KR102544020B1 - A composition for forming a light emitting layer and an organic electroluminescent device containing the composition for forming the light emitting layer - Google Patents

Abstract

An object of the present invention is to provide an organic electroluminescent device having a long operating life and excellent storage stability, and to provide a composition for forming a light emitting layer suitable therefor, specifically, a light emitting material, a non-emitting material and an organic solvent. A composition for forming a light emitting layer of an organic electroluminescent device, comprising: one or more light emitting materials may be used, and the non-light emitting material is a high Tg compound having a glass transition temperature of 130°C or higher and a glass transition temperature of 100°C or lower. A material comprising a low Tg compound, the content of the low Tg compound relative to all non-luminescent materials is 10 to 70% by weight, and at least one of the non-luminescent materials is a material having a pyrimidine skeleton or a triazine skeleton. To provide a composition for forming a light emitting layer.

Description

A composition for forming a light emitting layer and an organic electroluminescent device containing the composition for forming the light emitting layer

The present invention relates to a composition for forming a light emitting layer and an organic electroluminescent device containing the composition for forming a light emitting layer.

BACKGROUND OF THE INVENTION In recent years, organic electroluminescent elements have been actively developed as a technology for manufacturing light emitting devices such as displays and lightings because they can emit light in various colors with a simple element configuration.

An organic electroluminescent device emits light by injecting holes and electrons from an anode and a cathode, allowing each charge to reach a light emitting layer, and recombination of charges in the light emitting layer. Based on this principle, it has been studied to improve the light emitting efficiency by forming a light emitting layer using a composition for forming a light emitting layer that usually contains not only a light emitting material but also a charge transport material, and allowing electric charges to remain in the light emitting layer (see Patent Document 1). ).

On the other hand, allowing charges to stay in the light emitting layer deteriorates the current-voltage characteristics of the organic electroluminescent device. In order to retain charge in one layer, it is usually performed by a method of creating a trap level of charge in a film and retaining charge or the like. According to these methods, it is possible to increase the luminous efficiency by allowing the charge to stay in the light emitting layer, but at the same time, it leads to deterioration of the current-voltage characteristic, that is, to an increase in the drive voltage of the organic electroluminescent element. Since power consumption increases as the driving voltage increases, a technique for reducing the driving voltage reduction by, for example, setting the total number of charge transport materials contained in the composition for forming a light emitting layer to three or more has been proposed (Patent Documents). 2).

However, in the case of increasing the type of charge transport material, it is considered that there are still insufficient studies on how to improve the driving life, which is an important characteristic of organic electroluminescence devices, and how to maintain storage stability at high temperatures.

Japanese Unexamined Patent Publication No. 2005-219513 International Publication WO2013/069338 pamphlet

An object of the present invention is to provide an organic electroluminescent device having a long drive life and excellent storage stability, and an object thereof is to provide a composition for forming a light emitting layer suitable therefor.

Regarding this subject, as a result of intensive examination by the present inventors, by using a compound having a glass transition temperature higher than a predetermined temperature and a compound lower than a predetermined temperature in the composition for forming a light emitting layer, the driving life is long and the storage is stored at high temperature. It has been found that an organic electroluminescent device whose driving life is hardly reduced even after the present invention is obtained.

This invention was achieved based on this knowledge, and makes the following a summary.

[1] A composition for forming a light emitting layer of an organic electroluminescent device, comprising a light emitting material, a non-emitting material and an organic solvent, wherein the non-emitting material comprises a high Tg compound having a glass transition temperature of 130°C or higher and a glass transition temperature of 100°C or less, the content of the low Tg compound relative to all the non-luminescent materials is 8 to 70% by mass, and at least one of the non-luminescent materials has a pyrimidine skeleton or a triazine skeleton. A composition for forming a light emitting layer.

[2] The composition for forming a light emitting layer according to [1], wherein the molecular weight of all the non-light emitting materials in the composition for forming a light emitting layer is 1.0% by mass or more relative to the total amount of all the non-light emitting materials, and the molecular weight is 5000 or less.

[3] The composition for forming a light emitting layer according to [1] or [2], wherein all of the light emitting materials have a molecular weight of 5000 or less.

[4] The light-emitting layer according to any one of [1] to [3], wherein the material having a pyrimidine skeleton or a triazine skeleton contained in the composition for forming a light-emitting layer is the high-Tg compound and/or the low-Tg compound. composition for formation.

[5] The composition for forming a light emitting layer according to any one of [1] to [4], wherein a weighted average glass transition temperature of all the non-light emitting materials contained in the composition for forming a light emitting layer is 100°C or higher.

[6] The composition for forming a light-emitting layer according to [1] to [5], wherein the low-Tg compound is a compound in which monocyclic compounds are bonded directly and/or via a linking group.

[7] The composition for forming a light-emitting layer according to any one of [1] to [6], wherein the low-Tg compound contains only compounds in which aromatic hydrocarbon monocyclic compounds are bonded directly and/or via a linking group.

[8] The composition for forming a light-emitting layer according to any one of [1] to [7], wherein the low-Tg compound is a compound represented by structural formula (A) below.

[In Formula (A), R ¹ to R ¹⁵ each independently represent a hydrogen atom, a phenyl group having 6 to 30 carbon atoms, or a monovalent compound in which a monocyclic aromatic hydrocarbon compound is bonded.]

[9] An organic electroluminescent device having a light emitting layer formed by wet film formation using the composition for forming a light emitting layer according to any one of [1] to [8].

According to the present invention, after storage at a high temperature, an organic electroluminescent device having a long drive life and high luminous efficiency can be obtained.

1 is a schematic cross-sectional view showing an example of an embodiment of an organic electroluminescent device of the present invention.
2 is a schematic cross-sectional view showing another example of an embodiment of the organic electroluminescent device of the present invention.

The embodiment of the composition for forming a light emitting layer of the present invention, an organic electroluminescent device and a method for producing the same will be described in detail below, but the following description is an example (a representative example) of an embodiment of the present invention, and the present invention is the gist thereof As long as it does not exceed, it is not specific to these contents.

[Composition for Forming Light-Emitting Layer]

The composition for forming a light-emitting layer of the present invention is used for forming a light-emitting layer of an organic electroluminescent device, and contains a light-emitting material, a non-light-emitting material and an organic solvent, and the non-light-emitting material has a glass transition temperature (hereinafter referred to as Tg). It includes a high Tg compound having a Tg of 130°C or higher and a low Tg compound having a Tg of 100°C or lower.

(luminescent material)

As the light emitting material, any known material normally used as a light emitting material for an organic electroluminescent element can be used, and there is no particular limitation, and a material that emits light at a desired light emission wavelength and has good light emission efficiency may be used. The light emitting material may be a fluorescent light emitting material or a phosphorescent light emitting material, but from the viewpoint of internal quantum efficiency and low heat generation, a phosphorescent light emitting material is preferable.

As the phosphorescence emitting material, for example, the long-period periodic table (hereinafter referred to as "periodic table" unless otherwise specified refers to the long-period periodic table.) A metal selected from Groups 7 to 11 is included as a central metal. Werner type complexes or organometallic complexes to be used are exemplified.

As the metal selected from groups 7 to 11 of the periodic table, preferably, ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, gold and the like are mentioned. As a metal selected from groups 7 to 11 of the periodic table, iridium and platinum are more preferable.

As the ligand of the complex, an aryl group such as an arylpyridine ligand, a heteroarylpyridine ligand, an arylpyrazole ligand, a heteroarylpyrazole ligand, or a ligand in which pyridine, pyrazole, or phenanthroline or the like is bonded to a heteroaryl group is preferable. , Phenylpyridine ligands and phenylpyrazole ligands are particularly preferred.

As a phosphorescence emitting material, specifically, tris (2-phenylpyridine) iridium, tris (2-phenylpyridine) ruthenium, tris (2-phenylpyridine) palladium, bis (2-phenylpyridine) platinum, tris (2-phenyl Pyridine) osmium, tris (2-phenylpyridine) rhenium, octaethyl platinum porphyrin, octaphenyl platinum porphyrin, octaethyl palladium porphyrin, octaphenyl palladium porphyrin and the like.

In particular, as the organometallic complex of the phosphorescence emitting material, preferably, a compound represented by the following formula (I) is exemplified.

ML _(qj) L' _j (I)

(In formula (I), M represents a metal, and q represents the valence of the metal. In addition, L and L' represent a bidentate ligand. j represents the number of 0, 1 or 2. L or L When there are a plurality of each ', a plurality of L or L' may be the same or different, respectively.)

In formula (I), M represents an arbitrary metal. Specific examples of preferred M include the metals described above as metals selected from Groups 7 to 11 of the periodic table.

In Formula (I), the bidentate ligand L represents a ligand having the following partial structure.

In the partial structure of L, ring A1 represents an aromatic ring group which may have a substituent. The aromatic ring group in the present invention may be an aromatic hydrocarbon group or an aromatic heterocyclic group.

In the partial structure of L, ring A2 represents a nitrogen-containing aromatic heterocyclic group which may have a substituent.

In addition, in Formula (I), as the bidentate ligand L', the ligand shown below is mentioned.

As an organometallic complex of a phosphorescent light-emitting material in the present invention, from the viewpoint of being easy to interact with a non-luminescent material coexisting in the light-emitting layer, the molecule has a relatively three-dimensional and bulky bidentate ligand having the above formula (I) The compounds shown are preferred.

Further, for example, a fluorescent light emitting material for blue and a phosphorescent light emitting material for green and red may be used in combination with a fluorescent light emitting material and a phosphorescent light emitting material.

In addition, for the purpose of improving the solubility in the solvent used for preparing the composition for forming the light emitting layer used when forming the light emitting layer by the wet film forming method, the symmetry or rigidity of the molecule of the light emitting material is reduced, or It is preferable to introduce a lipophilic substituent.

As for the light emitting material, only any one type may be used, and two or more types may be used together in arbitrary combinations and ratios.

The molecular weight of the light emitting material in the present invention is preferably 5000 or less, more preferably 4000 or less, and particularly preferably 3000 or less. The molecular weight of the light emitting material in the present invention is usually 400 or more, preferably 600 or more, more preferably 800 or more, and particularly preferably 1000 or more. In this molecular weight range, it is considered that the light emitting materials do not aggregate and are uniformly mixed with the non-light emitting material, so that a light emitting layer with high light emitting efficiency can be obtained.

The molecular weight of the light emitting material has a high Tg, melting point, decomposition temperature, etc., and the light emitting material and the formed light emitting layer have excellent heat resistance, and deterioration in film quality due to gas generation, recrystallization, migration of molecules, etc., and thermal decomposition of the material A larger one is preferable from the viewpoint that an increase in impurity concentration or the like does not easily occur. On the other hand, the molecular weight of the light emitting material is preferably small in terms of easy purification of the organic compound and easy dissolution in a solvent.

(non-luminous material)

The non-luminescent material in the present invention refers to all non-volatile materials other than the luminescent material. A non-volatile material is a material other than the organic solvent in the composition for forming a light emitting layer, and refers to a material included in the light emitting layer when the light emitting layer is formed. As the non-luminescent material, at least a high Tg compound and a low Tg compound described later are included, but materials other than these may also be included.

In the present invention, from the viewpoint of the durability of the organic electroluminescent element against the electric charge, at least one of the non-luminescent materials is a material having a pyrimidine skeleton or a triazine skeleton, and at least one of a high Tg compound or a low Tg compound described later It is preferable that this is a material having a pyrimidine skeleton or a triazine skeleton. Further, any one of the non-luminescent materials is more preferably a material having a triazine skeleton, and it is particularly preferable that at least one of the high-Tg compound or low-Tg compound described later is a material having a triazine skeleton, and a low-Tg compound described later. A material having this triazine skeleton is most preferred.

In the composition for forming a light emitting layer of the present invention, the molecular weight of all non-luminescent materials having a content of 1.0% by mass or more relative to the total amount of all non-luminescent materials contained in the composition for forming a light-emitting layer is preferably 5000 or less, more preferably It is 4000 or less, particularly preferably 3000 or less, most preferably 2000 or less, and usually 300 or more, preferably 350 or more, and more preferably 400 or more.

<High Tg compound>

The high Tg compound of the present invention is a compound exhibiting a Tg of 130°C or higher. As the high Tg compound, those having a Tg of 130° C. or higher may be appropriately selected from compounds usually used for forming the light emitting layer of an organic electroluminescent element. As the high Tg compound, a charge transport material usually contained in the light emitting layer is preferable.

The compound having a Tg of 130°C or higher is preferably a compound in which a condensed ring structure of three or more rings is bonded to a central skeleton having excellent charge transport properties. In particular, it is preferable that it is a compound having two or more condensed ring structures of three or more rings and/or a compound having at least one condensed ring of five or more rings. With these compounds, the rigidity of the molecules increases, and the effect of suppressing the degree of molecular motion in response to heat is easily obtained.

In addition, the condensed ring of three or more rings and the condensed ring of five or more rings of the high Tg compound preferably have an aromatic hydrocarbon ring or an aromatic heterocyclic ring from the viewpoint of charge transportability and material durability.

As the central skeleton excellent in charge transportability, specifically, an aromatic structure, an aromatic amine structure, a triarylamine structure, a dibenzofuran structure, a naphthalene structure, a phenanthrene structure, a phthalocyanine structure, a porphyrin structure, a thiophene structure, a benzylphenyl structure, Fluorene structure, quinacridone structure, triphenylene structure, carbazole structure, pyrene structure, anthracene structure, phenanthroline structure, quinoline structure, pyridine structure, pyrimidine structure, triazine structure, oxadiazole structure or imidazole structure, etc.

Among them, compounds having a pyridine structure, a pyrimidine structure, or a triazine structure are more preferable, and a compound having a pyrimidine structure or a triazine structure is still more preferable from the viewpoint of being a material with excellent electron transport properties and a relatively stable structure. .

The high-Tg compound in the present invention is preferably a material having a structure excellent in electron transportability from the point of view that the light emitting material itself can suppress deterioration of the light emitting material due to transport of electrons and can extend the drive life. do.

Further, compounds having a structure having excellent hole transport properties are also preferred, and among the core skeletons having excellent charge transport properties, a carbazole structure, a dibenzofuran structure, a triarylamine structure, a naphthalene structure, a phenanthrene structure or a pyrene structure have a hole transport property. It is preferable as an excellent structure, and a carbazole structure, a dibenzofuran structure, or a triarylamine structure is more preferable.

The high-Tg compound in the present invention is preferably a material having a structure excellent in hole-transport property from the viewpoint that the light-emitting material itself can suppress deterioration of the light-emitting material due to transport of holes and can extend the drive life. do.

As described above, the high Tg compound of the present invention preferably has a condensed ring structure of three or more rings, and is a compound having two or more condensed ring structures of three or more rings and/or a compound having at least one condensed ring of five or more rings. it is more preferable Examples of the condensed ring structure having three or more rings include an anthracene structure, a phenanthrene structure, a pyrene structure, a chrysene structure, a naphthacene structure, a triphenylene structure, a fluorene structure, a benzofluorene structure, an indenofluorene structure, An indolofluorene structure, a carbazole structure, an indenocarbazole structure, an indolocarbazole structure, a dibenzofuran structure, a dibenzothiophene structure, etc. are mentioned. From the viewpoint of charge transportability and solubility, a phenanthrene structure, a fluorene structure, an indenofluorene structure, a carbazole structure, an indenocarbazole structure, an indolocarbazole structure, a dibenzofuran structure, and a dibenzothiophene structure. At least one selected from the group is preferable, and a carbazole structure or an indolocarbazole structure is more preferable from the viewpoint of durability against electric charges.

The molecular weight of the high Tg compound in the present invention is usually 5000 or less, preferably 4000 or less, more preferably 3000 or less, and most preferably 2000 or less. The molecular weight of the high Tg compound in the present invention is usually 300 or more, preferably 350 or more, and more preferably 400 or more.

The molecular weight of the high-Tg compound is preferably large in view of the difficulty of deterioration in film quality due to gas generation, recrystallization, molecular migration, and the like. On the other hand, the molecular weight of the high Tg compound is preferably small in terms of easy purification of the organic compound and easy dissolution in a solvent.

The Tg of the high Tg compound in the present invention is arbitrary as long as the effect of the present invention is not significantly impaired as long as it is 130°C or higher. The Tg of the high-Tg compound in the present invention is preferably 135°C or higher, more preferably 140°C or higher, from the viewpoint of stabilizing the film during storage at a high temperature. In addition, the Tg of the high Tg compound in the present invention is usually 250°C or less, preferably 200°C or less, more preferably 180°C or less, still more preferably 160°C, from the viewpoint of high solubility in organic solvents. below

For example, in the case of using an organic electroluminescent element for a vehicle-mounted display, etc., the temperature inside the vehicle may exceed 80°C when the vehicle is parked under a blazing sun in summer, so the vehicle-mounted display may exceed 100°C. Reliability in the high-temperature storage test is required. Therefore, a general high-temperature storage test of an organic electroluminescent element is usually performed at 100°C or higher, and is about 120°C at the highest. In addition, changes in film properties and morphology near Tg actually occur gradually before and after Tg. From the above points, the Tg of the high Tg compound in the present invention is 130°C or higher, which is a temperature sufficiently higher than in the storage test. Further, from the viewpoint of further suppressing changes in film properties and morphology in a long-term high-temperature storage test, a higher Tg is more preferable. On the other hand, the Tg of the high Tg compound is preferably low from the viewpoint of solubility in solvents and device stability by suppression of crystallization in the film.

The composition for forming a light emitting layer of the present invention should contain at least one high-Tg compound, but may contain a plurality of them.

<Low Tg compound>

The low-Tg compound of the present invention is a compound exhibiting a Tg of 100°C or less. As a low-Tg compound, it is preferable that it is a compound in which monocyclic compounds bonded to each other through a direct bond and/or a linking group. The compound may have a substituent, and the substituent is not particularly limited, but an alkyl group or an aralkyl group is preferable from the viewpoint of excellent solubility and ink storage stability.

The linking group is usually not particularly limited as long as it is an atom or a substituent that can be used as a material for an organic electroluminescent device. Specifically, examples of the divalent linking group include an oxygen atom, a sulfur atom, an alkylene group, a sulfo group, and a carbonyl group; A nitrogen atom as a trivalent linking group; As the tetravalent linking group, a silicon atom is preferable. Here, the linking group means that a monocyclic compound is bonded to all of the bonding hands. In addition, these linking groups may connect monocyclic compounds, or may connect compounds in which monocyclic compounds bond directly to each other. In addition, the monocyclic compounds connected at this time or the compounds in which monocyclic compounds are directly bonded to each other may have the same structure or different structures. For example, when a nitrogen atom is a linking group and a compound in which monocyclic compounds are directly bonded to each other is an aryl group, triarylamine is indicated, and the three substituents of the triarylamine may be the same or different. As the linking group, a nitrogen atom or an alkylene group is more preferable from the viewpoints that the torsion of adjacent rings is greater, the planarity of the molecule is low, and crystallization by molecular packing is less likely to occur. Further, from the viewpoint of durability against electric charge, a compound containing only a direct bond is more preferable.

As a low-Tg compound, what is necessary is just to select suitably what satisfy|fills the said conditions normally from the compound normally used for the formation of the light emitting layer of an organic electroluminescence element, As a low-Tg material, specifically, monocyclic compounds are directly bonded and/or At least one compound selected from the group consisting of an aromatic structure, an aromatic amine structure, a thiophene structure, a benzylphenyl structure, a pyridine structure, a pyrimidine structure, a triazine structure, an oxadiazole structure, and an imidazole structure. A compound having a structure of is preferred. A compound in which aromatic hydrocarbon monocyclic compounds are bonded to each other through a direct bond and/or a linking group, and a compound having an aromatic structure, an aromatic amine structure, or a benzylphenyl structure is more preferable from the viewpoint of being more excellent in charge transportability.

As the low-Tg compound, a compound in which monocyclic compounds are bonded to each other through a direct bond and/or a linking group is preferable from the viewpoint that the planarity as a molecule is low and crystallization by molecular packing is difficult to occur. On the other hand, from the viewpoint that the effect of hydrogen bonding is small, rotation of the bond is easy, and the planarity of the molecule can be lowered, a compound in which aromatic hydrocarbon monocyclic compounds are bonded directly through a bond and / or a linking group is more preferable. Furthermore, it is preferable that the low-Tg compound contained in the composition for forming a light emitting layer of the present invention contains only a compound in which aromatic hydrocarbon monocyclic compounds are directly bonded to each other in view of excellent charge durability.

In particular, as a low Tg compound in which aromatic hydrocarbon monocyclic compounds are directly bonded, a compound represented by the following formula (A) is preferable.

In Formula (A), R ¹ to R ¹⁵ each independently represent a hydrogen atom, a phenyl group having 6 to 30 carbon atoms, or a monovalent compound in which a monocyclic aromatic hydrocarbon compound is bonded.

The low-Tg compound having the structure of formula (A) has high durability against electric charges and has a structure that easily achieves both molecular motion and stability due to heat or the like. In addition, since the structure of formula (A) is a compound in which only aromatic hydrocarbon monocycles are bonded, gaps between high Tg compounds are readily filled, which is preferable. Further, the structure of formula (A) is preferable because when the high Tg compound has a condensed ring structure of 3 or more rings or a condensed ring structure of 5 or more rings, it is easy to fill the gap between the high Tg compounds generated by the condensed ring. do.

In addition, in the structure of formula (A), when the condensed ring contains an aromatic hydrocarbon ring or an aromatic heterocycle, the affinity with the formula (A), which is an aromatic hydrocarbon compound, increases, and the state in which the gap between the high Tg compounds is filled It is thought that it is more stable, and it is preferable.

In addition, a preferable low-Tg compound in the present invention is a compound in which monocyclic compounds are bonded to each other through a direct bond and/or a linking group. Among these, pyridine-based compounds, pyrimidine-based compounds, and triazine-based compounds, which are materials having excellent electron transport properties and relatively stable structures, are preferable. With these compounds, it becomes possible to suppress deterioration of the light emitting material due to transport of electrons by the light emitting material itself, and to further increase the drive life.

The low-Tg compound in the present invention is a material with excellent electron transport properties and a relatively stable structure in that the light emitting material itself suppresses deterioration of the light emitting material due to transport of electrons and can extend the drive life. it is desirable

On the other hand, the low-Tg compound in the present invention is a material having a structure excellent in hole-transport property in that the light-emitting material itself can suppress deterioration of the light-emitting material due to transport of holes and can extend the drive life. it is desirable

As a structure excellent in hole-transport property, a dicycloalkyl arylamine structure, a cycloalkyl diarylamine structure, and a triarylamine structure are preferable. Among these, from a durable viewpoint, a triarylamine structure is more preferable.

The molecular weight of the low-Tg compound in the present invention is usually 5000 or less, preferably 4000 or less, more preferably 3000 or less, and most preferably 2000 or less. Moreover, the molecular weight of the low-Tg compound in this invention is 300 or more normally, Preferably it is 350 or more, More preferably, it is 400 or more.

The molecular weight of the low-Tg compound is preferably large in view of the difficulty of deterioration in film quality due to gas generation, recrystallization, migration of molecules, and the like. On the other hand, the molecular weight of the low-Tg compound is preferably small in terms of easy purification of the organic compound and easy dissolution in a solvent.

The Tg of the low-Tg compound in the present invention is arbitrary as long as the effect of the present invention is not significantly impaired as long as it is 100°C or less. The Tg of the low-Tg compound in the present invention is preferably 95°C or lower, more preferably 90°C or lower. The Tg of the low-Tg compound in the present invention is usually 60°C or higher, preferably 70°C or higher, more preferably 80°C or higher, still more preferably 85°C or higher.

The Tg of the low-Tg compound in the present invention is preferably low from the viewpoint of solubility in solvents and device stability by suppression of crystallization in the film. On the other hand, the Tg of the low-Tg compound is preferably high from the viewpoints of ensuring non-volatility and thermal stability in element fabrication process and preservation of elements.

The composition for forming a light emitting layer according to the present invention may contain at least one low-Tg compound, but may also contain a plurality of low-Tg compounds.

(organic solvent)

The composition for forming a light emitting layer of the present invention is preferably formed as a light emitting layer using a wet film forming method such as an inkjet method. The organic solvent used in the present invention is not particularly limited as long as it dissolves or disperses light-emitting layer materials such as light-emitting materials and non-light-emitting materials satisfactorily.

As the solubility of the organic solvent, it is preferable to dissolve the luminescent material and the non-luminescent material in an amount of usually 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, respectively, at 25°C and 1 atm. do. Although specific examples of the organic solvent are given below, the organic solvent is not limited to these unless the effect of the present invention is impaired.

Examples of the organic solvent include alkanes such as n-decane, cyclohexane, ethylcyclohexane, decalin, and bicyclohexane; Aromatic hydrocarbons, such as toluene, xylene, methicylene, cyclohexylbenzene, tetramethylcyclohexanone, and tetralin; halogenated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene, and trichlorobenzene; 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, 2, aromatic ethers such as 4-dimethylanisole and diphenyl ether; aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate; alicyclic ketones such as cyclohexanone, cyclooctanone, and pencon; alicyclic alcohols such as cyclohexanol and cyclooctanol; aliphatic ketones such as methyl ethyl ketone and dibutyl ketone; aliphatic alcohols such as butanol and hexanol; aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA); etc. can be mentioned.

Among the above, it is preferably at least one selected from the group consisting of alkanes and/or aromatic hydrocarbons, more preferably toluene, xylene and cyclohexylbenzene. With these, it is non-polar and is not easily affected by moisture, and the material is easy to dissolve and the ink is easy to be stably stored.

These organic solvents may be used individually by 1 type, and may use two or more types in arbitrary combinations and ratios.

Further, in order to obtain a more uniform film, it is preferable that the organic solvent evaporates at an appropriate rate from the liquid film immediately after film formation. For this reason, the boiling point of the organic solvent is usually 80°C or higher, preferably 100°C or higher, and more preferably 120°C or higher. In addition, the boiling point of the organic solvent is usually 270°C or less, preferably 250°C or less, and more preferably 230°C or less.

(About the composition ratio of the composition for forming the light emitting layer)

The composition for forming a light emitting layer of the present invention may contain other components appropriately as long as it contains at least the high Tg compound and the low Tg compound as described above as non-light emitting materials. However, it is necessary that the content of the low-Tg compound (hereinafter simply referred to as the content of the low-Tg compound) with respect to all non-luminescent materials included in the composition for forming a light-emitting layer is 8 to 70% by mass, and that it is 10 to 70% by mass. more preferable The content of the low-Tg compound is 8% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. The content of the low-Tg compound is 80% by mass or less, preferably 70% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, and particularly preferably 35% by mass or less.

The content of the low-Tg compound is preferably high in terms of solubility in solvents, ink retention stability after dissolution, and difficulty in crystallization of the light-emitting layer, making the light-emitting surface uniform and stable. On the other hand, the content of the low-Tg compound is preferably low in view of the fact that it is difficult to change the morphology of the film during high-temperature storage of the element.

The content rate of the high-Tg compound with respect to all the non-luminescent materials contained in the composition for forming the light-emitting layer (hereinafter simply referred to as the content rate of the high-Tg compound) is preferably 10% by mass or more, more preferably 15% by mass or more, and 90 mass % or less is preferable, and 70 mass % or less is more preferable.

Contrary to low Tg compounds, the content of the high-Tg compound is preferably low in terms of solubility in solvents, storage stability after dissolution, difficulty in crystallization of the light-emitting layer, and uniformity and stability of the light-emitting surface, and the high temperature of the element. A high value is preferable from the point where a change in the morphology of the film during storage is difficult to occur.

The content of the light emitting material in the total nonvolatile materials included in the composition for forming the light emitting layer is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 40% by mass or less, and 30% by mass. % or less is more preferred.

(Action mechanism of the present invention)

It is estimated that the heat resistance of the film is improved by including the high-Tg compound, and a uniform film can be formed at the time of film formation by including the low-Tg compound.

High-Tg compounds tend to crystallize at the time of film formation and are rigid compounds, and therefore high-Tg compounds are difficult to come into close contact with each other on a molecular level, thereby reducing the charge transportability of the film. However, it is presumed that if the low-Tg compound is present, the low-Tg compound will fill the gap between the rigid high-Tg compounds, suppress crystallization of the high-Tg compound, and form a uniform film.

Further, when a composition containing a low-Tg compound and a high-Tg compound is wet-formed, it is dried in a state where the low-Tg compound and the high-Tg compound are uniformly mixed. That is, it is considered that a film in which a gap between rigid high Tg compounds is filled with a low-Tg compound can be easily formed, and a uniform film excellent in transportability can be easily formed. In the conventional vacuum heating evaporation method, since materials are deposited as clusters, it is considered that it is difficult for low-Tg compounds to fill gaps between high-Tg compounds.

Further, in the film, since the low-Tg compound exists between the high-Tg compounds, it is thought that a film with high heat resistance in which crystallization of the high-Tg compound is suppressed is determined.

In addition, since heat resistance is insufficient when only a low-Tg compound is used for an organic electroluminescent element, it was thought that storage at a high temperature promotes deterioration of the organic electroluminescent element or accelerates deterioration by driving with electricity. Surprisingly, in the present invention, by mixing a low-Tg compound and a high-Tg compound, an unexpected effect was found that the heat resistance of the organic electroluminescent device is improved by the interaction between the low-Tg compound and the high-Tg compound. This is presumed to be because the thermal motion of the low-Tg compound due to heat during high-temperature storage or heat generation during energized drive is suppressed by the high-Tg compound present in the vicinity of the low-Tg compound.

By including the low-Tg compound, solubility in organic solvents is improved, storage stability of the composition can be secured, crystallization in the film of the organic electroluminescent device can be suppressed, and drive life at room temperature can be shortened. can be long In addition, by including a high-Tg compound, it is possible to suppress changes in film properties and morphology under high-temperature storage at around 100° C., which is a concern due to low-Tg compounds, and stable long drive life that does not change even after high-temperature storage can be obtained. .

The reason why the Tg of the high Tg compound is 130° C. or higher is as described above.

In addition, when the Tg of the low-Tg compound is 100° C. or less, the interaction with the high-Tg compound is suppressed, and the effect of suppressing crystallization of the low-Tg compound tends to be easily expressed. When there is a difference of 30 ° C. or more as in the present invention, it is considered that the effects derived from each other's Tg are sufficiently expressed.

The difference in Tg between the high Tg compound and the low Tg compound is not particularly limited, but is preferably 30°C or higher, more preferably 40°C or higher, and still more preferably 50°C or higher. Moreover, 70 degrees C or less is preferable and 65 degrees C or less is more preferable. When the value is equal to or greater than the lower limit, the Tg difference increases to some extent, and the high-Tg compound becomes less susceptible to the influence of the molecular motion of the low-Tg compound, so that the morphology of the film hardly changes even at a high temperature. Moreover, when it is less than or equal to the above upper limit, the high-Tg compound and the low-Tg compound are more uniformly mixed in the film.

The content of the low-Tg compound is 8 to 70% by mass as described above. When it is 8% by mass or more, there is an influence of the intermolecular interaction of the high Tg compound, and crystallization in the film and the organic solvent is easily suppressed. In addition, when the content is 70% by mass or less, the change in crystallinity caused by the low-Tg compound during high-temperature storage can be absorbed by the remaining less than 30% by mass of other materials, and there is a tendency that the change in morphology of the entire film can be suppressed. there is.

Either the high-Tg compound or the low-Tg compound is a pyrimidine skeleton or a triazine skeleton with high electron transportability and excellent structural stability, and the probability of electron localization on the light emitting material is reduced, and stable light emission can be obtained. Therefore, the effect of increasing the lifespan described above can be sufficiently obtained.

Further, if the low-Tg compound is a compound in which monocyclic compounds are bonded directly and/or via a linking group, the planarity as a molecule is lowered, and crystallization by molecular packing becomes more difficult to occur. Therefore, the effect of suppressing crystallization can be further obtained.

The molecular weight of each non-luminescent material having a content of 1.0% by mass or more relative to the total amount of all non-luminescent materials contained in the composition for forming a light-emitting layer of the present invention is preferably 5000 or less. When the molecular weight is within this range, it is preferable to form a film in a state in which most of the non-luminescent materials are uniformly mixed.

When the high molecular weight compound is small in the film, three-dimensional molecular entanglement is suppressed, and the high Tg compound and the low Tg compound are easily mixed uniformly. As a result, generation of minute regions where low-Tg compounds are gathered is suppressed, and stability during high-temperature storage is easily obtained. In addition, microscopic regions where high Tg compounds are gathered are generated during film formation to suppress crystallization during film formation, making it easier to obtain a uniform film and improving the characteristics of the organic electroluminescent device.

In addition, when the molecular weight is below the upper limit, the solubility of the compound in the solvent is improved, the entanglement of molecular chains in the solvent is suppressed, and impurities (ie, substances causing deterioration) are easily removed.

In this invention, it is preferable that it is 100 degreeC or more, and, as for the weighted average glass transition temperature of all the non-luminescent materials contained in the composition for light emitting layer formation, it is more preferable that it is 115 degreeC or more. The weighted average glass transition temperature is preferably 150°C or lower, and more preferably 145°C or lower. When the weighted average glass transition temperature is 100° C. or higher, the morphology of the film is less likely to change under the influence of heat during high-temperature storage or heat generated in the organic electroluminescent device when energized, that is, the driving life is longer. In addition, when the weighted average glass transition temperature is 150°C or less, gaps between molecules are easily filled, and charge transport properties in the film and thus drive life are improved.

(Other non-luminous materials)

Examples of non-luminescent materials that the composition for forming a light-emitting layer of the present invention may contain in addition to the high-Tg compound and the low-Tg compound include charge transport materials and additives such as antioxidants.

<Third Charge Transport Material>

The composition for forming a light-emitting layer of the present invention may contain a charge transport material that does not belong to either of the high-Tg compound or the low-Tg compound. For convenience, this is referred to as the third charge transport material. As the third charge transport material, a material having a skeleton having excellent charge transport properties is preferable.

As the skeleton having excellent charge transport properties, specifically, an aromatic structure, an aromatic amine structure, a triarylamine structure, a dibenzofuran structure, a naphthalene structure, a phenanthrene structure, a phthalocyanine structure, a porphyrin structure, a thiophene structure, a benzylphenyl structure, flue Orene structure, quinacridone structure, triphenylene structure, carbazole structure, pyrene structure, anthracene structure, phenanthroline structure, quinoline structure, pyridine structure, pyrimidine structure, triazine structure, oxadiazole structure, imidazole structure etc. can be mentioned.

Among them, at least one selected from the group consisting of compounds having a pyridine structure, a pyrimidine structure, and a triazine structure is more preferable, from the viewpoint of being a material with excellent electron transport properties and a relatively stable structure, and a pyrimidine structure, and/or or more preferably a compound having a triazine structure.

The third charge transport material in the present invention is a material having a structure excellent in electron transport properties in that the light emitting material itself can suppress deterioration of the light emitting material due to transport of electrons and can further extend the drive life. it is desirable

Further, compounds having a structure having excellent hole transport properties are also preferred, and among the core skeletons having excellent charge transport properties, a carbazole structure, a dibenzofuran structure, a triarylamine structure, a naphthalene structure, a phenanthrene structure or a pyrene structure have a hole transport property. It is preferable as an excellent structure, and a carbazole structure, a dibenzofuran structure, or a triarylamine structure is more preferable.

The third charge transport material in the present invention is a material having a structure excellent in hole transport properties in that the light emitting material itself can suppress deterioration of the light emitting material due to transport of holes and can extend the drive life. it is desirable

The molecular weight of the third charge transport material in the present invention is arbitrary as long as the effect of the present invention is not significantly impaired. The molecular weight of the third charge transport material in the present invention is usually 5000 or less, preferably 4000 or less, more preferably 3000 or less, and most preferably 2000 or less. Further, the molecular weight of the third charge transport material in the present invention is usually 300 or more, preferably 350 or more, and more preferably 400 or more.

The molecular weight of the third charge transport material is preferably large in view of less likely to cause deterioration in film quality due to gas generation, recrystallization, molecular migration, and the like. On the other hand, the molecular weight of the third charge transport material is preferably small in terms of easy purification of the organic compound and easy dissolution in a solvent.

The composition for forming a light-emitting layer of the present invention preferably contains a third charge transport material that does not belong to either of the high-Tg compound or the low-Tg compound. In addition, two or more types of third charge transport materials may be used.

[Method of Forming Light Emitting Layer]

The light emitting layer according to the present invention is formed by a wet film forming method using the above-described composition for forming a light emitting layer of the present invention.

(Method of Forming Light-Emitting Layer by Wet Film Formation)

In the present invention, the wet film forming method refers to a film forming method, that is, a method of forming a film by employing a wet film forming method as a coating method and drying the coated film. As the coating method, for example, spin coating method, dip coating method, die coating method, bar coating method, blade coating method, roll coating method, spray coating method, capillary coating method, ink jet method, nozzle printing method, screen A printing method, a gravure printing method, a flexographic printing method, etc. are mentioned. Among these film formation methods, a spin coating method, a spray coating method, an inkjet method, a nozzle printing method, and the like are preferable.

In the case of forming the light emitting layer by the wet film forming method, usually, a composition for forming a light emitting layer prepared by dissolving the above-mentioned light emitting material, high Tg compound, low Tg compound, and other materials used as necessary in an appropriate organic solvent is used. It is formed by forming a film and removing the organic solvent by heating, reduced pressure, or the like.

As a method for removing the organic solvent, heating or reduced pressure can be used. As a heating means used in the heating method, a clean oven, a hot plate, or the like is preferable from the point of imparting heat evenly to the entire film.

The heating temperature in the heating step is arbitrary as long as the effect of the present invention is not significantly impaired, but a higher temperature is preferable in terms of shortening the drying time, and a lower temperature is preferable in terms of less damage to the material. .

The upper limit is usually 250°C or less, preferably 200°C or less, and more preferably 150°C or less. The lower limit is usually 30°C or higher, preferably 50°C or higher, and more preferably 80°C or higher. When the temperature is below the upper limit, decomposition or crystallization of the normally used charge transport material or phosphorescent light emitting material can be suppressed. Moreover, by being more than the said lower limit, the removal time of a solvent can be shortened. The heating time in the heating step is appropriately determined depending on the boiling point and vapor pressure of the solvent in the composition for forming a light emitting layer, the heat resistance of the material, and the heating conditions.

[Measurement method of glass transition temperature (Tg)]

The measuring method of Tg in this invention is as follows.

Using a differential scanning calorimeter, measurements were made at a heating rate of 10 °C/min from room temperature of 25 °C to 300 °C, and the central temperature of the inflection point representing the glass transition in the resulting DSC curve was defined as Tg. Measurement conditions are shown below.

<Glass transition point temperature measurement conditions>

Differential Scanning Calorimeter (DSC): Shimadzu DTA-50

Sample amount: about 4 mg

Sample vessel: aluminum pan

atmosphere: atmospheric

Temperature range: room temperature 25°C to 300°C

Heating rate: 10°C/min

The weighted average glass transition temperature is the sum of the Tg of each non-luminescent material obtained by the above method multiplied by the weight ratio of each non-luminescent material for all non-luminescent materials.

[Layer structure and manufacturing method of organic electroluminescence device]

Hereinafter, an example of an embodiment such as a general layer configuration of an organic electroluminescent device according to the present invention and a manufacturing method thereof will be described with reference to FIG. 1 .

1 is a schematic cross-sectional view showing a structural example of an organic electroluminescent device 10 according to the present invention. In FIG. 1, 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, and 5 is a A light emitting layer, 6 represents a hole blocking layer, 7 represents an electron transport layer, 8 represents an electron injection layer, and 9 represents a cathode, respectively.

A known material can be used as a material applied to these structures, and there is no particular limitation, but typical materials and manufacturing methods for each layer are described below as examples. In the case of citing publications, articles, etc., the contents can be appropriately applied and applied within the common sense of those skilled in the art.

(Substrate (1))

The substrate 1 serves as a support for the organic electroluminescent element, and usually a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, or the like is used. Among these, a glass plate and a plate made of a transparent synthetic resin such as polyester, polymethacrylate, polycarbonate, or polysulfone are preferred. The substrate 1 is preferably made of a material having high gas barrier properties in view of the fact that deterioration of the organic electroluminescent element due to outside air is difficult to occur. For this reason, especially when using a material with low gas barrier properties, such as a substrate made of synthetic resin, it is preferable to provide a dense silicon oxide film or the like on at least one surface of the substrate 1 to improve the gas barrier properties.

(Anode (2))

The anode 2 plays a function of injecting holes into the layer on the light emitting layer side. The anode 2 is usually made of a metal such as aluminum, gold, silver, nickel, palladium, or platinum; metal oxides such as oxides of indium and/or tin; metal halides such as copper iodide; It is composed of carbon black and conductive polymers such as poly(3-methylthiophene), polypyrrole, and polyaniline. Formation of the anode 2 is usually performed by a dry method such as a sputtering method or a vacuum deposition method in many cases. In addition, when forming the anode 2 using fine particles of metal such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, conductive polymer fine powder, etc., they are dispersed in an appropriate binder resin solution, and on a substrate It can also be formed by applying to. In addition, in the case of a conductive polymer, a thin film may be directly formed on a substrate by electropolymerization or the anode 2 may be formed by coating a conductive polymer on a substrate (Appl. Phys. Lett., Vol. 60, 2711). Page, 1992).

The anode 2 normally has a single-layer structure, but may have a laminated structure as appropriate. When the anode 2 has a laminated structure, another conductive material may be laminated on the first layer of the anode. The thickness of the anode 2 may be determined according to the required transparency and material. When especially high transparency is required, the thickness at which the transmittance|permeability of visible light becomes 60% or more is preferable, and the thickness at which 80% or more is more preferable. The thickness of the anode 2 is preferably 5 nm or more, preferably 10 nm or more, and usually 1000 nm or less, preferably 500 nm or less. On the other hand, when transparency is unnecessary, the thickness of the anode 2 may be arbitrarily determined according to the required strength, etc. In this case, the anode 2 may have the same thickness as the substrate 1.

When film formation is performed on the surface of the anode 2, impurities on the anode are removed by treatment with ultraviolet rays + ozone, oxygen plasma, argon plasma, etc. before film formation, and the ionization potential is adjusted to improve the hole injection performance It is desirable to improve.

(Hole Injection Layer (3))

A layer that plays a function of transporting holes from the anode side to the light emitting layer side is usually called a hole injection transport layer or a hole transport layer. In the case where there are two or more layers responsible for transporting holes from the anode side to the light emitting layer side, the layer closer to the anode side may be referred to as the hole injection layer 3. The hole injection layer 3 is preferably used from the viewpoint of enhancing the function of transporting holes from the anode to the light emitting layer side. In the case of using the hole injection layer 3, the hole injection layer 3 is usually formed on the anode.

The film thickness of the hole injection layer 3 is usually 1 nm or more, preferably 5 nm or more, and usually 1000 nm or less, preferably 500 nm or less.

The method of forming the hole injection layer 3 may be a vacuum deposition method or a wet film forming method. In terms of excellent film formability, it is preferable to form by a wet film forming method.

The hole injection layer 3 preferably contains a hole-transporting compound, and more preferably contains a hole-transporting compound and an electron-accepting compound. Furthermore, it is preferable to include a cation radical compound in the hole injection layer, and it is particularly preferable to include a cation radical compound and a hole transporting compound.

<Hole-transporting compound>

The composition for forming the hole injection layer usually contains a hole transporting compound to be the hole injection layer 3 . In addition, in the case of the wet film-forming method, a solvent is usually further contained. The composition for forming a hole injection layer preferably has high hole transport properties and can efficiently transport injected holes. For this reason, it is preferable that the hole mobility is high and impurities serving as traps are less likely to occur during production or use. In addition, those having excellent stability, low ionization potential, and high transparency to visible light are preferred. In particular, when the hole injection layer 3 is in contact with the light emitting layer 5, it is preferable not to quench the light emitted from the light emitting layer 5 or to form exciplex with the light emitting layer 5 so as not to lower the luminous efficiency. .

As the hole-transporting compound, a compound having an ionization potential of 4.5 eV to 6.0 eV is preferable from the viewpoint of a charge injection barrier from the anode 2 to the hole injection layer 3. Examples of the hole-transporting compound include aromatic amine compounds, phthalocyanine compounds, porphyrin compounds, oligothiophene compounds, polythiophene compounds, benzyl phenyl compounds, fluorene-linked tertiary amine compounds, and hydrazone compounds. , silazane-based compounds, quinacridone-based compounds, and the like.

Among the exemplary compounds described above, from the viewpoints of amorphousness and visible light transmittance, aromatic amine compounds are preferred, and aromatic tertiary amine compounds are particularly preferred. Here, the aromatic tertiary amine compound is a compound having an aromatic tertiary amine structure, and also includes a compound having a group derived from an aromatic tertiary amine.

The type of the aromatic tertiary amine compound is not particularly limited, but a polymeric compound having a weight average molecular weight of 1,000 or more and 1,000,000 or less (a polymeric compound in which repeating units are connected) is selected from the viewpoint of easy to obtain uniform light emission due to a surface smoothing effect. It is preferable to use Preferable examples of the aromatic tertiary amine high molecular compound include a high molecular compound having a repeating unit represented by the following formula (II).

(In formula (II), Ar ¹ and Ar ² each independently represent an aromatic group which may have a substituent or a heteroaromatic group which may have a substituent. Ar ³ to Ar ⁵ each independently may have a substituent. Represents an aromatic group or a heteroaromatic group which may have a substituent. Y represents a linking group selected from the following linking groups. In addition, in Ar ¹ to Ar ⁵ , two groups bonded to the same N atom combine with each other to form a ring. can also

A linking group is shown below.

(In the above formulas, Ar ⁶ to Ar ¹⁶ each independently represent an aromatic group which may have a substituent or a heteroaromatic group which may have a substituent. R ¹⁰⁵ and R ¹⁰⁶ are each independently a hydrogen atom or an arbitrary substituent indicates.)

As the aromatic group and the heteroaromatic group represented by Ar ¹ to Ar ¹⁶ , a group derived from a benzene ring, a naphthalene ring, a phenanthrene ring, a thiophene ring, or a pyridine ring is preferable from the viewpoints of the solubility, heat resistance, and hole injection/transport property of the polymer compound. , a group derived from a benzene ring or a naphthalene ring is more preferable.

As a specific example of the aromatic tertiary amine high molecular compound which has a repeating unit represented by Formula (II), what was described in the pamphlet of International Publication No. 2005/089024, etc. are mentioned.

<Electron-accepting compound>

The hole injection layer 3 preferably contains an electron-accepting compound because the conductivity of the hole injection layer 3 can be improved by oxidation of the hole-transporting compound.

As the electron-accepting compound, a compound having an oxidizing ability and an ability to accept one electron from the hole-transporting compound described above is preferable, specifically, a compound having an electron affinity of 4 eV or more is preferable, and a compound having an electron affinity of 5 eV or more is more preferable. do.

As such an electron-accepting compound, for example, one selected from the group consisting of triaryl boron compounds, metal halides, Lewis acids, organic acids, onium salts, salts of arylamines and metal halides, and salts of arylamines and Lewis acids, or 2 or more types of compounds etc. are mentioned. Specifically, substituted onium salts of organic groups such as 4-isopropyl-4'-methyldiphenyliodonium tetrakis (pentafluorophenyl) borate and triphenylsulfonium tetrafluoroborate (International Publication 2005/ pamphlet No. 089024); high-valent inorganic compounds such as iron (III) chloride (Japanese Patent Laid-Open No. 11-251067) and ammonium peroxodisulfate; cyano compounds such as tetracyanoethylene; Aromatic boron compounds, such as tris (pentafluorophenyl) borane (Japanese Unexamined-Japanese-Patent No. 2003-31365); fullerene derivatives and iodine; and the like.

<Cation radical compound>

As the cation radical compound, an ionic compound containing a cation radical, which is a chemical species obtained by removing one electron from a hole-transporting compound, and a counter anion, is preferable. However, when the cation radical is derived from a hole-transporting high molecular compound, the cation radical has a structure in which one electron is removed from the repeating unit of the high molecular compound.

The cation radical is preferably a chemical species obtained by removing one electron from the compound described above as a hole-transporting compound. As the hole-transporting compound, a chemical species obtained by removing one electron from a preferred compound is suitable in view of amorphousness, visible light transmittance, heat resistance, solubility, and the like.

Here, the cation radical compound can be produced by mixing the hole-transporting compound and the electron-accepting compound described above. That is, by mixing the hole-transporting compound and the electron-accepting compound, electron transfer occurs from the hole-transporting compound to the electron-accepting compound, and a cation ion compound containing a cation radical of the hole-transporting compound and a counteranion is generated.

A cationic radical compound derived from a polymer compound such as PEDOT/PSS (Adv. Mater., 2000, Vol. 12, page 481) or emeraldine hydrochloride (J. Phys. Chem., 1990, Vol. 94, page 7716), It is also produced by oxidative polymerization (dehydrogenation polymerization).

Oxidative polymerization here refers to chemically or electrochemically oxidizing a monomer in an acidic solution using peroxodisulfate or the like. In the case of this oxidative polymerization (dehydrogenation polymerization), the polymer is formed by oxidizing the monomer, and a cation radical is generated by removing one electron from the repeating unit of the polymer, which uses an acidic solution-derived anion as a counter anion.

<Formation of Hole Injection Layer 3 by Wet Film Formation>

In the case of forming the hole injection layer 3 by the wet film forming method, usually, a material to be the hole injection layer 3 is mixed with a soluble solvent (a solvent for the hole injection layer) to form a composition for forming the hole injection layer (for forming the hole injection layer). composition) is prepared, and this composition for forming the hole injection layer is applied onto a layer corresponding to the lower layer of the hole injection layer 3 (usually, the anode 2), formed into a film, and dried.

The concentration of the hole-transporting compound in the composition for forming a hole-injection layer is arbitrary as long as the effects of the present invention are not significantly impaired, but a lower one is preferable from the viewpoint of film thickness uniformity, and on the other hand, the hole-injection layer In terms of (3), where defects are less likely to occur, a higher one is preferable. Specifically, it is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and on the other hand, preferably 70% by mass or less, and more preferably 60% by mass or less, It is especially preferable that it is 50 mass % or less.

Examples of the solvent include ether-based solvents, ester-based solvents, aromatic hydrocarbon-based solvents, and amide-based solvents.

Examples of the ether solvent include aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol-1-monomethyl ether acetate (PGMEA), 1,2-dimethoxybenzene, and 1,3-dimethoxy aromatic ethers such as benzene, anisole, phenetol, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole; and the like. .

Examples of the ester solvent include aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate.

Examples of the aromatic hydrocarbon solvent include toluene, xylene, cyclohexylbenzene, 3-isopropylbiphenyl, 1,2,3,4-tetramethylbenzene, 1,4-diisopropylbenzene, and methylnaphthalene. can Examples of the amide solvent include N,N-dimethylformamide and N,N-dimethylacetamide.

In addition to these, dimethyl sulfoxide and the like can also be used.

In the formation of the hole injection layer 3 by the wet film forming method, usually, after preparing a composition for forming the hole injection layer, this is applied to a layer corresponding to the lower layer of the hole injection layer 3 (usually, the anode 2). It is performed by coating and forming a film on the surface and drying. After forming the hole injection layer 3, the coated film is usually dried by heating or drying under reduced pressure.

<Formation of hole injection layer 3 by vacuum deposition method>

In the case of forming the hole injection layer 3 by vacuum deposition, usually one or more of the constituent materials of the hole injection layer 3 (the aforementioned hole transporting compound, electron accepting compound, etc.) are placed in a vacuum container. Place them in the installed crucible (when two or more types of materials are used, usually put each in a separate crucible), evacuate the inside of the vacuum container to about 10 ^-4 Pa with a vacuum pump, and then heat the crucible (two or more types of materials). In the case of using materials, usually by heating each crucible), evaporating while controlling the evaporation amount of the material in the crucible (when using two or more types of materials, evaporating while controlling the evaporation amount independently of each material), A hole injection layer 3 is formed on the anode on the substrate placed facing the . In the case of using two or more types of materials, the hole injection layer 3 may be formed by putting the mixture in a crucible, heating and evaporating.

The degree of vacuum during vapor deposition is not limited as long as the effect of the present invention is not significantly impaired, but is usually 0.1×10 ^-6 Torr (0.13×10 ^-4 Pa) or more, 9.0×10 ^-6 Torr (12.0×10 ^-4 Pa) or less. The deposition rate is not limited as long as the effect of the present invention is not significantly impaired, but is usually 0.1 Å/sec or more and 5.0 Å/sec or less. The film formation temperature during vapor deposition is not limited as long as the effect of the present invention is not significantly impaired, but is preferably 10°C or higher and 50°C or lower.

(hole transport layer (4))

The hole transport layer 4 is a layer that serves to transport holes from the anode side to the light emitting layer side. Although the hole transport layer 4 is not an essential layer in the organic electroluminescent device of the present invention, it is preferable to use this layer in terms of enhancing the function of transporting holes from the anode 2 to the light emitting layer 5. . When using the hole transport layer 4, the hole transport layer 4 is normally formed between the anode 2 and the light emitting layer 5. In addition, when the hole injection layer 3 described above is present, it is formed between the hole injection layer 3 and the light emitting layer 5 .

The film thickness of the hole transport layer 4 is usually 5 nm or more, preferably 10 nm or more, and usually 300 nm or less, preferably 100 nm or less.

The formation method of the hole transport layer 4 may be a vacuum deposition method or a wet film forming method. In terms of excellent film formability, it is preferable to form by a wet film forming method.

The hole transporting layer 4 usually contains a hole transporting compound to be the hole transporting layer 4 . As the hole-transporting compound contained in the hole-transporting layer 4, in particular, two or more tertiary amines represented by 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl are included. starburst structures such as aromatic diamines in which two or more condensed aromatic rings are substituted with nitrogen atoms (Japanese Patent Laid-Open Publication No. 5-234681), 4,4',4"-tris(1-naphthylphenylamino)triphenylamine, etc. Aromatic amine compounds having (J. Lumin., Vol. 72-74, pp. 985, 1997), aromatic amine compounds containing tetramers of triphenylamine (Chem. Commun., pp. 2175, 1996), 2, Spiro compounds such as 2',7,7'-tetrakis-(diphenylamino)-9,9'-spirobifluorene (Synth. Metals, Vol. 91, p. 209, 1997), 4,4'- and carbazole derivatives such as N,N'-dicarbazole biphenyl, etc. Further examples thereof include polyvinylcarbazole, polyvinyltriphenylamine (Japanese Patent Laid-Open No. 7-53953), tetraphenylbenzidine. Polyarylene ether sulfone containing (Polym. Adv. Tech., Vol. 7, p. 33, 1996) and the like can also be preferably used.

<Formation of Hole Transport Layer 4 by Wet Film Formation>

In the case of forming the hole-transporting layer 4 by the wet film-forming method, the hole-injecting layer-forming composition is used instead of the hole-injecting layer-forming composition in the same manner as in the case of forming the hole-injecting layer 3 described above by the wet film-forming method. is formed using

In the case of forming the hole transport layer 4 by the wet film forming method, the composition for forming the hole transport layer usually further contains a solvent. As the solvent used in the composition for forming a hole transport layer, the same solvent as the solvent used in the composition for forming a hole injection layer described above can be used.

The concentration of the hole-transporting compound in the composition for forming a hole-transport layer can be set within the same range as the concentration of the hole-transporting compound in the composition for forming a hole-injection layer.

Formation of the hole transport layer 4 by the wet film forming method can be performed in the same manner as the method of forming the hole injection layer 3 described above.

<Formation of hole transport layer 4 by vacuum deposition method>

Also in the case of forming the hole-transporting layer 4 by vacuum evaporation, in the same manner as in the case of forming the above-described hole-injection layer 3 by vacuum evaporation, a composition for forming a hole-transporting layer is used instead of a composition for forming a hole-injecting layer. can be formed using Film formation conditions such as vacuum degree, deposition rate and temperature during deposition can be formed under the same conditions as during vacuum deposition of the hole injection layer 3 .

(Light emitting layer (5))

The light-emitting layer 5 is a layer that functions to emit light by recombination of holes injected from the anode 2 and electrons injected from the cathode 9 when an electric field is applied between the pair of electrodes. The light emitting layer 5 is a layer formed between the anode 2 and the cathode 9, and the light emitting layer 5 includes the hole injection layer 3 and the cathode when the hole injection layer 3 is present on the anode 2. (9), and when there is a hole transport layer (4) on the anode (2), it is formed between the hole transport layer (4) and the cathode (9).

The film thickness of the light emitting layer 5 is arbitrary as long as the effects of the present invention are not significantly impaired, but a thick film is preferable from the viewpoint that defects are less likely to occur in the film, and on the other hand, a thin film is preferable from the viewpoint that the driving voltage is easily lowered. do. Specifically, it is usually 3 nm or more, preferably 5 nm or more, and usually 200 nm or less, preferably 100 nm or less.

In addition, two or more light emitting layers may be provided in the organic electroluminescent element.

Details of the light emitting layer 5 are as described above.

In the case of forming light emitting layers other than the light emitting layer according to the present invention by vacuum deposition, they are formed as follows.

<Formation method of light emitting layer by vacuum deposition method>

In the case of forming the light emitting layer by the vacuum deposition method, usually, the constituent materials of the light emitting layer (the light emitting material, non-emitting material, etc.) are put into separate crucibles installed in a vacuum container, respectively, and the inside of the vacuum container is vacuum pumped to 10 ^- After exhausting to about ⁴ Pa, each crucible is heated, and the material in each crucible is evaporated while independently controlling the amount of evaporation, so that a light emitting layer is formed on a substrate or the like placed facing each crucible. Alternatively, the light emitting layer may be formed by putting a mixture of constituent materials into one crucible, heating and evaporating.

The degree of vacuum during vapor deposition is not limited as long as the effect of the present invention is not significantly impaired, but is usually 0.1×10 ^-6 Torr (0.13×10 ^-4 Pa) or more, 9.0×10 ^-6 Torr (12.0×10 ^-4 Pa) or less. The deposition rate is not limited as long as the effect of the present invention is not significantly impaired, but is usually 0.1 Å/sec or more and 5.0 Å/sec or less. The film formation temperature during vapor deposition is not limited as long as the effect of the present invention is not significantly impaired, but is preferably 10°C or higher and 50°C or lower.

(Hole blocking layer (6))

A hole blocking layer 6 may be provided between the light emitting layer 5 and the electron injection layer 8 described later. The hole blocking layer 6 is a layer laminated on the light emitting layer 5 so as to be in contact with the interface on the cathode side of the light emitting layer 5 .

The hole-blocking layer 6 serves to block holes moving from the anode 2 from reaching the cathode 9, and efficiently transports electrons injected from the cathode 9 toward the light emitting layer 5. has a role to play As the physical properties required of the material constituting the hole-blocking layer 6, electron mobility is high and hole mobility is low, energy gap (difference between HOMO and LUMO) is large, and the triplet excitation level (T1) is high. can hear

As a material for the hole-blocking layer 6 that satisfies these conditions, for example, bis(2-methyl-8-quinolinolato)(phenolato)aluminum, bis(2-methyl-8-quinolinolato) Mixed ligand complexes such as (triphenylsilanolato)aluminum, bis(2-methyl-8-quinolato)aluminum-μ-oxo-bis-(2-methyl-8-quinolinolato)aluminum dinuclear metal Metal complexes such as complexes, styryl compounds such as distyrylbiphenyl derivatives (Japanese Patent Laid-Open No. 11-242996), 3-(4-biphenylyl)-4-phenyl-5(4-tert-butylphenyl) Triazole derivatives such as -1,2,4-triazole (Japanese Patent Laid-Open No. 7-41759), phenanthroline derivatives such as basocuproin (Japanese Patent Laid-Open No. 10-79297), etc. can Further, compounds having at least one pyridine ring having positions 2, 4 and 6 described in the pamphlet of International Publication No. 2005/022962 are also suitable as a material for the hole-blocking layer 6.

The formation method of the hole-blocking layer 6 is not limited, and it can be formed similarly to the formation method of the light emitting layer 5 mentioned above.

The film thickness of the hole-blocking layer 6 is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.3 nm or more, preferably 0.5 nm or more, and usually 100 nm or less, preferably 50 nm or less. am.

(electron transport layer 7)

The electron transport layer 7 is provided between the light emitting layer 5 and the electron injection layer 8 for the purpose of further improving the current efficiency of the device.

The electron transport layer 7 is a compound capable of efficiently injecting electrons from the cathode 9 or the electron injection layer 8 between electrodes to which an electric field is applied and transporting the electrons efficiently in the direction of the light emitting layer 5. is formed with

As the electron-transporting compound used for the electron-transporting layer 7, a compound that has high electron injection efficiency from the cathode 9 or the electron-injecting layer 8 and can efficiently transport the injected electrons is usually preferable. Specific examples of the electron-transporting compound include metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393), metal complexes of 10-hydroxybenzo[h]quinoline, and oxa Diazole derivatives, distyrylbiphenyl derivatives, silole derivatives, 3-hydroxyflavone metal complexes, 5-hydroxyflavone metal complexes, benzoxazole metal complexes, benzothiazole metal complexes, trisbenzimidazolylbenzene (US Patent No. 5645948 specification), quinoxaline compound (Japanese Patent Laid-Open No. 6-207169), phenanthroline derivative (Japanese Patent Laid-Open No. 5-331459), 2-t-butyl-9,10-N,N' -Dicyanoantradimine, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide, and the like.

The film thickness of the electron transport layer 7 is usually 1 nm or more, preferably 5 nm or more, and usually 300 nm or less, preferably 100 nm or less.

The electron transport layer 7 is formed by laminating on the hole blocking layer 6 by a wet film forming method or a vacuum deposition method in the same manner as described above. Usually, a vacuum deposition method is used.

(electron injection layer 8)

An electron injection layer 8 may be provided between the cathode 9 and the electron transport layer 7 or the light emitting layer 5 . The electron injection layer 8 serves to efficiently inject electrons injected from the cathode 9 into the electron transport layer 7 or the light emitting layer 5 .

In order to perform electron injection efficiently, the material forming the electron injection layer 8 is preferably a metal having a low work function. Examples include alkali metals such as sodium and cesium, alkaline earth metals such as barium and calcium, and the like. As for the film thickness, 0.1 nm or more and 5 nm or less are preferable normally.

In addition, alkali metals such as sodium, potassium, cesium, lithium, and rubidium are doped into organic electron transport materials represented by nitrogen-containing heterocyclic compounds such as vasophenanthroline and metal complexes such as aluminum complexes of 8-hydroxyquinoline. (Described in Japanese Unexamined Patent Publication No. 10-270171, Japanese Unexamined Patent Publication No. 2002-100478, Japanese Unexamined Patent Publication No. 2002-100482, etc.), it is also possible to achieve both excellent film quality with improved electron injection and transport properties. It is desirable because it

The film thickness is usually 5 nm or more, preferably 10 nm or more, and usually 200 nm or less, preferably 100 nm or less.

The electron injection layer 8 is formed by laminating on the light emitting layer 5 or the hole blocking layer thereon by a wet film forming method or a vacuum deposition method.

Details in the case of the wet film forming method are the same as in the case of the light emitting layer 5 described above.

(cathode (9))

The cathode 9 serves to inject electrons into a layer on the side of the light emitting layer (such as the electron injection layer 8 or the light emitting layer 5). As the material of the cathode 9, it is possible to use the material used for the anode 2, but in performing electron injection efficiently, it is preferable to use a metal with a low work function, for example tin, Metals such as magnesium, indium, calcium, aluminum, and silver or alloys thereof are used. Specific examples include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy.

From the point of view of device stability, it is preferable to protect the cathode 9 containing a metal having a low work function by laminating a metal layer having a high work function and being stable against the atmosphere on the cathode 9 . Examples of the metal to be laminated include metals such as aluminum, silver, copper, nickel, chromium, gold, and platinum.

The film thickness of the negative electrode is usually the same as that of the positive electrode 2 .

(other floors)

The organic electroluminescent element of the present invention may have another layer as long as the effects of the present invention are not significantly impaired. That is, between the anode 2 and the cathode 9, you may have the other arbitrary layer mentioned above.

<Other element configurations>

It is also possible to stack the cathode, electron injection layer, light emitting layer, hole injection layer, and anode in the order of the structure opposite to the above description, that is, on the substrate.

Example

Next, the present invention will be described more specifically by examples, but the present invention is not limited to the description of the following examples, unless the gist thereof is exceeded.

(Example 1)

An organic electroluminescent device having the configuration shown in FIG. 1 was fabricated.

<Anode>

An indium-tin oxide (ITO) transparent conductive film with a thickness of 70 nm is deposited on a substrate 1 made of glass (sputter-formed product, sheet resistance 15 Ω) and patterned into 2 mm wide stripes by ordinary photolithography technology. Thus, the anode 2 was formed. The substrate 1 (ITO substrate) on which the anode 2 was formed was cleaned by ultrasonic cleaning with pure water and water washing with pure water in that order, then dried by nitrogen blowing, and finally subjected to ultraviolet ozone cleaning treatment.

<Hole injection layer>

Next, the hole injection layer 3 was formed by a wet film forming method as follows.

As the hole-transporting compound, 2.0% by mass of a high molecular compound (weight average molecular weight: 52000) having a repeating structure represented by the following formula (P1), and 4-isopropyl-4'-methyldiphenyliodonium tetrakis as an electron-accepting compound. A composition for forming a hole injection layer was prepared by dissolving 0.4% by mass of (pentafluorophenyl)borate in ethyl benzoate, and the composition for forming a hole injection layer was formed into a film on the ITO substrate by spin coating, and By heating and drying, a hole injection layer 3 having a film thickness of 32 nm was formed. Film formation conditions were as follows.

<Conditions for Film Formation>

Spin coat conditions: spinner speed 500 rpm/2 seconds → 2100 rpm/30 seconds

Heating and drying conditions: 1 hour left in a clean oven at 230 ° C.

<Hole Transport Layer>

Next, on the formed hole injection layer 3, a hole transport layer 4 was formed by a wet film forming method as follows.

As a crosslinkable compound, a polymer compound (HT-1) (weight average molecular weight: 53000) having a repeating structure shown below was dissolved in cyclohexylbenzene as a solvent to prepare a composition for forming a hole transport layer. The concentration of the high molecular compound (HT-1) in the composition for forming a hole transport layer was 2.0% by mass.

The composition for forming the hole transport layer is formed into a film on the hole injection layer 3 by spin coating and further heat-dried to cause a crosslinking reaction of the polymer compound (HT-1) and cure it, thereby forming a hole having a film thickness of 21 nm. A transport layer 4 was formed. Film formation conditions were as follows.

<Conditions for Film Formation>

Spin coat conditions: spinner speed 500 rpm/2 seconds → 2900 rpm/120 seconds

Heating and drying conditions: left on a hot plate at 230 ° C. for 1 hour

<Emitting layer>

Next, on the formed hole transport layer 4, a light emitting layer 5 was formed as follows. The compounds (HH-1), (HH-2), (H-1), (LH-1) and (D-1) shown below were mixed in a mass ratio of 35:20:35:10:15, A composition for forming a light emitting layer was prepared by dissolving the mixture in xylene to a concentration of 3.45% by mass, and the composition for forming a light emitting layer was formed into a film on the hole transport layer 4 under a nitrogen atmosphere by spin coating, followed by heating and drying , a light emitting layer 5 having a film thickness of 59 nm was formed. Film formation conditions were as follows.

<Conditions for Film Formation>

Spin coat conditions: spinner speed 500 rpm/2 seconds → 1700 rpm/120 seconds

Heating and drying conditions: left on a hot plate at 120 ° C. for 20 minutes

In addition, the Tg of the compounds (HH-1), (HH-2), (H-1) and (LH-1) are 159 ° C, 142 ° C, 113 ° C and 90 ° C, respectively, and are also non-luminescent materials. In terms of this, (HH-1) and (HH-2) correspond to the high Tg compound of the present invention, and (LH-1) correspond to the low Tg compound of the present invention. The low-Tg compound (LH-1) has a pyrimidine skeleton and is a compound in which monocyclic compounds are bonded directly and/or via a linking group.

The molecular weights of each compound are 968.4, 866.3, 636.3, 841.4 and 1363.9 for (HH-1), (HH-2), (H-1), (LH-1) and (D-1), respectively, all molecular weights. It was less than 5000. In addition, the content of the low-Tg compound with respect to the total amount of all non-luminescent materials included in the composition for forming a light emitting layer was 10% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 133°C.

<Hole Blocking Layer>

Next, on the formed light emitting layer 5, a compound (HB-1) shown below was formed as a hole-blocking layer 6 by vacuum deposition to a film thickness of 10 nm.

<Electron transport layer>

Next, on the formed hole-blocking layer 6, a compound (ET-1) shown below was formed as an electron transport layer 7 by a vacuum deposition method to a film thickness of 20 nm.

<Electron Injection Layer/Cathode>

Here, the element subjected to deposition up to the electron transport layer 7 is once taken out into the air from the vacuum deposition apparatus, and a 2 mm wide stripe shadow is formed as a mask for cathode deposition in a shape orthogonal to the ITO stripe serving as the anode. A mask is brought into close contact with the element, installed in a separate vacuum evaporation apparatus, and lithium fluoride (LiF) is applied as an electron injection layer 8 with a film thickness of 0.5 nm by the same vacuum evaporation method as for the electron transport layer 7, followed by a cathode 9 ), aluminum was laminated so as to have a film thickness of 80.0 nm.

<Sealing>

Then, in order to prevent deterioration of the element due to moisture in the atmosphere or the like during storage, sealing treatment was performed by the method described below.

In a nitrogen glove box connected to a vacuum evaporation apparatus, a photocurable resin was applied in a width of about 1 mm to the outer periphery of a glass plate having a size of 23 mm x 23 mm, and a moisture getter sheet was placed in the central portion. The substrate on which the formation of the cathode was completed was bonded so that the deposited surface faced the desiccant sheet. Thereafter, only the area where the photocurable resin was applied was irradiated with ultraviolet light, and the resin was cured. As a result, an organic electroluminescent device having a light emitting area portion having a size of 2 mm x 2 mm was obtained.

(Example 2)

In Example 1, compounds (HH-2), (LH-1), (LH-2), (H-1) and (D-1) are used as the non-emitting material and the light-emitting material included in the composition for forming the light emitting layer. ) was mixed in a mass ratio of 15:15:15:55:15, but an organic electroluminescent device was produced in the same manner as in Example 1. In addition, the compound (LH-2) was a compound having a structure shown below, a Tg of 87°C, and a molecular weight of 762.3. In addition, the content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 110°C.

(Example 3)

In Example 1, the compounds (HH-1), (H-2), (H-3), (LH-1) and (D-1) as the non-emitting material and the light-emitting material included in the composition for forming the light emitting layer ) was mixed at a mass ratio of 35:15:35:15:15, but an organic electroluminescent device was produced in the same manner as in Example 1. In addition, compounds (H-2) and (H-3) are compounds having structures shown below, Tg's were 129°C and 109°C, respectively, and molecular weights were 791.3 and 1157.5, respectively. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light-emitting layer was 15% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 127°C.

(Example 4)

In Example 1, compounds (HH-1), (LH-1) and (D-1) were mixed at a mass ratio of 70:30:15 as the non-emitting material and the emitting material included in the composition for forming the light emitting layer. An organic electroluminescent device was produced in the same manner as in Example 1 except for changing to the one. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 138°C.

(Example 5)

In Example 1, (HH-1), (H-2), (LH-1) and (D-1) were used as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer, 70:15: An organic electroluminescent device was produced in the same manner as in Example 1 except that the mixture was mixed at a mass ratio of 15:15. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light emitting layer was 15% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 144°C.

(Example 6)

In Example 1, (HH-1), (H-3), (LH-1) and (D-1) were used as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer, 35:35: An organic electroluminescent device was produced in the same manner as in Example 1 except that the mixture was mixed at a mass ratio of 30:15. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials included in the composition for forming a light emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 121°C.

(Comparative Example 1)

In Example 1, (LH-1), (LH-2), (H-3) and (D-1) were used as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer, 30:35: An organic electroluminescent device was produced in the same manner as in Example 1 except that the mixture was mixed at a mass ratio of 35:15. The weighted average glass transition temperature of all non-luminescent materials was 96°C.

(Comparative Example 2)

In Example 1, (HH-1), (HH-2) and (D-1) were mixed at a mass ratio of 70:30:15 as the non-luminescent material and the luminescent material included in the composition for forming a light emitting layer. An organic electroluminescent device was fabricated in the same manner as in Example 1 except for changing to that. The weighted average glass transition temperature of the entire non-luminescent material was 154°C.

<Evaluation of drive life of organic electroluminescent device>

Each organic electroluminescent device obtained in Examples 1 to 6 and Comparative Examples 1 and 2 was stored in a thermostat at 100°C for 72 hours, then driven at 15 mA/cm 2 , and the luminance was 15% when converted to 7000 cd/m 2 The decay life (LT85) was calculated. Then, among the comparative examples, the relative value when LT85 of Comparative Example 2 having a long LT85 was set to 1 (hereinafter referred to as "LT85 after heating") was determined. Table 1 shows the composition ratio of the composition for forming the light emitting layer of each Example and Comparative Example, and the evaluation results of the drive life.

(Example 7)

An organic electroluminescent device having the configuration shown in FIG. 2 was fabricated.

<Emitting layer>

As in Example 1, the hole transport layer 4 is formed from the anode, and as non-luminescent materials and luminescent materials included in the composition for forming a light emitting layer, (HH-3), (H-1), (LH-2) and ( D-1) was mixed in a mass ratio of 35:35:30:15, but a light emitting layer was formed in the same manner as in Example 1 except for changing. In addition, the compound (HH-3) is a compound having a structure shown below, a Tg of 132°C, and a molecular weight of 868.1. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 112°C.

<Electron transport layer>

Next, on the formed light-emitting layer 5, a mixture obtained by mixing compound ET-2 and compound 1 shown below at a mass ratio of 2:3 was formed as an electron transport layer 7 by vacuum deposition so as to have a film thickness of 20 nm. In addition, unlike Example 1, the hole blocking layer 6 was not formed.

<Cathode/Sealing>

Next, after laminating aluminum as the cathode 9 so as to have a film thickness of 80.0 nm, a sealing treatment was performed in the same manner as in Example 1. Also, unlike Example 1, the electron injection layer 8 was not formed.

(Example 8)

In Example 7, the compounds (HH-1), (LH-3) and (D-1) as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer were mixed in a mass ratio of 70:30:15. An organic electroluminescent device was produced in the same manner as in Example 7 except for changing to that. In addition, the compound (LH-3) was a compound having a structure shown below, a Tg of 95°C, and a molecular weight of 586.2. In addition, the content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light-emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 140°C.

(Example 9)

In Example 7, the compounds (HH-1), (LH-1), (LH-3) and (D-1) as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer were 70:15: An organic electroluminescent device was produced in the same manner as in Example 7 except that the mixture was mixed at a mass ratio of 15:15. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light-emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 139°C.

(Example 10)

In Example 7, the compounds (HH-1), (LH-1) and (D-1) as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer were mixed at a mass ratio of 70:30:15. An organic electroluminescent device was produced in the same manner as in Example 7 except for changing to that. The content of the low-Tg compound with respect to the total amount of all non-luminescent materials contained in the composition for forming a light emitting layer was 30% by mass, and the weighted average glass transition temperature of all non-luminescent materials was 138°C.

(Comparative Example 3)

In Example 7, the compounds (HH-1), (LH-4) and (D-1) as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer were mixed in a mass ratio of 70:30:15. An organic electroluminescent device was produced in the same manner as in Example 7 except for changing to that. In addition, the compound (LH-4) is a compound having a structure shown below, a Tg of 95°C, and a molecular weight of 930.2. In addition, the weighted average glass transition temperature of all the non-luminescent materials was 140°C.

(Comparative Example 4)

In Example 7, compounds (HH-1), (LH-5) and (D-1) as non-emitting materials and light emitting materials included in the composition for forming a light emitting layer were mixed in a weight ratio of 70:30:15. An organic electroluminescent device was produced in the same manner as in Example 7 except for changing to that. In addition, the compound (LH-5) is a compound having a structure shown below, a Tg of 86°C, and a molecular weight of 612.8. In addition, the weighted average glass transition temperature of all non-luminescent materials was 137°C.

(Comparative Example 5)

In Example 7, the compounds (HH-1), (LH-1) and (D-1) as the non-luminescent material and the luminescent material included in the composition for forming the light emitting layer were mixed in a mass ratio of 95:5:15. An organic electroluminescent device was produced in the same manner as in Example 7 except for changing to that. In addition, the weighted average glass transition temperature of all non-luminescent materials was 156°C.

<Evaluation of drive life of organic electroluminescent device>

Each organic electroluminescent device obtained in Examples 7 to 10 and Comparative Examples 3 to 5 was stored in a thermostat at 100°C for 72 hours, then driven at 15 mA/cm 2 , and the luminance was 15% when converted to 7000 cd/m 2 . The decay life (LT85) was calculated. And "LT85 after heating" was calculated|required as a relative value when LT85 of Comparative Example 5 which had the longest LT85 among comparative examples was 1. Table 2 shows the composition ratio of the composition for forming the light emitting layer of each Example and Comparative Example, and the evaluation results of the drive life.

In Table 1, in Examples 1 to 6 containing a high-Tg compound and a low-Tg compound as non-luminescent materials, Comparative Examples 1 and 2 containing only either a high-Tg compound or a low-Tg compound as non-luminescent materials , it is shown that LT85 is large and the voltage is also low even after heating.

In Table 2, Examples 7 to 10 containing a material having a pyrimidine skeleton or a triazine skeleton as a non-luminescent material and having a low Tg compound content in a specific range had a large LT85. On the other hand, in Comparative Examples 3 and 4 containing neither a material having a pyrimidine skeleton nor a material having a triazine skeleton as non-luminescent materials, the LT85 after heating is small. Further, in Comparative Example 5 in which a material having a pyrimidine skeleton or a triazine skeleton was included as the non-luminescent material, but the content of the low Tg compound was out of the specific range, the voltage after heating was high.

From the above, it can be seen that Examples 1 to 10 obtained high characteristics even after heating, and were excellent organic electroluminescent devices even after heating.

The present invention is a composition for forming a light emitting layer of an organic electroluminescent device, and various fields in which the organic electroluminescent device is used, such as a flat panel display (for example, for an OA computer or a wall-mounted television) or a light source utilizing the characteristics of a surface light emitting body (For example, a light source for a copying machine, a backlight source for a liquid crystal display or instruments), a display panel, a sign lamp, and a lighting device.

1: Substrate
2: anode
3: hole injection layer
4: hole transport layer
5: light emitting layer
6: hole blocking layer
7: electron transport layer
8: electron injection layer
9: cathode
10: organic electroluminescent element

Claims (9)

A composition for forming a light emitting layer of an organic electroluminescent device comprising a light emitting material, a non-light emitting material and an organic solvent,
The non-luminescent material includes a high-Tg compound having a glass transition temperature of 130°C or higher and a low-Tg compound having a glass transition temperature of 100°C or lower;
The content of the low Tg compound relative to all of the non-luminescent materials is 8 to 70% by mass;
A composition for forming a light emitting layer, wherein at least one of the non-emitting materials has a pyrimidine skeleton or a triazine skeleton. The composition for forming a light emitting layer according to claim 1, wherein the molecular weight of all the non-light emitting materials having a content of 1.0% by mass or more relative to the total amount of all the non-light emitting materials contained in the composition for forming a light emitting layer is 5000 or less. The composition for forming a light emitting layer according to claim 1 or 2, wherein the molecular weight of all of the light emitting materials is 5000 or less. The composition for forming a light emitting layer according to claim 1 or 2, wherein the material having a pyrimidine skeleton or a triazine skeleton included in the composition for forming a light emitting layer is the high Tg compound and/or the low Tg compound. The composition for forming a light emitting layer according to claim 1 or 2, wherein a weighted average glass transition temperature of all of the non-light emitting materials included in the composition for forming a light emitting layer is 100°C or higher. The composition for forming a light emitting layer according to claim 1 or 2, wherein the low-Tg compound is a compound in which monocyclic compounds are bonded directly or through a linking group. The composition for forming a light emitting layer according to claim 1 or 2, wherein the low-Tg compound includes only compounds in which aromatic hydrocarbon monocyclic compounds are bonded directly or through a linking group. The composition for forming a light emitting layer according to claim 1 or 2, wherein the low Tg compound is a compound represented by the following structural formula (A).

[In Formula (A), R ¹ to R ¹⁵ each independently represent a hydrogen atom, a phenyl group having 6 to 30 carbon atoms, or a monovalent compound in which a monocyclic aromatic hydrocarbon compound is bonded.] An organic electroluminescent device having a light emitting layer formed by wet film formation using the composition for forming a light emitting layer according to claim 1 or 2.

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