JP2005259492A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element with high luminous efficiency and also with superior drive durability. <P>SOLUTION: This is an organic electroluminescent element having an organic layer including a luminous layer between a pair of electrodes, and the element has a charge block layer inside the luminous layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence device that emits light by converting electric energy into light.

  An organic electroluminescent element (hereinafter also referred to as an organic EL element, a light emitting element, or an element of the present invention) has an organic layer including a light emitting layer between a pair of electrodes. In an EL element, when an electric field is applied between both electrodes, electrons are injected from the cathode, holes are injected from the anode, and the electrons and holes recombine in the light emitting layer to emit light.

An important issue in the organic electroluminescence device is to achieve both luminous efficiency and driving durability. Patent Document 1 discloses a phosphorescent organic electroluminescent element. This element is an excellent element that can obtain high luminous efficiency by using a specific aromatic hydrocarbon. However, Patent Document 1 only discloses an example in which a specific aromatic hydrocarbon is applied as a host material of a phosphorescent material that is a triplet light emitting material. There is a demand for a technology that achieves both luminous efficiency and driving durability at a high level. For example, even when the aromatic hydrocarbon described in Patent Document 1 is used, the optimum usage utilizing its physical characteristics, It is required to achieve both luminous efficiency and driving durability.
JP 2003-027048 A

  An object of the present invention is to provide an organic electroluminescent device having high luminous efficiency and excellent driving durability. It is another object of the present invention to provide a phosphorescent organic electroluminescent device having excellent luminous efficiency and driving durability.

The said subject is solved by the organic electroluminescent element of following (1)-(6).
(1) An organic electroluminescent device having an organic layer including a light emitting layer between a pair of electrodes, wherein the organic electroluminescent device has a charge blocking layer inside the light emitting layer.
(2) The organic electroluminescent element as described in (1) above, wherein the charge blocking layer is 1 layer or more and 20 layers or less.
(3) The organic electroluminescent element as described in (1) or 2 above, wherein the light emitting layer contains a phosphorescent material.
(4) The organic electroluminescent element as described in any one of (1) to (3) above, wherein the charge blocking layer contains an aromatic hydrocarbon not containing at least one of oxygen and nitrogen.
(5) The organic electroluminescent element as described in (4) above, wherein the aromatic hydrocarbon not containing at least one of oxygen and nitrogen is represented by the following general formula (1).

Wherein, R ¹ to R ⁶ represents a hydrogen atom or oxygen and substituents that do not contain at least one nitrogen.

  The organic electroluminescent element of the present invention has high luminous efficiency and excellent driving durability. According to the present invention, it is possible to provide a phosphorescent organic electroluminescent device excellent in both luminous efficiency and driving durability.

The element of the present invention is an organic electroluminescence element having an organic layer including a light emitting layer between a pair of electrodes, and having an electric charge blocking layer inside the light emitting layer.
The pair of electrodes includes an anode and a cathode, and the anode is usually provided on a substrate. At least one of the electrodes is transparent, and the anode is usually transparent.
The organic layer includes at least one light emitting layer, and may optionally have layers such as a hole transport layer and an electron transport layer, if desired. In the present invention, the organic layer preferably includes a light emitting layer, a hole transport layer, and an electron transport layer. The light emitting layer contains a light emitting material and a host material as required, the hole transport layer contains a hole transport material, and the electron transport layer contains an electron transport material.

The device of the present invention preferably has a configuration of transparent anode / hole transport layer / light emitting layer / electron transport layer / cathode. In some cases, the hole transport layer and the light-emitting layer, or the light-emitting layer and the electron transport layer are combined into one layer. Further, an electron blocking layer may be provided between the hole transport layer and the light emitting layer, and a hole blocking layer may be provided between the light emitting layer and the electron transport layer. A hole injection layer may be provided between the anode and the hole transport layer, and an electron injection layer may be provided between the cathode and the electron transport layer.
A typical layer structure including all of them is transparent anode / hole injection layer / hole transport layer / electron block layer / light emitting layer / hole block layer / electron transport layer / electron injection layer / cathode. At this time, the electron blocking layer and the hole injection layer are regarded as a part of the hole transport layer, and the hole blocking layer and the electron injection layer can be regarded as a part of the electron transport layer. Further, each layer may be divided into a plurality of secondary layers.

The charge blocking layer provided inside the light emitting layer has a function of blocking a target charge incompletely and partially passing it.
By providing a charge blocking layer inside the light emitting layer, a portion where charges (holes or electrons) stay inside the light emitting layer is dispersed, and a portion where the light emission density is concentrated is dispersed inside the light emitting layer. Durability can be improved. The main cause of drive degradation of organic electroluminescence devices is degradation of the light emitting material. In the present invention, the charge blocking layer makes the light emission density in the thickness direction uniform inside the light emitting layer, and as a result, the burden on the light emitting material is averaged. It is estimated that the durability is improved.
By changing the charge to be blocked in the charge blocking layer, it can be applied to both hole retention type devices and electron retention type devices. Of course, it can also be applied to phosphorescent devices and devices other than phosphorescent devices. It is.
Note that having the charge blocking layer inside the light emitting layer means that the charge blocking layer is sandwiched between two or more light emitting layers. That is, it means that the charge blocking layer is located between the anode side first layer (the light emitting layer closest to the anode side) and the cathode side first layer (the light emitting layer closest to the cathode side) in the light emitting layer.

An example of a preferred embodiment of the element of the present invention is shown in a schematic sectional view in FIG.
The element 11 of this embodiment includes a transparent electrode (anode) 2, an organic layer 3, and a cathode 4 on a substrate 1. The organic layer 3 has a hole injection layer 5, a hole transport layer 6, a light emitting layer 8 having a charge blocking layer 7 inside, and an electron transport layer 9, and is laminated in this order from the transparent electrode 2 side. .

Another preferred embodiment of the element of the present invention is shown in a schematic cross-sectional view in FIG. The element of this embodiment has three charge blocking layers 7 inside the light emitting layer 8.
By providing a large number of charge blocking layers inside the light emitting layer as described above, the portion where the light emission density is concentrated is more dispersed inside the light emitting layer, so that the durability can be further improved.
The number of charge blocking layers inside the light emitting layer is preferably 1 or more and 20 or less, more preferably 1 or more and 10 or less, still more preferably 1 or more and 5 or less, and particularly preferably 1 or more and 3 or less. . In this case, the light emitting layer has substantially two or more and 21 or less layers, and has a laminated structure in which the light emitting layers and the charge blocking layers are alternately laminated.

Still another preferred embodiment of the element of the present invention is shown in schematic cross-sectional views in FIGS.
As in the case of the element shown in FIG. 3, the electron transport layer may not be provided.
The element shown in FIG. 4 has a hole blocking layer 10 between the first cathode-side layer of the light emitting layer 8 and the electron transport layer 9. The hole blocking layer 10 prevents the hole from coming from the light emitting layer 8 to the electron transport layer 9 and increases the probability that electrons and holes are combined, thereby improving the light emission efficiency.
Note that the configuration of the element of the present invention is not limited to that described above, and appropriate modifications and improvements can be made.

Hereafter, each layer which comprises the element of this invention is demonstrated in detail.
-Charge blocking layer-
In the element of the present invention, the charge blocking layer provided inside the light emitting layer incompletely blocks the target charge, and since it is inside the light emitting layer, it is important to have a function of allowing a part of the charge to pass therethrough. is there. That is, the charge blocking layer in the present invention is a layer that has a blocking ability of charges (holes or electrons) but does not completely block the charges. For this reason, 0.5-5 nm is preferable and, as for the film thickness per layer of a charge block layer, 1-2 nm is more preferable. The charge blocking layer preferably contains a charge transport material together with a material having a high charge blocking ability. The mixing ratio of the charge transporting material to the material having a high charge blocking ability is 0.01 to 10% by mass, preferably 0.05 to 2% by mass, and particularly preferably 0.1 to 1% by mass. Ma

  The charge blocking layer in the present invention preferably has an ability to transport opposite charges (electrons for the hole blocking layer, holes for the electron blocking layer) that are not to be blocked. Also from the viewpoint of this function, the film thickness per charge blocking layer is preferably 0.5 to 5 nm, more preferably 1 to 2 nm. It is also preferable to include an opposite charge transport material, and the mixing ratio of the opposite charge transport material to the charge blocking material is preferably 0.01 to 10% by mass, more preferably 0.05 to 2% by mass, ˜1% by weight is particularly preferred.

  The position of the charge blocking layer in the light emitting layer is not particularly limited. However, in order to make the light emission density uniform, it is preferable to install the charge blocking layer so that the portions where the light emission density is concentrated are dispersed as much as possible. As described above, the number of charge blocking layers is preferably 1 or more and 20 or less. The total thickness of the charge blocking layer inside the light emitting layer is not particularly limited, but is preferably 1 to 20 nm from the viewpoint of not increasing the driving voltage more than necessary. In addition, the ratio of the total thickness of the charge blocking layer to the total thickness of the light emitting layer is preferably 0.1 to 50% and more preferably 1 to 10% from the viewpoint of light emission efficiency.

The charge blocking layer of the present invention may be a hole blocking layer or an electron blocking layer. Whether the charge blocking layer is a hole blocking layer or an electron blocking layer is selected depending on which part of the light emitting layer has a high light emission density.
When the light emission density at the cathode side interface of the light emitting layer is high, charge transfer in the light emitting layer is dominated by holes, and therefore it is preferable to provide a hole blocking layer. On the contrary, when the light emission density at the anode side interface of the light emitting layer is high, the charge transfer in the light emitting layer is dominated by electrons, and therefore it is preferable to provide an electron blocking layer.

The element of the present invention is preferably a phosphorescent organic electroluminescent element containing a phosphorescent light emitting material as a light emitting material. In this case, it is preferable that the energy of the triplet lowest excitation level T1 of the material used for the charge blocking layer is higher than the T1 energy of the phosphorescent light emitting material because quenching of the phosphorescent light emitting material can be prevented. The T1 energy of a substance can be calculated from the long wavelength end of the phosphorescence spectrum.
A phosphorescent organic electroluminescent device using an iridium complex as a luminescent material has a high emission density at the cathode side interface as described above. In such a case, it is preferable to provide a hole blocking layer in the light emitting layer.

The material used for the charge blocking layer is preferably an aromatic hydrocarbon that does not contain at least one of oxygen and nitrogen. Such an aromatic hydrocarbon is preferable because of its high durability. In particular, it is more preferable not to include both oxygen and nitrogen, and an aromatic hydrocarbon consisting only of carbon and hydrogen is particularly preferable.
As the aromatic hydrocarbon not containing at least one of oxygen and nitrogen, a compound represented by the following general formula (1) is preferably used.

In General formula (1), R < ¹ > -R < ⁶ > represents the substituent which does not contain at least 1 type of a hydrogen atom or oxygen and nitrogen.
Here, examples of the substituent include alkyl groups (for example, methyl, ethyl, iso-propyl, tert-butyl, cyclohexyl, etc.), alkenyl groups (for example, vinyl, allyl, 2-butenyl, 3-pentenyl, etc.), alicyclic groups. Saturated hydrocarbon groups (eg cyclopentadienyl, cyclooctatetraenyl etc.), alkynyl groups (eg ethynyl, propargyl, 3-pentynyl etc.), aryl groups (eg phenyl, naphthyl, phenanthrenyl, triphenylene-2-yl, fluorenyl, Spirobisfluorenylidene-2-yl, etc.), silyl groups and the like. Each of these groups may further have the substituents listed here.
R ^{1 to} R ⁶ may be the same as or different from each other. R ^{1 to} R ⁶ may be bonded to each other to form a ring.

The molecular weight of the compound represented by the general formula (1) is preferably 200 or more and 2400 or less, more preferably 300 or more and 2000 or less, and particularly preferably 400 or more and 1600 or less.
When the light emitting layer contains a phosphorescent material, the T1 energy of the compound represented by the general formula (1) is preferably equal to or higher than the T1 energy of the phosphorescent material.

  Although the specific example of a compound represented by General formula (1) below is shown, this invention is not limited to these.

-Board-
It is preferable that the substrate used in the present invention does not scatter or attenuate light emitted from the organic layer. Specific examples include yttrium-stabilized zirconia (YSZ), inorganic materials such as glass, polyesters such as polyethylene terephthalate, polybutylene phthalate, and polyethylene naphthalate, polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, and polycycloolefin. , Organic materials such as norbornene resin and poly (chlorotrifluoroethylene). In the case of an organic material, it is preferable that it is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, and workability.
There is no restriction | limiting in particular about the shape of a board | substrate, a structure, a magnitude | size, It can select suitably according to the use, purpose, etc. of a light emitting element. Generally, the shape is a plate shape. The structure may be a single layer structure, a laminated structure, may be formed of a single member, or may be formed of two or more members.
The substrate may be colorless and transparent or colored and transparent, but is preferably colorless and transparent in that it does not scatter or attenuate the light emitted from the light emitting layer.
The substrate can be provided with a moisture permeation preventive layer (gas barrier layer) on the front surface or back surface (transparent electrode side). As a material for the moisture permeation preventive layer (gas barrier layer), inorganic materials such as silicon nitride and silicon oxide are preferably used. The moisture permeation preventing layer (gas barrier layer) can be formed by, for example, a high frequency sputtering method.
The thermoplastic substrate may be further provided with a hard coat layer, an undercoat layer or the like as necessary.

-Anode-
As the anode, it is usually only necessary to have a function as an anode for supplying holes to the organic layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light emitting device. , Can be appropriately selected from known electrodes.
As a material of the anode, for example, a metal, an alloy, a metal oxide, an organic conductive compound, or a mixture thereof can be preferably cited, and a material having a work function of 4.0 eV or more is preferable. Specific examples include semiconducting metal oxides such as tin oxide (ATO, FTO) doped with antimony or fluorine, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc. Metals such as gold, silver, chromium and nickel, and mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, polyaniline, polythiophene and polypyrrole Organic conductive materials, and a laminate of these and ITO.

The anode is suitable for materials such as printing methods, wet methods such as coating methods, physical methods such as vacuum deposition methods, sputtering methods and ion plating methods, and chemical methods such as CVD and plasma CVD methods. Can be formed on the substrate in accordance with a method appropriately selected in consideration of the above. For example, when ITO is selected as the anode material, the anode can be formed according to a direct current or high frequency sputtering method, a vacuum deposition method, an ion plating method, or the like. Further, when an organic conductive compound is selected as the material for the anode, it can be performed according to a wet film forming method.
There is no restriction | limiting in particular as a formation position of the anode in a light emitting element, Although it can select suitably according to the use and objective of this light emitting element, forming on a board | substrate is preferable. In this case, the anode may be formed on the entire one surface of the substrate, or may be formed on a part thereof.
The patterning of the anode may be performed by chemical etching such as photolithography, or may be performed by physical etching using a laser or the like, or may be performed by vacuum deposition or sputtering with a mask overlapped. It may be performed by a lift-off method or a printing method.

The thickness of the anode can be appropriately selected depending on the material, and is usually 10 nm to 50 μm, preferably 50 nm to 20 μm. The resistance value of the anode is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less.
The anode is preferably transparent in order to extract light emitted from the anode side, and the transmittance is preferably 60% or more, and more preferably 70% or more. This transmittance can be measured according to a known method using a spectrophotometer. In this case, the anode may be colorless and transparent or colored and transparent.
The anode is described in detail in “New Development of Transparent Electrode Film”, published by CMC (1999), supervised by Yutaka Sawada, and these can be applied to the present invention. When using a plastic substrate with low heat resistance, an anode formed using ITO or IZO at a low temperature of 150 ° C. or lower is preferable.

-Cathode-
As the cathode, it is usually only necessary to have a function as a cathode for injecting electrons into the organic layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element, It can select suitably from well-known electrodes.
Examples of the material for the cathode include metals, alloys, metal oxides, electrically conductive compounds, and mixtures thereof, and those having a work function of 4.5 eV or less are preferable. Specific examples include alkali metals (eg, Li, Na, K, Cs, etc.), alkaline earth metals (eg, Mg, Ca, etc.), gold, silver, lead, aluminum, sodium-potassium alloys, lithium-aluminum alloys, magnesium. -Rare earth metals such as silver alloys, indium, ytterbium, and the like. These may be used alone, but two or more can be suitably used in combination from the viewpoint of achieving both stability and electron injection.
Among these, alkali metals and alkaline earth metals are preferable from the viewpoint of electron injection properties, and materials mainly composed of aluminum are preferable from the viewpoint of excellent storage stability.
The material mainly composed of aluminum is aluminum alone, or an alloy or mixture of aluminum and 0.01 to 10% by weight of alkali metal or alkaline earth metal (for example, lithium-aluminum alloy, magnesium-aluminum alloy, etc.). Say. The cathode material is described in detail in JP-A-2-15595 and JP-A-5-121172.

There is no restriction | limiting in particular in the formation method of a cathode, It can carry out according to a well-known method. For example, suitability with the above materials from among wet methods such as printing methods, coating methods, physical methods such as vacuum deposition methods, sputtering methods and ion plating methods, chemical methods such as CVD and plasma CVD methods, etc. It can be formed according to a method appropriately selected in consideration. For example, when a metal or the like is selected as the cathode material, one or more of them can be simultaneously or sequentially performed according to a sputtering method or the like.
The patterning of the cathode may be performed by chemical etching such as photolithography, may be performed by physical etching using a laser, etc., may be performed by vacuum deposition or sputtering with a mask overlapped, lift-off method, You may carry out by the printing method.
There is no restriction | limiting in particular as a formation position of the cathode in the light emitting laminated body obtained by laminating | stacking an electrode and an organic layer, You may form in the whole on an organic layer, and you may form in the part.
Further, a dielectric layer made of an alkali metal or alkaline earth metal fluoride or oxide may be inserted between the cathode and the organic layer with a thickness of 0.1 to 5 nm. This dielectric layer can also be regarded as a kind of electron injection layer. The dielectric layer can be formed by, for example, a vacuum deposition method, a sputtering method, an ion plating method, or the like.

The thickness of the cathode can be appropriately selected depending on the material and cannot be generally defined, but is usually 10 nm to 5 μm, and preferably 50 nm to 1 μm.
The cathode may be transparent or opaque. The transparent cathode can be formed by depositing a thin cathode material to a thickness of 1 to 10 nm and further laminating a transparent conductive material such as ITO or IZO.

-Organic layer-
--Formation of organic layer--
Each layer of the organic layer is formed by a dry film formation method such as a vapor deposition method or a sputtering method, a dipping method, a spin coating method, a dip coating method, a casting method, a die coating method, a roll coating method, a bar coating method or a gravure coating method. The film can be suitably formed by any of the method, the transfer method, the printing method, and the like.

--- Light emitting layer--
The light emitting layer is a layer having a function of receiving holes from the anode side when an electric field is applied, receiving electrons from the cathode side, and providing a field for recombination of holes and electrons to emit light.
The light emitting layer includes a light emitting material. The light emitting material may be a single material or a mixture of plural kinds. The light emitting layer may contain a charge transport material called a host material. When the light emitting layer includes a host material, the light emitting material may be referred to as a dopant. In some cases, the roles of the host material and the light-emitting material cannot be clearly distinguished. In the present invention, as already described, the light-emitting layer has a charge blocking layer.

The luminescent material may be fluorescent or phosphorescent.
Examples of fluorescent light emitting materials include benzoxazole, benzimidazole, benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene, tetraphenylbutadiene, naphthalimide, coumarin, perylene, perinone, oxadiazole, aldazine, pyralidine, cyclopentadiene, bis Styrylanthracene, quinacridone, pyrrolopyridine, thiadiazolopyridine, cyclopentadiene, styrylamine, aromatic dimethylidin compounds, quinacridone, various metal complexes represented by 8-quinolinol metal complexes and rare earth complexes, polythiophene, polyphenylene, polyphenylene vinylene And the like, and organic silanes, derivatives of these compounds, and the like.

  Examples of phosphorescent materials include transition metal atoms or complexes containing lanthanoid atoms. The transition metal atom is not particularly limited, but is preferably ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, or platinum, and more preferably rhenium, iridium, or platinum. The lanthanoid atoms are lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutesium. Among these lanthanoid atoms, neodymium, europium and gadolinium are preferable.

Examples of the ligand of the complex include G.I. Wilkinson et al., Comprehensive Coordination Chemistry, Pergamon Press, 1987, H. Yersin, "Photochemistry and Photophysics of Coordination Compounds" Springer-Verlag, 1987, Yamamoto Akio, "Organic Metal Chemistry-Fundamentals and Applications-" Examples thereof include ligands described in Huafusasha 1982 issue and the like. Specific examples of preferred ligands include halogen ligands (preferably chlorine ligands), nitrogen-containing heterocyclic ligands (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, phenanthroline), diketone coordination. Ligands (such as acetylacetone), carboxylic acid ligands (such as acetic acid ligand), carbon monoxide ligands, isonitrile ligands, cyano ligands, more preferably nitrogen-containing heterocyclic coordination It is a child. The complex may have one transition metal atom in the compound, or may be a so-called binuclear complex having two or more. Different metal atoms may be contained at the same time.
A particularly preferable metal complex as the phosphorescent material used in the present invention is an iridium or platinum complex having phenylpyridines as a ligand.

  The host material may be a single material or a mixture of a plurality of types. Examples of host materials that can be used in the present invention include carbazole derivatives, benzoxazole derivatives, benzimidazole derivatives, benzothiazole derivatives, styrylbenzene derivatives, polyphenyl derivatives, diphenylbutadiene derivatives, tetraphenylbutadiene derivatives, coumarin derivatives, oxadiazoles. Derivatives, aldazine derivatives, cyclopentadiene derivatives, pyridine derivatives, pyrazine derivatives, pyrimidine derivatives, pyridazine derivatives, triazine derivatives, tetrazine derivatives, quinoline derivatives, quinoxaline derivatives, quinazoline derivatives, cinnoline derivatives, quinolidine derivatives, phthalazine derivatives, imidazopyridine derivatives, purines Derivatives, acridine derivatives, phenazine aluminum complexes, iridium complexes, zinc complexes, gallium complexes, etc. It is.

Although the film thickness of a light emitting layer is not specifically limited, Usually, the thing of the range of 1 nm-500 nm is preferable, More preferably, it is 5 nm-200 nm, More preferably, it is 10 nm-100 nm.
In order to form a light-emitting layer composed of a mixture of a host material and a light-emitting material, the host material and the light-emitting material may be vaporized at the same time and stacked on the substrate while controlling the rate of the light-emitting material by controlling the evaporation rate. A solution in which the host material and the light-emitting material are dissolved together at an appropriate concentration may be applied by a spin coating method, or may be formed by using a spray method or an ink jet method.

--- Hole transport layer--
The hole transport layer is mainly composed of a hole transport material. The hole transport material may be a single material or a mixture of a plurality of types. Examples of hole transport materials include carbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, Examples include styryl anthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, and the like.

  The hole transport layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having different compositions. Further, as described above, a structure such as a hole injection layer and a hole transport layer may be formed from the anode side. Usually, a compound having a smaller ionization potential than the hole transport layer is selected for the hole injection layer. Examples of the compound used for the hole injection layer include phthalocyanines. Although the total film thickness of a positive hole transport layer is not specifically limited, Usually, the range of 1 nm-200 nm is preferable, More preferably, it is 5 nm-100 nm, More preferably, it is 10 nm-50 nm.

--Electron transport layer--
The electron transport layer has a function of receiving electrons from the cathode and transporting them to the light emitting layer. Specifically, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, fluorenone derivatives, anthraquinodimethane derivatives, anthrone derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, carbodiimide derivatives, fluorenylidenemethane derivatives, Distyrylpyrazine derivatives, aromatic ring tetracarboxylic acid anhydrides such as naphthalene and perylene, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives and various metal complexes represented by metal phthalocyanine, benzoxazole and benzothiazole as ligands It contains electron transport materials such as metal complexes and organosilane derivatives.

  Although the film thickness of an electron carrying layer is not specifically limited, Usually, the thing of the range of 1 nm-200 nm is preferable, More preferably, it is 5 nm-100 nm, More preferably, it is 10 nm-70 nm. The electron transport layer may have a single-layer structure composed of one or more of the materials described above, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions. Further, as described above, the electron injection layer and the electron transport layer may be configured from the cathode side. In such a case, a compound having an electron affinity greater than that of the electron transport layer is usually selected for the electron injection layer.

In the present invention, the entire light emitting element may be protected by a protective layer. As a material for the protective layer, any material may be used as long as it has a function of preventing substances that promote device deterioration such as moisture and oxygen from entering the device. Specific examples thereof include metals such as In, Sn, Pb, Au, Cu, Ag, Al, Ti, and Ni, MgO, SiO, SiO ₂ , Al ₂ O ₃ , GeO, NiO, CaO, BaO, and Fe ₂ O. ₃ , metal oxides such as Y ₂ O ₃ and TiO ₂ , metal nitrides such as SiN _x and SiN _x O _y , metal fluorides such as MgF ₂ , LiF, AlF ₃ and CaF ₂ , polyethylene, polypropylene, polymethyl Monomer mixture containing methacrylate, polyimide, polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene, tetrafluoroethylene and at least one comonomer A copolymer obtained by copolymerization of a copolymer having a cyclic structure in the copolymer main chain. Copolymer, 1% by weight of the water absorbing water absorption material, water absorption of 0.1% or less of moisture-proof material, and the like. There is no particular limitation on the method for forming the protective layer. For example, vacuum deposition, sputtering, reactive sputtering, MBE (molecular beam epitaxy), cluster ion beam, ion plating, plasma polymerization (high frequency excitation ions) Plating method), plasma CVD method, laser CVD method, thermal CVD method, gas source CVD method, coating method, printing method, and transfer method can be applied.

  Furthermore, in the present invention, the entire element may be sealed using a sealing container. Further, a moisture absorbent or an inert liquid may be sealed in a space between the sealing container and the light emitting element. The moisture absorbent is not particularly limited, but for example, barium oxide, sodium oxide, potassium oxide, calcium oxide, sodium sulfate, calcium sulfate, magnesium sulfate, phosphorus pentoxide, calcium chloride, magnesium chloride, copper chloride, fluorine Examples thereof include cesium fluoride, niobium fluoride, calcium bromide, vanadium bromide, molecular sieve, zeolite, and magnesium oxide. The inert liquid is not particularly limited, and examples thereof include paraffins, liquid paraffins, fluorinated solvents such as perfluoroalkane, perfluoroamine, and perfluoroether, chlorinated solvents, and silicone oils. .

The light-emitting element of the present invention obtains light emission by applying a direct current (which may include an alternating current component as necessary) voltage (usually 2 to 40 volts) or a direct current between the anode and the cathode. Can do.
Regarding the driving of the light emitting device of the present invention, JP-A-2-148687, JP-A-6-301355, JP-A-5-290080, JP-A-7-134558, JP-A-8-234485, JP-A-8-2441047, US Pat. No. 5,828,429. No. 6023308, Japanese Patent No. 2784615, etc. can be used.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

(Example 1)
1. Preparation of phosphorescent organic electroluminescent device (1) Preparation of comparative device (TC-1) Washing container of 0.5 mm thick, 2.5 cm square ITO glass substrate (manufactured by Geomat Corp., surface resistance 10Ω / □) And ultrasonically washed in 2-propanol, and then subjected to UV-ozone treatment for 30 minutes. The following layers were sequentially deposited on this transparent anode (ITO) by vacuum deposition.
The vapor deposition rate in the examples of the present invention is 0.2 nm / second unless otherwise specified. The deposition rate was measured using a quartz resonator. The film thicknesses described below were also measured using a crystal resonator.

(Hole injection layer)
Copper phthalocyanine: film thickness 10nm
(Hole transport layer)
NPD: film thickness 22nm
(Light emitting layer)
CBP = 95 mass%, Ir (ppy) ₃ = 5 mass% mixed layer: film thickness 30 nm
(Electron transport layer 1)
BAlq: film thickness 10 nm
(Electron transport layer 2)
Electron transport material Alq: film thickness 40 nm

Subsequently, a patterned mask (a mask having a light emitting region of 2 mm × 2 mm) was placed on the electron transport layer, and lithium fluoride was deposited by 1 nm at a deposition rate of 0.1 nm / second to form an electron injection layer. Finally, metal aluminum was deposited to a thickness of 100 nm to form a cathode.
This was placed in a glove box substituted with argon gas, sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Chiba Nagase), and a comparative element (TC-1). Got.

In TC-1, NPD is a hole transport material, CBP is a host material, Ir (ppy) ₃ is a green phosphorescent material, and BAlq and Alq are electron transport materials. CBP is the most commonly used host material for phosphorescent organic electroluminescence devices. Organic Electronics Vol. 4, page 81 (2003, published by Elsevier) has a HOMO level (ionization potential) of 6.1 eV, LUMO level ( The electron affinity) is noted as 2.8 eV.

(2) Creation of the element (TC-2 to 10) of the present invention The element (TC-2 to 7) of the present invention was produced in the same manner as the comparative element (TC-1) except that the layer structure was changed as follows. )created.

(Hole injection layer)
Copper phthalocyanine: film thickness 20nm
(Hole transport layer)
NPD: film thickness 22nm
(Light emitting layer 1)
CBP = 95 mass%, Ir (ppy) ₃ = 5 mass% mixed layer: film thickness 15 nm
(Charge blocking layer (hole blocking layer))
Compounds listed in Table 1: Film thicknesses listed in Table 1 (light emitting layer 2)
CBP = 95 mass%, Ir (ppy) ₃ = 5 mass% mixed layer: film thickness 15 nm
(Electron transport layer 1)
BAlq: film thickness 10 nm
(Electron transport layer 2)
Electron transport material Alq: film thickness 40 nm

2. Evaluation of Light-Emitting Element Organic electroluminescent elements (TC-1 to 13) were evaluated by the following methods.
Using a source measure unit type 2400 manufactured by Toyo Technica, a direct current voltage was applied to the device to emit light, and the luminance, emission spectrum, and current value were measured. The quantum efficiency of light emission was calculated from the light emission spectrum and current value when the luminance was 200 Cd / m ² .
Next, the light-emitting device was a continuous driving test of the constant current under the condition of the initial luminance 1000 Cd / m ^2, the time which the luminance becomes 500 Cd / m ² was defined as luminance half-life (T _1/2), the drive A measure of durability. These results are shown in Table 1. Green light emission was observed in all the elements.

3. Evaluation of material properties (1) Ionization potential An organic substance to be measured was deposited on a glass substrate so as to have a thickness of 50 nm. The ionization potential of this membrane was measured with a UV photoelectron analyzer AC-1 (manufactured by Riken Keiki Co., Ltd.) under the normal temperature and normal pressure. CBP has an ionization potential value of 6.0 eV, which is 0.1 eV apart from the above-mentioned Organic Electronics, Vol. 4, page 81 (2003, published by Elsevier). it is conceivable that.

(2) Electron affinity The ultraviolet-visible absorption spectrum of the film used for measuring the ionization potential was measured, and the excitation energy was determined from the energy at the long wavelength end of the absorption spectrum. The electron affinity was calculated from the excitation energy and the value of the ionization potential. For compounds whose excitation energy could not be determined, the electron affinity could not be determined.

(3) T1 energy The phosphorescence spectrum of the film | membrane used for the ionization potential measurement was measured at 77K, and it calculated | required from T1 energy from the value of the short wavelength end of the obtained phosphorescence spectrum.
Table 2 shows the ionization potential, electron affinity, and T1 energy of the compounds used in this example.

From the results of Table 1, it can be seen that the elements (TC-2 to 10) of the present invention have higher luminous efficiency and higher driving durability (large T _1/2 ) than the comparative example (TC-1). . The effect due to the film thickness of the hole blocking layer is 1 nm> 2 nm> 4 nm. The order of the effects of the compounds used for the hole blocking layer is CB-7>CB-9> CB-5.

(Example 2)
1. Preparation of phosphorescent organic electroluminescent device (1) Preparation of comparative device (TC-21) 0.5 mm thick, 2.5 cm square ITO glass substrate (manufactured by Geomat Corp., surface resistance 10Ω / □) in a cleaning container Then, after ultrasonic cleaning in 2-propanol, UV-ozone treatment was performed for 30 minutes. The following layers were deposited on this transparent anode (ITO) by vacuum deposition.

(Hole injection layer)
Copper phthalocyanine: film thickness 20nm
(Hole transport layer)
NPD: film thickness 22nm
(Light emitting layer)
BAlq = 95 mass%, Ir (piq) ₃ = 5 mass% mixed layer: film thickness 30 nm
(Electron transport layer 1)
BAlq: film thickness 10 nm
(Electron transport layer 2)
Electron transport material Alq: film thickness 40 nm

In TC-21, Ir (piq) ₃ is a red phosphorescent material. BAlq is used as an electron transporting host material and an electron transporting material.

Subsequently, a patterned mask (a mask having a light emitting region of 2 mm × 2 mm) was placed on the electron transport layer, and lithium fluoride was deposited by 1 nm at a deposition rate of 0.1 nm / second to form an electron injection layer. Finally, metal aluminum was deposited to a thickness of 100 nm to form a cathode.
This is put in a glove box substituted with argon gas, sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Chiba Nagase), and a comparative element (TC-21). Got.

(2) Preparation of element (TC-12, 13) of the present invention The element (TC-12, 13) of the present invention was produced in the same manner as the comparative element (TC-21) except that the layer structure was changed as follows. )created.

(Hole injection layer)
Copper phthalocyanine: film thickness 20nm
(Hole transport layer)
NPD: film thickness 22nm
(Light emitting layer 1)
BAlq = 95 mass%, Ir (piq) ₃ = 5 mass% mixed layer: film thickness 15 nm
(Charge block layer (electronic block layer))
Compounds listed in Table 3: Film thicknesses listed in Table 3 (light emitting layer 2)
BAlq = 95 mass%, Ir (piq) ₃ = 5 mass% mixed layer: film thickness 15 nm
(Electron transport layer 1)
BAlq: film thickness 10 nm
(Electron transport layer 2)
Electron transport material Alq: film thickness 40 nm

2. Evaluation of Light-Emitting Element Organic electroluminescent elements (TC-21 to 23) were evaluated by the following methods.
Using a source measure unit type 2400 manufactured by Toyo Technica, a direct current voltage was applied to the device to emit light, and the luminance, emission spectrum, and current value were measured. The quantum efficiency of light emission was calculated from the light emission spectrum and current value when the luminance was 200 Cd / m ² .
Next, the light-emitting device was a continuous driving test of the constant current under the condition of the initial luminance 300 cd / m ^2, the time which the luminance became 150 cd / m ² was defined as luminance half-life (T _1/2), the drive A measure of durability.
These results are shown in Table 3. Note that red light emission was observed in all the elements.
The physical properties of the materials are shown in Table 2.

From the results of Table 3, it can be seen that the device of the present invention (TC-22 to 23) has higher luminous efficiency and higher driving durability (large T _1/2 ) than the comparative example (TC-21). . The effect of the thickness of the electron blocking layer is larger as the film thickness is thinner, such as 1 nm> 2 nm.

  As described above, according to the present invention, the luminous efficiency and durability of the phosphorescent organic electroluminescent element can be improved at the same time.

It is a schematic sectional drawing which shows one Embodiment of the organic electroluminescent element of this invention. It is a schematic sectional drawing which shows one Embodiment of the organic electroluminescent element of this invention. It is a schematic sectional drawing which shows one Embodiment of the organic electroluminescent element of this invention. It is a schematic sectional drawing which shows one Embodiment of the organic electroluminescent element of this invention.

Explanation of symbols

1 Substrate 2 Transparent electrode (anode)
DESCRIPTION OF SYMBOLS 3 Organic layer 4 Cathode 5 Hole injection layer 6 Hole transport layer 7 Charge block layer 8 Light emitting layer 9 Electron transport layer 10 Hole block layer 11 Organic electroluminescent element

Claims (5)

  An organic electroluminescent device having an organic layer including a light emitting layer between a pair of electrodes, wherein the organic electroluminescent device has a charge blocking layer inside the light emitting layer.   The organic electroluminescent device according to claim 1, wherein the charge blocking layer is 1 layer or more and 20 layers or less.   The organic electroluminescent element according to claim 1, wherein the light emitting layer contains a phosphorescent light emitting material.   The organic electroluminescent element according to claim 1, wherein the charge blocking layer contains an aromatic hydrocarbon not containing at least one of oxygen and nitrogen. The organic electroluminescence device according to claim 4, wherein the aromatic hydrocarbon not containing at least one of oxygen and nitrogen is represented by the following general formula (1).

Wherein, R ¹ to R ⁶ represents a hydrogen atom or oxygen and substituents that do not contain at least one nitrogen.

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