WO2013157563A1 - Organic electroluminescence element - Google Patents

Abstract

The purpose of the present invention is to provide an organic electroluminescence element having high light-emission efficiency and a long lifespan, and in particular, to provide an organic electroluminescence element having an excellent color-rendering performance and a stable chromaticity even at a low driving voltage. This organic electroluminescence element has at least a positive electrode, a hole transportation layer, a light-emitting layer including a phosphorescent compound, an electron transportation layer, and a negative electrode; the organic electroluminescence element being characterized in having quantum dots in the interface between the light-emitting layer and the hole transportation layer and/or the interface between the light-emitting layer and the electron transportation layer.

Description

Organic electroluminescence device

The present invention relates to an organic electroluminescence element. More specifically, the present invention relates to an organic electroluminescence element having high luminous efficiency and a long life, and particularly relates to an organic electroluminescence element having excellent color rendering properties and stable chromaticity even at a low driving voltage.

In recent years, organic electroluminescence elements using organic substances (hereinafter, abbreviated as “organic EL elements” where appropriate) are promising for use as solid light-emitting inexpensive large-area full-color display elements and writing light source arrays. Research and development is actively underway.

The organic EL element is composed of an organic functional layer (single layer portion or multilayer portion) having a thickness of only about 0.1 μm containing an organic light emitting material between a pair of anode and cathode formed on a film. It is a thin film type all solid state device. When a relatively low voltage of about 2 to 20 V is applied to such an organic EL element, electrons are injected into the organic functional layer from the cathode and holes are injected from the anode. It is known that light emission can be obtained by releasing energy as light when these electrons and holes recombine in the light emitting layer and the formed excitons return to the ground state. It is a technology that is expected as lighting.

In addition, recently discovered organic EL devices that use phosphorescence can realize a luminous efficiency that is approximately four times that of previous methods that use fluorescence. Research and development of organic functional layer layers and electrodes are conducted all over the world. In particular, as one of the measures to prevent global warming, application to lighting fixtures, which occupy much of human energy consumption, has begun to be studied. There are many attempts to reduce costs.

In white light emitting panels for lighting, high efficiency and long life are required.In particular, in the long life, organic EL elements have low performance against fluorescent lamps and white LEDs. There is a need for long-life technology.

As a method of solving these problems, there is a method of using “quantum dots” that are inorganic light emitting substances as the light emitting compounds. In addition to a sharp emission spectrum, quantum dots are inorganic and have good durability and can be dispersed in various solvents, so that they can be applied to coating processes.

For example, in Patent Document 1, white light emission is achieved by forming quantum dots on the emission side surface of the light emitting element and supplementing the emission color of the light emitting layer by light emission that is photoexcited in a down-conversion manner. However, in this method, the light emission lifetime depends on the light emitting layer material, and a sufficiently long lifetime has not been obtained yet. On the other hand, Patent Document 2 achieves white light emission by using two types of quantum dots or a polymer material exhibiting fluorescence emission in combination with the hole transport layer.

In addition, as one of the factors that decrease the luminous efficiency, the hole mobility of the hole transport material constituting the hole transport layer is often larger than the electron mobility of the electron transport material constituting the electron transport layer. As a result, the holes supplied from the anode penetrate the light emitting layer, and there are few opportunities for recombination in the light emitting layer. As a method for solving these problems, there is a method of installing a hole blocking layer, an electron blocking layer, and an exciton blocking layer at the interface between the light emitting layer and the adjacent layer of the light emitting layer. For example, Patent Document 3 discloses a technique in which quantum dots are used as a light emitting layer material, the hole mobility of a hole transport material forming a hole transport layer is adjusted, and an electron blocking ability is provided. Patent Document 4 discloses a light emitting device having an exciton generation layer sandwiched between two quantum dot monomolecular films.

However, in these methods, since the amount of quantum dots that easily cause concentration quenching is limited, it cannot be said that the luminance efficiency is sufficient. In addition, in order to obtain good quality white light emission, that is, white light emission with high color rendering properties, it is conceivable to add various kinds of quantum dots having different particle diameters. Because it is difficult, color rendering is insufficient. There is also a problem of so-called color misregistration in which chromaticity is not stable during continuous driving.

JP 2006-190682 A JP 2006-66395 A JP 2009-88276 A JP 2009-87754 A

The present invention has been made in view of the above problems and circumstances, and the problem to be solved is to provide an organic electroluminescence device with high luminous efficiency and long life, and in particular, excellent color rendering and low driving voltage. However, it is to provide an organic electroluminescence device having stable chromaticity.

As a result of examining the cause of the above-mentioned problem in order to solve the above-mentioned problems, the present inventor has found that at least one of the interface between the light-emitting layer and the hole transport layer and the interface between the light-emitting layer and the electron transport layer. Thus, the present inventors have found that the light emission efficiency, the light emission life and the color rendering properties are improved by having the quantum dots in the present invention.

That is, the above-mentioned problem according to the present invention is solved by the following means.

1. An organic electroluminescence device having at least an anode, a hole transport layer, a light-emitting layer containing a phosphorescent compound, an electron transport layer, and a cathode, wherein the interface between the light-emitting layer and the hole transport layer and the light emission An organic electroluminescence device comprising a quantum dot on at least one of an interface between a layer and the electron transport layer.

2. 2. The organic electroluminescence device according to claim 1, wherein quantum dots are present at both the interface between the light emitting layer and the hole transport layer and the interface between the light emitting layer and the electron transport layer.

3. 3. The organic electroluminescence device according to claim 1, wherein a band gap of the phosphorescent compound is 0.1 eV or more smaller than a band gap of the quantum dots.

4. 4. The organic electroluminescence device according to any one of the first to third aspects, wherein the light emitting layer contains a host compound, and the band gap of the host compound is larger than the band gap of the quantum dots by 0.1 eV or more. Luminescence element.

5. The first to fourth aspects, wherein the quantum dots are made of at least Si, Ge, GaN, GaP, CdS, CdSe, CdTe, InP, InN, ZnS, In ₂ S ₃ , ZnO, CdO, or a mixture thereof. The organic electroluminescent element according to any one of the items.

6. 6. The organic electroluminescence device according to any one of items 1 to 5, wherein an average particle size of the quantum dots is in a range of 1 to 20 nm.

7. 7. The organic electroluminescent element according to any one of the first to sixth aspects, wherein the phosphorescent compound contained in the light emitting layer is represented by the following general formula (1).

 

(In the general formula (1), R ₁ represents a substituent. Z represents a group of nonmetallic atoms necessary to form a 5- to 7-membered ring. N1 represents an integer of 0 to 5. B ₁ to B ₅ represents a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, at least one represents a nitrogen atom, M ₁ represents a group 8 to group 10 metal in the periodic table, and X ₁ and X ₂ represent carbon Represents an atom, a nitrogen atom or an oxygen atom, L ₁ represents an atomic group forming a bidentate ligand with X ₁ and X ₂ , m1 represents an integer of 1, 2 or 3, m2 represents 0, (It represents an integer of 1 or 2, m1 + m2 is 2 or 3.)
8). 8. The organic electroluminescent element according to any one of the first to seventh aspects, wherein the light emitting layer contains a host compound represented by the following general formula (2).

 

(In the general formula (2), X represents NR ′, O, S, CR′R ″, or SiR′R ″. R ′ and R ″ each represents a hydrogen atom or a substituent. Ar ₁ and Ar ₂ represents an aromatic ring, which may be the same or different, and n represents an integer of 0 to 4.)
9. X in the said General formula (2) represents an oxygen atom, The organic electroluminescent element of the said 8th item | term characterized by the above-mentioned.

By the above means of the present invention, it is to provide an organic electroluminescence device having a high luminous efficiency and a long lifetime, and particularly to provide an organic electroluminescence device having excellent color rendering properties and stable chromaticity even at a low driving voltage. it can.

Although the manifestation mechanism or action mechanism of the effect of the present invention is not clarified, it is possible to emit light efficiently in the light emitting layer without diffusing excitons, electrons, or holes generated in the light emitting layer. it is conceivable that. The quantum dots are considered to function as a blocking layer that prevents electrons and holes from passing through the light emitting layer.

Schematic sectional view showing an example of the configuration of the organic electroluminescence element of the present invention Schematic sectional view showing a modification of FIG. Schematic sectional view showing a modification of FIG.

The organic electroluminescent device of the present invention is an organic electroluminescent device having at least an anode, a hole transport layer, a light-emitting layer containing a phosphorescent compound, an electron transport layer and a cathode, and the light-emitting layer and the positive electrode. Quantum dots are included in at least one of the interface with the hole transport layer and the interface between the light emitting layer and the electron transport layer. This feature is a technical feature common to the inventions according to claims 1 to 9.

As an embodiment of the present invention, from the viewpoint of manifesting the effect of the present invention, it is preferable to have quantum dots at both the interface between the light emitting layer and the hole transport layer and the interface between the light emitting layer and the electron transport layer. preferable. In addition, it is preferable that the bandgap of the phosphorescent compound is 0.1 eV or more smaller than the bandgap of the quantum dots. Further, the light-emitting layer contains a host compound, and the bandgap of the host compound is The effect of the present invention is further enhanced by being larger than the band gap of the dots by 0.1 eV or more.

From the viewpoint of manifesting the effects of the present invention, the quantum dots are at least Si, Ge, GaN, GaP, CdS, CdSe, CdTe, InP, InN, ZnS, In ₂ S ₃ , ZnO, CdO, or a mixture thereof. Preferably it consists of. The average particle diameter of the quantum dots is preferably in the range of 1 to 20 nm.

In the present invention, the phosphorescent compound contained in the light emitting layer is preferably represented by the general formula (1). Moreover, from the viewpoint of manifesting the effect of the present invention, the light emitting layer preferably contains a host compound represented by the general formula (2), and X in the general formula (2) is oxygen. Preferably it represents an atom.

Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present application, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

In this application, “quantum dots” are semiconductor microcrystals with a diameter of several to several tens of nanometers that are formed to confine electrons (and holes) in a minute space and exhibit a quantum size effect. Say crystals.

Also, “band gap of quantum dots” refers to the energy difference (energy gap) between the valence band and conduction band of quantum dots.

“The band gap of the host compound, dopant compound, etc.” refers to the energy difference (energy gap) between the energy level of the highest occupied molecular orbital (HOMO) and the energy level of the lowest unoccupied molecular orbital (LUMO).

<< Structure of organic electroluminescence element >>
The configuration of the organic electroluminescence element of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the organic electroluminescence element of the present invention. As shown in FIG. 1, an organic electroluminescence element 100 (hereinafter also referred to as an organic EL element) according to a preferred embodiment of the present invention has a flexible support substrate 1. An anode 2 is formed on the flexible support substrate 1, an organic functional layer 20 is formed on the anode 2, and a cathode 8 is formed on the organic functional layer 20.

The organic functional layer 20 refers to each layer constituting the organic electroluminescence element 100 provided between the anode 2 and the cathode 8. The organic functional layer 20 includes, for example, a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, an electron injection layer 7, and in addition, a hole block layer, an electron block layer, and the like. May be included. The anode 2, the organic functional layer 20, and the cathode 8 on the flexible support substrate 1 are sealed with a flexible sealing member 10 through a sealing adhesive 9.

In addition, the layer structure (refer FIG. 1) of the organic electroluminescent element 100 shows only the preferable specific example, and this invention is not limited to this. For example, the organic EL device of the present invention may have the following layer structures (i) to (viii).
(I) Flexible support substrate / anode / light emitting layer / electron transport layer / cathode / thermal conductive layer / sealing adhesive / sealing member (ii) flexible support substrate / anode / hole transport layer / light emission Layer / electron transport layer / cathode / thermal conductive layer / sealing adhesive / sealing member (iii) flexible support substrate / anode / hole transport layer / light emitting layer / hole block layer / electron transport layer / cathode / Heat conduction layer / adhesive for sealing / sealing member (iv) flexible support substrate / anode / hole transport layer / light emitting layer / hole block layer / electron transport layer / cathode buffer layer / cathode / heat conduction Layer / adhesive for sealing / sealing member (v) flexible support substrate / anode / anode buffer layer / hole transport layer / light emitting layer / hole block layer / electron transport layer / cathode buffer layer / cathode / heat Conductive layer / sealing adhesive / sealing member (vi) glass support / anode / hole injection layer / light emitting layer / electron injection layer / cathode / sealing member (vii) glass support / Anode / hole injection layer / hole transport layer / light emitting layer / electron injection layer / cathode / sealing member (viii) glass support / anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / Electron injection layer / cathode / sealing member << Organic functional layer of organic EL element >>
Subsequently, the detail of the said organic functional layer which comprises the organic EL element of this invention is demonstrated.

(1) Injection layer: hole injection layer, electron injection layer In the organic EL device of the present invention, the injection layer can be provided as necessary. As the injection layer, there are an electron injection layer and a hole injection layer. As described above, the injection layer may exist between the anode and the light emitting layer or the hole transport layer and between the cathode and the light emitting layer or the electron transport layer.

The injection layer referred to in the present invention is a layer provided between the electrode and the organic functional layer in order to lower the driving voltage and improve the light emission luminance. “The organic EL element and its industrialization front line (November 30, 1998, NT. The details are described in Volume 2, Chapter 2, “Electrode Materials” (pages 123 to 166) of “S.

The details of the hole injection layer are described, for example, in JP-A-9-45479, JP-A-9-260062, and JP-A-8-288069. Injection materials include triazole derivatives, oxadiazole derivatives, imidazole derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives. , Polymers containing silazane derivatives, aniline copolymers, polyarylalkane derivatives, or conductive polymers, preferably polythiophene derivatives, polyaniline derivatives, polypyrrole derivatives, more preferably It is a thiophene derivative.

The details of the electron injection layer are described in, for example, JP-A-6-325871, JP-A-9-17574, and JP-A-10-74586, and specific examples thereof include strontium and aluminum. A metal buffer layer, an alkali metal compound buffer layer typified by lithium fluoride, an alkaline earth metal compound buffer layer typified by magnesium fluoride, and an oxide buffer layer typified by aluminum oxide. In the present invention, the buffer layer (injection layer) is desirably a very thin film, and potassium fluoride and sodium fluoride are preferable. The film thickness is about 0.1 nm to 5 μm, preferably 0.1 to 100 nm, more preferably 0.5 to 10 nm, and most preferably 0.5 to 4 nm.

(2) Hole transport layer As the hole transport material constituting the hole transport layer, the same compounds as those applied in the hole injection layer can be used, but further, porphyrin compounds, aromatics It is preferable to use a 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, as well as those described in US Pat. No. 5,061,569 Having four condensed aromatic rings in the molecule, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-3 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units described in Japanese Patent No. 8688 are linked in a starburst type ( MTDATA) and the like.

Furthermore, polymer materials in which these materials are introduced into polymer chains or these materials are used as polymer main chains 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-4-297076, JP-A-2000-196140, JP-A-2001-102175, J. Pat. Appl. Phys. , 95, 5773 (2004), JP-A-11-251067, J. MoI. Huang et. al. It is also possible to use a hole transport material that has so-called p-type semiconducting properties, as described in the literature (Applied Physics Letters 80 (2002), p. 139), JP 2003-519432 A. it can.

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. The thickness of the hole transport layer is not particularly limited, but is usually about 5 nm to 5 μm, preferably 5 to 200 nm. This hole transport layer may have a single layer structure composed of one or more of the above materials.

Hereinafter, preferred specific examples ((1) to (60)) of compounds used for the hole transport material of the organic EL device of the present invention will be given, but the present invention is not limited thereto.

 

 

 

 

 

 

Note that n described in the above exemplary compounds represents the degree of polymerization and represents an integer having a weight average molecular weight in the range of 50,000 to 200,000. When the weight average molecular weight is 50,000 or more, there is no concern of mixing with other layers during film formation due to solubility in a solvent. Also, the luminous efficiency is good. When the weight average molecular weight is 200,000 or less, synthesis and purification are easy. The emission efficiency, voltage, and life of the organic EL element are not deteriorated by the impurities.

These polymer compounds are disclosed in Makromol. Chem. , Pages 193, 909 (1992) and the like.

(3) Electron transport layer The electron transport layer is made of a material having a function of transporting electrons, and in a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. The electron transport layer can be provided as a single layer or a plurality of layers.

Conventionally, in the case of a single electron transport layer and a plurality of layers, an electron transport material (also serving as a hole blocking material) used for an electron transport layer adjacent to the cathode side with respect to the light emitting layer is injected from the cathode. As long as it has a function of transmitting electrons to the light-emitting layer, any material can be selected and used from among conventionally known compounds. For example, fluorene derivatives, carbazole derivatives, azacarbazole And metal complexes such as derivatives, oxadiazole derivatives, triazole derivatives, silole derivatives, pyridine derivatives, pyrimidine derivatives, 8-quinolinol derivatives, and the like.

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.

Among these, carbazole derivatives, azacarbazole derivatives, pyridine derivatives and the like are preferable in the present invention, and more preferably an azacarbazole derivative.

The electron transport layer can be formed by thinning the electron transport material by a known method such as a spin coating method, a casting method, a printing method including an ink jet method, an LB method, and the like, preferably It can be formed by a wet process using a coating solution containing an electron transport material and a fluorinated alcohol solvent.

The thickness of the electron transport layer is not particularly limited, but is usually about 5 nm to 5 μm, preferably 5 to 200 nm. The electron transport layer may have a single layer structure composed of one or more of the above materials.

It is also possible to use an n-type electron transport layer doped with impurities as a guest material. Examples thereof include JP-A-4-297076, JP-A-10-270172, JP-A-2000-196140, 2001-102175, J.A. Appl. Phys. 95, 5773 (2004), and the like.

The electron transport layer in the present invention preferably contains an organic alkali metal salt. There are no particular restrictions on the type of organic substance, but formate, acetate, propionic acid, butyrate, valerate, caproate, enanthate, caprylate, oxalate, malonate, succinate Benzoate, phthalate, isophthalate, terephthalate, salicylate, pyruvate, lactate, malate, adipate, mesylate, tosylate, benzenesulfonate , Preferably formate, acetate, propionate, butyrate, valerate, caprate, enanthate, caprylate, oxalate, malonate, succinate, benzoate, more preferably Is preferably an alkali metal salt of an aliphatic carboxylic acid such as formate, acetate, propionate or butyrate, and the aliphatic carboxylic acid preferably has 4 or less carbon atoms. Most preferred is acetate.

The type of alkali metal of the organic alkali metal salt is not particularly limited, and examples thereof include Na, K, and Cs, preferably K, Cs, and more preferably Cs. Examples of the alkali metal salt of the organic substance include a combination of the organic substance and the alkali metal, preferably, formic acid Li, formic acid K, formic acid Na, formic acid Cs, acetic acid Li, acetic acid K, Na acetate, acetic acid Cs, propionic acid Li, Propionic acid Na, propionic acid K, propionic acid Cs, oxalic acid Li, oxalic acid Na, oxalic acid K, oxalic acid Cs, malonic acid Li, malonic acid Na, malonic acid K, malonic acid Cs, succinic acid Li, succinic acid Na, succinic acid K, succinic acid Cs, benzoic acid Li, benzoic acid Na, benzoic acid K, benzoic acid Cs, more preferably Li acetate, K acetate, Na acetate, Cs acetate, most preferably Cs acetate.

The content of these dope materials is preferably 1.5 to 35% by mass, more preferably 3 to 25% by mass, and most preferably 5 to 15% by mass with respect to the electron transport layer to be added.

(4) Light emitting layer The light emitting layer constituting the organic EL device of the present invention 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.

The light emitting layer according to the present invention is not particularly limited in its configuration as long as the phosphorescent compound contained therein satisfies the above requirements.

Also, there may be a plurality of layers having the same emission spectrum or emission maximum wavelength.

In the present invention, the total thickness of the light emitting layers is preferably in the range of 1 to 100 nm, and more preferably 50 nm or less because a lower driving voltage can be obtained. In addition, the sum total of the film thickness of the light emitting layer as used in this invention is a film thickness also including the said intermediate | middle layer, when a nonluminous intermediate | middle layer exists between light emitting layers. The film thickness of each light emitting layer is preferably adjusted in the range of 1 to 50 nm.

The individual light emitting layers may emit blue, green, and red colors, and there is no particular limitation on the film thickness relationship of each light emitting layer.

For the production of the light emitting layer, a light emitting compound or a host compound, which will be described later, is formed by forming a film by a known thinning method such as a vacuum deposition method, a spin coating method, a casting method, an LB method, or an ink jet method. Can do.

In the present invention, a plurality of phosphorescent compounds may be mixed in each light emitting layer, or a phosphorescent compound and a fluorescent compound may be mixed and used in the same light emitting layer.

In the present invention, the structure of the light emitting layer preferably contains a host compound and a phosphorescent compound and emits light from the phosphorescent compound.

(4.1) Host compound As the host compound contained in the light emitting layer of the organic EL device of the present invention, 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. Moreover, it becomes possible to mix different light emission by using multiple types of the luminescent compound mentioned later, and can thereby obtain arbitrary luminescent colors.

The host compound used in the present invention may be a conventionally known low molecular compound or a high molecular compound having a repeating unit, and a low molecular compound having a polymerizable group such as a vinyl group or an epoxy group (polymerizable host). Compound) may be used, but when a polymer material is used, since the compound is likely to take up the solvent and swell or gelate, the phenomenon that the solvent is unlikely to escape is likely to occur. Specifically, it is preferable to use a material having a molecular weight of 2,000 or less at the time of application, and it is more preferable to use a material having a molecular weight of 1,000 or less at the time of application.

As the known host compound, a compound that has a hole transporting ability and an electron transporting ability, prevents the emission of light from being increased in wavelength, and has a high Tg (glass transition temperature) is preferable. Here, the glass transition point (Tg) 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, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579 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. No. 2002-302516, No. 2002-305083, No. 2002-305084, No. 2002-308837, and the like.

The host compound is preferably a compound represented by the general formula (2).

 

In the general formula (2), X represents NR ′, O, S, CR′R ″ or SiR′R ″. R ′ and R ″ each represent a hydrogen atom or a substituent. Ar ₁ and Ar ₂ each represent an aromatic ring, which may be the same or different. N represents an integer of 0 to 4.

In X in the general formula (2), the substituents represented by R ′ and R ″ are each an alkyl group (for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a t-butyl group, a pentyl group, a hexyl group). Group, octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group etc.), cycloalkyl group (eg cyclopentyl group, cyclohexyl group etc.), alkenyl group (eg vinyl group, allyl group etc.), alkynyl group (eg Ethynyl group, propargyl group, etc.), aromatic hydrocarbon ring group (also called aromatic carbocyclic group, aryl group, etc.), for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl group, naphthyl group, Anthryl, azulenyl, acenaphthenyl, fluorenyl, phenanthryl, indenyl, pyreth Group, biphenylyl group, etc.), aromatic heterocyclic group (for example, pyridyl group, pyrimidinyl group, furyl group, pyrrolyl group, imidazolyl group, benzoimidazolyl group, pyrazolyl group, pyrazinyl group, triazolyl group (for example, 1,2,4) -Triazol-1-yl group, 1,2,3-triazol-1-yl group, etc.), oxazolyl group, benzoxazolyl group, thiazolyl group, isoxazolyl group, isothiazolyl group, furazanyl group, thienyl group, quinolyl group, Benzofuryl group, dibenzofuryl group, benzothienyl group, dibenzothienyl group, indolyl group, carbazolyl group, carbolinyl group, diazacarbazolyl group (one of the carbon atoms constituting the carboline ring of the carbolinyl group is replaced by a nitrogen atom) Quinoxalinyl group, pyridazinyl group Triazinyl group, quinazolinyl group, phthalazinyl group, etc.), heterocyclic group (eg, pyrrolidyl group, imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (eg, methoxy group, ethoxy group, propyloxy group, pentyloxy group, Hexyloxy group, octyloxy group, dodecyloxy group, etc.), cycloalkoxy group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), alkylthio group (eg, Methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio group (eg, cyclopentylthio group, cyclohexylthio group, etc.), arylthio group (eg, phenyl) Thio group, naphthylthio group, etc.), alkoxycarbonyl group (eg, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group (eg, phenyloxy) Carbonyl group, naphthyloxycarbonyl group, etc.), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylaminosulfonyl group, dodecyl) Aminosulfonyl group, phenylaminosulfonyl group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group, etc.), acyl group (for example, acetyl group, ethyl group) Rubonyl, propylcarbonyl, pentylcarbonyl, cyclohexylcarbonyl, octylcarbonyl, 2-ethylhexylcarbonyl, dodecylcarbonyl, phenylcarbonyl, naphthylcarbonyl, pyridylcarbonyl, etc.), acyloxy groups (eg acetyloxy) Group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group, etc.), amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethylcarbonylamino group, propyl) Carbonylamino group, pentylcarbonylamino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octylcarbonylamino group Dodecylcarbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group, etc.), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group, cyclohexylaminocarbonyl group) Octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylaminocarbonyl group, etc.), ureido group (for example, methylureido group, ethylureido group, pentyl) Ureido group, cyclohexylureido group, octylureido group, dodecylureido group, phenylureido group, naphthylureido group, 2-pyridylaminourei Group), sulfinyl group (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecylsulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group, etc.) ), Alkylsulfonyl groups (eg, methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group, etc.), arylsulfonyl groups or heteroarylsulfonyl groups (eg, phenylsulfonyl group) Naphthylsulfonyl group, 2-pyridylsulfonyl group, etc.), amino group (for example, amino group, ethylamino group, dimethylamino group, butylamino group, cyclopente) Luamino group, 2-ethylhexylamino group, dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group, etc.), halogen atom (eg, fluorine atom, chlorine atom, bromine atom etc.), fluorinated hydrocarbon group (eg. , Fluoromethyl group, trifluoromethyl group, pentafluoroethyl group, pentafluorophenyl group, etc.), cyano group, nitro group, hydroxy group, mercapto group, silyl group (for example, trimethylsilyl group, triisopropylsilyl group, triphenylsilyl group) Group, phenyldiethylsilyl group, etc.).

These substituents may be further substituted with the above substituents. A plurality of these substituents may be bonded to each other to form a ring.

Among these, X is preferably NR ′ or O, and more preferably, X is O, that is, the host compound used in the present invention is a dibenzofuran derivative.

R ′ is also referred to as an aromatic hydrocarbon group (aromatic carbocyclic group, aryl group, etc., for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl group, naphthyl group, anthryl group, Azulenyl, acenaphthenyl, fluorenyl, phenanthryl, indenyl, pyrenyl, biphenylyl) or aromatic heterocyclic groups (eg furyl, thienyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl) Group, imidazolyl group, pyrazolyl group, thiazolyl group, quinazolinyl group, phthalazinyl group, etc.) are particularly preferred.

The above aromatic hydrocarbon group and aromatic heterocyclic group may each have a substituent represented by R ′ or R ″ in X of the general formula (2).

In the general formula (2), examples of the aromatic ring represented by Ar ₁ and Ar ₂ include an aromatic hydrocarbon ring and an aromatic heterocyclic ring. The aromatic ring may be a single ring or a condensed ring, and may be unsubstituted or may have a substituent represented by R ′ and R ″ in X of the general formula (2).

In the general formula (2), the aromatic hydrocarbon ring represented by Ar ₁ and Ar ₂ is a benzene ring, biphenyl ring, naphthalene ring, azulene ring, anthracene ring, phenanthrene ring, pyrene ring, chrysene ring, naphthacene ring. , Triphenylene ring, o-terphenyl ring, m-terphenyl ring, p-terphenyl ring, acenaphthene ring, coronene ring, fluorene ring, fluoranthrene ring, naphthacene ring, pentacene ring, perylene ring, pentaphen ring, picene ring , Pyrene ring, pyranthrene ring, anthraanthrene ring and the like. These rings may further have substituents each represented by R ′ and R ″ in X of the partial structure represented by the general formula (2).

In the partial structure represented by the general formula (2), examples of the aromatic heterocycle represented by Ar ₁ and Ar ₂ include a furan ring, a dibenzofuran ring, a thiophene ring, an oxazole ring, a pyrrole ring, a pyridine ring, and a pyridazine. Ring, pyrimidine ring, pyrazine ring, triazine ring, benzimidazole ring, oxadiazole ring, triazole ring, imidazole ring, pyrazole ring, thiazole ring, indole ring, indazole ring, benzimidazole ring, benzothiazole ring, benzoxazole ring, Quinoxaline ring, quinazoline ring, cinnoline ring, quinoline ring, isoquinoline ring, phthalazine ring, naphthyridine ring, carbazole ring, carboline ring, diazacarbazole ring (one of the carbon atoms of the hydrocarbon ring constituting the carboline ring is a nitrogen atom) The substituted ring For example). These rings may further have substituents represented by R ′ and R ″ in the general formula (2).

Among the above, in the general formula (2), the aromatic ring represented by Ar ₁ and Ar ₂ is preferably a carbazole ring, carboline ring, dibenzofuran ring, or benzene ring, and more preferably used. , A carbazole ring, a carboline ring, and a benzene ring, more preferably a benzene ring having a substituent, and particularly preferably a benzene ring having a carbazolyl group.

In the general formula (2), the aromatic rings represented by Ar ₁ and Ar ₂ are each preferably a condensed ring of 3 or more rings, and as an aromatic hydrocarbon condensed ring in which 3 or more rings are condensed. Specifically, naphthacene ring, anthracene ring, tetracene ring, pentacene ring, hexacene ring, phenanthrene ring, pyrene ring, benzopyrene ring, benzoazulene ring, chrysene ring, benzochrysene ring, acenaphthene ring, acenaphthylene ring, triphenylene ring, Coronene ring, benzocoronene ring, hexabenzocoronene ring, fluorene ring, benzofluorene ring, fluoranthene ring, perylene ring, naphthperylene ring, pentabenzoperylene ring, benzoperylene ring, pentaphen ring, picene ring, pyranthrene ring, coronene ring, naphthocoronene ring , Ovalene ring, Anslaan Examples include a torene ring. In addition, these rings may further have the above substituent.

Specific examples of the aromatic heterocycle condensed with three or more rings include an acridine ring, a benzoquinoline ring, a carbazole ring, a carboline ring, a phenazine ring, a phenanthridine ring, a phenanthroline ring, a carboline ring, a cyclazine ring, Kindin ring, tepenidine ring, quinindrin ring, triphenodithiazine ring, triphenodioxazine ring, phenanthrazine ring, anthrazine ring, perimidine ring, diazacarbazole ring (any one of the carbon atoms constituting the carboline ring is a nitrogen atom Phenanthroline ring, dibenzofuran ring, dibenzothiophene ring, naphthofuran ring, naphthothiophene ring, benzodifuran ring, benzodithiophene ring, naphthodifuran ring, naphthodithiophene ring, anthrafuran ring, anthradifuran ring, Emissions tiger thiophene ring, anthradithiophene ring, thianthrene ring, phenoxathiin ring, such as thio fan train ring (naphthothiophene ring). In addition, these rings may further have a substituent.

In the general formula (2), n represents an integer of 0 to 4, preferably 0 to 2, and particularly preferably 1 to 2 when X is O or S.

In the present invention, a host compound having both a dibenzofuran ring and a carbazole ring is particularly preferable.

Specific examples (a-1 to a-41) of the host compound represented by the general formula (2) are shown below, but are not limited thereto.

 

 

 

 

 

 

 

 

(4.2) Luminescent Compound As the luminescent compound (also referred to as a luminescent dopant) according to the present invention, at least a phosphorescent compound (also referred to as a phosphorescent compound) is contained in the light emitting layer. In the present invention, a phosphorescent compound is a compound in which light emission from an excited triplet is observed, specifically a compound that emits phosphorescence at room temperature (25 ° C.) and has a phosphorescence quantum yield of 25. Although it is defined as a compound of 0.01 or more at ° C., a preferable phosphorescence quantum yield is 0.1 or more.

The above phosphorescence quantum yield can be measured by the method described in Spectra II, page 398 (1992 edition, Maruzen) of the Fourth Edition Experimental Chemistry Course 7. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescence quantum yield (0.01 or more) should just be achieved in any solvent.

There are two types of light emission principles of phosphorescent compounds. 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 phosphorescent. Transfer energy to the compound to obtain light emission from the phosphorescent compound. Another is the phosphorescent compound becomes a carrier trap, and recombination of carriers occurs on the phosphorescent compound, resulting in phosphorescence. Although it is a carrier trap type in which light emission from the light emitting compound can be obtained, in any case, the excited state energy of the phosphorescent light emitting compound is lower than the excited state energy of the host compound.

The phosphorescent compound can be appropriately selected from known compounds used for the light-emitting layer of the organic EL device, and preferably a complex system containing a metal of group 8 to 10 in the periodic table of elements. A compound, more preferably an iridium compound, an osmium compound, a platinum compound (platinum complex compound), or a rare earth complex, and most preferably an iridium compound.

The phosphorescent compound according to this embodiment preferably includes at least one blue phosphorescent compound. More preferably, it contains at least one blue phosphorescent compound and at least one phosphorescent compound having a band gap energy lower than that of the blue phosphorescent compound.

As the phosphorescent compound, a known compound can be used, but preferably a metal complex having a pyridine derivative as a ligand (phosphorescent compound) or phosphorescence represented by the general formula (1) The luminescent compound can be increased. More preferably, it is a phosphorescent compound represented by the general formula (1).

Hereinafter, the phosphorescent compound represented by the general formula (1), which is preferably used in the present invention, will be described.

 

In the general formula (1), R ₁ represents a substituent. Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring. n1 represents an integer of 0 to 5. B ₁ to B ₅ represent a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, and at least one represents a nitrogen atom. M ₁ represents a group 8 to group 10 metal in the periodic table. X ₁ and X ₂ represent a carbon atom, a nitrogen atom or an oxygen atom, and L ₁ represents an atomic group which forms a bidentate ligand together with X ₁ and X ₂ . m1 represents an integer of 1, 2, or 3, m2 represents an integer of 0, 1, or 2, and m1 + m2 is 2 or 3.

The phosphorescent compound represented by the general formula (1) according to the present invention has a HOMO energy level of −5.15 to −3.50 eV and a LUMO energy level of −1.25 to +1.00 eV. More preferably, the energy level of HOMO is −4.80 to −3.50 eV, and the energy level of LUMO is preferably −0.80 to +1.00 eV.

In the phosphorescent compound represented by the general formula (1), examples of the substituent represented by R ₁ include an alkyl group (eg, methyl group, ethyl group, propyl group, isopropyl group, tert-butyl group). Pentyl group, hexyl group, octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, etc.), cycloalkyl group (for example, cyclopentyl group, cyclohexyl group, etc.), alkenyl group (for example, vinyl group, allyl group, etc.) Alkynyl group (eg, ethynyl group, propargyl group, etc.), aromatic hydrocarbon ring group (also called aromatic carbocyclic group, aryl group, etc.), for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl Group, naphthyl group, anthryl group, azulenyl group, acenaphthenyl group, fluorenyl group, phenanthryl group, Ndenyl group, pyrenyl group, biphenylyl group, etc.), aromatic heterocyclic group (for example, pyridyl group, pyrimidinyl group, furyl group, pyrrolyl group, imidazolyl group, benzoimidazolyl group, pyrazolyl group, pyrazinyl group, triazolyl group (for example, 1, 2,4-triazol-1-yl group, 1,2,3-triazol-1-yl group, etc.), oxazolyl group, benzoxazolyl group, thiazolyl group, isoxazolyl group, isothiazolyl group, furazanyl group, thienyl group, A quinolyl group, a benzofuryl group, a dibenzofuryl group, a benzothienyl group, a dibenzothienyl group, an indolyl group, a carbazolyl group, a carbolinyl group, a diazacarbazolyl group (one of the carbon atoms constituting the carboline ring of the carbolinyl group is a nitrogen atom) Quinoxalinyl group) , Pyridazinyl group, triazinyl group, quinazolinyl group, phthalazinyl group, etc.), heterocyclic group (eg, pyrrolidyl group, imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (eg, methoxy group, ethoxy group, propyloxy group, Pentyloxy group, hexyloxy group, octyloxy group, dodecyloxy group, etc.), cycloalkoxy group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), alkylthio Group (for example, methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio group (for example, cyclopentylthio group, cyclohexylthio group, etc.), arylthio group For example, phenylthio group, naphthylthio group, etc.), alkoxycarbonyl group (eg, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group (eg, Phenyloxycarbonyl group, naphthyloxycarbonyl group, etc.), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylaminosulfonyl group) , Dodecylaminosulfonyl group, phenylaminosulfonyl group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group, etc.), acyl group (for example, Cetyl group, ethylcarbonyl group, propylcarbonyl group, pentylcarbonyl group, cyclohexylcarbonyl group, octylcarbonyl group, 2-ethylhexylcarbonyl group, dodecylcarbonyl group, phenylcarbonyl group, naphthylcarbonyl group, pyridylcarbonyl group, etc.), acyloxy group ( For example, acetyloxy group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group, etc.), amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethylcarbonyl) Amino group, propylcarbonylamino group, pentylcarbonylamino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octylca Sulfonylamino group, dodecylcarbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group, etc.), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group, Cyclohexylaminocarbonyl group, octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylaminocarbonyl group, etc.), ureido group (for example, methylureido group, ethyl) Ureido group, pentylureido group, cyclohexylureido group, octylureido group, dodecylureido group, phenylureido group, naphthylureido group, 2-pi Diylaminoureido group, etc.), sulfinyl group (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecylsulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group) Group), alkylsulfonyl group (eg methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group etc.), arylsulfonyl group or heteroarylsulfonyl group (eg phenyl Sulfonyl group, naphthylsulfonyl group, 2-pyridylsulfonyl group, etc.), amino group (for example, amino group, ethylamino group, dimethylamino group, butyryl Group, cyclopentylamino group, 2-ethylhexylamino group, dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group, etc.), cyano group, nitro group, hydroxy group, mercapto group, silyl group (for example, trimethylsilyl group) , Triisopropylsilyl group, triphenylsilyl group, phenyldiethylsilyl group, etc.). Of these substituents, preferred are an alkyl group and an aryl group.

Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring. Examples of the 5- to 7-membered ring formed by Z include a benzene ring, naphthalene ring, pyridine ring, pyrimidine ring, pyrrole ring, thiophene ring, pyrazole ring, imidazole ring, oxazole ring and thiazole ring. Of these, a benzene ring is preferred.

B ₁ to B ₅ represent a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, and at least one represents a nitrogen atom. The aromatic nitrogen-containing heterocycle formed by these five atoms is preferably a monocycle. Examples include pyrrole ring, pyrazole ring, imidazole ring, triazole ring, tetrazole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, oxadiazole ring, and thiadiazole ring. Among these, a pyrazole ring and an imidazole ring are preferable, and an imidazole ring in which B2 and B5 are nitrogen atoms is particularly preferable. These rings may be further substituted with the above substituents. Preferred as the substituent are an alkyl group and an aryl group, and more preferably an aryl group.

L ₁ represents an atomic group that forms a bidentate ligand together with X ₁ and X ₂ . Specific examples of the bidentate ligand represented by X ₁ -L ₁ -X ₂ include, for example, substituted or unsubstituted phenylpyridine, phenylpyrazole, phenylimidazole, phenyltriazole, phenyltetrazole, pyrazabol, picolinic acid And acetylacetone. These groups may be further substituted with the above substituents.

m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2, and m1 + m2 is 2 or 3. Especially, the case where m2 is 0 is preferable. As the metal represented by M ₁ , a transition metal element belonging to Group 8 to 10 of the periodic table (also simply referred to as a transition metal) is used, among which iridium and platinum are preferable, and iridium is more preferable.

Hereinafter, specific compounds (D-1 to D-133) of phosphorescent compounds preferably used in the present invention are exemplified, but the present invention is not limited thereto.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(4.3) Quantum dot In this invention, it has a quantum dot in at least any one of the interface of a light emitting layer and the said positive hole transport layer, and the interface of the said light emitting layer and the said electron transport layer.

In the present application, “quantum dots” are semiconductor microcrystals having a diameter of several to several tens of nanometers formed to confine electrons (and holes) in a minute space and exhibit a quantum size effect. .

When the quantum dot is present at the interface between the light emitting layer and the hole transport layer, it functions as a hole blocking layer. When the quantum dot is present at the interface between the light emitting layer and the electron transport layer, the electron blocking layer is used. Function as. In the present invention, the quantum dots function as a block layer. The light emission is preferably made from a phosphorescent compound, but does not prevent light emission from the quantum dots.

The quantum dots may exist at the interface between the light emitting layer and the hole transport layer as shown in FIG. 1, or may exist at the interface between the light emitting layer and the electron transport layer as shown in FIG. . In this, it is preferable that the quantum dot exists in the interface of a light emitting layer and a positive hole transport layer. This seems to be because holes have a higher mobility than electrons and effectively prevent holes from penetrating through the light emitting layer. Moreover, as shown in FIG. 3, you may exist in the interface of both the light emitting layer and the layer adjacent to a light emitting layer.

In the present invention, the interface refers to a boundary surface between the light emitting layer and the hole transport layer or the light emitting layer and the electron transport layer, and the quantum dot exists in contact with the light emitting layer and the hole transport layer or the light emitting layer and the electron transport layer. The quantum dot becomes a monomolecular layer, and a monomolecular layer may be formed between the light emitting layer and the hole transporting layer or between the light emitting layer and the electron transporting layer, which is a preferred embodiment.

In the present invention, the quantum dots are preferably uniformly dispersed at the interface. When the quantum dots are embedded in the light emitting layer, the hole transport layer, or the electron transport layer, the function as a block layer is effective. It becomes difficult and is not preferable.

The presence at the interface can be observed using a cross-sectional SEM (scanning electron microscope) or a transmission electron microscope (TEM).

In the present invention, by having quantum dots at least at the interface between the hole transport layer or the electron transport layer adjacent to the light emitting layer, the light emission efficiency of the organic EL element, the low driving voltage and the long lifetime can be achieved.

This is thought to be due to the fact that it is possible to efficiently emit light in the light emitting layer without diffusing excitons, electrons, or holes generated in the light emitting layer by including quantum dots in one or both of the interfaces. . In the present invention, the quantum dots are considered to function as a blocking layer that prevents electrons and holes from passing through the light emitting layer.

This effect is significant when the band gap of the host compound in the light emitting layer is larger than the band gap of the quantum dots. Specifically, the band gap of the host compound is preferably 0.1 eV or more larger than the band gap of the quantum dots.

Further, the band gap of the phosphorescent compound in the light emitting layer is preferably smaller than the band gap of the quantum dots. Specifically, the band gap of the phosphorescent compound is preferably 0.1 eV or more smaller than the band gap of the quantum dots.

In the present invention, the band gap of the host compound and the band gap of the phosphorescent compound are the energy between the energy level of the highest occupied molecular orbital (HOMO) and the energy level of the lowest unoccupied molecular orbital (LUMO). Difference (energy gap). Moreover, the band gap of a quantum dot means the energy difference (energy gap) of the valence band and conduction band of a quantum dot.

A band gap measuring method will be described. In the present invention, Tauc plot, which is known as one of photochemical measurement techniques, is used for band gap measurement. However, the present invention is not limited to this method as long as a physically equivalent characteristic value can be obtained. The measurement principle of band gap energy (E ₀ ) using Tauc plot is shown below.

In the region of relatively large absorption near the optical absorption edge on the long wavelength side of the semiconductor material, between the light absorption coefficient α and the light energy hν (where h is the Planck constant and ν is the frequency) and the bandcap energy E ₀ . The following formula (I) is considered to hold.

Formula (I) αhν = B (hν−E ₀ ) ²
Therefore, an absorption spectrum is measured, and hν is plotted (so-called Tauc plot) with respect to (αhν) to the 0.5th power, and the value of hν at α = 0 obtained by extrapolating the straight line section is obtained. The gap energy E ₀ is obtained.

Observation of light absorption can be performed in a wavelength range of 350 to 800 nm using an ultraviolet-visible near-infrared spectrophotometer (“V-7200 type”, manufactured by JASCO Corporation). It can be measured by a transmission method using a sample thin film.

Quantum dots are particles of a predetermined size having a quantum confinement effect. Specifically, the particle diameter of the quantum dots (fine particles) is preferably 1 to 20 nm, and more preferably 1 to 10 nm. The energy level E of such a fine particle is generally expressed by the formula (II) where the Planck constant is “h”, the effective mass of the electron is “m”, and the radius of the fine particle is “R”. .

Formula (II) E∝h ² / mR ²
As shown by the formula (II), the band gap of the fine particles increases in proportion to “R ⁻² ”, and the so-called quantum dot effect is obtained. Thus, the band gap value of a quantum dot can be controlled by controlling and defining the particle diameter of the quantum dot. That is, by controlling and defining the particle diameter of the fine particles, it is possible to provide diversity not found in ordinary atoms.

The block layer preferably has a wide band gap. The particle size of the quantum dots is preferably 1 to 20 nm, more preferably 1 to 10 nm, and particularly preferably 1 to 3 nm. A specific band gap is preferably in the range of 1.8 eV to 3.2 eV, more preferably 2.2 eV to 3.0 eV, and most preferably 2.6 eV to 3.0 eV.

As a method for measuring the average particle diameter, a known method can be used. For example, the quantum dot particles are observed with a transmission electron microscope (TEM), and the number average particle size of the particle size distribution is obtained therefrom, or the particle size distribution of the quantum dots is measured by a dynamic light scattering method. Examples thereof include a method for obtaining the number average particle size and a method for deriving the particle size distribution from the spectrum obtained by the X-ray small angle scattering method using the particle size distribution simulation calculation of the quantum dots. In the present invention, the particle size was measured by a dynamic scattering method using a particle size measuring device (“ZETASIZER Nano Series Nano-ZS” manufactured by Malvern).

Examples of the constituent material of the quantum dot include a simple substance of a group 14 element of the periodic table such as carbon, silicon, germanium, and tin, a simple substance of a group 15 element of the periodic table such as phosphorus (black phosphorus), and a periodicity of selenium, tellurium, and the like. Table 16 group element simple substance, compound consisting of a plurality of periodic table group 14 elements such as silicon carbide (SiC), tin oxide (IV) (SnO ₂ ), tin sulfide (II, IV) (Sn (II) Sn (IV) S ₃ ), tin sulfide (IV) (SnS ₂ ), tin sulfide (II) (SnS), tin selenide (II) (SnSe), tin telluride (II) (SnTe), lead sulfide (II) ) (PbS), lead selenide (II) (PbSe), lead telluride (II) (PbTe) periodic table group 14 element and periodic table group 16 element compound, boron nitride (BN), phosphorus Boron bromide (BP), boron arsenide (BAs), aluminum nitride (AlN), Aluminum nitride (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN) ), Indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), etc., a compound of a periodic table group 13 element and a periodic table group 15 element (or III-V compound semiconductor), sulfide Aluminum (Al ₂ S ₃ ), Aluminum selenide (Al ₂ Se ₃ ), Gallium sulfide (Ga ₂ S ₃ ), Gallium selenide (Ga ₂ Se ₃ ), Gallium telluride (Ga ₂ Te ₃ ), Indium oxide ( In ₂ O ₃ ), indium sulfide (In ₂ S ₃ ), indium selenide (In ₂ Se ₃₎ ), Compounds of Group 13 elements of the periodic table and Group 16 elements of the periodic table, such as indium telluride (In ₂ Te ₃ ), thallium (I) chloride (TlCl), thallium bromide (I) (TlBr), iodine Compounds of periodic table group 13 elements and periodic table group 17 elements such as thallium (I) fluoride (TlI), zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride ( ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), etc. the compounds of the periodic table group 12 element and periodic table group 16 element (or II-VI compound semiconductor), arsenic sulfide (III) (as ₂ S _3), selenium arsenic (III) (as ₂ Se ₃ Telluride arsenic _{(III) (As 2 Te 3} ), antimony sulfide _{(III) (Sb 2 S 3} ), selenium antimony _{(III) (Sb 2 Se 3} ), antimony telluride (III) (Sb ₂ Te ₃ ), Bismuth sulfide (III) (Bi ₂ S ₃ ), bismuth selenide (III) (Bi ₂ Se ₃ ), bismuth telluride (III) (Bi ₂ Te ₃ ), etc. the compounds of the group 16 element, copper oxide _{(I) (Cu 2 O)} , copper selenide (I) (Cu ₂ Se) periodic table compounds of the group 11 element and periodic table group 16 element such as, chloride Periodic table Group 11 elements and periods such as copper (I) (CuCl), copper bromide (I) (CuBr), copper iodide (I) (CuI), silver chloride (AgCl), silver bromide (AgBr) A compound with a group 17 element, a periodic table such as nickel (II) oxide (NiO), a group 10 element and a periodic table first The compounds of the group elements, cobalt oxide (II) (CoO), compounds of cobalt sulfide (II) (CoS) periodic table Group 9 element and Periodic Table Group 16 element such as, triiron tetraoxide (Fe ₃ O ₄ ), compounds of Group 8 elements of the periodic table such as iron (II) sulfide (FeS), and elements of Group 16 of the periodic table, Group 7 elements of the periodic table such as manganese (II) (MnO) and periodic table Compounds with group 16 elements, compounds of group 6 elements of the periodic table and elements of group 16 of the periodic table, such as molybdenum (IV) sulfide (MoS ₂ ), tungsten oxide (IV) (WO ₂ ), vanadium (II) oxide (VO), vanadium oxide (IV) (VO ₂ ), compounds of periodic table group 5 elements such as tantalum oxide (V) (Ta ₂ O ₅ ), etc., and titanium oxide (TiO ₂ , _{Ti 2 O 5, Ti 2 O} 3, Ti 5 O 9 , etc.) and the like of the periodic table group 4 element and a periodic table group 16 source Compound with magnesium sulfide (MgS), compounds of Group 2 elements and Periodic Table Group 16 element such as magnesium selenide (MgSe), cadmium oxide (II) chromium _{(III) (CdCr 2 O 4} ) , Cadmium selenide (II) chromium (III) (CdCr ₂ Se ₄ ), copper (II) sulfide (III) (CuCr ₂ S ₄ ), mercury (II) selenide (III) (HgCr ₂ Se ₄ ) Examples include chalcogen spinels such as barium titanate (BaTiO ₃ ), etc., but compounds of group 14 elements of the periodic table and group 16 elements of the periodic table such as SnS ₂ , SnS, SnSe, SnTe, PbS, PbSe, PbTe, etc. GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb and other III-V compound semiconductors, Ga ₂ O ₃ , Ga ₂ S ₃ , Ga ₂ Se ₃ , Ga ₂ Te _{3, In 2 O 3, In} 2 S 3, In 2 Se 3, In 2 Te periodic table compounds of Group 13 elements and the periodic table group 16 elements such as _{3, ZnO, ZnS, ZnSe,} ZnTe, CdO, II-VI group compound semiconductors such as CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, As ₂ O ₃ , As ₂ S ₃ , As ₂ Se ₃ , As ₂ Te ₃ , Sb ₂ O ₃ , Sb ₂ S ₃ , a compound of a group 15 element of the periodic table and a group 16 element of the periodic table, such as Sb ₂ Se ₃ , Sb ₂ Te ₃ , Bi ₂ O ₃ , Bi ₂ S ₃ , Bi ₂ Se ₃ , Bi ₂ Te ₃ , Compounds of Group 2 elements of the periodic table and Group 16 elements of the periodic table, such as MgS and MgSe, are preferred, among which Si, Ge, GaN, GaP, InN, InP, Ga ₂ O ₃ , Ga ₂ S ₃ , In _2. O ₃ , In ₂ S ₃ , ZnO, ZnS, CdO, CdS are more preferable. . Since these substances do not contain highly toxic negative elements, they are excellent in environmental pollution resistance and biological safety, and are advantageous for the formation of light-emitting elements. Of these materials, CdSe, ZnSe, and CdS are preferable in terms of light emission stability. From the viewpoints of luminous efficiency, high refractive index, and safety, ZnO and ZnS quantum dots are preferable. Moreover, said material may be used by 1 type and may be used in combination of 2 or more type.

Note that the above-described quantum dots may be doped with a small amount of various elements as impurities as necessary.

The surface of the quantum dot is preferably coated with an inert inorganic coating layer or a coating composed of an organic ligand. That is, the surface of the quantum dot preferably has a core region composed of quantum dots and a shell region composed of an inert inorganic coating layer or organic ligand. The core / shell structure is preferably formed of at least two types of compounds, and a gradient structure may be formed of two or more types of compounds. This effectively prevents aggregation of the quantum dots in the coating liquid, improves the dispersibility of the quantum dots, improves the luminance efficiency, and prevents color shifts that occur when driven continuously. Can be suppressed. Further, the light emission characteristics can be stably obtained by the presence of the coating layer.

Further, when the surface of the quantum dots is coated with a coating, a surface modifier as described later can be reliably supported in the vicinity of the surface of the quantum dots. The thickness of the coating is not particularly limited, but is preferably 0.1 to 10 nm, and more preferably 0.1 to 5 nm. In general, if the emission color can be controlled by the size of the quantum dots and the thickness of the coating is within the above range, the thickness of the coating is less than one quantum dot from the thickness corresponding to several atoms. Thus, quantum dots can be filled with high density, and a sufficient amount of light emission can be obtained. Further, the presence of the coating can suppress the transfer of non-emissive electron energy due to the defects existing on the particle surfaces of the core particles and the electron traps on the dangling bonds, and the decrease in quantum efficiency can be suppressed.

(4.4) Functional surface modifier It is preferable that the surface modifier has adhered to the surface vicinity of the quantum dot in the coating liquid. Thereby, especially the dispersibility of the quantum dot in a coating liquid can be made excellent. Also, by attaching a surface modifier to the surface of the quantum dots during the manufacture of the quantum dots, the shape of the formed quantum dots has a high sphericity, and the particle size distribution of the quantum dots can be kept narrow. Therefore, for example, it can be made particularly excellent.

These functional surface modifiers may be those directly attached to the surface of the quantum dot, or those attached via the shell (the surface modifier is directly attached to the shell, It may be that which is not in contact.

Examples of the surface modifier include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; tripropylphosphine, tributylphosphine, trihexylphosphine, trioctylphosphine, and the like. Trialkylphosphines; polyoxyethylene alkylphenyl ethers such as polyoxyethylene n-octylphenyl ether and polyoxyethylene n-nonylphenyl ether; tri (n-hexyl) amine, tri (n-octyl) amine, tri ( tertiary amines such as n-decyl) amine; tripropylphosphine oxide, tributylphosphine oxide, trihexylphosphine oxide, trioctylphosphineoxy Organic phosphorus compounds such as tridecylphosphine oxide; polyethylene glycol diesters such as polyethylene glycol dilaurate and polyethylene glycol distearate; organic nitrogen compounds such as nitrogen-containing aromatic compounds such as pyridine, lutidine, collidine and quinolines; hexylamine; Aminoalkanes such as octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine; dialkyl sulfides such as dibutyl sulfide; dialkyl sulfoxides such as dimethyl sulfoxide and dibutyl sulfoxide; sulfur-containing aromatics such as thiophene Organic sulfur compounds such as compounds; higher fatty acids such as palmitic acid, stearic acid and oleic acid; alcohols; sorbitan fatty acid esters; fatty acid-modified poly Stealtes; tertiary amine-modified polyurethanes; polyethyleneimines, and the like. When the quantum dots are prepared by the method described later, the surface modifier is coordinated to the fine particles in the high-temperature liquid phase. In particular, trialkylphosphines, organic phosphorus compounds, aminoalkanes, tertiary amines, organic nitrogen compounds, dialkyl sulfides, dialkyl sulfoxides, organic sulfur compounds Higher fatty acids and alcohols are preferred. By using such a surface modifier, the dispersibility of the quantum dots in the coating solution can be made particularly excellent. Moreover, the shape of the quantum dot formed at the time of manufacture of a quantum dot can be made into a higher sphericity, and the particle size distribution of a quantum dot can be made sharper.

(4.5) Manufacturing method of quantum dot As a manufacturing method of a quantum dot, the manufacturing method of the following quantum dots etc. which are performed conventionally are mentioned, However, It is not limited to these, Well-known arbitrary The method can be used.

For example, as a process under high vacuum, a molecular beam epitaxy method, a CVD method, etc .; As a liquid phase production method, an aqueous raw material is used, for example, alkanes such as n-heptane, n-octane, isooctane, or benzene, toluene. Inverted micelles, which exist as reverse micelles in non-polar organic solvents such as aromatic hydrocarbons such as xylene, and crystal growth in this reverse micelle phase, inject a thermally decomposable raw material into a high-temperature liquid-phase organic medium Examples thereof include a hot soap method for crystal growth and a solution reaction method involving crystal growth at a relatively low temperature using an acid-base reaction as a driving force, as in the hot soap method.

Any method can be used from these production methods, and among these, the liquid phase production method is preferable.

In the liquid phase production method, an organic surface modifier present on the surface during the synthesis of quantum dots is referred to as an initial surface modifier. For example, examples of the initial surface modifier in the hot soap method include trialkylphosphines, trialkylphosphine oxides, alkylamines, dialkyl sulfoxides, alkanephosphonic acid and the like. These initial surface modifiers are preferably exchanged for the above-described functional surface modifiers by an exchange reaction.

Specifically, for example, the initial surface modifier such as trioctylphosphine oxide obtained by the above-described hot soap method is obtained by performing the functional surface modification described above by an exchange reaction performed in a liquid phase containing the functional surface modifier. It is possible to replace it with an agent.

The following shows an example of a method for producing quantum dots.

<1> Production example 1 of quantum dots
First, CdO powder (1.6 mmol, 0.206 g; Aldrich, + 99.99%) and oleic acid (6.4 mmol, 1.8 g; Aldrich, 95%) were mixed with 40 ml of trioctylamine (TOA, Aldrich, 95 %). The mixed solution was heat-treated at 150 ° C. while stirring at a high speed, and the temperature was raised to 300 ° C. while N ₂ was allowed to flow. Then, at 300 ° C., 0.2 ml of 2.0 mol / L Se (Alfa Aesar) added to trioctylphosphine (TOP, Strem, 97%) is injected into the Cd-containing mixture at high speed.

After 90 seconds, 1.2 mmol of n-octanethiol added to TOA (210 μl in 6 ml) is injected at a rate of 1 ml / min using a syringe pump and reacted for 40 minutes.

Next, 0.92 g of zinc acetate and 2.8 g of oleic acid are dissolved in 20 ml of TOA at 200 ° C. in an N ₂ atmosphere to prepare a 0.25 mol / L Zn precursor solution.

Next, a 16 ml aliquot of Zn-oleic acid solution (heated at 100 ° C.) is injected into the Cd-containing reaction medium at a rate of 2 ml / min. Thereafter, 6.4 mmol of n-octanethiol in TOA (1.12 ml in 6 ml) is injected at a rate of 1 ml / min using a syringe pump.

The entire reaction takes 2 hours. After the reaction is complete, the product is cooled to about 50-60 ° C. and the organic sludge is removed by centrifugation (5,600 rpm). Add ethanol (Fisher, HPLC grade) until there is no opaque mass. Next, the precipitate obtained by centrifugation is dissolved in toluene (Sigma-Aldrich, Anhydrous 99.8%) to obtain a CdSe / CdS / ZnS core-shell quantum dot colloidal solution.

<2> Production example 2 of quantum dots
When a quantum dot having a core / shell structure of CdSe / ZnS is to be obtained, (CH ₃ ) ₂ Cd (dimethyl cadmium), TOPSe (tricylphosphine selenium) is used as an organic solvent using TOPO (trioctylphosphine oxide) as a surfactant. A precursor material corresponding to the core (CdSe) is injected to generate a crystal, and is maintained at a high temperature for a certain period of time so that the crystal grows at a certain size, and then corresponds to the shell (ZnS). CdSe / ZnS quantum dots capped with TOPO can be obtained by injecting the precursor material so that a shell is formed on the surface of the core already formed.

<3> Production example 3 of quantum dots
Under an argon stream, 7.5 g of tri-n-octylphosphine oxide (TOPO) (manufactured by Kanto Chemical Co.), 2.9 g of stearic acid (manufactured by Kanto Chemical Co., Ltd.), 620 mg of n-tetradecylphosphonic acid (manufactured by AVOCADO), And 250 mg of cadmium oxide (made by Wako Pure Chemical Industries Ltd.) was added, and it heat-mixed at 370 degreeC. After naturally cooling this to 270 ° C., a solution of 200 mg of selenium (STREM CHEMICAL) dissolved in 2.5 ml of tributylphosphine (manufactured by Kanto Chemical Co.) was added in advance, dried under reduced pressure, and CdSe coated with TOPO. Get fine particles.

Next, 15 g of TOPO was added to the obtained CdSe fine particles and heated, and subsequently, a solution of 1.1 g of zinc diethyldithiocarbamate (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 10 ml of trioctylphosphine (manufactured by Sigma Aldrich) was added at 270 ° C. Then, nanoparticles with CdSe nanocrystals with TOPO fixed on the surface and ZnS as the core (hereinafter also referred to as TOPO fixed quantum dots) were obtained. In addition, the quantum dot of this state is soluble in organic solvents, such as toluene and tetrahydrofuran (THF).

Thereafter, the prepared TOPO fixed quantum dots were dissolved in THF, heated to 85 ° C., and N-[(S) -3-mercapto-2-methylpropionyl] -L-proline (Sigma) dissolved in ethanol there. (Aldrich) 100 mg was added dropwise and refluxed for about 12 hours. After refluxing for 12 hours, an aqueous NaOH solution was added, and the mixture was heated at 90 ° C. for 2 hours to evaporate THF. The obtained unpurified quantum dots are purified and concentrated using ultrafiltration (Millipore, “Microcon”) and Sephadex column (Amersham Biosciences, “MicroSpin G-25 Columns”). A hydrophilic quantum dot in which N-[(S) -3-mercapto-2-methylpropionyl] -L-proline is immobilized on the surface of the quantum dot can be produced.

(4.6) Quantum Dot Formation Method Quantum separated from various material layers by applying a mixture of materials such as hole transport materials, electron transport materials, light emitting layer materials and quantum dots by spin coating. A dot layer can be formed at the interface. In addition, a dry method such as a microcontact printing method that transfers a self-assembled monolayer onto a substrate using a patterned PDMS (polydimethylsiloxane) stamp or the like, or a coating solution containing quantum dots Examples of the method include spin coating.

"anode"
As the anode constituting the organic EL device, an electrode material made of a metal, an alloy, an electrically conductive compound or a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such electrode substances include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) that can form a transparent conductive film may be used. For the anode, these electrode materials may be formed into a thin film by a method such as vapor deposition or sputtering, and a desired shape pattern may be formed by a photolithography method, or when pattern accuracy is not so high (about 100 μm or more) A pattern may be formed through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. Or when using the substance which can be apply | coated like an organic electroconductivity compound, wet film forming methods, such as a printing system and a coating system, can also be used. When light emission is extracted from the anode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually in the range of 10 to 1000 nm, preferably in the range of 10 to 200 nm.

"cathode"
On the other hand, as the cathode, a material having a low work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is 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. Among these, from the point of durability against electron injection and oxidation, etc., a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function than this, for example, a magnesium / silver mixture, Suitable are a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, a lithium / aluminum mixture, aluminum and the like. The cathode 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 cathode 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 to 200 nm. In order to transmit the emitted light, if either one of the anode or the cathode of the organic EL element is transparent or translucent, the emission luminance is advantageously improved.

In addition, a transparent or translucent cathode can be produced by forming the above metal on the cathode with a film thickness of 1 to 20 nm and then forming the conductive transparent material mentioned in the description of the anode thereon. By applying this, an organic EL element in which both the anode and the cathode are transmissive can be produced.

《Support substrate》
The support substrate (hereinafter also referred to as a substrate, substrate, substrate, support, etc.) that can be used in the organic EL device of the present invention is not particularly limited in the type of glass, plastic, etc., and is transparent. May be opaque. When extracting light from the support substrate side, the support substrate is preferably transparent. Examples of the transparent support substrate preferably used include glass, quartz, and a transparent resin film. Since the effect of suppressing high-temperature storage stability and chromaticity variation appears greatly in a flexible substrate than a rigid substrate, a particularly preferable support substrate has flexibility that can give flexibility to an organic EL element. Resin film.

Examples of the resin film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyethylene, polypropylene, cellophane, cellulose diacetate, cellulose triacetate (TAC), cellulose acetate butyrate, and cellulose acetate propionate ( CAP), cellulose esters such as cellulose acetate phthalate, cellulose nitrate or derivatives thereof, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide , Polyethersulfone (PES), polyphenylene sulfide, polysulfones Cycloolefin resins such as polyetherimide, polyetherketoneimide, polyamide, fluororesin, nylon, polymethylmethacrylate, acrylic or polyarylate, Arton (trade name, manufactured by JSR) or Appel (trade name, manufactured by Mitsui Chemicals) Can be mentioned.

The surface of the resin film may be formed with an inorganic film, an organic film, or a hybrid film of both, and the water vapor permeability (25 ± 0.5 ° C.) measured by a method according to JIS K 7129-1992. , And a relative humidity (90 ± 2)% RH) of 0.01 g / (m ² · 24 h) or less is preferable, and oxygen permeability measured by a method according to JIS K 7126-1987 is also preferable. The film is preferably a high barrier film having a degree of 10 ⁻³ cm ³ / (m ² · 24 h · atm) or less and a water vapor permeability of 10 ⁻³ g / (m ² · 24 h) or less. More preferably, the degree is 10 ⁻⁵ g / (m ² · 24 h) or less.

As a material for forming the barrier film, any material may be used as long as it has a function of suppressing intrusion of factors that cause deterioration of the organic EL element such as moisture and oxygen. For example, silicon oxide, silicon dioxide, silicon nitride, or the like is used. Can do. In order to further improve the brittleness of the film, it is more preferable to have a laminated structure of these inorganic layers and layers made of organic materials. Although there is no restriction | limiting in particular about the lamination order of an inorganic layer and an organic functional layer, It is preferable to laminate | stack both alternately several times.

The method for forming the barrier film is not particularly limited. For example, the vacuum deposition method, sputtering method, reactive sputtering method, molecular beam epitaxy method, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma A polymerization method, a plasma CVD method, a laser CVD method, a thermal CVD method, a coating method, and the like can be used, but an atmospheric pressure plasma polymerization method as described in JP-A-2004-68143 is particularly preferable.

Examples of the opaque support substrate include metal plates such as aluminum and stainless steel, films, opaque resin substrates, ceramic substrates, and the like. In the organic EL device of the present invention, the external extraction efficiency of light emission at room temperature is preferably 1% or more, more preferably 5% or more. Here, the external extraction quantum efficiency (%) = the number of photons emitted to the outside of the organic EL element / the number of electrons sent to the organic EL element × 100.

<< Sealing (sealing adhesive, sealing member) >>
As a sealing means applicable to the organic EL element of the present invention, for example, a method of adhering a sealing member, an electrode, and a support substrate with an adhesive can be mentioned. As a sealing member, it should just be arrange | positioned so that the display area | region of an organic EL element may be covered, and concave plate shape or flat plate shape may be sufficient. Further, transparency and electrical insulation are not particularly limited.

Specific examples include a glass plate, a polymer plate / film, and a metal plate / film. Examples of the glass plate include soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer plate include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide, and polysulfone. Examples of the metal plate include those made of one or more metals or alloys selected from the group consisting of stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum, silicone, germanium, and tantalum.

In the present invention, a polymer film and a metal film can be preferably used because the element can be thinned. Furthermore, the polymer film has an oxygen permeability measured by a method according to JIS K 7126-1987 of 1 × 10 ⁻³ cm ³ / (m ² · 24 h · atm) or less, according to JIS K 7129-1992. The water vapor permeability (25 ± 0.5 ° C., relative humidity (90 ± 2)% RH) measured by the above method is preferably 1 × 10 ⁻³ g / (m ² · 24 h) or less.

For processing the sealing member into a concave shape, sandblasting, chemical etching, or the like is used.

Specific examples of the adhesive include photocuring and thermosetting adhesives having reactive vinyl groups such as acrylic acid oligomers and methacrylic acid oligomers, and moisture curing adhesives such as 2-cyanoacrylates. Can be mentioned. Moreover, heat | fever and chemical curing types (two-component mixing), such as an epoxy type, can be mentioned. Moreover, hot-melt type polyamide, polyester, and polyolefin can be mentioned. Moreover, a cationic curing type ultraviolet curing epoxy resin adhesive can be mentioned.

In addition, since an organic EL element may deteriorate by heat processing, what can be adhesively cured from room temperature to 80 ° C. is preferable. Further, a desiccant may be dispersed in the adhesive. Application | coating of the adhesive agent to a sealing part may use commercially available dispenser, and may print like screen printing.

It is also preferable to cover the electrode and the organic functional layer on the outer side of the electrode facing the support substrate with the organic functional layer in between, and form an inorganic or organic layer in contact with the support substrate to form a sealing film Can be. In this case, the material for forming the film may be any material that has a function of suppressing intrusion of elements that cause deterioration of elements such as moisture and oxygen. For example, silicon oxide, silicon dioxide, silicon nitride, or the like may be used. it can. Further, in order to improve the brittleness of the film, it is preferable to have a laminated structure of these inorganic layers and layers made of organic materials. The method for forming these films is not particularly limited. For example, vacuum deposition method, sputtering method, reactive sputtering method, molecular beam epitaxy method, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma A polymerization method, a plasma CVD method, a laser CVD method, a thermal CVD method, a coating method, or the like can be used.

In order to form a gas phase and a liquid phase in the gap between the sealing member and the display area of the organic EL element, an inert gas such as nitrogen or argon, an inert gas such as fluorinated hydrocarbon or silicon oil is used. It is preferable to inject a liquid. A vacuum is also possible. Moreover, a hygroscopic compound can also be enclosed inside.

Examples of the hygroscopic compound include metal oxides (for example, sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide, aluminum oxide) and sulfates (for example, sodium sulfate, calcium sulfate, magnesium sulfate, cobalt sulfate). Etc.), metal halides (eg calcium chloride, magnesium chloride, cesium fluoride, tantalum fluoride, cerium bromide, magnesium bromide, barium iodide, magnesium iodide etc.), perchloric acids (eg perchloric acid) Barium, magnesium perchlorate, and the like), and anhydrous salts are preferably used in sulfates, metal halides, and perchloric acids.

Sealing includes casing type sealing (can sealing) and close contact type sealing (solid sealing), but solid sealing is preferable from the viewpoint of thinning. Moreover, when producing a flexible organic EL element, since sealing is also required for the sealing member, solid sealing is preferable.

In the following, a preferred embodiment when performing solid sealing will be described.

As the sealing adhesive according to the present invention, a thermosetting adhesive, an ultraviolet curable resin, or the like can be used, but preferably a thermosetting adhesive such as an epoxy resin, an acrylic resin, or a silicone resin, more preferably moisture resistant. It is an epoxy thermosetting adhesive resin that is excellent in water resistance and water resistance and has little shrinkage during curing.

The water content of the sealing adhesive according to the present invention is preferably 300 ppm or less, more preferably 0.01 to 200 ppm, and most preferably 0.01 to 100 ppm. The moisture content referred to in the present invention may be measured by any method. For example, a volumetric moisture meter (Karl Fischer), an infrared moisture meter, a microwave transmission moisture meter, a heat-dry weight method, GC / MS , IR, DSC (differential scanning calorimeter), TDS (temperature programmed desorption analysis). Further, using a precision moisture meter AVM-3000 (Omnitech) or the like, moisture can be measured from a pressure increase caused by evaporation of moisture, and moisture content of a film or a solid film can be measured.

In the present invention, the moisture content of the sealing adhesive can be adjusted by, for example, placing it in a nitrogen atmosphere with a dew point temperature of −80 ° C. or lower and an oxygen concentration of 0.8 ppm, and changing the time. Further, it can be dried in a vacuum state of 100 Pa or less while changing the time. Further, the sealing adhesive can be dried only with an adhesive, but can also be placed in advance on the sealing member and dried.

When close sealing (solid sealing) is performed, as the sealing member, for example, a 50 μm thick PET (polyethylene terephthalate) laminated with an aluminum foil (30 μm thick) is used. Using this as a sealing member, it is uniformly applied to the aluminum surface using a dispenser, a sealing adhesive is placed in advance, the resin substrate 1 and the sealing member 5 are aligned, and then both are crimped ( 0.1-3 MPa) and a temperature of 80-180 ° C. for close contact / bonding (adhesion), and close sealing (solid sealing).

Heating or pressure bonding time varies depending on the type, amount, and area of the adhesive, but temporary bonding is performed at a pressure of 0.1 to 3 MPa, and heat curing time is in the range of 5 seconds to 10 minutes at a temperature of 80 to 180 ° C. Just choose. The use of a heated crimping roll is preferred because it allows simultaneous crimping (temporary bonding) and heating, and eliminates internal voids at the same time. As a method for forming the adhesive layer, a coating method such as roll coating, spin coating, screen printing, or spray coating, or a printing method can be used depending on the material.

As described above, solid sealing is a form in which there is no space between the sealing member and the organic EL element substrate and the resin is covered with a cured resin. Examples of the sealing member include metals such as stainless steel, aluminum, and magnesium alloys, polyethylene terephthalate, polycarbonate, polystyrene, nylon, plastics such as polyvinyl chloride, and composites thereof, glass, and the like. In the case of a resin film, a laminate of gas barrier layers such as aluminum, aluminum oxide, silicon oxide, and silicon nitride can be used as in the case of a resin substrate.

The gas barrier layer can be formed by sputtering, vapor deposition or the like on both surfaces or one surface of the sealing member before molding the sealing member, or may be formed on both surfaces or one surface of the sealing member after sealing by a similar method. . Also in this case, the oxygen permeability is 1 × 10 ⁻³ cm ³ / (m ² · 24 h · atm) or less, the water vapor permeability (25 ± 0.5 ° C., relative humidity (90 ± 2)% RH) is 1 It is preferable that it is below 10 < ^-3 > g / (m < ² > * 24h).

The sealing member may be a film laminated with a metal foil such as aluminum. As a method for laminating the polymer film on one side of the metal foil, a generally used laminating machine can be used. As the adhesive, polyurethane-based, polyester-based, epoxy-based, acrylic-based adhesives and the like can be used. You may use a hardening | curing agent together as needed. A hot melt lamination method, an extrusion lamination method and a coextrusion lamination method can also be used, but a dry lamination method is preferred.

In addition, when the metal foil is formed by sputtering or vapor deposition and is formed from a fluid electrode material such as a conductive paste, it may be produced by a method of forming a metal foil on a polymer film as a base material. Good.

《Protective film, protective plate》
In order to increase the mechanical strength of the organic EL element, a protective film or a protective plate may be provided outside the sealing film on the side facing the support substrate with the organic functional layer interposed therebetween or on the outer side of the sealing film. In particular, when sealing is performed with a sealing film, the mechanical strength is not necessarily high, and thus it is preferable to provide such a protective film and a protective plate. As a material that can be used for this, the same glass plate, polymer plate / film, metal plate / film, etc. used for the sealing can be used, but the polymer film is light and thin. Is preferably used.

In the present invention, it is preferable to have a light extraction member between the flexible support substrate and the anode or at any position on the light emission side from the flexible support substrate. Examples of the light extraction member include a prism sheet, a lens sheet, and a diffusion sheet. Moreover, the diffraction grating introduce | transduced in the interface which raise | generates total reflection, or any medium, a diffusion structure, etc. are mentioned.

Usually, in an organic electroluminescence element that emits light from a substrate, a part of the light emitted from the light emitting layer causes total reflection at the interface between the substrate and air, causing a problem of loss of light. In order to solve this problem, the prism surface, lens-like processing is applied to the surface of the substrate, or the prism sheet, the lens sheet and the diffusion sheet are attached to the surface of the substrate, thereby suppressing the total reflection and the light extraction efficiency. To improve. In order to increase the light extraction efficiency, a method of introducing a diffraction grating or a method of introducing a diffusion structure in an interface or any medium that causes total reflection is known.

<< Method for Manufacturing Organic EL Element >>
As an example of the method for producing an organic EL device of the present invention, a method for producing an organic EL device comprising an anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode will be described.

First, a desired electrode material, for example, a thin film made of an anode material is formed on a suitable substrate by a thin film forming method such as vapor deposition or sputtering so as to have a thickness of 1 μm or less, preferably 10 to 200 nm. An anode is produced.

Next, an organic functional layer (organic compound thin film) of a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer, which are organic EL element materials, is formed thereon.

The step of forming the organic functional layer mainly includes: (i) a step of applying and laminating the coating liquid constituting the organic functional layer on the anode of the support substrate; and (ii) a coating liquid after coating and lamination. And drying.

In the step (i), as a method for forming each layer, as described above, a vapor deposition method, a wet process (for example, spin coating method, casting method, die coating method, blade coating method, roll coating method, ink jet method, printing method, spray coating). Method, curtain coating method, LB method (Langmuir Brodgett method and the like can be used), and at least quantum dots are preferably formed using a wet process.

In the formation of the organic functional layer other than the hole injection layer, a wet process is preferable in the present invention because it is easy to obtain a homogeneous film and it is difficult to generate pinholes. Film formation by a coating method such as a method, a die coating method, a blade coating method, a roll coating method or an ink jet method is preferred.

Examples of the liquid medium for dissolving or dispersing the organic EL material according to the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene, xylene, and mesitylene. Aromatic hydrocarbons such as cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin, and dodecane, and organic solvents such as dimethylformamide (DMF) and dimethylsulfoxide (DMSO) can be used. Moreover, as a dispersion method, it can disperse | distribute by dispersion methods, such as an ultrasonic wave, high shear force dispersion | distribution, and media dispersion | distribution.

In addition, the preparation step for dissolving or dispersing the organic EL material according to the present invention and the application step until the organic EL material is applied on the substrate are preferably in an inert gas atmosphere. Since the film can be formed without degrading the performance of the organic EL element even if it is not carried out in step 1, it may not be carried out in an inert gas atmosphere. In this case, the manufacturing cost can be suppressed, which is more preferable.

(Ii) In the step (ii), the coated and laminated organic functional layer is dried. The term “drying” as used herein refers to a reduction to 0.2% or less when the solvent content of the film immediately after coating is 100%.

As a means for drying, those generally used can be used, and examples thereof include reduced pressure or pressure drying, heat drying, air drying, IR drying, and electromagnetic wave drying. Of these, heat drying is preferable, the temperature is equal to or higher than the boiling point of the solvent having the lowest boiling point in the organic functional layer coating solvent, and the temperature is lower than (Tg + 20) ° C. of the material having the lowest Tg among the Tg of the organic functional layer material. Most preferably, it is held at In the present invention, more specifically, it is preferable to hold and dry at 80 ° C. or higher and 150 ° C. or lower, and more preferable to hold and dry at 100 ° C. or higher and 130 ° C. or lower.

The atmosphere when drying the coating liquid after coating / lamination is preferably an atmosphere having a volume concentration of a gas other than the inert gas of 200 ppm or less, but it is not necessarily in an inert gas atmosphere as in the liquid preparation coating process. It may not be necessary. In this case, the manufacturing cost can be suppressed, which is more preferable. The inert gas is preferably a rare gas such as nitrogen gas and argon gas, and most preferably nitrogen gas in terms of production cost.

The coating / laminating and drying processes of these layers may be single wafer manufacturing or line manufacturing. Further, the drying process may be performed while being conveyed on the line, but from the viewpoint of productivity, it may be deposited or rolled in a non-contact manner in a roll form.

After these layers are dried, a thin film made of a cathode material is formed thereon by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably in the range of 50 nm to 200 nm. By providing, a desired organic EL element can be obtained. After the heat treatment, the organic EL element can be produced by adhering the close-sealing or sealing member to the electrode and the support substrate with an adhesive.

<Application>
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, backlights for watches and liquid crystals, 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. Furthermore, it can be used in a wide range of applications such as general household appliances that require a display device, but it can be used effectively as a backlight of a liquid crystal display device combined with a color filter, and as a light source for illumination. it can. In the organic EL device of the present invention, patterning may be performed by a metal mask, an ink jet printing method, or the like at the time of film formation, if necessary. In the case of patterning, only the electrode may be patterned, the electrode and the light emitting layer may be patterned, or the entire layer of the element may be patterned. In the fabrication of the element, a conventionally known method is used. Can do.

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 "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

Example 1
<Production of quantum dots>
A quantum dot having an average particle diameter of 2.0 nm was produced as follows.

Under an argon stream, 7.5 g of tri-n-octylphosphine oxide (TOPO) (manufactured by Kanto Chemical Co.), 2.9 g of stearic acid (manufactured by Kanto Chemical Co., Ltd.), 620 mg of n-tetradecylphosphonic acid (manufactured by AVOCADO) Then, 250 mg of cadmium oxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was heated and mixed at 370 ° C. After naturally cooling this to 270 ° C., a solution in which 200 mg of selenium (STREM CHEMICAL) was dissolved in 2.5 ml of tributylphosphine (manufactured by Kanto Chemical Co., Inc.) was added in advance, dried under reduced pressure, and coated with TOPO. CdSe quantum dots were obtained.

Further, the amount of cadmium oxide and selenium was increased so as to obtain the target particle size by the above method, and quantum dots having average particle sizes of 2.7 nm and 4.0 nm were prepared by the same method.

The average particle size of these quantum dots was measured by a dynamic light scattering method.

<< Production of organic EL element >>
(1) Production of Organic EL Element 1 (1.1) Production of Gas Barrier Flexible Film As a flexible film (supporting substrate), a polyethylene naphthalate film (a film made by Teijin DuPont, hereinafter abbreviated as PEN). ) On the entire surface on the side where the first electrode is formed, using an atmospheric pressure plasma discharge treatment apparatus having the structure described in JP-A-2004-68143, an inorganic substance composed of SiOx is continuously formed on the flexible film. A gas barrier film is formed to a thickness of 500 nm, and has a gas barrier property of oxygen permeability of 0.001 cm ³ / m ² · day · atm or less and water vapor permeability of 0.001 g / m ² · day · atm or less. A film was prepared.

(1.2) Formation of first electrode layer A 120 nm thick ITO (Indium Tin Oxide) film is formed on the prepared gas barrier flexible film by sputtering, and patterned by photolithography. An electrode layer (anode) was formed. The pattern was such that the light emission area was 50 mm square.

(1.3) Formation of hole injection layer The patterned ITO substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes. On this substrate, a solution of poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (abbreviated as PEDOT / PSS, manufactured by Bayer, Baytron P Al 4083) diluted to 70% with pure water at 3000 rpm for 30 seconds. After film formation by a spin coating method, the film was dried at 200 ° C. for 1 hour to provide a hole injection layer having a thickness of 30 nm.

(1.4) (Formation of hole transport layer and quantum dot monolayer)
This substrate was transferred to a nitrogen atmosphere using nitrogen gas (grade G1), and a liquid mixture of a hole transport material (Exemplary Compound (60) (Mw = 8000)) and quantum dots having an average particle diameter of 4.0 nm ( A dispersion obtained by dispersing 0.5% of 1: 1) in chlorobenzene was formed by spin coating at 1500 rpm for 30 seconds, and then kept at 160 ° C. for 30 minutes to separate the hole transport layer having a thickness of 30 nm from the layer separation. A single molecular layer consisting of quantum dots was formed.

(1.5) Formation of Light-Emitting Layer Next, a light-emitting layer composition having the following composition was formed by spin coating at 1500 rpm for 30 seconds, and then held at 120 ° C. for 30 minutes to form a light-emitting layer having a thickness of 40 nm. .

<Light emitting layer composition>
Illustrative compound a-38 (host compound) 13.950 parts by mass Illustrative compound D-66 (blue phosphorescent compound) 2.450 mass parts Illustrative compound D-80 (green phosphorescent compound) 0.025 parts by mass Exemplified Compound D-67 (Red Phosphorescent Compound) 0.025 parts by mass Toluene 2000 parts by mass (1.6) Formation of Quantum Dot Layer Single quantum dots having an average particle size of 4.0 nm prepared above on the luminescent layer A molecular film was formed. This monomolecular film was formed by a microcontact printing method.

(1.7) Formation of Electron Transport Layer Subsequently, a solution prepared by dissolving 20 mg of the following compound A as an electron transport material in 4 ml of tetrafluoropropanol (TFPO) was formed by spin coating at 1500 rpm for 30 seconds. Then, it hold | maintained at 120 degreeC for 30 minute (s), and set it as the electron carrying layer with a film thickness of 30 nm.

 

(1.8) Formation of electron injection layer and cathode Subsequently, the substrate was attached to a vacuum deposition apparatus without being exposed to the atmosphere. A molybdenum resistance heating boat containing sodium fluoride and potassium fluoride is attached to a vacuum deposition apparatus, and the vacuum chamber is depressurized to 4 × 10 ⁻⁵ Pa, and then the boat is energized and heated. A thin film having a thickness of 1 nm is formed on the electron transport layer at a rate of 0.02 nm / second with sodium fluoride, and then an electron with a thickness of 1.5 nm on the sodium fluoride at a rate of 0.02 nm / second in the same manner. An injection layer was formed. Subsequently, 100 nm of aluminum was deposited to form a cathode.

(1.9) Sealing and production of organic EL element Subsequently, a sealing member was bonded using a commercially available roll laminating apparatus to produce an organic EL element.

As a sealing member, a flexible aluminum foil (made by Toyo Aluminum Co., Ltd.) having a thickness of 30 μm, a polyethylene terephthalate (PET) film (12 μm thickness) and an adhesive for dry lamination (two-component reaction type urethane) (Adhesive layer thickness of 1.5 μm) was used.

A thermosetting adhesive as a sealing adhesive was uniformly applied to the aluminum surface at a thickness of 20 μm along the adhesive surface (shiny surface) of the aluminum foil using a dispenser. This was dried under a vacuum of 100 Pa or less for 12 hours. Furthermore, it moved to a nitrogen atmosphere with a dew point temperature of −80 ° C. or lower and an oxygen concentration of 0.8 ppm, dried for 12 hours or longer, and adjusted the water content of the sealing adhesive to 100 ppm or lower.

As the thermosetting adhesive, an epoxy adhesive mixed with the following (A) to (C) was used.

(A) Bisphenol A diglycidyl ether (DGEBA)
(B) Dicyandiamide (DICY)
(C) Epoxy adduct curing accelerator As described above, the sealing substrate is closely attached and arranged so as to cover the joint between the extraction electrode and the electrode lead so as to be in the form shown in FIG. Using a roll, it was tightly sealed under thick deposition conditions, a pressure roll temperature of 120 ° C., a pressure of 0.5 MPa, and an apparatus speed of 0.3 m / min.

As described above, the organic EL device 1 having quantum dots with an average particle diameter of 4.0 nm at the interfaces of both the light emitting layer and the electron transport layer and between the light emitting layer and the hole transport layer was produced.

(2) Preparation of organic EL devices 2 to 13 The same manner as in the organic EL device 1 except that the quantum dots, phosphorescent compounds and host compounds having the particle sizes shown in Table 1 were changed as shown in Table 1. Thus, organic electroluminescence elements 2 to 13 were produced.

 

(3) Measurement of the band gap of each material The band gap of each material is measured by measuring the absorption spectrum as described above, and plotting hν with respect to (αhν) to the 0.5th power (Tauc plot). It calculated | required from the value of h (nu) in (alpha) = 0 which extrapolated the linear area.

Table 2 shows the measurement results.

 

<< Evaluation of organic EL elements >>
Each of the organic EL elements 1 to 13 was evaluated as follows.

(1) Measurement of luminous efficiency Each of the organic EL devices prepared above was allowed to emit light at room temperature (about 23 ° C.) under a constant current of ^2.5 mA / cm ² , and the emission luminance L immediately after the start of emission was measured as spectral emission. The luminance was measured using a luminance meter CS-2000 (manufactured by Konica Minolta Optics).

Next, a relative light emission luminance was determined with the light emission luminance of the organic EL element 13 as a comparative example being 1.0, and this was used as a measure of the light emission efficiency (external extraction quantum efficiency). It represents that it is excellent in luminous efficiency, so that a numerical value is large.

(2) Measurement of driving voltage The driving voltage was measured when each organic EL element was allowed to emit light at room temperature (about 23 ° C.) under a constant current condition of ^2.5 mA / cm ² .

Next, the difference in the driving voltage of each organic electroluminescence element was determined based on the driving voltage of the organic EL element 13 as a comparative example. The smaller the numerical value, the lower the driving voltage for the comparative organic EL element 13, and the lower the voltage driving performance.

(3) Evaluation of color rendering properties From the spectral distribution characteristic results measured with the above spectral radiance meter, the color rendering index was obtained for each organic EL element based on JIS Z 8726, and the average color rendering index was derived. It was described in.

(4) Evaluation of continuous drive stability (life) Each sample is wound around a cylinder with a radius of 5 cm, and then continuously driven in a state where each sample is bent, and the luminance is measured using the above-mentioned spectral radiance meter CS-2000. The time (LT50) required for the measured luminance to be halved was determined. The driving condition was set to a current value of 4000 cd / m ² at the start of continuous driving.

The relative value which set LT50 of the comparative example sample 1 to 1.00 was calculated | required, and this was made into the scale of continuous drive stability. The evaluation results are shown in Table 1. In Table 1, it shows that it is excellent in continuous drive stability (long life), so that a numerical value is large.

(5) Evaluation of chromaticity stability before and after element lifetime evaluation Next, the chromaticity (CIE color system x, y) before and after the winding process was measured with the above spectral radiance meter, and the chromaticity before the winding process. Each color difference (Δx and Δy) of the chromaticity (x, y) before the winding process with respect to (x, y) was obtained and used as a measure of chromaticity stability. The smaller the numerical value, the smaller the color shift and the better the chromaticity stability.

The above results are shown in Table 3.

 

As shown in Table 1, the organic EL elements 1 to 12 of the present invention have higher emission luminance (emission efficiency) and lower driving voltage than the comparative organic EL element 13, and further have color rendering properties and lifetime. Improved and stable chromaticity. Moreover, it is more preferable to have a quantum dot in the interface of a light emitting layer and a hole transport layer than it is to have a quantum dot in the interface of a light emitting layer and an electron carrying layer, and also the organic EL element which has a quantum dot in both interfaces It can be seen that good results are obtained.

The organic electroluminescence element of the present invention has high luminous efficiency, long life, excellent color rendering, stable chromaticity even at low driving voltage, and can be suitably used for display devices, displays, and various light sources.

DESCRIPTION OF SYMBOLS 1 Flexible support substrate 2 Anode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 Electron injection layer 8 Cathode 9 Sealing adhesive 10 Flexible sealing member 11 Quantum dot 20 Organic functional layer 100 Organic electroluminescence device

Claims (9)

1. An organic electroluminescence device having at least an anode, a hole transport layer, a light-emitting layer containing a phosphorescent compound, an electron transport layer, and a cathode, wherein the interface between the light-emitting layer and the hole transport layer and the light emission An organic electroluminescence device comprising a quantum dot on at least one of an interface between a layer and the electron transport layer.
2. 2. The organic electroluminescence device according to claim 1, wherein quantum dots are provided at both an interface between the light emitting layer and the hole transport layer and an interface between the light emitting layer and the electron transport layer.
3. 3. The organic electroluminescence device according to claim 1, wherein a band gap of the phosphorescent compound is 0.1 eV or more smaller than a band gap of the quantum dots.
4. The organic electroluminescence according to any one of claims 1 to 3, wherein the light emitting layer contains a host compound, and the band gap of the host compound is 0.1 eV or more larger than the band gap of the quantum dots. element.
5. The quantum dot is composed of at least Si, Ge, GaN, GaP, CdS, CdSe, CdTe, InP, InN, ZnS, In ₂ S ₃ , ZnO, CdO, or a mixture thereof. 5. The organic electroluminescence device according to any one of 4 above.
6. 6. The organic electroluminescence device according to claim 1, wherein an average particle diameter of the quantum dots is in a range of 1 to 20 nm.
7. 7. The organic electroluminescence device according to claim 1, wherein the phosphorescent compound contained in the light emitting layer is represented by the following general formula (1).
   

   

   (In the general formula (1), R ₁ represents a substituent. Z represents a group of nonmetallic atoms necessary to form a 5- to 7-membered ring. N1 represents an integer of 0 to 5. B ₁ to B ₅ represents a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, at least one represents a nitrogen atom, M ₁ represents a group 8 to group 10 metal in the periodic table, and X ₁ and X ₂ represent carbon Represents an atom, a nitrogen atom or an oxygen atom, L ₁ represents an atomic group forming a bidentate ligand with X ₁ and X ₂ , m1 represents an integer of 1, 2 or 3, m2 represents 0, (It represents an integer of 1 or 2, m1 + m2 is 2 or 3.)
8. 8. The organic electroluminescent device according to claim 1, wherein the light emitting layer contains a host compound represented by the following general formula (2).
   

   

   (In the general formula (2), X represents NR ′, O, S, CR′R ″, or SiR′R ″. R ′ and R ″ each represents a hydrogen atom or a substituent. Ar ₁ and Ar ₂ represents an aromatic ring, which may be the same or different, and n represents an integer of 0 to 4.)
9. The organic electroluminescence device according to claim 8, wherein X in the general formula (2) represents an oxygen atom.

Images