JP2003282265A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element realizing a long service life and high luminous efficiency by specifying a luminescent organic substance doped into an organic luminescent layer. <P>SOLUTION: This organic electroluminescent element is provided, between a positive electrode 1 and a negative electrode 2, with the luminescent layers 3 each formed of an organic material with the luminescent organic substance doped. The element is provided with a plurality of luminescent layers 3a, 3b and 3c formed of the organic materials with luminescent organic substances different from one another doped, and a luminescent organic substance having an energy gap larger than those of the luminescent organic substances doped into the other luminescent layers 3b and 3c is doped into the luminescent layer 3a positioned on the nearest side to the negative electrode 2. By specifying the energy gaps of the luminescent organic substances doped into the luminescent layers 3 like this, the efficiency of carrier movement and energy movement between the adjacent luminescent layers 3 can be enhanced. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device used for flat panel displays, backlights for liquid crystal displays, illumination light sources and the like.

[0002]

2. Description of the Related Art As a light emitter used for a flat panel display, a backlight for a liquid crystal display, a light source for illumination, etc., a flat panel display is made thinner, an electronic device having a liquid crystal display is made smaller and thinner, or a lighting device. In recent years, there has been an increasing demand for thin, lightweight, and highly efficient products due to the liberalization of the shape of the. As an element that can meet such requirements, an organic electroluminescence element (organic electroluminescence element) has been attracting attention.

The fact that the organic electroluminescent device emits light at a low voltage is described by C. of Eastman Kodak Company. W. Tang et al. Showed for the first time in an element having a structure in which two thin films are laminated between electrodes (Appl. Phys. Lett.,
51, 12, 913 (1987)). And after this,
The organic electroluminescent device can emit light with high brightness of about 100 to 100,000 cd / m ² at a low voltage of about 10 V such as a battery, and can emit a large number of colors by combining the materials forming the fluorescent material. Because it can be used as a very thin surface light emitter, it has attracted attention in the industrial world,
Organic electroluminescent devices having various thin film structures, which are improvements in device structure, have been studied.

Here, the basic device structure of the organic electroluminescent device is anode / organic light emitting layer / cathode, but in addition, the structure of anode / hole transport layer / organic light emitting layer / electron transport layer / cathode, Anode / hole injection layer / hole transport layer / organic emission layer / electron transport layer / cathode configuration, anode / hole injection layer / organic emission layer / electron transport layer / electron injection layer / cathode configuration, anode / hole injection Various configurations such as a layer / organic light emitting layer / electron injection layer / cathode configuration can be mentioned.

Optimization of each of the above layers has been studied for the purpose of improving the luminous efficiency of the organic electroluminescent device. That is, the ionization potential of each layer,
Various studies have been conducted on the device structure from the viewpoint of electron affinity, and the hole-electron recombination efficiency is improved by blocking holes and electrons at the interface between the organic light-emitting layer and the carrier transport layer. A number of device configurations have been proposed that can be confined inside. For example, JP 2000
In JP-A-68057, by forming an organic light emitting layer in a plurality of layers, increasing the ionization potential of each organic light emitting layer from the anode to the cathode, and defining the electron affinity of the organic light emitting layer, Attempts have been made to realize long life and high luminous efficiency. In addition, JP-A-10
In Japanese Patent No. 74584, an attempt is made to improve the luminous efficiency by defining the magnitude relationship between the electron affinity and the ionization potential of the host material forming the hole transport layer and the electron transport layer.

[0006]

As described above, in the prior art, attempts have been made to define the electron affinity and ionization potential of a host material forming a plurality of organic light emitting layers. No studies have been made on organic substances, and in this respect, the studies on prolonging the life and increasing the luminous efficiency of organic electroluminescent elements have been insufficient.

The present invention has been made in view of the above points, and an organic electroluminescent device having a long life and high light emission efficiency is defined by defining a light emitting organic substance to be doped in a light emitting layer. It is intended to provide.

[0008]

The organic electroluminescent device according to claim 1 of the present invention is an organic electroluminescent device comprising a light emitting layer made of an organic material doped with a light emitting organic substance between an anode and a cathode. The device has a plurality of light emitting layers made of organic materials doped with different light emitting organic substances, and the energy gap of the light emitting organic substance doped in the other light emitting layer in the light emitting layer closest to the cathode side. It is characterized in that it is doped with a luminescent organic material having a larger energy gap.

According to a second aspect of the present invention, in the first aspect, three or more light emitting layers are provided, and each light emitting layer is such that the energy gap value of the light emitting organic substance becomes smaller from the one located on the cathode side. Is doped with a luminescent organic material.

According to a third aspect of the present invention, in the adjacent light emitting layers according to the first or second aspect, the value of the electron affinity (EA) (unit eV) of the light emitting organic substance to be doped is in the light emitting layer on the anode side. Value of EA of doped luminescent organic material ≧ E of luminescent organic material doped in the luminescent layer on the cathode side
It is characterized in that each light emitting layer is doped with a light emitting organic substance so as to satisfy the relationship of the value A of −0.3.

According to a fourth aspect of the invention, the value of the ionization potential (IP) of the luminescent organic substance doped in the adjacent light emitting layers according to any one of the first to third aspects (unit e).
V) is the value of IP of the luminescent organic substance doped in the luminescent layer on the anode side ≦ I of the luminescent organic substance doped in the luminescent layer on the cathode side
It is characterized in that each light emitting layer is doped with a light emitting organic substance so as to satisfy the relationship of P value + 0.3.

Here, the electron affinity (Electron)
Affinity) corresponds to an absolute value of a value representing a conduction band level of an organic substance with respect to a vacuum level, and is an ionization potential (Ionization Potentia).
l) corresponds to the absolute value of the value representing the valence band level of the organic substance with respect to the vacuum level. The energy gap corresponds to the difference between the ionization potential and the electron affinity of each organic substance.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

The organic electroluminescent device according to the present invention comprises an anode 1
A plurality of organic light emitting layers 3 made of an organic material doped with a light emitting organic substance (fluorescent substance) are provided between the cathode and the cathode 2. The laminated structure of the organic electroluminescent element of the present invention is
As long as the plurality of light emitting layers 3 between the anode 1 and the cathode 2 correspond to the present invention, any one can be used. FIG. 1 shows an example of an organic electroluminescent device,
The anode 1 made of a transparent conductive film or the like is laminated on the surface of the substrate 10, a plurality of organic light emitting layers 3 are laminated on the surface of the anode 1 through the hole transport layer 11, and further on the light emitting layer 3. The cathode 2 is laminated on the cathode via the electron transport layer 12. An organic electroluminescent element, that is, an organic electroluminescent element (organic EL element) can be formed with this as a basic configuration, and a positive voltage is applied to the anode 1.
When a negative voltage is applied to the cathode 2, the electrons injected into the light emitting layer 3 via the electron transport layer 12 and the holes injected into the light emitting layer 3 via the hole transport layer 11 are generated in the light emitting layer 3. Light is emitted upon binding. Here, by forming the light emitting layer 3 in a structure of a plurality of layers or more, an organic electroluminescent device having a high light emitting efficiency in an arbitrary color tone can be obtained, and in particular, a single light emitting organic substance such as white is used. It is possible to easily and optionally obtain a luminescent color that is difficult to realize with the single luminescent layer 3.

In the present invention, the light emitting layer 3 made of an organic material doped with a light emitting organic material is formed by laminating a plurality of layers. In the embodiment of FIG. 1, three light emitting layers 3a, 3b and 3c are laminated. And the present invention is directed to a plurality of light emitting layers 3a, 3b, 3c.
The value of the energy gap of the light-emitting organic substance doped in the light-emitting layer 3a closest to the cathode 2 as the light-emitting organic substance doped in the second is equal to the energy gap of the light-emitting organic substance doped in the other light-emitting layers 3b, 3c. When the light emitting layer 3 is composed of three or more layers, the value of the energy gap of the light emitting organic material is from the light emitting layer 3a closest to the cathode 2 to the light emitting layer. 3b and the light emitting layer 3c are sequentially doped so that the light emitting organic material is selected so as to become smaller.

As the light-emitting organic substance that can be used in the light-emitting layer 3 in the present invention, any known substance can be used. For example, anthracene, naphthalene,
Pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole,
Bisbenzoxazoline, bisstyryl, cyclopentadiene, quinoline metal complex, tris (8-hydroxyquinolinato) aluminum complex, tris (4-methyl-8)
-Quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzoquinoline metal complex, tri- (p
-Terphenyl-4-yl) amine, 1-aryl-
2,5-di (2-thienyl) pyrrole derivative, pyran,
A quinacridone, a rubrene, a distilbenzene derivative, a distilarylene derivative, and a group containing a light-emitting compound of these are included in a part of the molecule, but not limited thereto. Further, not only compounds derived from fluorescent dyes represented by these compounds, but also light emitting materials capable of phosphorescent emission from the triplet state can be preferably used.

As the host material of the light emitting layer 3, both an electron transporting material and a hole transporting material can be used. It is also possible to use a mixture of these, and in the state where there is a concentration gradient in the layer, the proportion of hole transporting material is large on the anode 1 side, and the electron transporting property becomes closer to the cathode 2 side. It is also possible to use it by increasing the ratio of the material. The electron-transporting host material and the hole-transporting host material are not particularly limited, but the hole-transporting layer 11 described later is used.
It can be appropriately selected and used from the materials constituting the above and the materials constituting the electron transport layer 12.

The host material of the light emitting layer 3 may have either an electron transporting property or a hole transporting property. For example, the light emitting layer 3a closest to the cathode 2 is an electron transporting host material and another light emitting layer 3 is used.
b and 3c are formed using a hole transporting host material, the light emitting layers 3a and 3b on the side closer to the cathode 2 are electron transporting host materials, and the light emitting layer 3c closest to the anode 1 is a hole transporting host. The light emitting layer 3a closest to the cathode 2 is formed of a material, and an electron transporting host material is used as the intermediate light emitting layer 3
b is a mixture of an electron transporting host material and a hole transporting host material, the light emitting layer 3c closest to the anode 1 is formed using a hole transporting host material, or the light emitting layers 3a, 3 are formed.
b, 3c are all formed of an electron transporting host material, or all of the light emitting layers 3a, 3b, 3c are formed of a mixture of an electron transporting host material and a hole transporting host material, or It can be formed of a host material having the above concentration gradient. From the viewpoint of device life, it is preferable to provide at least one light emitting layer 3 made of a hole transporting host material and at least one light emitting layer 3 made of an electron transporting host material, but the present invention is not limited thereto. In addition, it is preferable to optimize the combination of the host material and the light-emitting organic material from the viewpoint of carrier injection property and energy transfer to the doped light-emitting organic material. The materials may be different in each light emitting layer 3, and the configuration can be set arbitrarily from the viewpoint of device performance, manufacturing process, and the like.

In the present invention, as described above, among the plural light emitting layers 3, the light emitting layer 3a located closest to the cathode 2 side is doped with the other light emitting layers 3b and 3c as the light emitting organic substance.
A material having an energy gap larger than that of the light-emitting organic substance to be doped with is used. When the light emitting layer 3 has a multi-layer structure of three or more layers,
In each of the light emitting layers 3a, 3b, 3c, the light emitting layer 3a located closest to the cathode 2 is doped with a light emitting organic substance having the largest energy gap and is separated from the cathode 2. Therefore, the light emitting layer 3b and the light emitting layer 3c are arranged in this order. It is preferable to dope the luminescent material so that the energy gap becomes smaller successively.
If the light-emitting organic substance doped in each of the plurality of light-emitting layers 3 does not satisfy this condition, the efficiency of carrier transfer and energy transfer between the adjacent light-emitting layers 3 is lowered, and the object of the present invention is achieved. Will be difficult.

Further, in the present invention, in the adjacent light emitting layers 3, the value (unit eV) of the electron affinity (EA) of the light emitting organic substance doped in each light emitting layer 3 is set to have the following relationship. Is preferred.

EA value of luminescent organic material doped in anode-side luminescent layer ≧ EA value of luminescent organic material doped in cathode-side luminescent layer-0.3 where adjacent luminescent layer 3 The term "is not limited to the case where the light emitting layers 3 are in direct contact with each other, and may be the case where a non-light emitting layer such as an insulating layer is formed between the light emitting layers 3.
If this condition is not satisfied, the efficiency with which electrons injected from the cathode 2 are injected from the adjacent one light emitting layer 3 to the light emitting layer 3 on the anode 1 side may decrease, and the chromaticity stability of the organic electroluminescent device may be reduced. Properties, lifespan, luminous efficiency, etc. may decrease, which is not preferable.

Further, in the present invention, in adjacent light emitting layers, the value (unit eV) of the ionization potential (IP) of the light emitting organic substance doped in each light emitting layer 3 is set to have the following relationship. preferable.

IP value of light-emitting organic substance doped in the light-emitting layer on the anode side ≦ IP value of light-emitting organic substance doped in the light-emitting layer on the cathode side + 0.3 Unless this condition is satisfied, the anode 1 The efficiency of the holes injected from the adjacent one light emitting layer 3 being injected into the light emitting layer 3 on the cathode 2 side may be reduced, and the chromaticity stability, life, light emission efficiency, etc. of the organic electroluminescent element may be reduced. It is not preferable because it may occur.

The relationship among the energy gap, the electron affinity (EA), and the ionization potential (IP) of the light emitting organic substance satisfying the above conditions is illustrated for the light emitting layers 3a, 3b and 3b having the three-layer structure as shown in FIG. . For example, as shown in FIG. 2, the EA values of the light emitting organic material doped in the light emitting layers 3a, 3b and 3c are L1, L2 and L3, and IP is H.
1, H2, H3, the energy gaps of the light emitting layers 3a, 3b, 3c are H1-L1, H2-L2, and
H3-L3. And from the above conditions of the energy gap, H1-L1> H2-L2, H2-L2> H3
-L3. Further, from the above conditions of the electron affinity (EA), L2-L1 ≧ −0.3 and L3-L2 ≧ −0.3. Further, from the above conditions of the ionization potential (IP), H2-H1≤0.3 and H3-H2≤0.3. Electrons injected from the cathode 2 can be efficiently injected into the adjacent light emitting layer 3 on the side of the anode 1 by selecting a light emitting organic material to be doped into each light emitting layer 3 so as to satisfy such a condition. At the same time, holes injected from the anode 1 can be efficiently injected into the adjacent light emitting layer 3 on the cathode 2 side, and chromaticity stability, life, light emission efficiency, etc. of the organic electroluminescent device can be improved. Is.

In the present invention, the luminescent organic substance doped in each luminescent layer 3 may be used alone or in combination of two or more. When a plurality of types of luminescent organic substances are doped, one or more sets of luminescent organic substances to be doped in an arbitrary luminescent layer 3 and the luminescent layer 3 adjacent to the luminescent layer 3 have the above energy gap and electron affinity. It is sufficient that the conditions (EA) and ionization potential (IP) are satisfied.
In the above description, the light-emitting layer 3 has a three-layer structure as an example, but it is needless to say that the same can be applied to the case where the light-emitting layer 3 has four or more layers. As a method of doping the light-emitting organic substance, a method of co-evaporating the host material and the light-emitting organic substance, a method of alternately depositing the host material and the light-emitting organic substance, or a method of depositing the host material and then emitting the light-emitting substance There are a method of vapor-depositing and diffusing a light-emitting organic substance into the host material, a method of applying a liquid in which the host material and the light-emitting organic substance are dissolved by spin coating or the like to form the light-emitting layer 3, and the like. It can be used without any particular limitation as long as it is a method of allowing a light-emitting organic substance to coexist.

On the other hand, the material constituting the hole transport layer 11 (or hole injection layer) has the ability to transport holes, has the effect of injecting holes from the anode 1, and is superior to the light emitting layer 3. A compound having a hole injection effect, preventing electrons from moving to the hole transport layer 11 and having an excellent thin film forming ability can be mentioned. Specifically, a phthalocyanine derivative, a naphthalocyanine derivative, a porphyrin derivative, N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD) or 4,4 ′ -Bis [N- (naphthyl)-
Aromatic diamine compounds such as N-phenyl-amino] biphenyl (α-NPD), oxazole, oxadiazole, triazole, imidazole, imidazolone, stilbene derivative, pyrazoline derivative, tetrahydroimidazole, polyarylalkane, butadiene, 4,
4 ', 4 "-tris (N- (3-methylphenyl) N-
Phenylamino) triphenylamine (m-MTDAT
A), and polyvinylcarbazole, polysilane, polyethylene dioiside thiophene (PEDOT), PT
Polymer materials such as PDES ([Chemical Formula 1]) can be mentioned.
It is not limited to these.

[0027]

[Chemical 1]

The electron-transporting material forming the electron-transporting layer 12 has an electron-transporting ability, has an electron-injecting effect from the cathode 2, and has an excellent electron-injecting effect on the light-emitting layer 3. In addition, the electron transport layer 12 for holes
And a compound excellent in thin film forming ability can be mentioned. Specifically, fluorene, bathophenanthroline, bathocuproine, anthraquinodimethane, diphenoquinone, oxazole, oxadiazole, triazole, imidazole, anthraquinodimethane, 4,4′-N, N′-dicarbazole biphenyl (CBP) Etc., those compounds, a metal complex compound, or a nitrogen-containing five-membered ring derivative. Specific examples of the metal complex compound include tris (8-hydroxyquinolinato) aluminum, tri (2-methyl-8-hydroxyquinolinato) aluminum, tris (8-hydroxyquinolinato) gallium, Screw (10
-Hydroxybenzo [h] quinolinate) beryllium,
There are bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8-quinolinato) (1-naphtholate) aluminum and the like. ,
It is not limited to these. As the nitrogen-containing five-membered ring derivative, an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative is preferable. Specifically, 2,5-bis (1-phenyl) -1,3,4-oxazole, 2,5-bis (1
-Phenyl) -1,3,4-thiazole, 2,5-bis (1-phenyl) -1,3,4-oxadiazole, 2
-(4'-tert-butylphenyl) -5- (4 "-
Biphenyl) 1,3,4-oxadiazole, 2,5-
Bis (1-naphthyl) -1,3,4-oxadiazole, 1,4-bis [2- (5-phenylthiadiazolyl)] benzene, 2,5-bis (1-naphthyl) -1,
3,4-triazole, 3- (4-biphenylyl)-
4-phenyl-5- (4-t-butylphenyl) -1,
2,4-triazole and the like are included, but are not limited thereto. Further, polymer materials used for polymer organic light emitting devices can also be used. For example, polyparaphenylene and its derivative, fluorene and its derivative, and the like.

The electron transport layer 12 may be doped with an alkali metal, an alkaline earth metal or a rare earth. For example, one in which cesium is doped into bathophenanthroline at a molar ratio of 1: 1 to form the electron transport layer 12 can be mentioned.

Further, as the other members constituting the organic electroluminescence device, for example, the substrate 10 holding the laminated devices, the anode 1, the cathode 2, etc., those conventionally used can be used as they are. .

As the above-mentioned substrate 10, when light emitted from the light-emitting layer 3 is emitted through the substrate 10, a light-transmissive substrate is used. It may be colored to some extent or may be ground glass. For example, a transparent glass plate such as soda lime glass or non-alkali glass, a plastic film or a plastic plate prepared from a resin such as polyester, polyolefin, polyamide, epoxy resin or fluororesin by an arbitrary method can be used. Furthermore, by containing particles, powders, bubbles, etc. having a different refractive index from the base material of the substrate 10 in the substrate 10,
It is also possible to use one having a light diffusion effect.
Further, when the light emitted from the light emitting layer 3 is emitted without passing through the substrate 10, the substrate 10 does not necessarily have a light transmitting property. Any substrate 10 can be used as long as it does not impair the light emission characteristics, life characteristics, etc. of the organic electroluminescent element. In particular, in order to reduce the temperature rise due to the heat generation of the organic electroluminescent element during energization, heat treatment is performed. It is also possible to use the substrate 10 having high conductivity.

The above-mentioned anode 1 is an electrode for injecting holes into the device. As this anode 1, an electrode material made of a metal, an alloy, an electrically conductive compound having a large work function, or a mixture thereof is used. Is preferable, and it is particularly preferable to use an electrode material having a work function of 4 eV or more. Specific examples of such electrode materials include metals such as gold, CuI, ITO (indium-tin oxide), and Sn.
Conductive transparent materials such as O ₂ , ZnO, and IZO (indium-zinc oxide) can be used. For example, the anode 1 can be formed as a thin film by depositing these electrode materials on the substrate 10 by a method such as a vacuum vapor deposition method or a sputtering method. When light emitted from the light emitting layer 3 is transmitted through the anode 1 and is irradiated from the substrate 10 to the outside, the light transmittance of the anode 1 is preferably 70% or more. The sheet resistance of the anode 1 is preferably several hundred Ω / □ or less, and particularly preferably 100 Ω / □ or less. Further, the film thickness of the anode 1 is preferably set to 500 nm or less, more preferably 10 nm or less, though it varies depending on the material in order to control the light transmittance of the anode 1 and the characteristics such as sheet resistance as described above. It is in the range of 200 nm.

The cathode 2 is an electrode for injecting electrons into the light emitting layer 3, and the cathode 2 is an electrode material made of a metal, an alloy, an electrically conductive compound or a mixture thereof having a small work function. Is preferably used, and it is preferable to use an electrode material having a work function of 5 eV or less. As such an electrode material, an alkali metal, a halide of an alkali metal, an oxide of an alkali metal, an alkaline earth metal, or the like, or an alloy of these with another metal can be used, for example, sodium. , Sodium-
Examples include potassium alloys, lithium, magnesium, magnesium-silver mixtures, magnesium-indium mixtures, aluminum-lithium alloys, Al / LiF mixtures, and the like. Besides these, aluminum,
An Al / Al ₂ O ₃ mixture or the like can also be used. Moreover, when an alkali metal oxide, an alkali metal halide, or a metal oxide is used as a base, the above work function is 5
Materials with eV or less (or alloys containing them)
The cathode 2 can also be manufactured by laminating one or more layers. For example, alkali metal / Al stack, alkali metal halide / alkaline earth metal / Al stack, Al ₂ O ₃ /
As an example, stacking of Al and the like can be given. Also I
The cathode 2 may be made of a transparent electrode typified by TO or IZO, and the light emitted from the light emitting layer 3 may be extracted from the cathode 2 side. Further, lithium, sodium, cesium, are added to the electron transport layer 12 at the interface of the cathode 2.
You may dope alkali metals, such as calcium, and alkaline earth metals.

The cathode 2 can be manufactured by forming the above electrode material into a thin film by a method such as a vacuum vapor deposition method or a sputtering method. When the light emitted from the light emitting layer 3 is transmitted through the cathode 2 and is emitted to the outside, the cathode 2 preferably has a light transmittance of 70% or more. Here, the film thickness of the cathode 2 differs depending on the material in order to control the characteristics such as the light transmittance of the cathode 2 as described above, but it is usually preferably set to 500 nm or less, and preferably 100 to 200 nm. It is good to set the range. Further, in forming the cathode metal, in order to suppress the influence of heat radiation from the evaporation source, it is preferable to set the thickness to a thinner range of 50 to 100 nm. This thickness may be thicker when the deposition rate is increased. Even more preferably, the thickness is 25
It is preferable that the range is ˜50 nm. The reason is that when the light emitting area becomes large, the problem of light emission stoppage due to a short circuit easily occurs, but by making the thickness of the cathode metal thin,
The cathode metal of the short circuit part is removed by the stimulus at the time of short circuit,
It becomes an open mode in which only that part does not illuminate, and it is possible to suppress the defect that the entire light emitting part stops emitting light. Further, a metal such as Al is laminated on the cathode 2 by sputtering, or a polymer such as a fluorine-based compound, a fluorine-based polymer, or another organic molecule is deposited, sputtered, or CV.
It is also possible to form by D, plasma polymerization, a method of ultraviolet curing after coating, heat curing, or another method.

[0035]

EXAMPLES Next, the present invention will be specifically described with reference to examples. The energy gap, electron affinity (EA), and ionization potential (I
The values of P) are collectively shown in Table 1, and the light emitting layers 3a, 3b, 3
The configuration of c is shown in Table 2 collectively.

Example 1 A substrate 10 having a thickness of 0.7
Using a transparent glass plate of mm, ITO (indium-tin oxide) was sputtered on one surface of the substrate 10 to form the anode 1 composed of a transparent electrode having a sheet resistance of 7Ω / □. Then, this was ultrasonically cleaned with acetone, pure water and isopropyl alcohol for 15 minutes and then dried.

Next, this substrate 10 was set in a vacuum vapor deposition apparatus, and 4,4'-bis [N- (naphthyl)-was prepared under a reduced pressure of 1 × 10 ^-6 Torr (1.33 × 10 ^-4 Pa). N-phenyl-amino] biphenyl (manufactured by Dojindo Laboratories Ltd .: hereinafter abbreviated as α-NPD) is deposited to a thickness of 1000Å,
The hole transport layer 11 was formed on the anode 1.

Next, α-NP is formed on the hole transport layer 11.
D and a product name "DCJTB" manufactured by Eastman Kodak Co., Ltd. as a luminescent organic substance at a molar ratio of 98: 2 of 100Å
A thick film was co-evaporated to form a light emitting layer 3c doped with DCJTB. Further, a distyryl biphenyl derivative (“DPVBi” manufactured by Idemitsu Kosan Co., Ltd .: chemical formula 1) and rubrene (chemical formula 2) as a light-emitting organic substance were co-deposited at a molar ratio of 98: 2 to a thickness of 50 Å to dope rubrene. Luminous layer 3
b was formed. Furthermore, DPVBi and a DSA derivative as a light-emitting organic substance (“BCzVB manufactured by Idemitsu Kosan Co., Ltd.
i ″: chemical formula 3) was co-evaporated at a molar ratio of 94: 6 to a thickness of 400 Å to form a light emitting layer 3a doped with BCzVBi. In addition, the vapor deposition rate of the organic layer is 1 to 2
It was set to Å / s.

[0039]

[Chemical 2]

[0040]

[Chemical 3]

[0041]

[Chemical 4]

Next, on the light emitting layer 3a, bathophenanthroline (BCP manufactured by Dojindo Laboratories Co., Ltd.) and Cs were co-evaporated at a molar ratio of 1: 1 to form an electron transport layer 1 having a film thickness of 200Å.
2 is formed, and finally, 10 Al is deposited on the electron transport layer 12.
The cathode 2 was formed by vapor deposition with a thickness of 1500Å at a deposition rate of Å / s to obtain an organic electroluminescent device having a structure as shown in FIG.

Example 2 By co-evaporating α-NPD and rubrene at a molar ratio of 98: 2 to a film thickness of 100 Å,
The light emitting layer 3c doped with rubrene is formed, and DPVBi
And the luminescent organic substance, Sigma Aldrich Japan KK's product name "Coumarin 6"
Is co-deposited with a molar ratio of 98: 2 to a film thickness of 50Å to form a coumarin 6-doped light-emitting layer 3b.
VBi and BCzVBi with a molar ratio of 94: 6 and a film thickness of 400Å
1 was obtained in the same manner as in Example 1 except that the light emitting layer 3a doped with BCzVBi was formed by co-evaporation.

(Comparative Example 1) DPVBi and BCzVBi were co-evaporated at a molar ratio of 94: 6 to a film thickness of 100Å to form a light emitting layer 3c doped with BCzVBi as a light emitting organic substance and a light emitting layer 3b was not formed. Without DPVB
i and DCJTB were co-deposited in a molar ratio of 98: 2 to a film thickness of 400Å to produce DCJTB as a luminescent organic substance.
An organic electroluminescent device was obtained in the same manner as in Example 1 except that the light emitting layer 3a doped with was formed.

Comparative Example 2 DPVBi and BCzVBi were co-evaporated at a molar ratio of 94: 6 to a film thickness of 100Å to form a light emitting layer 3c doped with BCzVBi as a light emitting organic substance, and DPVBi and rubrene were mixed at a molar ratio of DPVBi and rubrene. 9
The light emitting layer 3b doped with rubrene as a light emitting organic substance is formed by co-evaporation with a film thickness of 50Å at 8: 2, and DPVBi and DCJTB are formed at a film thickness of 4 at a molar ratio of 98: 2.
An organic electroluminescent device was obtained in the same manner as in Example 1, except that the light emitting layer 3a doped with DCJTB as a light emitting organic substance was formed by co-evaporation with 00Å.

(Comparative Example 3) DPVBi and BCzVBi were co-evaporated at a molar ratio of 98: 2 to a film thickness of 100Å to form a light emitting layer 3c doped with BCzVBi as a light emitting organic substance and a light emitting layer 3b was not formed. Without DPVB
By co-evaporating i and coumarin 6 in a molar ratio of 98: 2 to a film thickness of 400Å, coumarin 6 as a luminescent organic substance was obtained.
An organic electroluminescent device was obtained in the same manner as in Example 1 except that the light emitting layer 3a doped with was formed.

[0047]

[Table 1]

Table 2 shows the composition of each of the light emitting devices 3a, 3b and 3c for Examples 1 and 2 and Comparative Examples 1 to 3 above.

[0049]

[Table 2]

Further, the above-mentioned Examples 1-2 and Comparative Examples 1--2
3, the energy gap of the light emitting organic material doped in the light emitting elements 3a, 3b, 3c, the electron affinity (E
A) and ionization potential (IP) are summarized in Table 3.

[0051]

[Table 3]

Chromaticity, power consumption, quantum efficiency and half life of the organic electroluminescent devices obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were measured as described above, and the results are shown in Table 4. It was

The chromaticity of the organic electroluminescent device was evaluated by CIE chromaticity coordinates. For the measurement, an organic electroluminescence device was connected to a power source (“KEYTHLEY236 model” manufactured by Toyo Technica), and a brightness of 200 c was obtained using a multi-channel analyzer (“PMA-10” manufactured by Hamamatsu Photonics KK).
It was carried out under the condition of d / m ² . The brightness was measured with "BM-5A" manufactured by Topcon Corporation.

The power consumption of the organic electroluminescent device is measured by using the organic electroluminescent device as a power source (“KEYTH” manufactured by Toyo Technica Co., Ltd.).
LEY236 model ”), and calculated from the value in the state of emitting light under the condition of 200 cd / m ² .

The quantum efficiency of the organic electroluminescent element was calculated from the emission spectrum of the organic electroluminescent element, the luminance, the applied voltage, and the amount of current based on a standard method.

To measure the half-life of the organic electroluminescent device, a current value at which the initial emission luminance becomes 200 cd / m ² is determined in advance, and then a predetermined current is applied to the organic electroluminescent device using a constant current power source. The brightness is 100 cd /
By measuring the time until it reaches m ² ,
This time was defined as the half life.

[0057]

[Table 4]

As can be seen from Table 4, the organic electroluminescent devices of Examples 1 and 2 have low power consumption, high quantum efficiency, and excellent luminous efficiency, and have a long half-life and a long life. It was confirmed that high luminous efficiency can be realized.

[0059]

As described above, the organic electroluminescent device according to claim 1 of the present invention has an organic electroluminescent device including a light emitting layer made of an organic material doped with a light emitting organic substance between an anode and a cathode. The device has a plurality of light emitting layers made of organic materials doped with different light emitting organic substances, and the energy gap of the light emitting organic substance doped in the other light emitting layer in the light emitting layer closest to the cathode side. Since the luminescent organic material having a larger energy gap is doped, the energy gap of the luminescent organic material to be doped in the luminescent layer is defined in this way, so that the efficiency of carrier transfer and energy transfer between the adjacent luminescent layers is improved. Therefore, the organic electroluminescent device can have a long life and high luminous efficiency.

The invention of claim 2 is characterized in that, in claim 1, three or more light emitting layers are provided, and the value of the energy gap of the light emitting organic substance in each light emitting layer is gradually decreased from the one positioned on the cathode side. Since the luminescent organic material is doped in the luminescent layer, by defining the energy gap of the luminescent organic material to be doped in the luminescent layer in this way, the efficiency of carrier transfer and energy transfer between the adjacent luminescent layers can be further improved. Therefore, the organic electroluminescent device can have a long life and high luminous efficiency.

According to a third aspect of the present invention, in the adjacent light emitting layers according to the first or second aspect, the value of the electron affinity (EA) (unit eV) of the light emitting organic substance to be doped is in the light emitting layer on the anode side. EA value of doped luminescent organic material ≧ value of EA of luminescent organic material doped in cathode-side luminescent layer −0.
Since each light emitting layer is doped with a light emitting organic material so as to satisfy the relationship of 3, the electron affinity (EA) of the light emitting organic material to be doped in the light emitting layer is defined as described above, and thus the light emitting organic material is injected from the cathode. The efficiency with which the generated electrons are injected from the adjacent one light emitting layer to the light emitting layer on the anode side can be increased, and the life of the organic electroluminescent element and the high light emitting efficiency can be realized.

Further, the invention of claim 4 is the value of the ionization potential (IP) of the luminescent organic substance to be doped (unit e in the adjacent luminescent layers according to claim 1).
V) satisfies the relationship of IP value of luminescent organic material doped in anode-side luminescent layer ≦ IP value of luminescent organic material doped in cathode-side luminescent layer + 0.3 Since the light emitting layer is doped with the light emitting organic substance, the ionization potential (I
By defining P) in this way, it is possible to increase the efficiency with which holes injected from the anode are injected into the light emitting layer on the cathode side from one adjacent light emitting layer, and the life of the organic electroluminescent device is prolonged. It is possible to realize high luminous efficiency.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of an example of an organic electroluminescence device.

FIG. 2 is a front view showing a schematic configuration of a light emitting layer of the same.

[Explanation of symbols]

1 anode 2 cathode 3 light emitting layer 3a, 3b, 3c light emitting layer

Continued front page    (72) Inventor Junji Kido             Sanro, 2-6 Chuo, Yonezawa City, Yamagata Prefecture             Do Yonezawa Chuo 408 (72) Inventor Kenji Tsubaki             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works             Within the corporation (72) Inventor Yukihiro Kondo             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works             Within the corporation (72) Inventor Yasuhisa Kishigami             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works             Within the corporation (72) Inventor Kenji Kono             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works             Within the corporation F-term (reference) 3K007 AB03 AB11 DA06 DB03

Claims (4)

[Claims] 1. An organic electroluminescent device comprising a light emitting layer made of an organic material doped with a light emitting organic substance between an anode and a cathode, wherein a plurality of layers made of organic materials doped with different light emitting organic substances are provided. And a light emitting layer positioned closest to the cathode is doped with a light emitting organic substance having an energy gap larger than that of another light emitting organic substance doped in the other light emitting layer. And an organic electroluminescent device. 2. The light emitting layer comprises three or more layers, and each light emitting layer is doped with a light emitting organic substance so that the value of the energy gap of the light emitting organic substance is gradually decreased from the one located on the cathode side. The organic electroluminescent element according to claim 1, wherein 3. A value of an electron affinity (EA) of a light-emitting organic substance doped in adjacent light emitting layers (unit: eV)
Is the value of EA of the light-emitting organic substance doped in the light-emitting layer on the anode side ≧ E of the light-emitting organic substance doped in the light-emitting layer on the cathode side
3. The organic electroluminescent device according to claim 1, wherein each light emitting layer is doped with a light emitting organic substance so as to satisfy the relationship of the value A of −0.3. 4. The value (unit: eV) of the ionization potential (IP) of the light-emitting organic substance to be doped in the adjacent light-emitting layers is such that the IP value of the light-emitting organic substance doped in the light-emitting layer on the anode side ≦ I of a luminescent organic material doped in the luminescent layer on the cathode side
4. The organic electroluminescent device according to claim 1, wherein each light emitting layer is doped with a light emitting organic substance so as to satisfy the relationship of the value of P + 0.3.