber of the vacuum deposition apparatus.

更に、タングステン製抵抗加熱ボードにアルミニウム、銀を入れ、真空蒸着装置の第２真空槽に取り付けた。
まず、第１真空槽を４×１０^−４Ｐａまで減圧した後、α−ＮＰＤの入った前記加熱ボードに通電して加熱し、蒸着速度０．１ｎｍ／秒〜０．２ｎｍ／秒でＩＴＯ層上に膜厚２０ｎｍの正孔注入／正孔輸送層を設けた。
更に、前記ホスト化合物Ｈ４の入った前記加熱ボードとＩｒ−４の入ったボードをそれぞれ独立に通電して、発光ホストであるＨ４と発光ドーパントであるＩｒ−４の蒸着速度が１００：６になるように調節し、膜厚３０ｎｍの発光層を設けた。
次いで、ＢＡｌｑの入った前記加熱ボードに通電して加熱し、蒸着速度０．１ｎｍ／秒〜０．２ｎｍ／秒で膜厚１０ｎｍの正孔阻止層を設けた。更に、Ａｌｑ_３の入った前記加熱ボードを通電して加熱し蒸着速度０．１ｎｍ／秒〜０．２ｎｍ／秒で膜厚３５ｎｍの電子輸送層（第４の層）を設けた。
（電子注入層の形成）
次に、フッ化カリウムの入った前記加熱ボードに通電して加熱し、蒸着速度０．０１ｎｍ／秒〜０．０２ｎｍ／秒で膜厚１ｎｍのフッ化カリウム層を形成し、電子注入層（第２の層）を設けた。
（陰極の形成）
次いで、基板を５×１０^−５Ｐａまで減圧した第２真空糟に移動し、アルミニウムを蒸着速度０．２〜０．４ｎｍ／秒で１００ｎｍの膜厚となるまで蒸着した。
（素子の封止）
〈保護層（無機防湿膜）の形成〉
作製された有機ＥＬ素子を使用し、蒸着法で、５×１０^−１Ｐａの真空下にて、保護層（無機防湿膜）形成材料として窒化ケイ素を使用し、陽極の取り出し電極及び陰極の取り出し電極の一部を除いて、陰極の上に陽極の取り出し電極を除いた部分の水平投影面積に対して４５％（有機化合物層である発光層の水平投影面積に対しては１２９％）になるようにして厚さ１００ｎｍの保護層（無機防湿膜）をパターン成膜で形成した。
〈絶縁層（接着剤の塗設）の形成〉
引き続き、保護層の水平投影面積に合わせ保護層上に厚さ４０μｍの絶縁層（接着剤層）を陽極及び陰極の取り出し電極の部分を除き塗設した。尚、接着剤として、大日本インキ株式会社製エポキシ樹脂ＥＰＩＣＬＯＮ８５０と、日本化成株式会社製接着付与剤ヒッタイトＳ、及び日本油脂株式会社製有機過酸化物パークミルＨを、この順で１００／３／１（重量部）で混合したものを用いた。
〈ガラス封止部材の保護層（無機防湿膜）への固定〉
引き続き、ガラス封止部材として厚さ０．７ｍｍのガラスを使用し、保護層（無機防湿膜）の上に塗設した絶縁層（接着剤）の上にガラス封止部材を、０．９×１０^−０Ｐａで真空引きしながら、押圧０．１ＭＰａで貼合した後、大気圧８０℃環境下にて３時間放置して貼着し固定した。

Furthermore, aluminum and silver were put into a resistance heating board made of tungsten and attached to the second vacuum chamber of the vacuum evaporation apparatus.
First, after reducing the pressure of the first vacuum chamber to 4 × 10 ⁻⁴ Pa, the heating board containing α-NPD was energized and heated, and the ITO layer was deposited at a deposition rate of 0.1 nm / second to 0.2 nm / second. A hole injection / hole transport layer having a thickness of 20 nm was provided thereon.
Further, the heating board containing the host compound H4 and the board containing Ir-4 are energized independently, and the deposition rate of H4 as the light emitting host and Ir-4 as the light emitting dopant becomes 100: 6. Thus, a light emitting layer having a thickness of 30 nm was provided.
Next, the heating board containing BAlq was energized and heated to provide a 10 nm thick hole blocking layer at a deposition rate of 0.1 nm / second to 0.2 nm / second. Further, the heating board containing Alq ₃ was heated by energization to provide an electron transport layer ( fourth layer) having a film thickness of 35 nm at a deposition rate of 0.1 nm / second to 0.2 nm / second.
(Formation of electron injection layer)
Next, the heating board containing potassium fluoride is energized and heated to form a 1 nm-thickness potassium fluoride layer at a deposition rate of 0.01 nm / second to 0.02 nm / second, and an electron injection layer (first 2 layers).
(Formation of cathode)
Next, the substrate was moved to a second vacuum bottle whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and aluminum was vapor deposited at a vapor deposition rate of 0.2 to 0.4 nm / second until a film thickness of 100 nm was obtained.
(Element sealing)
<Formation of protective layer (inorganic moisture barrier film)>
Using the produced organic EL element, by vapor deposition, under a vacuum of 5 × 10 ⁻¹ Pa, using silicon nitride as a protective layer (inorganic moisture barrier film) forming material, taking out the anode and taking out the cathode Except for a part of the electrode, it is 45% with respect to the horizontal projected area of the portion excluding the anode extraction electrode on the cathode (129% with respect to the horizontal projected area of the light emitting layer which is an organic compound layer). In this way, a protective layer (inorganic moisture barrier film) having a thickness of 100 nm was formed by pattern deposition.
<Formation of insulating layer (adhesive coating)>
Subsequently, an insulating layer (adhesive layer) having a thickness of 40 μm was applied on the protective layer in accordance with the horizontal projection area of the protective layer, excluding the portions of the anode and cathode extraction electrodes. In addition, Dainippon Ink Co., Ltd. epoxy resin EPICLON850, Nippon Kasei Co., Ltd. adhesion grant agent Hittite S, and Nippon Oil & Fats Co., Ltd. organic peroxide park mill H in this order are 100/3/1. What was mixed by (weight part) was used.
<Fixing of glass sealing member to protective layer (inorganic moisture barrier film)>
Subsequently, 0.7 mm thick glass was used as the glass sealing member, and the glass sealing member was 0.9 × on the insulating layer (adhesive) coated on the protective layer (inorganic moisture-proof film). While being vacuumed at 10 ⁻⁰ Pa and pasting at a pressure of 0.1 MPa, it was left for 3 hours in an atmospheric pressure 80 ° C. environment for pasting and fixing.

<Preparation of organic EL element 102>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 101.
(Formation of cathode)
Next, the substrate was moved to a second vacuum chamber whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and aluminum was deposited at a deposition rate of 0.2 to 0.4 nm / second until a film thickness of 35 nm was obtained.
(Element sealing)
The organic EL element 102 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 103>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 101.
(Formation of cathode)
Next, the substrate was moved to a second vacuum chamber whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and aluminum was deposited at a deposition rate of 0.2 to 0.4 nm / second until a film thickness of 25 nm was obtained.
(Element sealing)
The organic EL element 103 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 104>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 101.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and aluminum was vapor deposited at a vapor deposition rate of 0.2 to 0.4 nm / second until a film thickness of 15 nm was obtained.
(Element sealing)
The organic EL element 104 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 105>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 1051.
(Formation of cathode)
Next, the substrate was moved to a second vacuum chamber whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and aluminum was deposited at a deposition rate of 0.2 to 0.4 nm / second until a film thickness of 10 nm was obtained.
(Element sealing)
The organic EL element 105 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 106>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 101.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and silver was deposited at a deposition rate of 0.2 to 0.4 nm / second until a film thickness of 100 nm was obtained.
(Element sealing)
The organic EL element 106 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 107>
(Formation of anode to luminescent layer)
The film from the anode to the light emitting layer was formed by the same method as that for the organic EL element 101.
(Formation of electron transport layer (fourth layer))
The heating board containing Alq ₃ was energized and heated to provide an electron transport layer having a film thickness of 5 nm at a deposition rate of 0.1 nm / second to 0.2 nm / second.
(Formation of alkali metal-containing electron transport layer (third layer))
The heating board containing Alq ₃ is energized and heated, and at the same time, the heating board containing potassium fluoride is energized and heated, and the ratio of deposition rate is Alq ₃ : potassium fluoride = 1: 0.2. And an electron transport layer doped with 20% by volume of alkali metal with a film thickness of 30 nm at a film formation rate of potassium fluoride of 0.1 nm / second was provided.
(Formation of electron injection layer)
Next, the heating board containing potassium fluoride is energized and heated to form a potassium fluoride layer having a thickness of 1 nm at a deposition rate of 0.01 nm / second to 0.02 nm / second, and an electron injection layer is provided. It was.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and silver was deposited at a deposition rate of 0.02 to 0.03 nm / second until a film thickness of 33 nm was obtained.
(Element sealing)
The organic EL element 107 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 108>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 107.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and silver was deposited at a deposition rate of 0.02 to 0.03 nm / second until a film thickness of 25 nm was obtained.
(Element sealing)
The organic EL element 108 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 109>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 107.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and silver was deposited at a deposition rate of 0.02 to 0.03 nm / second until a film thickness of 15 nm was obtained.
(Element sealing)
The organic EL element 109 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 110>
(Formation of anode to electron injection layer)
The layers from the anode to the electron injection layer were formed by the same method as that for the organic EL element 107.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and silver was deposited at a deposition rate of 0.02 to 0.03 nm / second until a film thickness of 10 nm was obtained.
(Element sealing)
The organic EL element 110 was sealed in the same manner as the organic EL element 101.

<Preparation of organic EL element 111>
(Formation of anode to electron transport layer)
The film from the anode to the electron transport layer was formed by the same method as that for the organic EL element 107.
(Formation of alkali metal-containing electron transport layer (third layer))
The heating board containing Alq ₃ is energized and heated, and at the same time, the heating board containing lithium fluoride is energized and heated, so that the deposition rate ratio becomes Alq ₃ : lithium = 1: 0.2. Thus, an electron transport layer doped with 20% by volume of an alkali metal with a film thickness of 30 nm was provided at a film formation rate of potassium fluoride of 0.1 nm / second.
(Formation of electron injection layer)
Next, the heating board containing lithium fluoride is energized and heated to form a 1 nm-thick potassium fluoride layer at a deposition rate of 0.01 nm / second to 0.02 nm / second, and an electron injection layer is provided. It was.
(Formation of cathode)
Next, the substrate was moved to a second vacuum trough whose pressure was reduced to 5 × 10 ⁻⁵ Pa, and silver was deposited at a deposition rate of 0.02 to 0.03 nm / second until a film thickness of 33 nm was obtained.
(Element sealing)
The organic EL element 107 was sealed in the same manner as the organic EL element 101.

[Evaluation of organic EL elements]
About each produced said organic EL element, it evaluated according to the following method.
(Voltage measurement)
With respect to each organic EL element produced above, the voltage of each organic EL element is measured as the voltage when the sum of the front luminances on both the anode side and the cathode side becomes 1000 cd / m ^2, and the organic EL element is used as a comparison. The relative value when the driving voltage of 101 was 100 was determined.
A spectral radiance meter CS-1000 (manufactured by Konica Minolta Sensing) was used for the measurement of luminance. The closer the obtained voltage value is to 100 and the smaller the value is, the better the result.
Moreover, the ratio of the luminance on both sides when the sum of the front luminances on both sides was 1000 cd / m ² was determined.

(Measurement of luminous efficiency)
For each of the organic EL devices produced above, the external extraction quantum efficiency (%) when a ^2.5 mA / cm ² constant current was passed was measured.
For the measurement, a spectral radiance meter CS-1000 (manufactured by Konica Minolta Sensing) was used. At this time, the external extraction quantum efficiency was calculated from the total value of the luminance (double-sided total luminance [Cd / m ² ]) measured from both sides of the organic EL element.
Based on the measurement result of the obtained external extraction quantum efficiency (%), a relative value when the external extraction quantum efficiency (%) of the organic EL element 101 was set to 100 was obtained, and this was used as a measure of luminous efficiency. The larger the relative value of the external quantum efficiency, the higher the light emission efficiency, which represents a preferable result.
The results obtained as described above are shown in Table 1.

  As is clear from the results shown in Table 1, the organic EL device according to the present invention uses a metal whose extinction coefficient at 550 nm is 5.0 or less, and has a standard electrode potential in the electron transport layer or the electron injection layer. Since an alkali metal that is nobler than −3.0 V (vs. SHE) is used, it is recognized that the luminous efficiency and driving voltage from the cathode side are excellent. In particular, it can be seen that the light emitting efficiency and driving voltage are excellent when a double-sided light emitting device is used, and the light emission balance on both sides is also excellent.

Example 2
With respect to the organic EL element 106 described in Example 1, organic EL elements 201 to 211 were produced in the same manner as the organic EL element 101 except that the cathode configuration was changed to that shown in Table 2. In addition, a single film sample was prepared by heating vapor deposition on quartz glass, except for the organic EL element, only for the cathode configuration.
The produced organic EL element was evaluated in the same manner as in Example 1. Further, the surface roughness Ra of the quartz glass single film sample was evaluated by an atomic force microscope. The results are shown in Table 2.

As is clear from the results shown in Table 2, the organic EL device according to the present invention uses a metal having an extinction coefficient of 5.0 or less at 550 nm, even when different types of metals are mixed, and an electron transport layer. In addition, since an alkali metal having a standard electrode potential nobler than −3.0 V (vs. SHE) is used for the electron injection layer, it is recognized that the emission efficiency and driving voltage from the cathode side are excellent. In particular, it can be seen that the light emitting efficiency and driving voltage are excellent when a double-sided light emitting device is used, and the light emission balance on both sides is also excellent.
It can also be seen that the cathode layer is particularly excellent when the surface roughness Ra is 10 nm or less.
Further, after the organic EL elements 101, 106, 205, and 211 were stored at a constant temperature of 70 ° C. for 500 hours, the organic EL elements were evaluated for driving voltage, luminance, and luminescent pixels. The change in electrical characteristics was extremely small, within + 7% before storage and within ± 3% luminance. Further, neither the edge portion of the light emitting pixel became dark nor the occurrence of black spots could be confirmed.

Example 3
The organic EL elements 105 and 110 produced in Example 1 and the organic EL elements 205 and 211 produced in Example 2 were produced under the same conditions up to the electron injection layer. After forming the cathode layer, the line width was 100 μm. An organic EL device is similarly used except that a 2 mm pitch stripe mask (this means that an auxiliary electrode having a width of 100 μm and an interval of 2 mm can be formed after vapor deposition) is used, and aluminum is vapor deposited to a film thickness of 100 nm. The organic EL elements were designated as 301, 302, 303, and 304 in this order. Furthermore, the same organic EL element was produced from these organic EL elements except that the film thickness of the cathode layer was changed to 5 nm, and the respective organic EL elements were designated as 311, 312, 313 and 314 in this order.
The drive voltage and luminous efficiency of the produced organic EL element were measured in the same manner as in Example 1. Moreover, the transmittance of the organic EL element was also measured. The transmittance was measured with an NDH-5000 type haze meter manufactured by Nippon Denshoku Industries Co., Ltd. The results are shown in Table 3.

  As is apparent from the results shown in Table 3, when the auxiliary electrode is provided on the surface of the thin film dissimilar metal mixed cathode, the driving voltage is further reduced, and even when the thin film dissimilar metal mixed cathode is further thinned, the driving is low. It can be seen that the voltage is maintained, the transmittance of the organic EL element is improved, the transparency is higher, and the light emission efficiency on both sides is improved.

Example 4
The organic EL elements 105 and 110 produced in Example 1 and the organic EL elements 205 and 211 produced in Example 2 and the electron injection layer were produced under the same conditions, and after forming the cathode layer, Each organic EL element is moved to the first vacuum chamber, heated by energizing the heating board containing molybdenum trioxide (MoO ₃ ), and deposited at a deposition rate of 0.1 nm / second to 0.13 nm / second. A 30 nm MoO ₃ layer was formed, and a sputtering buffer layer (inorganic layer) was provided.
Next, each organic EL element is transported into a chamber of a radio frequency (RF) sputtering apparatus, and an RF output of 300 W, a substrate, and a substrate are introduced while introducing a mixed gas of oxygen and argon (oxygen ratio: 2.2 vol%) using ITO as a target. Sputtering was performed for 180 seconds using a mask patterned up to the light emitting area part electrode extraction part under a pressure of 2.2 × 10 ⁻¹ Pa under the condition of a distance of 17.8 mm between ITO targets, and a film thickness of 135 nm. A patterned ITO thin film (transparent conductive layer) was formed on the MoO ₃ layer (inorganic layer). 401 is the organic EL element with the above-described changes to the organic EL element 105, 402 is the organic EL element with the above-mentioned changes to the organic EL element 110, 403 is the organic EL element with the above-mentioned changes to the organic EL element 205, and the organic EL An organic EL element obtained by adding the above-described change to the element 211 was designated as 404.
Further, for the organic EL elements 401 to 404, the same organic EL elements were prepared except that the thickness of each cathode layer was changed to 5 nm, and the respective organic EL elements were sequentially designated as 411, 412, 413, and 414. .
Table 4 shows the results obtained by measuring the driving voltage, the light emission efficiency, and the transmittance of the organic EL element in the same manner as in Example 3.

As is clear from the results shown in Table 4, even when an ITO film was formed as the transparent conductive layer and a sputtering buffer layer (inorganic layer) made of MoO ₃ was used in order to use the RF sputtering method for the film formation, It can be seen that the device emits light at a low driving voltage and has higher luminous efficiency than that of aluminum having a comparatively high extinction coefficient, and is an extremely transparent device.

Example 5
Organic EL elements 105 and 110 produced in Example 1 and organic EL elements 205 and 211 produced in Example 2 were produced under the same conditions up to the electron injection layer, and the cathode layer was made of each of the materials used. Were formed to have the same film thickness of 3 mm as shown in Table 5.
Next, after each organic EL element is moved to the first vacuum chamber, it is striped with a line width of 2 mm and a pitch of 200 μm (this means that a film with a width of 2 mm is formed with an interval of 200 μm. using the deposition mask), the Alq ₃ filled in the heating boat was deposited by evaporation to a thickness 150 nm, it was sputtered buffer layer (inorganic layer) was formed. Thereafter, in the same manner as in Example 4, the film was transferred into a chamber of an RF sputtering apparatus, and ITO was deposited to a thickness of 135 nm by sputtering to provide a transparent conductive layer. The organic EL element 105 in which the change is made is 501, the organic EL element in which the change is made in the organic EL element 110 is 502, the organic EL element in which the change is made in the organic EL element 205 is 503, and the organic EL element An organic EL element obtained by adding the above-described change to the element 211 was designated as 504.
Table 5 shows the results obtained by measuring the driving voltage, light emission efficiency, and transmittance of the organic EL element in the same manner as in Example 1.

As is clear from the results shown in Table 5, the Alq ₃ sputter buffer layer (inorganic layer) is patterned, and the sputtered ITO (transparent conductive layer) is in a very small area and the film thickness is further reduced. It can be seen that the drive voltage is lowered by contact with the thin metal cathode layer. Moreover, it turns out that it has become the more preferable organic EL element excellent in the see-through property by making the transmittance | permeability of an organic EL element improved because the film thickness of the thin film metal cathode layer was made thinner.

Example 6
Regarding the organic EL elements 411, 412, 413, and 414 produced in Example 4, the metal thin film cathode layer was set to 3 nm and the line width was formed on the MoO ₃ layer (inorganic layer) in the same manner as in Example 3. An auxiliary electrode was formed by vapor-depositing aluminum to a thickness of 100 nm using a vapor deposition mask having a stripe shape of 100 μm and a pitch of 2 mm (which means that an auxiliary electrode having a width of 100 μm and an interval of 2 mm can be formed after vapor deposition). Except for the above, an organic EL element was similarly produced. The organic EL element 601 is changed to the organic EL element 411, the organic EL element 412 is changed to the organic EL element 602, the organic EL element 413 is changed to the organic EL element 603, and the organic EL element is changed to 603. An organic EL element obtained by adding the above-described change to the element 414 was designated as 604.
The driving voltage, luminous efficiency, and transmittance of the organic EL element were measured in the same manner as in Example 1. The results are shown in Table 6.

As is clear from the results shown in Table 6, the organic EL device in which the thin-film metal cathode layer was further thinned and the aluminum auxiliary electrode was formed on the MoO ₃ layer (inorganic layer) had a lower driving voltage. And it turns out that the transmittance | permeability of an organic EL element is also improving.

Example 7
Regarding the organic EL element 110 produced in Example 1, a layer (second layer) made of an alkali metal or the alkali metal compound, or an alkaline earth metal or the alkaline earth metal compound, and an alkali metal or the alkali metal compound Or an alkali metal or the alkali metal compound, or an alkaline earth metal or the alkaline earth metal compound of a layer (third layer) made of an organic electron transport material containing an alkaline earth metal or an alkaline earth metal compound Organic EL elements 701 to 703 were produced in the same manner except that was replaced with the compounds shown in Table 7.
The driving voltage, light emission efficiency, and transmittance of the organic EL element were measured in the same manner as in Example 3. Further, the ratio of the luminance of both surfaces when the sum of the initial luminances of the front surfaces of both surfaces was 10,000 cd was obtained. Furthermore, the organic EL element was continuously driven at the current value when the initial luminance on the front side was 1000 cd, and the time until the luminance became 500 cd was measured. The results are shown in Table 7.

  As is clear from the results shown in Table 7, the material doped in the electron transport layer (third layer) and the material constituting the electron injection layer (second layer), which are the structures of the present invention, are the same. In this case, it can be seen that the drive life of the element is particularly excellent.

10 unit 11 first layer (metal layer, cathode)
12 Second layer (electron injection layer)
13 Third layer (electron transport layer)
14 Fourth layer (electron transport layer)
15 Organic layer or inorganic layer 16 Transparent conductive layer 17 Auxiliary electrode

Claims (7)

A first layer containing a metal having a thickness of 0.1 to 30 nm and an extinction coefficient at 550 nm of 5.0 or less;
Standard electrode potential is −3 V vs. A second layer of an alkali metal or the alkali metal compound that is noble than SHE, or an alkaline earth metal or the alkaline earth metal compound;
Standard electrode potential is −3 V vs. A third layer made of an organic electron transport material containing an alkali metal that is noble than SHE or the alkali metal compound, or an alkaline earth metal or alkaline earth metal compound;
An organic electroluminescence device comprising a unit in which a fourth layer made of only an organic electron transporting material is laminated in this order.   2. The organic electroluminescence device according to claim 1, wherein a surface roughness Ra of a surface opposite to the surface in contact with the second layer of the first layer is 1 nm or more and 10 nm or less.   The organic electroluminescence element according to claim 1, wherein an auxiliary electrode is laminated on a surface of the first layer opposite to the second layer. An organic layer made of an organic material or an inorganic layer made of an inorganic material is laminated on the surface of the first layer opposite to the second layer,
The organic electroluminescence element according to claim 1, wherein a transparent conductive layer is laminated on a surface of the organic layer or the inorganic layer opposite to the second layer.   The organic electroluminescence device according to claim 4, wherein the organic layer and the inorganic layer have a certain pattern shape.   The organic electroluminescence element according to claim 4, wherein an auxiliary electrode is laminated on a surface of the transparent conductive layer opposite to the organic layer or the inorganic layer. The alkali metal or alkali metal compound of the second layer, or the alkaline earth metal or alkaline earth metal compound, and the alkali metal or alkali metal compound contained in the third layer, or the alkaline earth metal or alkaline earth The organic electroluminescent element according to claim 1, wherein the organometallic compound is the same.

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