JP2006279014A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element of blue phosphorescence, while achieving high luminous efficiency and high drive durability. <P>SOLUTION: The organic electroluminescent element has a luminous layer and a plurality of organic compound layers including a hole transport layer between a pair of electrodes. The luminous layer contains a blue phosphorescent material and a host material having the minimum excitation triplet energy (T<SB>1</SB>) of 272 kJ/mol (65 kcal/mol) or higher. The positive hole transport layer consists of a plurality of layers, including a layer adjacent to the luminous layer. The organic electroluminescent element satisfies the relation Ip1>Ip2>Ip3, where Ip1 represents the ionization potential of the luminous layer, Ip2 represents the ionization potential of the positive hole transport layer adjacent to the luminous layer, and Ip3 represents the ionization potential of another hole transport layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  The organic electroluminescent element is composed of an organic compound layer including at least a light emitting layer and a pair of electrodes sandwiching the organic compound layer. When an electric field is applied between both electrodes, electrons are injected from the cathode and holes are injected from the anode. These electrons and holes recombine in the light emitting layer to emit light.

  One of the important issues in organic electroluminescent devices is the development of blue phosphorescent organic electroluminescent devices (hereinafter referred to as “blue phosphorescent light emitting devices” as appropriate). What is important in the design of a blue phosphorescent light emitting element is to firstly achieve high luminous efficiency and secondly to achieve high driving durability.

  As a blue phosphorescent light emitting device in view of the above-mentioned problem, for example, Patent Document 1 discloses a difference in LUMO energy level and HOMO energy level between a hole blocking layer and a light emitting layer, and A blue phosphorescent light emitting element focusing on the relationship between the band gap and molecular weight of a host compound is disclosed. However, the blue phosphorescent light emitting element disclosed in the document is not sufficiently high in light emission efficiency and driving durability.

The light emitting layer of the blue phosphorescent light emitting element includes a blue phosphorescent light emitting material and a host material. The blue phosphorescent light emitting material usually has a lowest excited triplet energy (T ₁ ) (hereinafter referred to as “T ₁ energy” as appropriate) of 272 kJ / mol (65 kcal / mol) or more. Therefore, hosts having a high host material having the T ₁ energy of more 272kJ / mol (65kcal / mol) to achieve the luminous efficiency but is required, 272kJ / mol (65kcal / mol) or more the T ₁ energy The material has a problem that it is difficult to inject electric charges (holes or electrons), resulting in poor driving durability.

Thus, the present condition is that the blue phosphorescence light emitting element which was compatible with high luminous efficiency and high drive durability is not yet provided.
JP 2004-6287 A

  It is an object of the present invention to provide a blue phosphorescent organic electroluminescent device that achieves both high luminous efficiency and high driving durability.

As a result of intensive studies, the present inventors have used a blue phosphorescent material and a host material having a T ₁ energy of 272 kJ / mol (65 kcal / mol) or more, and provided a light-emitting layer and a plurality of charge transport layers. Furthermore, it has been found that by controlling the ionization potential and / or electron affinity between the light emitting layer and the plurality of charge transport layers so as to satisfy a predetermined relationship, it is possible to achieve both high light emission efficiency and high driving durability. The invention has been completed.

The above problems are solved by the following organic electroluminescent elements <1> to <6>.
<1> Between a pair of electrodes, a light-emitting layer containing a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more, and hole transport An organic electroluminescent device having a plurality of organic compound layers including a layer, wherein the hole transport layer is composed of a plurality of layers including a layer adjacent to the light emitting layer, and the ionization potential of the light emitting layer is Ip1, adjacent to the light emitting layer An organic electroluminescent element characterized by satisfying a relationship of Ip1>Ip2> Ip3, where Ip2 is an ionization potential of a hole transport layer and Ip3 is an ionization potential of another hole transport layer. (Hereinafter, it may be referred to as “first aspect” of the present invention.)

<2> The organic electroluminescence according to <1>, wherein the lowest excited triplet energy (T ₁ ) of the hole transport layer adjacent to the light emitting layer is 272 kJ / mol (65 kcal / mol) or more. element.

<3> A light-emitting layer containing a blue phosphorescent material and a host material having a minimum excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes, and an electron transport layer An organic electroluminescence device having a plurality of organic compound layers containing, wherein the electron transport layer is composed of a plurality of layers including a layer adjacent to the light emitting layer, and the electron affinity of the light emitting layer is Ea1, and the electron transport adjacent to the light emitting layer When the electron affinity of the layer is Ea2 and the electron affinity of the other electron transport layer is Ea3, the relationship of Ea1 <Ea2 <Ea3 is satisfied, and the lowest excited triplet energy (T ₁ ) of the electron transport layer adjacent to the light emitting layer Is an organic electroluminescent element characterized by being 272 kJ / mol (65 kcal / mol) or more. (Hereinafter, it may be referred to as “second aspect” of the present invention.)

<4> A light emitting layer and a hole transport layer containing a blue phosphorescent material and a host material having a minimum excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes And an organic electroluminescence device having a plurality of organic compound layers including an electron transport layer, wherein the hole transport layer and the electron transport layer are each composed of a plurality of layers including a layer adjacent to the light emitting layer, and the ionization of the light emitting layer The potential is Ip1, the ionization potential of the hole transport layer adjacent to the light emitting layer is Ip2, the ionization potential of the other hole transport layer is Ip3, the electron affinity of the light emitting layer is Ea1, and the electrons of the electron transport layer adjacent to the light emitting layer are When the affinity is Ea2 and the electron affinity of the other electron transport layer is Ea3, the relationship of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3 is satisfied and adjacent to the light emitting layer An organic electroluminescence device characterized in that the lowest excited triplet energy (T ₁ ) of the electron transport layer is 272 kJ / mol (65 kcal / mol) or more. (Hereinafter, it may be referred to as “third aspect” of the present invention.)

<5> The organic electroluminescence according to <4>, wherein the lowest excited triplet energy (T ₁ ) of the hole transport layer adjacent to the light emitting layer is 272 kJ / mol (65 kcal / mol) or more. element.

<6> First and second light-emitting layers containing a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes , A hole transport layer, and an organic electroluminescence device having a plurality of organic compound layers including an electron transport layer, wherein the hole transport layer is composed of a plurality of layers including a layer adjacent to the first light emitting layer. The layer is composed of a plurality of layers including a layer adjacent to the second light emitting layer. The first and second light emitting layers each contain different host materials, the ionization potential of the first light emitting layer is Ip1, and the positive light emitting layer adjacent to the light emitting layer is positive. The ionization potential of the hole transport layer is Ip2, the ionization potential of the other hole transport layer is Ip3, the electron affinity of the second light-emitting layer is Ea1, the electron affinity of the electron transport layer adjacent to the light-emitting layer is Ea2, and other electron transport An organic electroluminescent element characterized by satisfying the relationship of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3 when the electron affinity of the layer is Ea3. (Hereinafter, it may be referred to as the “fourth aspect” of the present invention.)

<7> The minimum excited triplet energy (T ₁ ) of the electron transport layer adjacent to the light emitting layer and the hole transport layer adjacent to the light emitting layer is both 272 kJ / mol (65 kcal / mol) or more. The organic electroluminescent element according to <6>.

  ADVANTAGE OF THE INVENTION According to this invention, the blue electroluminescent organic electroluminescent element which can make high luminous efficiency and high drive durability compatible can be provided.

Hereinafter, the organic electroluminescence device of the present invention (hereinafter also referred to as “organic EL device” or “light emitting device”) will be described in detail. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In the first embodiment of the present invention, light emission containing a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes. An organic electroluminescent device having a layer and a plurality of organic compound layers including a hole transport layer, wherein the hole transport layer is composed of a plurality of layers including a layer adjacent to the light emitting layer, and the ionization potential of the light emitting layer is set to Ip1 An organic electroluminescent device satisfying a relationship of Ip1>Ip2> Ip3, where Ip2 is an ionization potential of a hole transport layer adjacent to the light emitting layer and Ip3 is an ionization potential of another hole transport layer It is.
With the above configuration, it is possible to achieve both high luminous efficiency and high driving durability.

In the first embodiment, it is preferable that the T ₁ energy of the hole transport layer adjacent to the light emitting layer is 272 kJ / mol (65 kcal / mol) or more from the viewpoint of improving the light emission efficiency.

Although the action resulting from the above configuration is not necessarily clear, the host material having T ₁ energy of 272 kJ / mol (65 kcal / mol) or higher contained in the light emitting layer exhibits high light emission efficiency and is adjacent to the light emitting layer. In addition, a plurality of hole transport layers including a layer to be formed are provided, and the relationship between ionization potentials between the light emitting layer and the plurality of hole transport layers is controlled, so that injection of charges (holes) is promoted and high driving is achieved. It is estimated that durability is exhibited. In addition, in this embodiment, as a layer adjacent to the light emitting layer, one of the features is that a layer having the highest ionization potential among the plurality of hole transport layers is provided. As a result, the charge injection barrier is lowered and the retention of charge at the layer interface is suppressed. As a result, the deterioration of the material is suppressed, and it is assumed that this contributes to the improvement of driving durability. .

In the second aspect of the present invention, a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more are contained between a pair of electrodes. And an organic electroluminescent element having a plurality of organic compound layers including an electron transport layer, wherein the electron transport layer is composed of a plurality of layers including a layer adjacent to the light emitting layer, and the electron affinity of the light emitting layer is expressed as Ea1. When the electron affinity of the electron transport layer adjacent to the light emitting layer is Ea2 and the electron affinity of the other electron transport layer is Ea3, the relationship of Ea1 <Ea2 <Ea3 is satisfied, and the lowest electron transport layer adjacent to the light emitting layer An organic electroluminescent element characterized by having an excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more.
With the above configuration, it is possible to achieve both high luminous efficiency and high driving durability.

Although the action resulting from the above configuration is not necessarily clear, the host material having T ₁ energy of 272 kJ / mol (65 kcal / mol) or higher contained in the light emitting layer exhibits high light emission efficiency and is adjacent to the light emitting layer. A plurality of electron transport layers including an electron transport layer having a T ₁ energy of 272 kJ / mol (65 kcal / mol) or more, and a relationship of electron affinity between the light emitting layer and the plurality of electron transport layers. By controlling, it is presumed that charge (electron) injection is promoted and high driving durability is exhibited. In addition, in this embodiment, as a layer adjacent to the light emitting layer, one of the features is that it has an electron transport layer having a T ₁ energy of 272 kJ / mol (65 kcal / mol) or more. By adopting it, the charge injection barrier is lowered and the charge retention at the layer interface is suppressed. As a result, the deterioration of the material is suppressed and it is assumed that it contributes to the improvement of driving durability. The

In addition, when the organic electroluminescent element of the present invention is a mode in which the first and second modes are combined, the driving durability can be further improved, and the third mode of the present invention is such a mode. This is an organic electroluminescent element. That is, the third aspect of the present invention contains a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes. An organic electroluminescent device having a plurality of organic compound layers including a light emitting layer, a hole transport layer, and an electron transport layer, each of the hole transport layer and the electron transport layer including a plurality of layers adjacent to the light emitting layer The ionization potential of the light emitting layer is Ip1, the ionization potential of the hole transport layer adjacent to the light emitting layer is Ip2, the ionization potential of the other hole transport layer is Ip3, the electron affinity of the light emitting layer is Ea1, and the light emitting layer When the electron affinity of the electron transport layer adjacent to Ea2 is Ea2 and the electron affinity of other electron transport layers is Ea3, the relationship of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3 is satisfied. And, the lowest excited triplet energy of the electron transport layer adjacent to the luminescent layer (T ₁₎ is an organic electroluminescence device which characterized in that 272kJ / mol (65kcal / mol) or more.
As in the third aspect, a plurality of hole transport layers and electron transport layers are adjacent to the light emitting layer, and further, the relationship between the ionization potential and the electron affinity in each layer is controlled, thereby exhibiting higher driving durability. Can do.

In the third aspect, from the viewpoint of improving the light emission efficiency, the T ₁ energy of the hole transport layer adjacent to the light emitting layer is also preferably 272 kJ / mol (65 kcal / mol) or more.

Moreover, as an organic electroluminescent element of this invention, from a viewpoint of further improving drive durability, you may comprise a light emitting layer in two layers from which a host material differs, and the 4th aspect of this invention takes this structure. It is an organic electroluminescent element. That is, the fourth aspect of the present invention contains a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes. An organic electroluminescent device having a plurality of organic compound layers including first and second light emitting layers, a hole transport layer, and an electron transport layer, wherein the hole transport layer includes a layer adjacent to the first light emitting layer The electron transport layer is composed of a plurality of layers including a layer adjacent to the second light emitting layer, and each of the first and second light emitting layers contains different host materials, and the ionization potential of the first light emitting layer is increased. Ip1, the ionization potential of the hole transport layer adjacent to the light emitting layer is Ip2, the ionization potential of the other hole transport layer is Ip3, the electron affinity of the second light emitting layer is Ea1, and the electrons of the electron transport layer adjacent to the light emitting layer Affinity Ea2, the electron affinity of the other electron-transporting layer when a Ea3, an organic electroluminescent device characterized by satisfying the relation of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3.

In the fourth aspect, the lowest excited triplet energy (T ₁ ) of the electron transport layer adjacent to the light emitting layer and the hole transport layer adjacent to the light emitting layer are both 272 kJ / mol (65 kcal / mol) or more. It is preferable.

Here, the ionization potential of each layer in the light emitting device of the present invention means an ionization potential of a material having the lowest ionization potential among materials contained in the layer of 10% by mass or more. As the ionization potential in this specification, a value measured at room temperature and in the atmosphere using AC-1 (manufactured by Riken Keiki Co., Ltd.) was adopted. The measurement principle of AC-1 is described in Chiyaya Adachi et al., “Organic thin film work function data collection”, published by CMC Publishing Co.
The electron affinity of each layer in the light emitting device of the present invention means the electron affinity of a material having the highest electron affinity among materials contained in the layer of 10% by mass or more. The electron affinity in the present invention was determined by measuring the ultraviolet-visible absorption spectrum of the film used for measuring the ionization potential and obtaining the excitation energy 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. In this specification, the UV-visible absorption spectrum was measured with a UV3100 spectrophotometer manufactured by Shimadzu Corporation.

The lowest triplet excitation energy (T ₁ energy) in the present invention was determined from the energy at the short wavelength end of the phosphorescence spectrum by measuring the phosphorescence spectrum of the film used for ionization potential measurement. As the lowest triplet excitation energy in this specification, a value measured under a temperature condition of 77K using F4500 manufactured by Hitachi, Ltd. was adopted.

  In each light emitting device of the present invention, the relationship between the light emitting layer, the hole transport layer adjacent to the light emitting layer, the ionization potential of the other hole transport layer, and / or the light emitting layer, the electron transport layer adjacent to the light emitting layer, It is necessary that the relationship of the electron affinity of the other electron transport layer satisfies a predetermined relationship. That is, in the first mode, the relationship of Ip1> Ip2> Ip3 is satisfied, in the second mode, the relationship of Ea1 <Ea2 <Ea3 is satisfied, and in the third and fourth modes, Ip1> Ip2> It is necessary to satisfy the relationship of Ip3 and Ea1 <Ea2 <Ea3.

  As in the first, second, and third aspects, when the light emitting layer is a single layer, the ionization potential (Ip1) of the light emitting layer is preferably 6.4 eV or less, more preferably 6.3 eV or less, and 6. 2 eV or less is particularly preferable. The electron affinity (Ea1) of the light emitting layer is preferably 2.1 eV or more, more preferably 2.2 eV or more, and particularly preferably 2.3 eV or more.

  As in the fourth aspect, when the light emitting layer is two layers, the ionization potential (Ip1) of the light emitting layer on the anode side (first light emitting layer) is preferably 6.4 eV or less, more preferably 6.3 eV or less, 6.2 eV or less is particularly preferable. The electron affinity (Ea1) of the light emitting layer (second light emitting layer) on the cathode side is preferably 2.1 eV or more, more preferably 2.2 eV or more, and particularly preferably 2.3 eV or more.

The ionization potential (Ip2) of the hole transport layer adjacent to the light emitting layer is preferably 6.2 to 5.3 eV, more preferably 6.1 to 5.4 eV, and particularly preferably 6.0 to 5.5 eV.
The ionization potential (Ip3) of the other hole transport layer is preferably 5.8 eV or less, more preferably 5.7 eV or less, and particularly preferably 5.6 eV or less.

The electron affinity (Ea2) of the electron transport layer adjacent to the light emitting layer is preferably 2.2 to 3.1 eV, more preferably 2.3 to 3.0 eV, and particularly preferably 2.4 to 2.9 eV.
The electron affinity (Ea3) of the other electron transport layer is preferably 2.6 eV or more, more preferably 2.7 eV or more, and particularly preferably 2.8 eV or more.

The relationship between the ionization potential or the electron affinity in the present invention is controlled by selecting and combining the materials showing the above ionization potential or electron affinity from the materials constituting each layer.
In order to satisfy the relationship of ionization potential (Ip1>Ip2> Ip3) in the present invention, the combination of materials constituting each layer includes, for example, NPD as another hole transport layer material, and holes adjacent to the light emitting layer. Examples of the transport layer material include HTM-1, which will be described later, and Host-1, which will be described later as the light emitting layer material (host material).
Further, as a combination of materials constituting each layer, which is suitable for satisfying the relationship of electron affinity (Ea1 <Ea2 <Ea3), for example, Alq as another electron transport layer material, and an electron transport layer material adjacent to the light emitting layer Examples of ETM-1, which will be described later, and Host-2 which will be described later as a light emitting layer material (host material).
The details of materials that can be used for each layer in the present invention will be described later.

The elements constituting the organic electroluminescent element of the present invention will be further described.
Organic electroluminescence devices are roughly classified into a bottom emission method and a top emission method. The present invention can be preferably applied to any method. Hereinafter, the present invention will be described in detail by taking a bottom emission method as an example. A bottom emission type organic electroluminescent device usually has an anode / hole transport layer / light emitting layer / cathode configuration from the substrate side, or an anode / hole transport layer / light emitting layer / electron transport layer / cathode from the substrate side. It has a configuration. In the present invention, the light-emitting layer has a plurality of hole transport layers including a layer adjacent to the light-emitting layer, and / or a plurality of electrons including a light-emitting layer and a layer adjacent to the light-emitting layer. It is necessary to have a configuration having a transport layer. Furthermore, each layer may be divided into a plurality of secondary layers.
Moreover, it is preferable that at least one electrode of an anode and a cathode is transparent from the property of a light emitting element. Usually, the anode is transparent.

  A typical configuration of the bottom emission light-emitting device of the present invention includes, from the substrate side, (1) a configuration of a transparent anode / a plurality of hole transport layers / light-emitting layers / electron transport layers / cathodes (first embodiment), ( 2) Configuration of transparent anode / hole transport layer / light emitting layer / multiple electron transport layers / cathode (second embodiment) or (3) transparent anode / multiple hole transport layers / single layer or two layers A configuration of light emitting layer / a plurality of electron transport layers / cathodes (third and fourth modes) is adopted.

<Board>
The substrate used in the present invention preferably does not scatter or attenuate light emitted from the organic compound 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 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>
The anode usually has a function as an anode for supplying holes to the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element. Thus, it can be appropriately selected from known electrodes. As described above, the anode is usually provided as a transparent anode.
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.

  For example, the anode is a wet method such as a printing method, a coating method, a physical method such as a vacuum deposition method, a sputtering method, an ion plating method, a chemical method such as a CVD method, a plasma CVD method, and the like. It can be formed on the substrate according to a method appropriately selected in consideration of suitability. For example, when ITO is selected as the material for the transparent anode, the transparent 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. Moreover, when selecting an organic electroconductive compound as a material of a transparent anode, it can carry out according to the 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 purpose of a 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, 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 transparent anode is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less.

  When the anode is provided as a transparent anode and light emission is taken out from the anode side, the transmittance is preferably 60% or more, 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 having low heat resistance, an anode formed using ITO or IZO at a low temperature of 150 ° C. or lower is preferable.

<Cathode>
The cathode usually has a function as a cathode for injecting electrons into the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element. Thus, it can be appropriately selected from 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-silver alloys, rare earth metals such as indium and 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 mass of an 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, Even if it may be formed in the whole on the organic compound layer, it may be formed in the part Good.

  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 compound 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 compound layer>
-Formation of organic compound layer-
The method for forming the organic compound layer of the present invention is not particularly limited, but resistance heating vapor deposition, electrophotography, electron beam method, sputtering method, molecular lamination method, coating method (spray coating method, dip coating method, impregnation method, roll) Coating method, gravure coating method, reverse coating method, roll brush method, air knife coating method, curtain coating method, spin coating method, flow coating method, bar coating method, micro gravure coating method, air doctor coating, blade coating method, squeeze Coating methods, transfer roll coating methods, kiss coating methods, cast coating methods, extrusion coating methods, wire bar coating methods, screen coating methods, etc.), ink jet methods, printing methods, transfer methods and the like are possible. Among these, the resistance heating vapor deposition method, the coating method, and the transfer method are preferable in consideration of the characteristics of the element, the ease of manufacture, the cost, and the like. When the light-emitting element has a stacked structure of two or more layers, it can be manufactured by combining the above methods.

  In the case of the coating method, it can be dissolved or dispersed together with the resin component. Examples of the resin component include polyvinyl chloride, polycarbonate, polystyrene, polymethyl methacrylate, polyester, polysulfone, polyphenylene oxide, polybutadiene, and poly (N-vinylcarbazole). , Hydrocarbon resin, ketone resin, phenoxy resin, polyamide, ethyl cellulose, vinyl acetate, ABS resin, polyurethane, melamine resin, unsaturated polyester resin, alkyd resin, epoxy resin, silicon resin and the like.

-Hole transport layer, hole injection layer-
The material of the hole transport layer or the hole injection layer has any one of the function of injecting holes from the anode, the function of transporting holes, and the function of blocking electrons injected from the cathode. That's fine. Specific examples include carbazole, imidazole, dibenzazepine, tribenzoazepine, triazole, oxazole, oxadiazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, styrylanthracene, fluorenone, hydrazone, stilbene , Silazane, aromatic tertiary amine compound, styrylamine, aromatic dimethylidin compound, porphyrin compound, polysilane compound, poly (N-vinylcarbazole), aniline copolymer, thiophene oligomer, polythiophene, etc. Examples include molecular oligomers, organometallic complexes, transition metal complexes, and derivatives of the above compounds.

In the present invention, the material for the hole transport layer adjacent to the light emitting layer is preferably carbazole, phenylenediamine, arylamine, aromatic tertiary amine compound, dibenzoazepine, or tribenzoazepine among the above-mentioned materials. More preferred are group III tertiary amine compounds and tribenzazepine.
Among the above hole transport layers, carbazole, phenylenediamine, arylamine, aromatic tertiary amine compounds, dibenzoazepine, and tribenzoazepine are preferable among the above materials, and carbazole, aromatic tertiary amine. More preferred is the compound, tribenzoazepine.

  In the first, third and fourth aspects of the present invention, the ionization potential of the light emitting layer is Ip1, the ionization potential of the hole transport layer adjacent to the light emitting layer is Ip2, and the ionization potential of the other hole transport layer is Ip3. In this case, it is necessary to satisfy the relationship of Ip1> Ip2> Ip3, and in selecting a material constituting a plurality of hole transport layers, the relationship with the material included in the light emitting layer described later is considered. The

  The plurality of hole transport layers are configured such that the ionization potential of the layer located on the light emitting layer side is larger than the ionization potential of the layer located on the anode side. For example, if two other hole transport layers are provided in addition to the hole transport layer adjacent to the light emitting layer, the ionization potential (Ip3-1) of the other hole transport layer located on the light emitting layer side and The relationship between the ionization potential (Ip3-2) and other hole transport layers located on the anode side is configured such that Ip3-1> Ip3-2.

As described above, in each aspect of the present invention, the T ₁ energy of the hole transport layer adjacent to the light emitting layer is preferably 272 kJ / mol (65 kcal / mol) or more, and preferably 276 kJ / mol (66 kcal / mol). More preferably, it is more preferably 280 kJ / mol (67 kcal / mol) or more.

  The film thicknesses of the hole injection layer and the hole transport layer are not particularly limited, but are usually preferably in the range of 1 nm to 5 μm, more preferably 5 nm to 1 μm, and still more preferably 10 nm to 500 nm. is there. The hole transport layer may have a single-layer structure composed of one or more of the above-described materials, or a multilayer structure composed of a plurality of layers having the same composition or different compositions.

-Electron transport layer, electron injection layer-
The material of the electron transport layer or the electron injection layer may be any material having any one of the function of injecting electrons from the cathode, the function of transporting electrons, and the function of blocking holes injected from the anode. . Specific examples thereof include, for example, pyridine, pyrimidine, triazole, triazine, oxazole, phenanthroline, oxadiazole, imidazole, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, Typical examples are metal complexes of aromatic ring tetracarboxylic acid anhydrides such as distyrylpyrazine, silole, imidazopyridine, naphthaleneperylene, phthalocyanine, 8-quinolinol derivatives, metal phthalocyanine, benzoxazole, and benzothiazole. Various metal complexes, or derivatives of the above compounds.

In the present invention, as the material for the electron transport layer adjacent to the light emitting layer, among the above, pyridine, pyrimidine, triazine, phenanthroline, oxadiazole, imidazole, silole, and imidazopyridine are preferable, and triazine, oxadiazole, imidazole, More preferred is imidazopyridine.
Among the above-mentioned materials for the other electron transport layer, pyridine, pyrimidine, triazine, phenanthroline, oxadiazole, imidazole, silole, and imidazopyridine are preferable, and triazine, phenanthroline, oxadiazole, imidazole, silole, imidazo Pyridine is more preferred.

In the second, third and fourth aspects of the present invention, the electron affinity of the light emitting layer is Ea1, the electron affinity of the electron transport layer adjacent to the light emitting layer is Ea2, and the electron affinity of the other electron transport layers is Ea3. Sometimes, it is necessary to satisfy the relationship of Ea1 <Ea2 <Ea3, and in selecting a material constituting the plurality of electron transport layers, a relationship with a material included in the light emitting layer described later is considered.
The plurality of electron transport layers are configured such that the electron affinity of the layer located on the light emitting layer side is smaller than the electron affinity of the layer located on the cathode side.

  The film thicknesses of the electron injection layer and the electron transport layer are not particularly limited, but are usually preferably in the range of 1 nm to 5 μm, more preferably 5 nm to 1 μm, and still more preferably 10 nm to 500 nm. The electron injection layer and the electron transport layer may have a single-layer structure made of one or more of the materials described above, or may have a multilayer structure made up of a plurality of layers having the same composition or different compositions.

As described above, in the second and third aspects of the present invention, the T ₁ energy of the electron transport layer closest to the light emitting layer is required to be 272 kJ / mol (65 kcal / mol) or more. Also in this aspect, it is preferable that it is 272 kJ / mol (65 kcal / mol) or more. The T ₁ energy of the electron transport layer adjacent to the light emitting layer is preferably 272 kJ / mol (65 kcal / mol) or more, more preferably 276 kJ / mol (66 kcal / mol) or more, and 280 kJ /. More preferably, it is more than mol (67 kcal / mol).

-Light emitting layer-
The light emitting layer in the present invention needs to contain a blue phosphorescent light emitting material and a host material having a T ₁ energy of 272 kJ / mol (65 kcal / mol) or more (hereinafter referred to as “specific host material” as appropriate). And as long as the effect of this invention is not impaired, you may contain another material.
The host receives holes from the hole transport layer or hole injection layer when voltage is applied, and also receives electrons from the electron injection layer or electron transport layer, functions to move the injected charge, and recombination of holes and electrons. It is a material having the function of generating excitons by providing a field of the above, and the function of transferring excitation energy.
The specific host material in the present invention is required to have a T ₁ energy of 272 kJ / mol (65 kcal / mol) or more, more preferably 276 kJ / mol (66 kcal / mol) or more, and 280 kJ / mol (67 kcal). / Mol) or more.

  Examples of host materials that can be used in the present invention include, for example, benzoxazole, benzimidazole, benzothiazole, polyphenyl, coumarin, oxadiazole, pyralidine, pyrrolopyridine, thiadiazolopyridine, aromatic dimethylidin compounds, carbazole, imidazole. , Triazole, oxazole, oxadiazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, fluorenone, hydrazone, silazane, aromatic tertiary amine compound, aromatic dimethylidin compound, porphyrin compound, Various metal complexes represented by polysilane compounds, poly (N-vinylcarbazole), metal complexes having benzoxazole or benzothiazole as a ligand, or the above compounds Conductor, and the like. The host material may be a single material or a mixture of a plurality of types.

When a plurality of host materials are used for the light emitting layer, all of the host materials used may be a specific host material, or a specific host material and another host material may be used in combination.
When the specific host material and other host materials are used in combination, the content ratio of the host material contained in the light emitting layer is preferably 1: 1 to 100: 1 by mass ratio, and 4: 1 to 20: 1. Is more preferable.

  In the fourth aspect of the present invention, each of the first light emitting layer and the second light emitting layer needs to contain different specific host materials.

  Examples of blue phosphorescent materials include complexes containing transition metal atoms or lanthanoid atoms. Although it does not specifically limit as a transition metal atom, Preferably, ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, and platinum are mentioned, More preferably, they are rhenium, iridium, and platinum. Examples of lanthanoid atoms include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Of these lanthanoid atoms, neodymium, europium, and gadolinium are preferred.

  Examples of the ligand of the complex include G.I. Wilkinson et al., Comprehensive Coordination Chemistry, Pergamon Press, 1987, H.C. Examples include ligands described in Yersin's "Photochemistry and Photophysics of Coordination Compounds" published by Springer-Verlag 1987, Akio Yamamoto "Organic Metal Chemistry-Fundamentals and Applications-" . 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 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 metal complex particularly preferable as the blue phosphorescent light-emitting material used in the present invention is an iridium or platinum complex having phenylpyridines as a ligand. The blue phosphorescent material may be a single material or a mixture of plural types.

  To form a light-emitting layer consisting of a mixture of a blue phosphorescent material and a host material, the host and the light-emitting material are evaporated at the same time, and the ratio of the light-emitting material is controlled by controlling the evaporation rate, and then laminated on the substrate. Alternatively, a solution in which the host and the light emitting material are dissolved together at an appropriate concentration may be applied by a spin coating method, or may be produced by using a spray method, an ink jet method, or the like.

Although the thickness of a light emitting layer is not specifically limited, Usually, it is preferable that they are 1 nm-500 nm, it is more preferable that they are 5 nm-200 nm, and it is still more preferable that they are 10 nm-100 nm.
Further, as in the fourth aspect, also in the case of providing two light emitting layers, the thickness of each light emitting layer is not particularly limited, but is preferably 1 nm to 250 nm,
It is more preferably 2 nm to 100 nm, and further preferably 5 nm to 50 nm.

<Protective 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 suppressing the entry of elements that promote element deterioration such as moisture and oxygen into the element. 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 SiNx and SiNxOy, metal fluorides such as MgF ₂ , LiF, AlF ₃ and CaF ₂ , polyethylene, polypropylene, polymethyl methacrylate, polyimide, Copolymerizing polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, a copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene, and a monomer mixture containing tetrafluoroethylene and at least one comonomer. Copolymer obtained, and a fluorine-containing copolymer having a cyclic structure in the copolymer main chain. Examples thereof include an elemental copolymer, a water-absorbing substance having a water absorption of 1% or more, and a moisture-proof substance having a water absorption of 0.1% or less.

  There is also 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) (Ion plating method), plasma CVD method, laser CVD method, thermal CVD method, gas source CVD method, coating method, printing method, transfer method can be applied.

<Sealing>
Furthermore, in this invention, you may seal the whole element of this invention 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. .

<Element drive>
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 transparent anode and the cathode. be able to. Regarding the driving of the light-emitting element of the present invention, JP-A-2-148687, JP-A-6-301355, JP-A-5-29080, JP-A-7-134558, JP-A-8-234585, and JP-A-8-2441047. No. 5,828,429, No. 6023308, Japanese Patent No. 2784615, and the like can be used.

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

1. Preparation of organic electroluminescence device (1) Preparation of organic electroluminescence device (TC-11) of Example Glass substrate having 0.5 mm thickness and 2.5 cm square ITO film (manufactured by Geomat Corp., surface resistance 10Ω / □) Was put into a washing container and subjected to ultrasonic cleaning in 2-propanol, followed by UV-ozone treatment for 30 minutes. The following organic compound layers were sequentially deposited on the transparent anode (ITO film) 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.
In addition, the value of the ionization potential of each organic compound layer and electron affinity in TC-11 is written together in the structure of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: film thickness 30nm
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Light emitting layer)
Mixed layer of Host-1 = 95 mass% and BPM-1 = 5 mass%: film thickness 35 nm
Ionization potential: 6.0 eV, electron affinity: 2.4 eV
(First electron transport layer)
BAlq: film thickness 5 nm
Ionization potential: 5.9 eV, electron affinity: 2.9 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, Host-1, BPM-1, BAlq, and Alq are shown below.

Finally, 0.1 nm of lithium fluoride and 100 nm of metal aluminum were deposited in this order to form a cathode.
This is put in a glove box substituted with argon gas without being exposed to the atmosphere, and sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba Co., Ltd.). And the organic electroluminescent element (TC-11) of the Example was obtained.

(2) Preparation of organic electroluminescent device (TC-13) of example The organic electroluminescent device (TC-11) of the example was manufactured in the same manner as the organic electroluminescent device (TC-11) of the example except that the organic compound layer configuration was changed as follows. An organic electroluminescent element (TC-13) was produced. The ionization potential and electron affinity value of each organic compound layer in TC-13 are shown together in the configuration of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: film thickness 30nm
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Light emitting layer)
Mixed layer of Host-1 = 95 mass% and BPM-1 = 5 mass%: film thickness 35 nm
Ionization potential: 6.0 eV, electron affinity: 2.4 eV
(First electron transport layer)
ETM-1: film thickness 5nm
Ionization potential: 6.5 eV, electron affinity: 2.6 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, Host-1, BPM-1 and Alq are as described above. The structure of ETM-1 is shown below.

(3) Preparation of organic electroluminescent element (TC-14) of Example In the same manner as the organic electroluminescent element (TC-11) of the example, except that the configuration of the organic compound layer was changed as follows, The organic electroluminescent element (TC-14) of the Example was produced. The values of ionization potential and electron affinity of each organic compound layer in TC-14 are shown together in the configuration of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: 25 nm film thickness
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Third hole transport layer)
HTM-1: 5 nm
Ionization potential: 5.8 eV, electron affinity: 2.2 eV
(Light emitting layer)
Mixed layer of Host-1 = 95 mass% and BPM-1 = 5 mass%: film thickness 35 nm
Ionization potential: 6.0 eV, electron affinity: 2.4 eV
(First electron transport layer)
ETM-1: film thickness 5nm
Ionization potential: 6.5 eV, electron affinity: 2.6 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, Host-1, BPM-1, ETM-1, and Alq are as described above. The structure of HTM-1 is shown below.

(4) Preparation of organic electroluminescent element (TC-15) of Example The organic electroluminescent element (TC-11) was subjected to the same method as the organic electroluminescent element (TC-11) of the example except that the configuration of the organic compound layer was changed as follows. An example test element (TC-15) was prepared. The ionization potential and electron affinity value of each organic compound layer in TC-15 are shown together in the configuration of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: 25 nm film thickness
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Third hole transport layer)
HTM-1: 5 nm
Ionization potential: 5.8 eV, electron affinity: 2.2 eV
(First light emitting layer)
Mixed layer of Host-1 = 95 mass% and BPM-1 = 5 mass%: film thickness 25 nm
Ionization potential: 6.0 eV, electron affinity: 2.4 eV
(Second light emitting layer)
Host-2 = 95 mass%, BPM-1 = 5 mass% mixed layer: film thickness 10 nm
Ionization potential: 6.6 eV, electron affinity: 2.5 eV
(First electron transport layer)
ETM-1: film thickness 5nm
Ionization potential: 6.5 eV, electron affinity: 2.6 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, HTM-1, Host-1, BPM-1, ETM-1 and Alq are as described above. The structure of Host-2 is shown below.

(5) Preparation of organic electroluminescent element (TC-21) of Example A glass substrate having a 0.5 mm thickness and a 2.5 cm square ITO film (manufactured by Geomat Co., Ltd., surface resistance 10Ω / □) is placed in a cleaning container, After ultrasonic cleaning in 2-propanol, UV-ozone treatment was performed for 30 minutes. The following organic compound layers were sequentially deposited on the transparent anode (ITO film) by vacuum deposition.
In addition, the value of the ionization potential and electron affinity of each organic compound layer in TC-21 is written together in the structure of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: film thickness 30nm
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Third hole transport layer)
TCTA: film thickness 5nm
Ionization potential: 5.7 eV, electron affinity: 2.3 eV
(Light emitting layer)
Mixed layer of MCP = 92 mass%, BPM-1 = 8 mass%: film thickness 30 nm
Ionization potential: 5.9 eV, electron affinity: 2.3 eV
(First electron transport layer)
BAlq: film thickness 5 nm
Ionization potential: 5.9 eV, electron affinity: 2.9 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, BPM-1, BAlq, and Alq are as described above. The structures of the TCTA and MCP are shown below.

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 without being exposed to the atmosphere, and sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba Co., Ltd.). And the organic electroluminescent element (TC-21) of the Example was obtained.

(6) Preparation of organic electroluminescent element (TC-22) of Example The organic electroluminescent element (TC-21) was prepared in the same manner as the organic electroluminescent element (TC-21) of the example except that the configuration of the organic compound layer was changed as follows An example organic electroluminescent element (TC-22) was produced. The values of ionization potential and electron affinity of each organic compound layer in TC-22 are shown together in the configuration of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: film thickness 30nm
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Third hole transport layer)
TCTA: film thickness 5nm
Ionization potential: 5.7 eV, electron affinity: 2.3 eV
(Light emitting layer)
Mixed layer of MCP = 92 mass%, BPM-1 = 8 mass%: film thickness 30 nm
Ionization potential: 5.9 eV, electron affinity: 2.3 eV
(First electron transport layer)
BCP: film thickness 5nm
Ionization potential: 6.5 eV, electron affinity: 3.0 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, TCTA, MCP, and Alq are as described above. The structure of BCP is shown below.

(7) Preparation of organic electroluminescent device (TC-23) of example The organic electroluminescent device (TC-21) of the example was changed in the same manner as the organic electroluminescent device (TC-21) of the example except that the organic compound layer configuration was changed as follows. An organic electroluminescent element (TC-23) was produced. The ionization potential and electron affinity value of each organic compound layer in TC-23 are shown together in the configuration of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: film thickness 30nm
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Third hole transport layer)
TCTA: film thickness 5nm
Ionization potential: 5.7 eV, electron affinity: 2.3 eV
(Light emitting layer)
Mixed layer of MCP = 92 mass%, BPM-1 = 8 mass%: film thickness 30 nm
Ionization potential: 5.9 eV, electron affinity: 2.3 eV
(First electron transport layer)
ETM-1: film thickness 5nm
Ionization potential: 6.5 eV, electron affinity: 2.6 eV
(Second electron transport layer)
Alq: film thickness 40 nm
Ionization potential: 5.8 eV, electron affinity: 3.0 eV

  The structures of NPD, TCTA, MCP, BPM-1, ETM-1 and Alq are as described above.

(8) Preparation of organic electroluminescent element (TC-24) of Example This method is the same as that of the organic electroluminescent element (TC-21) of the example except that the configuration of the organic compound layer is changed as follows. An organic electroluminescent device (TC-24) of the invention was produced. The ionization potential and electron affinity value of each organic compound layer in TC-24 are shown together in the configuration of each layer.

(First hole transport layer)
Copper phthalocyanine: film thickness 10nm
Ionization potential: 5.1 eV, electron affinity: 3.4 eV
(Second hole transport layer)
NPD: film thickness 30nm
Ionization potential: 5.4 eV, electron affinity: 2.4 eV
(Third hole transport layer)
MCP: film thickness 5nm
Ionization potential: 5.9 eV, electron affinity: 2.3 eV
(Light emitting layer)
Mixed layer of Host-2 = 92 mass%, BPM-1 = 8 mass%: film thickness 30 nm
Ionization potential: 6.6 eV, electron affinity: 2.5 eV
(First electron transport layer)
ETM-1: film thickness 5nm
Ionization potential: 6.5 eV, electron affinity: 2.6 eV
(Second electron transport layer)
BAlq: film thickness 40 nm
Ionization potential: 5.9 eV, electron affinity: 2.9 eV

  The structures of the NPD, MCP, Host-1, BPM-1, ETM-1, and BAlq are as described above.

2. Evaluation of material properties (1) Ionization potential Each compound used in the organic compound layer was deposited on a glass substrate so as to have a thickness of 50 nm. The ionization potential of this membrane was measured with an ultraviolet photoelectron analyzer AC-1 manufactured by Riken Keiki Co., Ltd. under normal temperature and normal pressure. In addition, about the ionization potential of ETM-1 and Host-2, it measured by UPS method using the film | membrane vapor-deposited to 50 nm thickness on the gold substrate.

(2) Electron affinity The ultraviolet-visible absorption spectrum of the film used for measuring the ionization potential was measured with a UV3100 spectrophotometer manufactured by Shimadzu Corporation, 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.
(3) T ₁ energy The phosphorescence spectrum of the film used for measuring the ionization potential was measured at a temperature condition of 77 K using F4500 manufactured by Hitachi, Ltd., and the T ₁ energy was calculated from the energy at the short wavelength end of the phosphorescence spectrum. Asked.

Table 1 shows the ionization potential, electron affinity, and T ₁ energy of the compounds used in Examples and Comparative Examples.

3. Evaluation of organic electroluminescent elements The organic electroluminescent elements (TC-11, 13-15, TC-21-24) obtained above were evaluated by the following methods.
(1) Evaluation of luminous efficiency When a voltage of 11 V was applied to the organic electroluminescent elements (TC-11, 13-15, TC-21-24), all were derived from the phosphorescent material (BPM-1). Blue light was emitted.
Moreover, the organic electroluminescent element (TC-11, 13-15, TC-21-24) is set in the emission spectrum measuring system (ELS1500) made by Shimadzu Corporation, and the luminous efficiency when the luminance is 100 Cd / m ^2. (External quantum efficiency) was measured. The results are shown in Tables 2 and 3.

(2) Evaluation of driving durability The obtained organic electroluminescent elements (TC-11, 13-15, TC-21-24) were set in an OLED test system ST-D type manufactured by Tokyo System Development Co., Ltd. AC pulse drive under the conditions of constant forward current 0.2mA, reverse constant voltage 10V, duty 50%, rest time, frequency 250 Hz, luminance half time (until the luminance drops to 50% of the initial luminance) Time) _t0.5 was determined. The results are shown in Tables 2 and 3.

As Table 2 shows, it turns out that the organic electroluminescent element (TC-11, 13-15) of an Example has high luminous efficiency and high drive durability. In particular, according to the third and fourth aspects of the present invention, both the hole transport layer and the electron transport layer are adjacent to the light emitting layer, and the relationship of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3 is satisfied. TC-14 and TC-15 in which the T ₁ energy of the hole transport layer and the electron transport layer adjacent to the light emitting layer are both 272 kJ / mol (65 kcal / mol) or more are the light emission efficiency and driving It can be seen that the durability is greatly improved.

As shown in Table 3, among the organic electroluminescent elements (TC-21 to 24) of the examples, the T ₁ energy of the adjacent layer on the cathode side of the light emitting layer is 272 kcal / mol (65 kJ / mol) or more. It can be seen that TC-23 to 24 have higher luminous efficiency and driving durability.

  As described above, it can be seen that the organic electroluminescent device of the present invention is a device in which luminous efficiency and driving durability are greatly improved.

Claims (7)

A light-emitting layer containing a blue phosphorescent material and a host material having a minimum excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more and a hole transport layer are included between the pair of electrodes An organic electroluminescent device having a plurality of organic compound layers, wherein the hole transport layer is composed of a plurality of layers including a layer adjacent to the light emitting layer, the ionization potential of the light emitting layer is Ip1, and the hole transport adjacent to the light emitting layer An organic electroluminescence device satisfying a relationship of Ip1>Ip2> Ip3, where Ip2 is an ionization potential of the layer and Ip3 is an ionization potential of another hole transport layer. 2. The organic electroluminescence device according to claim 1, wherein the lowest excited triplet energy (T ₁ ) of the hole transport layer adjacent to the light emitting layer is 272 kJ / mol (65 kcal / mol) or more. A plurality of light-emitting layers containing a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more and a plurality of electron-transport layers between a pair of electrodes An organic electroluminescent device having an organic compound layer, wherein the electron transport layer is composed of a plurality of layers including a layer adjacent to the light emitting layer, the electron affinity of the light emitting layer is Ea1, and the electrons of the electron transport layer adjacent to the light emitting layer are When the affinity is Ea2 and the electron affinity of the other electron transport layer is Ea3, the relationship of Ea1 <Ea2 <Ea3 is satisfied, and the lowest excited triplet energy (T ₁ ) of the electron transport layer adjacent to the light emitting layer is 272 kJ. / Mol (65 kcal / mol) or more, The organic electroluminescent element characterized by the above-mentioned. A light-emitting layer, a hole transport layer, and an electron containing a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more between a pair of electrodes An organic electroluminescence device having a plurality of organic compound layers including a transport layer, wherein the hole transport layer and the electron transport layer are each composed of a plurality of layers including a layer adjacent to the light emitting layer, and the ionization potential of the light emitting layer is set to Ip1 The ionization potential of the hole transport layer adjacent to the light emitting layer is Ip2, the ionization potential of the other hole transport layer is Ip3, the electron affinity of the light emitting layer is Ea1, and the electron affinity of the electron transport layer adjacent to the light emitting layer is Ea2. When the electron affinity of the other electron transport layer is Ea3, the relationship of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3 is satisfied, and the electron transport adjacent to the light emitting layer is satisfied. Lowest excited triplet energy of the layer (T ₁₎ An organic electroluminescent device which characterized in that 272kJ / mol (65kcal / mol) or more. The organic electroluminescence device according to claim 4, wherein the lowest excited triplet energy (T ₁ ) of the hole transport layer adjacent to the light emitting layer is 272 kJ / mol (65 kcal / mol) or more. First and second light-emitting layers containing a blue phosphorescent material and a host material having a lowest excited triplet energy (T ₁ ) of 272 kJ / mol (65 kcal / mol) or more and a hole between a pair of electrodes An organic electroluminescent device having a transport layer and a plurality of organic compound layers including an electron transport layer, wherein the hole transport layer comprises a plurality of layers including a layer adjacent to the first light-emitting layer, It consists of a plurality of layers including layers adjacent to two light emitting layers, the first and second light emitting layers each contain different host materials, the ionization potential of the first light emitting layer is Ip1, and the hole transport layer adjacent to the light emitting layer Ip2 is the ionization potential of the other hole transport layer, Ip3 is the ionization potential of the other hole transport layer, Ea1 is the electron affinity of the second light emitting layer, Ea2 is the electron affinity of the electron transport layer adjacent to the light emitting layer, The affinity when a Ea3, organic electroluminescent device characterized by satisfying the relation of Ip1>Ip2> Ip3 and Ea1 <Ea2 <Ea3. The minimum excited triplet energy (T ₁ ) of the electron transport layer adjacent to the light emitting layer and the hole transport layer adjacent to the light emitting layer is both 272 kJ / mol (65 kcal / mol) or more. 6. The organic electroluminescent element according to 6.