JP2008288344A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element which can further enhance luminous efficacy, has excellent stability, and also has a phosphorescent organic thin film material which can be formed by a wet process. <P>SOLUTION: This organic EL element has: a pair of opposite electrodes 20, 80; and single-layer or multilayer organic thin film layers 100 disposed between the electrodes 20 and 80, and at least one layer of the organic thin film layers 100 is a luminous layer 40. In the organic EL element, the luminous layer 40 contains at least a host compound and a guest compound, the host compound contains at least two kinds of host compounds consisting of a first host compound made of a hole transport material and a second host compound made of a phosphorescent metal complex, and the guest compound contains at least one kind of phosphorescent luminous material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic EL element that emits high-efficiency phosphorescence, and relates to a light-emitting element that can be suitably used in the fields of display elements, displays, backlights, electrophotography, illumination light sources, exposure light sources, signs, signboards, and interiors. Is.

An organic EL element is a self-luminous device that emits light by applying an electric field, injecting electrons and holes, and recombining them based on the same light emission principle as a light-emitting diode device made of an inorganic material. Since an organic thin film is used as a light emitting material, it is possible to emit light with high luminance and high efficiency at a low voltage, which is expected as a promising next generation display element.
In recent years, the manufacturing technology of organic EL elements has advanced dramatically, and small organic EL displays have already been put into practical use. From the viewpoint of putting large organic EL displays into practical use, further lowering of voltage is required. Therefore, further improvement in luminous efficiency has been demanded.

  The luminous efficiency of the organic EL element is determined by various factors, and one of the main factors is the exciton generation probability. If the exciton generation probability is high, the exciton is deactivated and radiated energy is increased, and the light emission efficiency is increased. The excitons are generated by recombination of electrons and holes, and can be divided into singlet excitons and triplet excitons. Further, light emission due to the energy deactivation process of the singlet excitons is defined as fluorescence emission, and light emission due to the energy deactivation process of the triplet excitons is defined as phosphorescence emission. Since the singlet excitons and the triplet excitons are considered to be generated at a ratio of 1: 3, if phosphorescence emission, which is light emission from the triplet exciton due to an energy deactivation process, can be used, light emission It was thought that efficiency could be improved.

  Conventionally, an organic EL element uses a fluorescent material for a light emitting layer, and fluorescence from a singlet exciton is extracted as light of the organic EL element. Based on the above consideration, in order to improve the luminous efficiency, an attempt was made to produce an organic EL element using a phosphorescent organic material, but the luminous efficiency could not be improved. In the conventional light emitting material, the generated triplet exciton has a long lifetime, and thus in the energy deactivation process, non-radiative thermal deactivation occurs preferentially over radiative deactivation, and light emission is performed efficiently. It was because it was not possible.

  However, as disclosed in Non-Patent Documents 1 and 2 and Patent Document 1, Bardot et al. Of Princeton University disclose an organic EL element using a phosphorescent organic material as a light-emitting layer, and can improve luminous efficiency. showed that. As the phosphorescent organic material, an organic metal complex having a transition metal such as platinum or iridium such as tris- (2-phenylpyridine) iridium is used as the light-emitting material, so that triplet excitons can stably emit light. By being able to be trapped in the material and radiating and deactivating without thermally deactivating from the material, it was possible to achieve high luminous efficiency as compared with an organic EL element using a conventional fluorescent material as a luminescent layer.

Since then, organic EL devices using phosphorescent materials have been actively researched. For example, Patent Document 2 discloses an organic EL device using a phosphorescent material made of an Ir complex having a specific partial structure. ing. As described above, organic EL elements using phosphorescent organic materials have begun to be expected for practical use of next-generation display elements.
However, in the organic EL device having the phosphorescent organic material, there are still unsolved problems such as improvement of luminous efficiency, reduction of driving voltage, improvement of color purity, and particularly improvement of luminous efficiency. Was demanded.
Considering future large screens and high-definition displays, we believe that wet processes such as spin coating, ink jet, and printing will be advantageous, so there is a need to develop organic thin film materials that can be deposited by wet processes. It was.
Special table 2003-526876 gazette JP 2005-276799 A M. A Baldo et al., Nature, 395, 151 (1998). M. A Baldo et al., Applied Physics Letters, 175, 4 (1999).

  The present invention has been made in view of the above circumstances, and is an organic EL device having a phosphorescent organic thin film material that can further improve luminous efficiency, has excellent stability, and can be formed by a wet process. The purpose is to provide.

In the case where the light emitting layer is composed of a mixture of a host material and a phosphorescent guest material, the process up to phosphorescence emission from the triplet exciton of the guest is considered as follows.
1. 1. Injection of holes and electrons into the light emitting layer Generation of host excitons by recombination of holes and electrons (singlet and triplet)
3. Transfer of excitation energy from host to guest (singlet and triplet)
4). 4. Guest triplet exciton generation Phosphorescence emission associated with deactivation of guest triplet excitons.

  Energy transfer and light emission in each process occur in competition with various deactivation processes that inhibit these processes. In order to increase the light emission efficiency of the organic EL element, it is essential to use a light emitting material with high light emission quantum efficiency as a guest material. And in order to make this guest material light-emit efficiently, selection of the host material surrounding the guest material in a light emitting layer is also very important. In other words, it is important to select an appropriate host material so that the excitation energy can be efficiently transferred from the host material to the guest material, and the energy transferred to the guest material does not return to the host material again. . Furthermore, from the viewpoint of durability of the organic EL element, the host material is required to have high film stability. Furthermore, in order to realize an organic EL element capable of forming a light emitting layer by a wet process, solubility in an organic solvent and excellent film formation in a wet process are also required.

  As a result of intensive investigations to realize an organic EL element that can achieve high-efficiency light emission, excellent stability, and capable of forming a light-emitting layer by a wet process, the present inventors have studied 3 In an organic EL device in which a light emitting layer composed of a material higher than components is formed by a wet process, a hole transporting material having a triphenylamine skeleton is used as a first host material (first main constituent material) of the light emitting layer. By using a phosphorescent metal complex such as an iridium complex as the second host material (second main constituent material) and a phosphorescent light emitting material as the guest material (sub constituent material), it is extremely efficient and stable. The present inventors have found that an organic EL element having excellent properties can be obtained, and have completed the present invention.

In order to achieve the above object, the present invention employs the following configuration. That is,
The organic EL device of the present invention has a pair of opposing electrodes and a single-layer or multilayer organic thin film layer disposed between the electrodes, and at least one of the organic thin film layers is a light-emitting layer. In the device, the light-emitting layer includes at least a host compound and a guest compound, and the host compound includes a first host compound made of a hole transport material and a second host compound made of a phosphorescent metal complex. At least two kinds of host compounds, and the guest compound contains at least one kind of phosphorescent light emitting material.

  The organic EL device of the present invention is the organic EL device as defined above, wherein the triplet energy level of the first host compound is higher than the triplet energy level of the guest compound, and The triplet energy level is preferably higher than the triplet energy level of the guest compound.

  The organic EL device of the present invention is an organic EL device as defined above, wherein the triplet energy level of the first host compound is preferably the same as or higher than the triplet energy level of the second host compound.

式中、ｎ_１〜ｎ_３は１〜３の整数を表し、Ａｒ_１〜Ａｒ_３は、それぞれ独立して、水素原子、アルキル基、アリール基を表すか、Ａｒ_１〜Ａｒ_３が置換しているベンゼン環と縮合して芳香環を形成しても良い。 The organic EL device of the present invention is an organic EL device as defined above, wherein the first host compound preferably has a triphenylamine skeleton represented by the following general formula (1).

In the formula, n _{1 to} n ₃ represent an integer of _{1 to 3} , and Ar _{1 to} Ar ₃ each independently represent a hydrogen atom, an alkyl group, or an aryl group, or Ar _{1 to} Ar ₃ are substituted. An aromatic ring may be formed by condensation with a benzene ring.

式中、ｎ_４、ｎ_５は、１〜４の整数を表し、Ａｒ_４〜Ａｒ_９は、それぞれ独立して、水素原子、アルキル基、アリール基を表すか、Ａｒ_４〜Ａｒ_９が置換しているベンゼン環と縮合して芳香環を形成しても良い。 The organic EL device of the present invention is an organic EL device as defined above, and the first host compound is preferably one that can be represented by the following general formulas (1) to (a).

In the formula, n ₄ and n ₅ each represent an integer of 1 to 4, and Ar _{4 to} Ar ₉ each independently represent a hydrogen atom, an alkyl group, or an aryl group, or Ar _{4 to} Ar ₉ are substituted. An aromatic ring may be formed by condensation with a benzene ring.

式中、ｎ_６、ｎ_７は１〜４の整数を表し、Ａｒ_１０〜Ａｒ_１５は、それぞれ独立して、水素原子、アルキル基、アリール基を表すか、Ａｒ_１０〜Ａｒ_１５が置換しているベンゼン環と縮合して芳香環を形成しても良い。また、Ｘは、２価の原子又は原子団；直鎖又は分岐もしくは環状のアルキレン基；又はアリール基を表す。 The organic EL device of the present invention is an organic EL device as defined above, and the first host compound is preferably one that can be represented by the following general formulas (1) to (b).

_Wherein, n 6, _{n 7} is an integer of 1 to _4, Ar 10 _{to Ar 15} are each independently hydrogen atom, an alkyl group, an aryl _group, Ar 10 _{to Ar 15} is substituted An aromatic ring may be formed by condensation with a benzene ring. X represents a divalent atom or atomic group; a linear or branched or cyclic alkylene group; or an aryl group.

式中、Ａｒ_１６〜Ａｒ_２４は、それぞれ独立して、水素原子、アルキル基、アリール基を表すか、Ａｒ_１６〜Ａｒ_２４が置換しているベンゼン環と縮合して芳香環を形成しても良い。また、Ｙは、３価の原子又は原子団；直鎖又は分岐もしくは環状のアルカントリイル基；又はアレーントリイル基を表す。 The organic EL device of the present invention is an organic EL device as defined above, and the first host compound is preferably one that can be represented by the following general formulas (1) to (c).

In the formula, each of Ar _{16 to} Ar ₂₄ independently represents a hydrogen atom, an alkyl group, or an aryl group, or may be condensed with a benzene ring substituted by Ar _{16 to} Ar ₂₄ to form an aromatic ring. good. Y represents a trivalent atom or atomic group; a linear or branched or cyclic alkanetriyl group; or an arenetriyl group.

式中、Ａｒ_２５〜Ａｒ_３３は、それぞれ独立して、水素原子、アルキル基、アリール基を表すか、Ａｒ_２５〜Ａｒ_３３が置換しているベンゼン環と縮合して芳香環を形成しても良い。 The organic EL device of the present invention is an organic EL device as defined above, and the first host compound is preferably one that can be represented by the following general formulas (1) to (d).

In the formula, Ar _{25 to} Ar ₃₃ each independently represent a hydrogen atom, an alkyl group, or an aryl group, or they may be condensed with a benzene ring substituted by Ar _{25 to} Ar ₃₃ to form an aromatic ring. good.

式中、Ｒ_１〜Ｒ_７は、それぞれ独立して、水素原子、アルキル基、アリール基、ハロゲン原子を表すか、Ｒ_１〜Ｒ_７が置換しているベンゼン環又はピリジン環と縮合して芳香環を形成しても良い。 The organic EL element of the present invention is the organic EL element defined above, and the second host compound is preferably an iridium complex represented by the following general formula (2).

In the formula, each of R _{1 to} R ₇ independently represents a hydrogen atom, an alkyl group, an aryl group, or a halogen atom, or condensed with a benzene ring or pyridine ring substituted by R _{1 to} R ₇ to give an aromatic A ring may be formed.

  The organic EL device of the present invention is the organic EL device defined above, and the guest compound is preferably a phosphorescent light emitting material having platinum or iridium atoms.

  The organic EL device of the present invention is an organic EL device as defined above, wherein a mass ratio (first host compound / second host compound) between the first host compound and the second host compound in the light emitting layer is It is preferable that it is 10 / 90-90 / 10.

  The organic EL element of the present invention is the organic EL element defined above, and the light emitting layer is preferably formed by a wet process.

  According to said structure, the organic EL element which can improve luminous efficiency more, is excellent in durability, and has the phosphorescent organic thin film material which can be formed into a film by a wet process can be provided.

Hereinafter, an example of the organic EL element which is an embodiment of the present invention will be described.
FIG. 1 is a schematic cross-sectional view illustrating an example of an organic EL element according to an embodiment of the present invention. In the organic EL device shown in FIG. 1, an anode 20 is formed on a substrate 10, and an organic thin film layer 100 including a hole injection layer 30, a light emitting layer 40, a hole blocking layer 50, and an electron transport layer 60 is further formed. In addition, the cathode 70 is laminated. The glass sealing tube 80 and the substrate 10 are bonded by a UV curable resin 90 so as to surround the organic EL element.

(substrate)
The substrate 10 may be made of a transparent material having excellent characteristics for blocking air, moisture, and the like. Not only inorganic materials such as glass and quartz, but also organic materials such as plastic films can be used.

When an organic material such as a plastic film is used as the substrate 10, it is preferable to provide a gas barrier layer.
The gas barrier layer is a thin film layer having an effect of blocking air, moisture, and the like, and is formed by forming a plurality of layers of SiO ₂ or SiN by CVD or high-frequency sputtering. Further, the substrate 10 may be provided with a hard coat layer or the like.

(anode)
The anode 20 is preferably made of a material having high conductivity and a large work function. The work function is preferably at least 4.0 eV. In the case where light is extracted from the anode side as the organic EL element, the anode 20 is preferably a transparent material. Generally, a conductive transparent oxide such as indium-tin-oxide (hereinafter referred to as ITO) or indium-zinc-oxide (hereinafter referred to as IZO) is used.

(Hole injection layer)
The hole injection layer 30 is made of an organic material having a high hole injection capability. Further, a material capable of taking holes from the anode 20 into the hole injection layer 30 with high efficiency and applying holes from the hole injection layer 30 into the light emitting layer 40 by applying an electric field. It is. An organic material that can exist stably as an organic thin film even when an electric field is applied is preferable. For example, a mixture of polyethylene dioxythiophene and polystyrene sulfonate such as PEDOT / PSS mixed material, polyaniline, polythiophene, etc. A conductive polymer material or the like can be used.

When the PEDOT / PSS mixed material is used, a spin coating method can be used.
For example, first, a predetermined amount of PEDOT / PSS is contained in an organic solvent to prepare a hole injection layer solution. Next, the substrate 10 is set at a predetermined position of a spin coater, set to a predetermined rotation speed, and then the hole injection layer solution is applied. The hole injection layer 30 having a predetermined thickness is formed by introducing it into a chamber at 180 ° C., performing a drying process, and removing the organic solvent.

  The organic solvent is preferably a polar solvent, and examples thereof include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, ethylene glycol, diethylene glycol, and glycerin.

The film thickness of the hole injection layer 30 is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 20 nm to 200 nm.
When the thickness of the hole injection layer 30 is less than 1 nm, the hole transport layer 30 has an island structure and does not form a layer, and thus cannot function as an organic EL element. On the contrary, when the thickness of the hole injection layer 30 exceeds 5 μm, the film thickness is large, so that the voltage required for light emission becomes too high and the light emission efficiency is lowered. Furthermore, a short circuit may occur, causing element destruction.

(Light emitting layer)
The light emitting layer 40 includes three or more component organic materials, that is, a first host compound made of a hole transport material, a second host compound made of a phosphorescent metal complex, and a guest compound made of a phosphorescent light emitting material. It is comprised including.
By using an organic material having three or more components as a constituent component of the light emitting layer 40, electrons and holes are accumulated in the light emitting layer 40, and the probability of occurrence of excitons generated by recombination of electrons and holes is increased. Can be increased. In addition, the generated excitons can be stably held at the triplet energy level of the guest compound. As a result, the light emission efficiency of the organic EL element can be improved.

The film thickness of the light emitting layer 40 is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and even more preferably 20 nm to 200 nm.
When the thickness of the light emitting layer 40 is less than 1 nm, the light emitting layer 40 has an island structure and does not form a layer, so that it cannot function as an organic EL element. On the contrary, when the thickness of the light emitting layer 40 is more than 5 μm, since the film thickness is thick, the voltage required for light emission becomes too high, and the light emission efficiency is lowered. Furthermore, a short circuit may occur, causing element destruction.

(First host compound)
The first host compound is a hole transport material that is a main component of the light emitting layer 40, and is the material having the highest triplet energy level in the light emitting layer 40.
As the first host compound, those having a triphenylamine skeleton represented by the following general formula (1) are preferable.

式中、ｎ_１〜ｎ_３は１〜３の整数を表し、Ａｒ_１〜Ａｒ_３としては、水素原子；メチル基、エチル基、イソプロピル基、ｔ−ブチル基等の炭素数１〜４のアルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等が挙げられる。また、Ａｒ_１〜Ａｒ_３が置換しているベンゼン環と縮合して形成する芳香環としては、ナフタレン環、アントラセン環、フェナントレン環等が挙げられる。

In the formula, n _{1 to} n ₃ represent an integer of _{1 to 3} , and Ar _{1 to} Ar ₃ represent a hydrogen atom; an alkyl having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, or a t-butyl group. Group; aryl groups such as phenyl group, tolyl group, xylyl group, mesityl group, t-butylphenyl group and biphenyl group; Examples of the aromatic ring formed by condensation with a benzene ring substituted by Ar _{1 to} Ar ₃ include a naphthalene ring, an anthracene ring, and a phenanthrene ring.

式中、ｎ_４、ｎ_５は１〜４の整数を表し、Ａｒ_４〜Ａｒ_９としては、水素原子；メチル基、エチル基、イソプロピル基、ｔ−ブチル基等の炭素数１〜４のアルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等が挙げられる。また、Ａｒ_４〜Ａｒ_９が置換しているベンゼン環と縮合して形成する芳香環としては、ナフタレン環、アントラセン環、フェナントレン環等が挙げられる。 Particularly, among the hole transport materials in which the first host compound has a triphenylamine skeleton as shown in the general formula (1), a triphenylamine that can be expressed by the following general formula (1)-(a) is used. A hole transport material having a structure in which two are connected is preferable.

In the formula, n ₄ and n ₅ represent an integer of 1 to ₄ , and Ar _{4 to} Ar ₉ are each a hydrogen atom; an alkyl having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, or a t-butyl group. Group; aryl groups such as phenyl group, tolyl group, xylyl group, mesityl group, t-butylphenyl group and biphenyl group; In addition, examples of the aromatic ring formed by condensation with a benzene ring substituted by Ar _{4 to} Ar ₉ include a naphthalene ring, an anthracene ring, and a phenanthrene ring.

式中、ｎ_６、ｎ_７は１〜４の整数を表し、Ａｒ_１０〜Ａｒ_１５としては、水素原子；メチル基、エチル基、イソプロピル基、ｔ−ブチル基等の炭素数１〜４のアルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等が挙げられる。また、Ａｒ_１０〜Ａｒ_１５が置換しているベンゼン環と縮合して形成する芳香環としては、ナフタレン環、アントラセン環、フェナントレン環等が挙げられる。また、２価の原子又は原子団のＸとしては、酸素原子；メチレン基、エチレン基、１，１−シクロヘキシレン基、１，２−シクロヘキシレン基、１，３−シクロヘキシレン基、フェニレン基等の直鎖、分岐又は環状のアルキレン基、もしくはアリーレン基等が挙げられる。 Further, among the hole transport materials in which the first host compound has a triphenylamine skeleton as shown in the general formula (1), there is a triphenylamine that can be expressed by the following general formulas (1) to (b). A hole transport material having a structure in which two are connected via a linking group X is preferred.

_Wherein, n 6, _{n 7} represents an integer of 1 to _4, the Ar 10 _{to Ar 15,} a hydrogen atom; a methyl group, an ethyl group, an isopropyl group, an alkyl having 1 to 4 carbon atoms a t- butyl group and the like Group; aryl groups such as phenyl group, tolyl group, xylyl group, mesityl group, t-butylphenyl group and biphenyl group; In addition, examples of the aromatic ring formed by condensation with a benzene ring substituted with Ar _{10 to} Ar ₁₅ include a naphthalene ring, an anthracene ring, and a phenanthrene ring. In addition, as X of the divalent atom or atomic group, oxygen atom; methylene group, ethylene group, 1,1-cyclohexylene group, 1,2-cyclohexylene group, 1,3-cyclohexylene group, phenylene group, etc. A linear, branched or cyclic alkylene group, or an arylene group.

式中、Ａｒ_１６〜Ａｒ_２４としては、水素原子；メチル基、エチル基、イソプロピル基、ｔ−ブチル基等の炭素数１〜４のアルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等が挙げられる。また、Ａｒ_１６〜Ａｒ_２４が置換しているベンゼン環と縮合して形成する芳香環としては、ナフタレン環、アントラセン環、フェナントレン環等が挙げられる。また、３価の原子又は原子団のＹとしては、窒素原子、リン原子、ホウ素原子；メチリジン基、ベンジリジン基、シクロヘキサントリイル基、ベンゼントリイル基等のアルカントリイル基又はアレーントリイル基等が挙げられる。 Further, among the hole transport materials in which the first host compound has a triphenylamine skeleton as shown in the general formula (1), a triphenylamine that can be expressed by the following general formulas (1) to (c) is used. A hole transport material having a structure in which three are connected via a connecting group Y is preferable.

In the formula, Ar _{16 to} Ar ₂₄ include a hydrogen atom; an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, and a t-butyl group; a phenyl group, a tolyl group, a xylyl group, a mesityl group, Examples thereof include aryl groups such as t-butylphenyl group and biphenyl group. In addition, examples of the aromatic ring formed by condensation with a benzene ring substituted by Ar _{16 to} Ar ₂₄ include a naphthalene ring, an anthracene ring, and a phenanthrene ring. In addition, as Y of the trivalent atom or atomic group, nitrogen atom, phosphorus atom, boron atom; alkanetriyl group such as methylidyne group, benzylidine group, cyclohexanetriyl group, benzenetriyl group, or arenetriyl group, etc. Is mentioned.

式中、Ａｒ_２５〜Ａｒ_３３としては、水素原子；メチル基、エチル基、イソプロピル基、ｔ−ブチル基等の炭素数１〜４のアルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等が挙げられる。また、Ａｒ_２５〜Ａｒ_３３が置換しているベンゼン環と縮合して形成する芳香環としては、ナフタレン環、アントラセン環、フェナントレン環等が挙げられる。 In addition, among the hole transport materials having the triphenylamine skeleton as shown in the general formula (1), the first host compound may be triphenylamine that can be expressed by the following general formulas (1) to (d). A hole transport material having a structure in which three carbazole groups are linked is more preferable.

In the formula, Ar _{25 to} Ar ₃₃ are each a hydrogen atom; an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, or a t-butyl group; a phenyl group, a tolyl group, a xylyl group, a mesityl group, Examples thereof include aryl groups such as t-butylphenyl group and biphenyl group. In addition, examples of the aromatic ring formed by condensation with a benzene ring substituted with Ar _{25 to} Ar ₃₃ include a naphthalene ring, an anthracene ring, and a phenanthrene ring.

Furthermore, although the specific example of said 1st host compound used in embodiment of this invention is shown next, this invention is not limited to these.
Here, the expressions (1-1) to (1-37) correspond to the general expression (1). In particular, formula (1-5) to formula (1-19) correspond to general formula (1)-(a), and formula (1-20) to formula (1-25) correspond to general formula (1). -(B), formulas (1-26) to (1-34) correspond to general formulas (1) to (c), and formulas (1-35) to (1-37) These correspond to the general formulas (1) to (d).

(Second host compound)
The second host compound is a phosphorescent metal complex that is a main component of the light emitting layer 40. Among the organic materials constituting the light emitting layer 40, the triplet energy is the same as that of the first host or next to the first host. High material.
As said 2nd host compound, what has an iridium complex shown by following General formula (2) is preferable.

式中、Ｒ_１〜Ｒ_７としては、水素原子；メチル基、エチル基、イソプロピル基、ブチル基、ｔ−ブチル基、ヘキシル基、オクチル基、ノニル基、デシル基、ウンデシル基、ドデシル基、トリデシル基、テトラデシル基、シクロヘキシル基等の、直鎖、分岐又は環状の炭素数１〜１６のアルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基；フッ素原子、塩素原子、臭素原子、ヨウ素原子等のハロゲン原子等が挙げられる。

In the formula, R _{1 to} R ₇ are each a hydrogen atom; methyl, ethyl, isopropyl, butyl, t-butyl, hexyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl Linear, branched or cyclic alkyl groups having 1 to 16 carbon atoms such as a group, tetradecyl group and cyclohexyl group; aryl groups such as phenyl group, tolyl group, xylyl group, mesityl group, t-butylphenyl group and biphenyl group A halogen atom such as a fluorine atom, a chlorine atom, a bromine atom or an iodine atom;

  Furthermore, although the specific example of the 2nd host compound used in embodiment of this invention is shown next, this invention is not limited to these.

(Guest compound)
The guest compound is a phosphorescent organic material that is a subcomponent of the light emitting layer 40, and is a material having the lowest triplet energy level among the organic materials constituting the light emitting layer 40. For example, a metal complex having a transition metal such as iridium or platinum is preferable.

  Next, although the specific example of the said guest compound used in embodiment of this invention is shown, this invention is not limited to these.

  The light emitting layer is formed by first preparing a light emitting layer solution and then applying and drying the light emitting layer solution on the hole injection layer by a wet process such as a spin coating method or an ink jet method.

  More specifically, for example, the substrate 10 on which the hole injection layer 30 is formed is set at a predetermined position of a spin coater, and after the light emitting layer solution is dropped, the substrate is rotated and applied at a predetermined speed. The rotation is stopped, and the substrate 10 taken out from the spin coater is introduced into a chamber set at 70 ° C. and held for 1 hour. Through this drying process, the organic solvent is removed, and the light emitting layer 40 having a predetermined thickness is formed.

  The light emitting layer solution is adjusted as follows. A predetermined amount of the first host compound and the second host compound are measured. The total amount of the first host compound and the second host compound is defined as the total amount of the host compound. Next, a predetermined amount of the guest compound is measured and added to the host compound. Finally, a predetermined amount of solvent is added and dissolved to prepare a light emitting layer solution. The ratio of the guest compound to the host compound in the light emitting layer is the ratio of the amount of the guest compound to the total amount of the host compound.

  The mass ratio of the host compound and the guest compound (guest compound / host compound) in the light emitting layer is preferably 0.1 / 99.9 to 50/50.

When the mass ratio (guest compound / host compound) is smaller than 0.1 / 99.9, the number of guest compounds is not sufficient, so even if a lot of excitation energy is generated due to recombination of electrons and holes. , All excitons cannot transfer energy to the guest compound, and the light emission efficiency cannot be improved.
When the mass ratio (guest compound / host compound) is larger than 50/50, the excitation energy generated by recombining electrons and holes is transferred to the guest compound, and the guest compound is in a triplet state. Even if excited, it is not preferable because energy is deactivated without light emission due to the effect of concentration quenching.

  The mass ratio of the first host compound and the second host compound (first host compound / second host compound) in the light emitting layer is preferably 10/90 to 90/10. More preferably, it is 30 mass ratio or more and less than 70 mass ratio.

  When the mass ratio (first host compound / second host compound) is smaller than 10/90, the intermolecular distance becomes too large due to the decrease in the ratio of the hole transport material, and the hole transport property of the entire light emitting layer is reduced. The light emission efficiency cannot be improved. In addition, when the mass ratio (first host compound / second host compound) is greater than 90/10, energy transfer from the first host to the second host is efficient due to a decrease in the ratio of the second host material. This is not preferable because it does not occur in

(Hole blocking layer)
Next, the substrate 10 on which the light emitting layer 40 is formed is set at a predetermined position in the chamber of the vacuum vapor deposition device, and the inside of the chamber is brought into a reduced pressure state. After reaching a predetermined reduced pressure state, the crucible containing the material of the hole blocking layer 50 is heated and evaporated to form the hole blocking layer 50 on the light emitting layer 40.

  The hole blocking layer 50 is preferably an organic thin film that can block holes that have hopped and moved inside the light emitting layer 40. For example, when the energy level of the ground state of the light-emitting layer 40 is compared with the energy level of the ground state of the hole blocking layer 50, the energy level of the ground state of the hole blocking layer 50 is Any material that is higher than the energy level of the state and has a large energy gap can be used as the hole blocking layer 50. This is because the holes that have moved can be prevented from entering the hole blocking layer 50 due to this energy gap. Holes that are prevented from entering the hole blocking layer 50 stay inside the light emitting layer 40 and contribute to the generation of excitons.

  As the organic material that can be used as the hole blocking layer 50, a general electron transporting material that satisfies the above conditions can be used. For example, 2,2 ′, 2 ″-(1,3,5-benzenetriyl) -tris [1-phenyl-1H-benzimidazole] (hereinafter, TPBI) can be used.

The thickness of the hole blocking layer 50 is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 20 nm to 200 nm.
When the thickness of the hole blocking layer 50 is less than 1 nm, the hole blocking layer 50 has an island structure and does not form a layer, so that it cannot function as an organic EL element. On the other hand, when the hole blocking layer 50 has a film thickness of more than 5 μm, the film thickness is too large, so that the voltage required for light emission becomes too high and the light emission efficiency is lowered. Furthermore, a short circuit may occur, causing element destruction.

(Electron transport layer)
Next, the crucible containing the material of the electron transport layer 60 is continuously heated under the reduced pressure condition with the position of the substrate 10 on which the hole blocking layer 50 is formed in the chamber of the vacuum apparatus as it is. The electron transport layer 60 is formed on the hole blocking layer 50 by vapor deposition.

The electron transport layer 60 is an organic material having a high electron transport capability, and is preferably a material that can be stably present as a thin film without being broken even when an electric field is applied. An organic material that can also be used as the hole blocking layer 40 can be appropriately selected and used.
For example, as a material of the electron transport layer 60, tris- (8-hydroxyquinoline) -aluminum (hereinafter, Alq ₃ ) can be exemplified.

The film thickness of the electron transport layer 60 is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 20 nm to 200 nm.
When the thickness of the electron transport layer 60 is less than 1 nm, the electron transport layer 60 has an island structure and does not form a layer, so that it cannot function as an organic EL element. On the contrary, when the film thickness of the electron transport layer 60 exceeds 5 μm, since the film thickness is thick, the voltage required for light emission becomes too high, and the light emission efficiency is lowered. Furthermore, a short circuit may occur, causing element destruction.

(cathode)
The cathode 70 is preferably made of a metal having a low work function. The work function is preferably at least 4.5 eV or less. By using a metal having a low work function, the electron injection barrier between the cathode 70 and the electron transport layer 60 can be lowered, and electrons can be easily injected from the cathode 70 into the electron transport layer 60. is there. Examples of the metal having a low work function include alkali metals such as Li and Cs, and alkaline earth metals such as Ca, Ba, and Mg.

However, since the metal having a low work function easily reacts with oxygen or moisture in the air, it is preferably formed as an alloy such as MgAg or a compound containing the metal such as LiF, LiO ₂ , or CsF. Alternatively, it is desirable to stack a metal having a high work function such as Al or Au on the alkali metal or alkaline earth metal.

(Glass sealing tube)
By adhering the glass sealing tube 80 to the substrate 10 using the UV curable resin 90, the device portion of the organic EL element is blocked from the outside world and can be less affected by air, moisture, and the like. The durability as an organic EL element and the element life can be greatly improved.
In addition, when performing glass sealing, the said effect can be strengthened by substituting the air inside the glass sealing tube 80 with nitrogen gas, and also introduce | transducing a desiccant into the glass sealing tube 80 inside.

In the embodiment of the present invention, the organic thin film layer 100 constituting each layer from the hole injection layer 30 to the electron transport layer 60 is formed by using a dry process by a vacuum deposition method and a wet process by a spin coating method. The entire organic thin film layer 100 may be formed using a single process.
As a method for forming the organic thin film layer 100 by the wet process, an inkjet method, a printing method, or the like can be used in addition to the spin coating method.
In the case of forming a large-screen, high-definition display with organic EL elements, it is preferable to form the organic thin film layer 100 using the wet process in terms of characteristics and manufacturing.

It is also possible to add another organic material to the light emitting layer 40, and the number of organic materials that can be added is not limited.
Hereinafter, effects of the embodiment of the present invention will be described.

  In the organic EL device according to the embodiment of the present invention, the three or more components constituting the light emitting layer include a first host compound made of a hole transport material, a second host compound made of a phosphorescent metal complex, and phosphorescence. Therefore, excitons generated by recombination of electrons, holes, and electrons and holes can be accumulated in the light emitting layer. In addition, the generated excitons can be held at the triplet energy level of the guest compound. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device according to an embodiment of the present invention, the triplet energy level of the first host compound is higher than the triplet energy level of the guest compound, and the triplet energy level of the second host compound is that of the guest compound. Since it is higher than the triplet energy level, the excitation energy can be efficiently transferred from the host compound to the guest compound. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device according to the embodiment of the present invention, the triplet energy level of the first host compound is the same as the triplet energy level of the second host compound or higher than the triplet energy level of the second host compound. Therefore, the excitation energy can be efficiently shifted from the triplet energy level of the first host compound to the triplet energy level of the second host compound. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device according to the embodiment of the present invention, the first host compound has a triphenylamine skeleton excellent in hole transport ability, and therefore, a large number of holes can be accumulated in the light emitting layer. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device according to the embodiment of the present invention, the second host compound is an iridium complex that can stably hold excitons at the triplet energy level. Exciton can be accumulated in the triplet energy level. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device according to the embodiment of the present invention, the guest compound is a phosphorescent light-emitting material having platinum or iridium atoms that can stably hold excitons at a triplet energy level. Excitons can be accumulated at the triplet energy level of the guest compound in the light emitting layer. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device according to the embodiment of the present invention, the proportion of the guest compound in the light emitting layer is 0.01% by mass to 50% by mass, and thus the triplet of the guest compound can be stably performed without quenching the concentration. Phosphorescence can be emitted from the energy level, and the light emission efficiency of the organic EL element can be improved.

  Since the organic EL element which is embodiment of this invention has the mass ratio of a 1st host compound and a 2nd host compound in the range of 10 / 90-90 / 10, the exciton produced | generated with the 1st host compound is used. It can transit to the triplet energy level of the second host compound and can be held stably. As a result, the light emission efficiency of the organic EL element can be improved.

In the organic EL device according to the embodiment of the present invention, an organic thin film layer such as a light emitting layer can be formed by a wet process. Therefore, a large vacuum required for a dry process is required in manufacturing a large organic EL display. A chamber or the like is not required, and the manufacturing can be simplified.
Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to these examples.

Example 1
(Element creation)
First, an anode made of ITO was formed on a glass substrate.

(Hole injection layer formation)
Next, a hole injection layer having a film thickness of 35 nm was formed on the anode by spin coating with a hole injection layer solution containing PEDOT / PSS and dried at 180 ° C.
PEDOT represents poly (3,4-ethylenedioxythiophene) and PSS represents polysulfostyrene (hereinafter the same).

(Light emitting layer formation)
First, 4,4′-bis [N- (1-naphthyl) -phenyl-amino] -biphenyl which is a hole transport material as the first host compound and is a compound represented by the formula (1-11) (hereinafter, α -NPD) is a compound represented by the formula (2-7) as the second host compound (bis (2-phenylpyridinato-N, C2 ^' ) iridium (III) 2,4-tridecane) 50 parts by mass of dionate), 3 parts by mass of tris (1-phenylisoquinolinolato-C ² , N) iridium (III), which is a compound represented by the formula (3-14) as a guest compound, A solution for a light emitting layer was prepared by dissolving in a 2-dichloroethane solution.
Next, the light emitting layer solution was applied onto the hole injection layer by a spin coating method to form a light emitting layer, which was dried at 70 ° C. for 1 hour. A light emitting layer composed of the three components having a thickness of 50 nm was formed.

(Hole blocking layer formation)
Next, a hole blocking layer made of TPBI having a thickness of 10 nm was formed on the light emitting layer by a vacuum deposition method.

(Electron transport layer formation)
Furthermore, an electron transport layer made of Alq ₃ having a thickness of 30 nm was formed on the hole blocking layer by a vacuum deposition method.

Finally, a cathode 7 made of a lithium fluoride film layer having a thickness of 0.5 nm and aluminum having a thickness of 100 nm was continuously deposited on the electron transport layer by a vacuum deposition method.
After film formation of the cathode, the organic EL element was transferred into a glove box filled with nitrogen gas, and was bonded to the element by using an ultraviolet curable resin as a sealing glass for sealing.

The light emitting characteristics of the obtained device were measured.
A positive voltage was applied to the ITO anode side of the organic EL element and a negative voltage was applied to the aluminum cathode side, and current, luminance, and emission spectrum characteristics were measured.

When voltage was applied, red light emission with an emission peak of 617 nm was obtained. From the emission spectrum, it was confirmed that the light emitted from the guest compound. A weak light emission component from the second host compound was also observed at around 520 nm. The CIE chromaticity coordinates at a luminance of 100 cd / m ² were (0.64, 0.35). The external light emission quantum efficiency at a luminance of 100 cd / m ² was 5.8%, and the power efficiency was 4.11 lm / W.
The experimental conditions and results of Example 1 are shown in Tables 1 and 2.

As shown in Table 2, the triplet energy levels of α-NPD, the compound represented by formula (2-7), and the compound represented by formula (3-14) are 2.3 eV, 2.3 eV, and It was 1.9 eV.
In Comparative Example 4, iridium (III) bis [(4,6-difluorophenyl) pyridinato-N, C ^{2 ′} ] picolinate (hereinafter referred to as FIrpic) as a material having a triplet energy higher than that of the first host. Was used.
In Comparative Example 5, since there is no suitable second host having a triplet energy lower than that of the compound represented by Formula (3-14), which is a red light emitting guest material, blue light emission having a higher triplet energy as a guest material. Using FIrpic as a guest material, a compound represented by the formula (2-7) was used as a second host having a triplet energy lower than that of the guest.

(Comparative Example 1)
Without using the second host compound, the proportion of the first host compound was 100 parts by mass, the same guest compound as in Example 1 was 3 parts by mass, these were dissolved in a 1,2-dichloroethane solution, and the light emitting layer solution was prepared. An organic EL device was produced in the same manner as in Example 1 except that the light emitting layer was formed by adjusting.

Red light emission with an emission peak of 616 nm was obtained. From the emission spectrum, it was confirmed that the light emitted from the guest compound. The CIE chromaticity coordinates at a luminance of 100 cd / m ² were (0.66, 0.33). The external light emission quantum efficiency at a luminance of 100 cd / m ² was 3.7%, and the power efficiency was 2.7 lm / W.
The experimental conditions and experimental results of Comparative Example 1 are shown in Tables 1 and 2.

(Example 2)
Implemented except that 1,1′-bis (di-4-toluylaminophenyl) cyclohexane (hereinafter referred to as TAPC), which is a compound represented by the formula (1-21), was used as the first host compound instead of α-NPD. In the same manner as in Example 1, an organic EL device was produced.

Red light emission with an emission peak of 618 nm was obtained. From the emission spectrum, it was confirmed that the light emitted from the guest compound. A weak light emission component from the second host compound was also observed at around 520 nm. The CIE chromaticity coordinates at a luminance of 100 cd / m ² were (0.61, 0.38). The external light emission quantum efficiency at a luminance of 100 cd / m ² was 4.9%, and the power efficiency was 2.8 lm / W.
The experimental conditions and results of Example 2 are shown in Tables 1 and 2.

(Comparative Example 2)
Without using the second host compound, the proportion of the first host compound was 100 parts by mass, the same guest compound as in Example 1 was 3 parts by mass, these were dissolved in a 1,2-dichloroethane solution, and the light emitting layer solution was prepared. An organic EL device was produced in the same manner as in Example 2 except that the light emitting layer was formed by adjusting.

Red light emission with an emission peak of 619 nm was obtained. From the emission spectrum, it was confirmed that the light emitted from the guest compound. The CIE chromaticity coordinates at a luminance of 100 cd / m ² were (0.64, 0.33). The external light emission quantum efficiency at a luminance of 100 cd / m ² was 2.1%, and the power efficiency was 0.9 lm / W.
The experimental conditions and experimental results of Comparative Example 2 are shown in Tables 1 and 2.

(Example 3)
As the first host compound, 4,4 ′, 4 ″ -tri (N-carbazolyl) triphenylamine (hereinafter, TCTA), which is a compound represented by the formula (1-35), was used instead of α-TPD. In the same manner as in Example 1, an organic EL element was produced.

Red light emission with an emission peak of 624 nm was obtained. From the emission spectrum, it was confirmed that the light emitted from the guest compound. A weak light emission component from the second host compound was also observed at around 520 nm. The CIE chromaticity coordinates at a luminance of 100 cd / m ² were (0.63, 0.36). The external light emission quantum efficiency at a luminance of 100 cd / m ² was 4.8%, and the power efficiency was 2.5 lm / W.

(Comparative Example 3)
Without using the second host compound, the proportion of the first host compound was 100 parts by mass, the same guest compound as in Example 1 was 3 parts by mass, these were dissolved in a 1,2-dichloroethane solution, and the light emitting layer solution was prepared. An organic EL device was produced in the same manner as in Example 3 except that the light emitting layer was formed by adjusting.

When the light emitting layer was formed by spin coating, the light emitting layer immediately crystallized and a homogeneous film could not be obtained, making it impossible to produce an organic EL device.
The experimental conditions and experimental results of Comparative Example 3 are shown in Tables 1 and 2.

(Comparative Example 4)
In the same manner as in Example 1 except that FIrpic, which is a phosphorescent material having a triplet energy larger than α-NPD, was used as the second host compound instead of the compound represented by formula (2-7). An organic EL element was produced.

Red light emission with an emission peak of 622 nm was obtained. From the emission spectrum, it was confirmed that the light emitted from the guest compound. The CIE chromaticity coordinates at a luminance of 100 cd / m ² were (0.68, 0.32). The external light emission quantum efficiency at a luminance of 100 cd / m ² was 3.4%, and the power efficiency was 1.3 lm / W.
The experimental conditions and experimental results of Comparative Example 4 are shown in Tables 1 and 2.

(Comparative Example 5)
An organic EL device was produced in the same manner as in Example 1 except that FIrpic was used as the guest compound.

Since the triplet energy of the guest compound is larger than the triplet energy of the first host compound and the second host compound, the triplet energy cannot be transferred to the guest compound, and the red light emission from the guest compound does not occur. Green light emission with an emission peak derived from the bihost compound of 524 nm was obtained. The external light emission quantum efficiency at a luminance of 100 cd / m ² was 1.8%, and the power efficiency was 3.5 lm / W. This is because the power efficiency looks higher than other elements, but the emission color is green with higher visibility.
The experimental conditions and experimental results of Comparative Example 5 are shown in Tables 1 and 2.

  The present invention relates to an organic EL element that emits high-efficiency phosphorescence, and can be suitably used in the fields of display elements, displays, backlights, electrophotography, illumination light sources, exposure light sources, signs, signboards, and interiors, It can be used in the lighting equipment and display industries.

It is a cross-sectional schematic diagram explaining an example of the organic EL element which is embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Substrate, 20 ... Anode, 30 ... Hole injection layer, 40 ... Light emitting layer, 50 ... Hole blocking layer, 60 ... Electron transport layer, 70 ... Cathode, 80 ... Glass sealing tube, 90 ... UV curable resin, 100: Organic thin film layer.

Claims (12)

In an organic EL element having a pair of opposing electrodes and a single-layer or multilayer organic thin film layer disposed between the electrodes, and at least one of the organic thin film layers being a light emitting layer,
The light emitting layer is configured to contain at least a host compound and a guest compound,
The host compound includes a first host compound made of a hole transport material and at least two kinds of host compounds of a second host compound made of a phosphorescent metal complex,
The organic EL device, wherein the guest compound includes at least one phosphorescent light emitting material.   The triplet energy level of the first host compound is higher than the triplet energy level of the guest compound, and the triplet energy level of the second host compound is higher than the triplet energy level of the guest compound. The organic EL element according to claim 1.   The organic EL device according to claim 1, wherein the triplet energy level of the first host compound is the same as or higher than the triplet energy level of the second host compound. . The organic EL device according to any one of claims 1 to 3, wherein the first host compound has a triphenylamine skeleton represented by the following general formula (1).

In the formula, n _{1 to} n ₃ represent an integer of _{1 to 3} , and Ar _{1 to} Ar ₃ each independently represent a hydrogen atom, an alkyl group, or an aryl group, or Ar _{1 to} Ar ₃ are substituted. An aromatic ring may be formed by condensation with a benzene ring. The EL device according to claim 1, wherein the first host compound is represented by the following general formula (1)-(a).

In the formula, n ₄ and n ₅ each represent an integer of 1 to 4, and Ar _{4 to} Ar ₉ each independently represent a hydrogen atom, an alkyl group, or an aryl group, or Ar _{4 to} Ar ₉ are substituted. An aromatic ring may be formed by condensation with a benzene ring. 5. The EL device according to claim 1, wherein the first host compound can be expressed by the following general formulas (1) to (b).

_Wherein, n 6, _{n 7} is an integer of 1 to _4, Ar 10 _{to Ar 15} are each independently hydrogen atom, an alkyl group, an aryl _group, Ar 10 _{to Ar 15} is substituted An aromatic ring may be formed by condensation with a benzene ring. X represents a divalent atom or atomic group; a linear or branched or cyclic alkylene group; or an aryl group. The EL device according to claim 1, wherein the first host compound is represented by the following general formulas (1) to (c).

In the formula, each of Ar _{16 to} Ar ₂₄ independently represents a hydrogen atom, an alkyl group, or an aryl group, or may be condensed with a benzene ring substituted by Ar _{16 to} Ar ₂₄ to form an aromatic ring. good. Y represents a trivalent atom or atomic group; a linear or branched or cyclic alkanetriyl group; or an arenetriyl group. 5. The EL device according to claim 1, wherein the first host compound can be represented by the following general formulas (1) to (d).

In the formula, Ar _{25 to} Ar ₃₃ each independently represent a hydrogen atom, an alkyl group, or an aryl group, or they may be condensed with a benzene ring substituted by Ar _{25 to} Ar ₃₃ to form an aromatic ring. good. The organic EL device according to claim 1, wherein the second host compound is an iridium complex represented by the following general formula (2).

In the formula, each of R _{1 to} R ₇ independently represents a hydrogen atom, an alkyl group, an aryl group, or a halogen atom, or condensed with a benzene ring or pyridine ring substituted by R _{1 to} R ₇ to give an aromatic A ring may be formed.   The organic EL device according to claim 1, wherein the guest compound is a phosphorescent light emitting material having platinum or iridium atoms.   The mass ratio (first host compound / second host compound) of the first host compound and the second host compound in the light emitting layer is 10/90 to 90/10. The organic EL element of any one of 10-10.   The organic EL device according to claim 1, wherein the light emitting layer is formed by a wet process.

Images