JP2010192476A - Organic electric-field light emitting device, organic el display, organic el illumination, and organic el signal apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electric-field light-emitting device that includes at least one organic layer formed by a wet film-forming method. <P>SOLUTION: The organic electric-field light-emitting device includes a positive electrode, a first organic layer, a light-emitting layer provided adjacently to the first organic layer, and a negative electrode in this order. The first organic layer and the light-emitting layer are formed by a wet film-forming method. The first organic layer is a layer formed by insolubilizing a compound containing a dissociable group or a group expressed by formula (1) (in the formula (1), a benzocyclobutene ring may have substituent groups; the substituent groups may form a ring by being bonded to each other). The light-emitting layer is an organic electric-field light-emitting device made of a low-molecular compound whose molecular weight is ≤5,000 and satisfies formula (2): 0.6≤n<SP>H</SP>/n<SP>E</SP>≤1.4 (in the formula (2), n<SP>H</SP>represents the refractive index of the first organic layer while n<SP>E</SP>represents the refractive index of the light-emitting layer). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element, and an organic EL display, an organic EL illumination, and an organic EL signal device including the same.

In recent years, organic electroluminescent elements have been actively developed as light emitting devices such as displays and lighting. This organic electroluminescent element injects positive and negative charges into an organic thin film between electrodes and takes out an excited state generated by recombination as light.
Organic electroluminescent devices that are currently in practical use are generally produced using a technique in which a relatively low molecular weight compound is heated under high vacuum conditions and vapor-deposited on an upper substrate. This method is used for small and medium-sized displays that have been put to practical use. Further, by adjusting the film thickness of the organic compound layer between the electrodes, it is possible to select the optical path length suitable for the emission wavelength, and it is possible to optimize the emission of each color of RGB. However, this vacuum evaporation method is difficult to uniformly deposit on a large area substrate and is not suitable for manufacturing a large display. Moreover, the utilization efficiency of the organic material which is a vapor deposition source is low, and there also exists a problem that manufacturing cost is high because the frequency | count of coating with a mask increases.

  On the other hand, as a means for producing these large-area organic EL panels, a method for producing an organic EL panel by a wet film formation method typified by a spin coating method, an ink jet method, a dip coating method, various printing methods and the like has been proposed. Yes. Although these methods are said to be advantageous in terms of cost compared with the vacuum vapor deposition method, various properties required for an organic electroluminescent display such as low voltage driving, high efficiency, and long life are difficult in a single layer wet film formation. Therefore, multilayer lamination by wet film formation is very important in aiming at high performance of the coating type organic electroluminescence device. Patent Document 1 discloses multi-layer lamination by coating, but an element having high driving stability has not been obtained, and there are still many problems in practical use.

Japanese Laid-Open Patent Publication No. 2004-19935

  An object of the present invention is to provide an organic electroluminescent device having a low driving voltage, high luminous efficiency, and long driving life in an organic electroluminescent device including at least one organic layer formed by a wet film-forming method. To do.

As a result of intensive studies by the present inventors, the inventors have found that the above problems can be solved by defining the refractive index of the light emitting layer and the organic layer adjacent to the anode side of the light emitting layer, and have reached the present invention.
That is, the present invention includes an anode, a first organic layer, a light emitting layer provided adjacent to the first organic layer, and a cathode in this order,
The first organic layer and the light emitting layer are formed by a wet film formation method,
The first organic layer is a layer formed by insolubilizing a compound having a group represented by the following formula (1) or a dissociating group,
The light emitting layer is an organic electroluminescent element composed of a low molecular weight compound having a molecular weight of 5,000 or less,
The present invention resides in an organic electroluminescent element, an organic EL display including the organic electroluminescent element, an organic EL illumination, and an organic EL signal device that satisfy the following formula (2).

(In the formula, n ^H represents the refractive index of the first organic layer, and n ^E represents the refractive index of the light emitting layer.)

It is sectional drawing which shows typically an example of the structure of the organic electroluminescent element of this invention.

Embodiments of the organic electroluminescent element, organic EL display, organic EL lighting, and organic EL signal device of the present invention will be described in detail. The description of the constituent elements described below is an example of the embodiment of the present invention (representative example). The present invention is not specified in these contents unless it exceeds the gist.
The organic electroluminescent element of the present invention includes an anode, a first organic layer, a light emitting layer provided adjacent to the first organic layer, and a cathode in this order, and the first organic layer and the light emitting layer include The first organic layer is formed by insolubilizing a compound having a group represented by the following formula (1) or a dissociating group, and the light emitting layer is formed by a wet film formation method. An organic electroluminescence device comprising a low molecular weight compound having a molecular weight of 5,000 or less, wherein the organic electroluminescence device satisfies the following formula (2).

(In the formula, n ^H represents the refractive index of the first organic layer, and n ^E represents the refractive index of the light emitting layer.)
<Organic layer>
In the present invention, the “organic layer” refers to a layer containing an organic compound.
In the organic electroluminescent element of the present invention, the organic layer refers to each layer disposed between the anode and the cathode.

Examples of the organic layer in the organic electroluminescence device of the present invention include a hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer.
[1. First organic layer]
The first organic layer in the present invention is an organic layer provided between the anode and the light emitting layer and provided adjacent to the light emitting layer. When two or more layers are included between the anode and the light emitting layer, the layer adjacent to the anode side of the light emitting layer is the first organic layer.

The refractive index of the first organic layer in the present invention is usually 1.0 or more, preferably 1.1 or more, and usually 3. when measured by the method described in the section <Method of measuring refractive index> described later. 0 or less, preferably 2.0 or less.
By setting it within this range, good hole injection property to the light emitting layer is realized, and good electrical characteristics can be obtained.

The first organic layer is a layer containing a hole transporting compound.
(1-1. Hole transporting compound)
The hole transporting compound is a hole transporting compound having a group represented by the following formula (1) or a dissociation group.

  The hole transporting compound may be a monomer (a compound having a single molecular weight) or an oligomer (a low molecular weight polymer compound having a repeating unit), or a polymer (a high molecular weight compound having a repeating unit). Molecular compound). The hole transporting compound is preferably a polymer compound having a repeating unit such as an oligomer or a polymer because it is excellent in film formability or heat resistance.

In order to obtain the constitution of the present invention, it is appropriately selected from the compounds described below.
(1-1-1. Molecular weight)
When the hole transporting compound is a monomer, the molecular weight is usually 5000 or less, preferably 2500 or less, preferably 300 or more, more preferably 500 or more. If the molecular weight exceeds this upper limit, purification may be difficult due to the high molecular weight of impurities, and if the molecular weight is lower than this lower limit, the glass transition temperature, melting point, vaporization temperature, etc. will decrease, so heat resistance will be reduced. It may be severely damaged.

  When the hole transporting compound is an oligomer or a polymer, its weight average molecular weight is usually 3,000,000 or less, preferably 1,000,000 or less, more preferably 500,000 or less, and usually 1 5,000 or more, preferably 2,500 or more, more preferably 5,000 or more. If the molecular weight exceeds this upper limit, purification may be difficult due to the high molecular weight of impurities, and if the molecular weight is lower than this lower limit, film formability may be reduced, and the glass transition temperature, melting point and vaporization temperature may be reduced. , The heat resistance may be significantly impaired.

  When the hole transporting compound is an oligomer or a polymer, its dispersity Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) is usually 3.0 or less, preferably 2.5 or less, more preferably. Is 2.0 or less, preferably 1.0 or more, more preferably 1.1 or more, and particularly preferably 1.2 or more. If the degree of dispersion exceeds this upper limit, purification may become difficult, solvent solubility may decrease, and film formability may decrease.

  In addition, the weight average molecular weight (and number average molecular weight) in this invention is determined by SEC (size exclusion chromatography) measurement. In SEC measurement, the elution time is shorter for higher molecular weight components, and the elution time is longer for lower molecular weight components. However, using the calibration curve calculated from the elution time of polystyrene (standard sample) with a known molecular weight, By converting, the weight average molecular weight (and number average molecular weight) is calculated.

(Dissociable group)
The hole transport material in the present invention is preferably a compound having a dissociating group.
Here, the dissociating group refers to a group that dissociates from a bonded aromatic hydrocarbon ring at 70 ° C. or more and is soluble in a solvent. Here, being soluble in a solvent means that the compound is dissolved in toluene at 0.1% by weight or more at room temperature in a state before reacting by irradiation with heat and / or active energy rays. The solubility in toluene is preferably 0.5% by weight or more, more preferably 1% by weight or more.

Such a dissociating group is preferably a group that thermally dissociates without forming a polar group on the aromatic hydrocarbon ring side, and more preferably a group that dissociates thermally by a reverse Diels-Alder reaction.
Furthermore, it is preferably a group that thermally dissociates at 100 ° C. or higher, and preferably a group that thermally dissociates at 300 ° C. or lower.

Specific examples of the dissociating group are as follows, but the present invention is not limited thereto.
A specific example in the case where the dissociating group is a divalent group is as shown in <Divalent dissociating group group A> below.
<Divalent dissociation group A>

A specific example in the case where the dissociating group is a monovalent group is as shown in <Monovalent dissociating group B> below.
<Monovalent dissociation group B>

(About formula (1))
In addition, the hole transport material in the present invention can cause a large difference in solubility in a solvent before and after a reaction (insolubilization reaction) caused by heat and / or active energy ray irradiation. It is preferable that it is group represented by Formula (1) at the point which is stable.

The group represented by the formula (1) may be directly bonded to an aromatic hydrocarbon group or aromatic heterocyclic group in the molecule, but may be bonded via a divalent group. As the divalent group, a group selected from an —O— group, a —C (═O) — group, or an (optionally substituted) —CH ₂ — group may be selected from 1 to 30 in any order. It is preferable to bind to an aromatic hydrocarbon group or an aromatic heterocyclic group via a divalent group formed by connecting them individually.

(Structure of hole transport material)
The material forming the first organic layer is preferably a material having a high hole transport capability and capable of efficiently transporting injected holes. Therefore, it is preferable that the ionization potential is small, the transparency to visible light is high, the hole mobility is large, the stability is high, and impurities that become traps are not easily generated during manufacturing or use. In many cases, since it is in contact with the light emitting layer, it is preferable not to quench the light emitted from the light emitting layer or to reduce the efficiency by forming an exciplex with the light emitting layer.

  As the material of the first organic layer, any material that has been conventionally used as a constituent material of the first organic layer may be used. For example, the hole transport property used in the above-described hole injection layer may be used. What was illustrated as a compound is mentioned. In addition, arylamine derivatives, fluorene derivatives, spiro derivatives, carbazole derivatives, pyridine derivatives, pyrazine derivatives, pyrimidine derivatives, triazine derivatives, quinoline derivatives, phenanthroline derivatives, phthalocyanine derivatives, porphyrin derivatives, silole derivatives, oligothiophene derivatives, condensed polycyclic aromatics Group derivatives, metal complexes and the like.

  Also, for example, polyvinylcarbazole derivatives, polyarylamine derivatives, polyvinyltriphenylamine derivatives, polyfluorene derivatives, polyarylene derivatives, polyarylene ether sulfone derivatives containing tetraphenylbenzidine, polyarylene vinylene derivatives, polysiloxane derivatives, polythiophenes Derivatives, poly (p-phenylene vinylene) derivatives, and the like. These may be any of alternating copolymer compounds, random polymer compounds, block polymer compounds, and graft copolymer compounds. Further, it may be a polymer having a branched main chain and three or more terminal portions, or a so-called dendrimer.

Of these, polyarylamine derivatives and polyarylene derivatives are preferred.
The polyarylamine derivative is preferably a polymer compound containing a repeating unit represented by the following formula (II). In particular, it is preferably a polymer compound composed of a repeating unit represented by the following formula (II). In this case, Ar ^a or Ar ^b may be different in each repeating unit.

(In Formula (II), Ar ^a and Ar ^b may each independently have a substituent,
Represents an aromatic hydrocarbon group or an aromatic heterocyclic group. )
Examples of the aromatic hydrocarbon group which may have a substituent include a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a perylene ring, a tetracene ring, a pyrene ring, a benzpyrene ring, a chrysene ring, a triphenylene ring, and an acenaphthene. Examples thereof include a group derived from a 6-membered monocyclic ring or a 2-5 condensed ring, such as a ring, a fluoranthene ring, a fluorene ring, and a group in which two or more rings are connected by a direct bond.

  Examples of the aromatic heterocyclic group which may have a substituent include a furan ring, a benzofuran ring, a thiophene ring, a benzothiophene ring, a pyrrole ring, a pyrazole ring, an imidazole ring, an oxadiazole ring, an indole ring, and a carbazole ring. , Pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuran ring, thienofuran ring, benzoisoxazole ring, benzoisothiazole ring, benzimidazole ring, pyridine ring, pyrazine ring, pyridazine Ring, pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring, sinoline ring, quinoxaline ring, phenanthridine ring, benzimidazole ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring, etc. Or a group and the rings of from 2-4 fused rings include groups formed by connecting a direct bond or two or more rings.

In view of solubility and heat resistance, Ar ^a and Ar ^b are each independently selected from the group consisting of a benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, triphenylene ring, pyrene ring, thiophene ring, pyridine ring, and fluorene ring. A group derived from a selected ring or a group formed by linking two or more benzene rings (for example, a biphenyl group or a terphenyl group) is preferable.
Among these, a group derived from a benzene ring (phenyl group), a group formed by connecting two benzene rings (biphenyl group), and a group derived from a fluorene ring (fluorenyl group) are preferable.

Examples of the substituent that the aromatic hydrocarbon group and the aromatic heterocyclic group in Ar ^a and Ar ^b may have include an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an alkoxycarbonyl group, and a dialkyl. Examples thereof include an amino group, a diarylamino group, an acyl group, a halogen atom, a haloalkyl group, an alkylthio group, an arylthio group, a silyl group, a siloxy group, a cyano group, an aromatic hydrocarbon ring group, and an aromatic heterocyclic group.

As the polyarylene derivative, an arylene group such as an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a substituent exemplified as Ar ^a or Ar ^b in the formula (II) is used as its repeating unit. The high molecular compound which has is mentioned.
As the polyarylene derivative, a polymer compound having a repeating unit composed of the following formula (III-1) and / or the following formula (III-2) is preferable.

(In formula (III-1), R ^a , R ^b , R ^c and R ^d are each independently an alkyl group, an alkoxy group, a phenylalkyl group, a phenylalkoxy group, a phenyl group, a phenoxy group, an alkylphenyl group, Represents an alkoxyphenyl group, an alkylcarbonyl group, an alkoxycarbonyl group, or a carboxy group, and t and s each independently represent an integer of 0 to 3. When t or s is 2 or more, they are contained in one molecule. A plurality of R ^a or R ^b may be the same or different, and adjacent R ^a or R ^b may form a ring.)

(In Formula (III-2), R ^e and R ^f are each independently the same as R ^a , R ^b , R ^c or R ^d in Formula (III-1) above. Independently, it represents an integer of 0 to 3. When r or u is 2 or more, a plurality of R ^e and R ^f contained in one molecule may be the same or different, and adjacent R ^e or R ^f may form a ring, and X represents an atom or a group of atoms constituting a 5-membered ring or a 6-membered ring.)
Specific examples of X are —O—, —BR—, —NR—, —SiR ₂ —, —PR—, —SR—, —CR ₂ — or a group formed by bonding thereof.

  The polyarylene derivative has a repeating unit represented by the following formula (III-3) in addition to the repeating unit represented by the following formula (III-1) and / or the following formula (III-2). Is preferred.

(In the formula (III-3), Ar ^{c to} Ar ^j each independently represents an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a substituent. Independently represents 0 or 1.)
Specific examples of Ar ^{c to} Ar ^j are the same as Ar ^a and Ar ^b in the formula (II).

Specific examples of the above formulas (III-1) to (III-3) and specific examples of polyarylene derivatives include those described in JP-A-2008-98619.
The structure of the hole transporting compound is not particularly limited, but is preferably a compound having a structure represented by the following formula (4) as a partial structure.

The above skeleton has a group represented by the formula (1) or a dissociation group through the above-described divalent group as necessary.
(1-1-5. Specific example)
Specific examples of the hole transporting compound in the present invention are shown below, but the present invention is not limited thereto.

(1-1-6. Other components)
As long as the effects of the present invention are not impaired, other components having a refractive index different from that of the hole transport compound may be included. By including other components having a refractive index different from that of the above hole transport compound, the value of the refractive index can be adjusted. As said component, filler resin, binder resin, etc. are mentioned.

As long as the effects of the present invention are not impaired, other components may further be included, and examples thereof include various electron accepting compounds, light emitting materials, leveling agents, coating properties improving agents such as antifoaming agents, and the like.
In addition, only 1 type may be used for another component, and 2 or more types may be used together in the combination and ratio of simmering.

When the organic layer is a single layer between the anode and the light emitting layer, that is, only the first organic layer, it is preferable that the first organic layer contains an electron-accepting compound described later.
(1-2. Composition)
When the first organic layer is formed by a wet film formation method, the hole transporting compound constituting the first organic layer and, if necessary, other components are mixed with an appropriate solvent for film formation. A composition (first organic layer forming composition) is prepared and used.

The content of the charge transporting compound in the first organic layer forming composition is usually 0.1% by weight or more, preferably 0.5% by weight or more, usually 50% by weight or less, preferably 20% by weight or less. is there. In addition, 2 or more types of hole transportable compounds may be contained in the 1st composition for organic layer formation, In that case, it is preferable that the sum total of 2 or more types becomes said range.
(solvent)
The first composition for forming an organic layer according to the present invention usually contains a solvent.

The solvent contained in the first organic layer forming composition according to the present invention is not particularly limited, but is usually 0.1% by weight, preferably 0.5% by weight, and more preferably 1%. It is a solvent that dissolves 0.0% by weight or more.
The boiling point of the solvent is usually 110 ° C. or higher, preferably 140 ° C. or higher, particularly 200 ° C. or higher, usually 400 ° C. or lower, and preferably 300 ° C. or lower. If the boiling point of the solvent is too low, the drying speed is too high and the film quality may be deteriorated. Further, if the boiling point of the solvent is too high, it is necessary to increase the temperature of the drying step, which may adversely affect other layers and the substrate.

  Specific examples include aromatic compounds such as toluene, xylene, methicylene, cyclohexylbenzene; halogen-containing solvents such as 1,2-dichloroethane, chlorobenzene, o-dichlorobenzene; ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol-1 -Aliphatic ethers such as monomethyl ether acetate (PGMEA), 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3 Ether solvents such as aromatic ethers such as dimethylanisole and 2,4-dimethylanisole; aliphatic esters such as ethyl acetate, n-butyl acetate, ethyl lactate and n-butyl lactate; phenyl acetate, propion Phenyl, methyl benzoate, ethyl benzoate, isopropyl benzoate, propyl benzoate, organic solvent an ester solvents such as benzoic acid n- butyl. These may be used alone or in combination of two or more.

The first composition for forming an organic layer may contain other components as long as the effects of the present invention are not impaired. Examples of other components include various electron-accepting compounds, light emitting materials, binder resins, leveling agents, coating properties improving agents such as antifoaming agents, and the like. In addition, only 1 type may be used for another component, and 2 or more types may be used together in the combination and ratio of simmering.
When the organic layer is a single layer between the anode and the light emitting layer, that is, only the first organic layer, the first organic layer-forming composition preferably contains an electron-accepting compound. .

In addition, when a leveling agent is included, examples of the leveling agent include a silicon-based surfactant,
Fluorine-type surfactant etc. are mentioned. Any one of the leveling agents may be used alone, or two or more thereof may be used in any combination and ratio. The content of the leveling agent in the first charge transport layer forming composition is usually 0.0001% by weight or more, preferably 0.001% by weight or more, and usually 1% by weight or less, preferably 0.1% by weight. % Or less. If the content of the leveling agent is too low, the leveling may be poor. If it is too high, the charge transport ability of the film may be reduced.

  Moreover, when an antifoamer is included, examples of the antifoamer include silicon oil, fatty acid ester, and phosphate ester. Any one type of antifoaming agent may be used alone, or two or more types may be used in any combination and ratio. The content of the antifoaming agent in the first charge transport layer forming composition is usually 0.0001% by weight or more, preferably 0.001% by weight or more, and usually 1% by weight or less, preferably 0.1%. It is in the range of weight percent or less. If the content of the antifoaming agent is too low, the defoaming effect may not be sufficient, and if it is too high, the charge transporting ability of the film may be reduced.

(1-3. Film formation method)
[Film formation method]
The first organic layer forming composition is formed on a substrate or another layer by a wet film forming method.
In the present invention, the wet film formation method includes, 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, screen printing method, A wet film formation method such as a gravure printing method or a flexographic printing method. Among these film forming methods, a spin coating method, a spray coating method, and an ink jet method are preferable. This is because the liquid property unique to the composition for wet film formation used in the organic electroluminescence device is met.

When using the wet film-forming method, the insolubilizing compound and other components used as necessary (additives that promote the crosslinking reaction, wet film-forming property improving agent, etc.) are dissolved in an appropriate solvent, and the above-mentioned first A composition for forming an organic layer is prepared. This composition is formed on a substrate or another layer by the above-described film forming method.
Furthermore, as described above, after the film formation, the insoluble compound undergoes an insolubilization reaction by heating and / or irradiation with active energy rays to obtain a film.

When the insolubilization method is heating, the heating method is not particularly limited, but the heating condition is that a film formed at 120 ° C. or higher, preferably 400 ° C. or lower is heated. The heating time is usually 1 minute or longer, preferably 24 hours or shorter.
The heating means is not particularly limited, and means such as placing a substrate or a laminate having the formed film on a hot plate or heating in an oven is used. For example, conditions such as heating on a hot plate at 120 ° C. or more for 1 minute or more can be used.

  When the insolubilization method is based on irradiation with active energy rays, direct irradiation using an ultraviolet, visible or infrared light source such as an ultra high pressure mercury lamp, high pressure mercury lamp, halogen lamp or infrared lamp, or the aforementioned light source Examples include a mask aligner incorporated and a method of irradiation using a conveyor type light irradiation device. Further, for example, there is a method of irradiating using a so-called microwave oven that irradiates a microwave generated by a magnetron. As the irradiation time, it is preferable to set conditions necessary for reducing the solubility of the film, but irradiation is usually performed for 0.1 seconds or longer, preferably 10 hours or shorter.

You may perform a heating and / or irradiation of an active energy ray individually or in combination, respectively. When combined, the order of implementation is not particularly limited.
In order to reduce the amount of moisture contained in the layer and / or the amount of moisture adsorbed on the surface of the layer after the heating and / or irradiation with active energy rays, it is performed in an atmosphere not containing moisture such as a nitrogen gas atmosphere. preferable. When performing heating and / or irradiation with active energy rays for the same purpose, it is particularly preferable to perform at least the process immediately before the formation of the upper layer in an atmosphere containing no moisture such as a nitrogen gas atmosphere.

The thickness of the first organic layer thus formed in the present invention is usually 3 nm or more, preferably 5 nm or more, more preferably 10 nm or more, and usually 100 nm or less, preferably 80 nm or less, more preferably 50 nm or less. It is.
[2. Light emitting layer]
In the present invention, an organic layer provided on the first organic layer, and between the electrodes (anode and cathode) to which an electric field is applied, holes injected from the anode and electrons injected from the cathode It is a layer which is excited by recombination with and becomes a main light emitting source.

The light emitting layer of the present invention is a layer made of a low molecular compound having a molecular weight of 5,000 or less.
The refractive index of the light emitting layer in the present invention is usually 1.0 or more, preferably 1.1 or more, and usually 3.0 or less, when measured by the method described in the section <Measurement method of refractive index> described later. Preferably it is 2.0 or less.
By setting it within this range, good hole injection property from the first organic layer to the light emitting layer is realized, and good electrical characteristics can be obtained.

  The light emitting layer contains at least a material having a light emitting property (light emitting material) as a constituent material, and preferably a material having a hole transporting property (hole transporting material) or an electron transporting property. Containing a compound (electron transporting compound). A light emitting material may be used as a dopant material, and a hole transporting compound, an electron transporting compound, or the like may be used as a host material. There is no particular limitation on the light-emitting material, and a material that emits light at a desired light emission wavelength and has favorable light emission efficiency may be used. Furthermore, the light emitting layer may contain other components having a molecular weight of 5,000 or less as long as the effects of the present invention are not significantly impaired. In addition, when forming a light emitting layer with a wet film-forming method, it is preferable to use a low molecular weight material in any case.

(2-1. Compound)
As a material used for a light emitting layer, there is no restriction | limiting in particular unless molecular weight is 5,000 or less and the effect of this invention is impaired, A well-known material is applicable. For example, a fluorescent material or a phosphorescent material may be used, but a phosphorescent material is preferable from the viewpoint of internal quantum efficiency.

For the purpose of improving the solubility in a solvent, it is preferable to reduce the symmetry and rigidity of the molecules of the luminescent material or to introduce a lipophilic substituent such as an alkyl group.
Hereinafter, examples of the fluorescent light emitting material among the light emitting materials will be described, but the fluorescent light emitting material is not limited to the following examples.
Examples of the fluorescent light-emitting material that gives blue light emission (blue fluorescent light-emitting material) include naphthalene, perylene, pyrene, anthracene, coumarin, chrysene, p-bis (2-phenylethenyl) benzene, and derivatives thereof.

Examples of the fluorescent light emitting material that gives green light emission (green fluorescent light emitting material) include quinacridone derivatives, coumarin derivatives, aluminum complexes such as Al (C ₉ H ₆ NO) _3, and the like.
Examples of the fluorescent light-emitting material that gives yellow light (yellow fluorescent light-emitting material) include rubrene and perimidone derivatives.

  Examples of fluorescent light-emitting materials (red fluorescent light-emitting materials) that emit red light include, for example, DCM (4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran) -based compounds, benzopyran derivatives, rhodamine derivatives. Benzothioxanthene derivatives, azabenzothioxanthene and the like.

As the phosphorescent material, for example, a long-period type periodic table (hereinafter referred to as a long-period type periodic table when referred to as “periodic table” unless otherwise specified) is selected from the seventh to eleventh groups. And an organometallic complex containing a metal.
Preferred examples of the metal selected from Groups 7 to 11 of the periodic table include ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold.

  As the ligand of the complex, a ligand in which a (hetero) aryl group such as a (hetero) arylpyridine ligand or a (hetero) arylpyrazole ligand and a pyridine, pyrazole, phenanthroline, or the like is connected is preferable. A pyridine ligand and a phenylpyrazole ligand are preferable. Here, (hetero) aryl represents an aryl group or a heteroaryl group.

  Specific examples of the phosphorescent material include tris (2-phenylpyridine) iridium, tris (2-phenylpyridine) ruthenium, tris (2-phenylpyridine) palladium, bis (2-phenylpyridine) platinum, tris (2- Phenylpyridine) osmium, tris (2-phenylpyridine) rhenium, octaethyl platinum porphyrin, octaphenyl platinum porphyrin, octaethyl palladium porphyrin, octaphenyl palladium porphyrin, and the like.

  The molecular weight of the compound used as the light emitting material is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 5000 or less, preferably 4000 or less, more preferably 3000 or less, and usually 100 or more, preferably 200 or more, more Preferably it is 300 or more, More preferably, it is the range of 400 or more. If the molecular weight of the luminescent material is too small, the heat resistance will be significantly reduced, gas generation will be caused, the film quality will be reduced when the film is formed, or the morphology of the organic electroluminescent element will be changed due to migration, etc. Sometimes come. On the other hand, if the molecular weight of the luminescent material is too large, it tends to be difficult to purify the luminescent material, or it may take time to dissolve in the solvent.

In addition, any 1 type may be used for the luminescent material mentioned above, and 2 or more types may be used together by arbitrary combinations and a ratio.
(Charge transport material)
The organic electroluminescent element of the present invention may further contain a charge transport material as a material constituting the light emitting layer.

In the present invention, only one type of charge transport material may be used, or two or more types may be used in any combination and ratio.
In the light emitting layer, it is preferable to use a light emitting material as a dopant material and a charge transport material as a host material.
The charge transport material may be a compound that has been conventionally used in a light emitting layer of an organic electroluminescent device, and particularly a compound that is used as a host material of the light emitting layer.

Specific examples of charge transport materials include aromatic amine compounds, phthalocyanine compounds, porphyrin compounds, oligothiophene compounds, polythiophene compounds, benzylphenyl compounds, compounds in which tertiary amines are linked by a fluorene group, hydrazone compounds Compounds, silazane compounds, silanamine compounds, phosphamine compounds, quinacridone compounds, anthracene compounds, pyrene compounds, carbazole compounds, pyridine compounds, phenanthroline compounds, oxadiazole compounds, silole compounds, etc. It is done.

For example, two or more condensed aromatic rings including two or more tertiary amines represented by 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl are substituted with nitrogen atoms. Aromatic amine compounds having a starburst structure (J. Lumin, etc.) such as aromatic diamines (Japanese Patent Laid-Open No. 5-234681), 4,4 ′, 4 ″ -tris (1-naphthylphenylamino) triphenylamine, etc. , 72-74, 985, 1997), an aromatic amine compound comprising a tetramer of triphenylamine (Chem. Commun., 2175, 1996), 2, 2 ′, 7, 7 ′. -Fluorene compounds such as tetrakis- (diphenylamino) -9,9'-spirobifluorene (Synth. Metals, 91, 209, 1997), 4,4'-N, N'- Carbazole compounds such as carbazole biphenyl, 2- (4-biphenylyl) -5- (p-tertiarybutylphenyl) -1,3,4-oxadiazole (tBu-PBD), 2,5-bis (1- Oxadiazole compounds such as naphthyl) -1,3,4-oxadiazole (BND), 2,5-bis (6 ′-(2 ′, 2 ″ -bipyridyl))-1,1-dimethyl-3 , 4-diphenylsilol (PyPySPyPy) and other silole compounds, bathophenanthroline (BPhen), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, bathocuproin) and other phenanthroline compounds It is done.

The molecular weight of the charge transport material is usually 5,000 or less, preferably 4,000 or less, more preferably 3,000 or less, and usually 100 or more, preferably 200 or more, more preferably 300 or more.
(2-1-1. Other components)
The light emitting layer may contain other components as long as the effects of the present invention are not impaired. Examples of other components include various electron-accepting compounds, light emitting materials, binder resins, leveling agents, coating properties improving agents such as antifoaming agents, and the like. In addition, only 1 type may be used for another component, and 2 or more types may be used together in the combination and ratio of simmering.

When the organic layer is a single layer between the anode and the light emitting layer, that is, only the first organic layer, it is preferable that the first organic layer contains an electron-accepting compound described later.
(2-2. Composition)
When the light emitting layer is formed by a wet film forming method, the light emitting material and the charge transporting material constituting the light emitting layer, and other components as necessary are mixed with an appropriate solvent to form a film forming composition (light emitting layer). A forming composition) is prepared and used.

(solvent)
Further, the solvent is not particularly limited as long as the light emitting material and the charge transporting material are well dissolved.
The solubility of the solvent is usually 0.01% by weight or more, preferably 0.05% by weight or more, more preferably 0.1% by weight or more, respectively, at normal temperature and normal pressure. It is preferable to do.

Although the specific example of a solvent is given to the following, as long as the effect of this invention is not impaired, it is not limited to these.
For example, alkanes such as n-decane, cyclohexane, ethylcyclohexane, decalin, and bicyclohexane; aromatic hydrocarbons such as toluene, xylene, methicylene, cyclohexylbenzene, and tetralin; halogenated aroma such as chlorobenzene, dichlorobenzene, and trichlorobenzene Group hydrocarbons: 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, 2,4-dimethyl Aromatic ethers such as anisole 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 Sanone, Cyclooctanone and Fencon; Alicyclic alcohols such as cyclohexanol and cyclooctanol; Aliphatic ketones such as methyl ethyl ketone and dibutyl ketone; Aliphatic alcohols such as butanol and hexanol; Ethylene And aliphatic ethers such as glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA).

Of these, alkanes and aromatic hydrocarbons are preferable. One of these solvents may be used alone, or two or more thereof may be used in any combination and ratio.
In order to obtain a more uniform film, it is preferable that the solvent evaporates from the liquid film immediately after the film formation at an appropriate rate. For this reason, the boiling point of the solvent is usually 80 ° C or higher, preferably 100 ° C or higher, more preferably 120 ° C or higher, and usually 270 ° C or lower, preferably 250 ° C or lower, more preferably 230 ° C or lower.

  The amount of the solvent used is arbitrary as long as the effects of the present invention are not significantly impaired, but is preferably 10 parts by weight or more, more preferably 50 parts by weight or more, particularly preferably 100 parts by weight of the composition for forming a light emitting layer. Is 80 parts by weight or more, preferably 99.95 parts by weight or less, more preferably 99.9 parts by weight or less, and particularly preferably 99.8 parts by weight or less. When the content is lower than the lower limit, the viscosity becomes too high, and the film forming workability may be lowered. On the other hand, when the value exceeds the upper limit, the film thickness obtained by removing the solvent after film formation cannot be obtained, so that film formation tends to be difficult. In addition, when mixing and using 2 or more types of solvents as a composition for light emitting layer formation, it is made for the sum total of these solvents to satisfy | fill this range.

Moreover, the composition for light emitting layer formation in this invention may contain various additives, such as a leveling agent and an antifoamer, for the purpose of improving film forming property.
(2-3. Film formation method)
The method for forming a light emitting layer in the present invention is preferably performed by a wet film forming method from the viewpoint of excellent film forming properties.

  After the application of the composition for forming a light emitting layer for producing the light emitting layer, the obtained coating film is dried and the solvent for the light emitting layer is removed to form the light emitting layer. The method of the wet film formation method is not limited as long as the effect of the present invention is not significantly impaired. For example, the wet film formation method in the present invention described in the above [Film formation method] can be mentioned. Coating method and inkjet method.

The solid content concentration of the light emitting material, hole transporting compound, electron transporting compound and the like in the composition for forming a light emitting layer is usually 0.01% by weight or more and usually 70% by weight or less. If this concentration is too large, film thickness unevenness may occur, and if it is too small, defects may occur in the film.
The thickness of the light emitting layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 3 nm or more, preferably 5 nm or more, and usually 200 nm or less, preferably 100 nm or less. If the light emitting layer is too thin, defects may occur in the film, and if it is too thick, the driving voltage may increase.

<Reason for obtaining the effect of the present invention>
The organic electroluminescent element of the present invention satisfies the following formula (1).
0.6 <n ^H / n ^E <1.4 (1)
(In the formula, n ^H represents the refractive index of the first organic layer, and n ^E represents the refractive index of the light emitting layer.)
More specifically, n ^H / n ^E is usually 0.6 or more, preferably 0.8 or more, and usually 1.4 or less, preferably 1.2 or less.

Within the above range, the charge injection property at the interface between the first organic layer and the light emitting layer is improved.
[Second organic layer]
The organic electroluminescent element of the present invention preferably has a second organic layer between the anode and the first organic layer. The second organic layer is a layer containing a hole transporting compound and an electron accepting compound.

(Hole transporting compound)
Moreover, in order to form a 2nd organic layer, you may use the compound which has the said insolubilization group as a hole transportable compound. In this case, as the hole transporting compound, a low molecular compound or a polymer compound may be used as long as it has a hole transporting ability.
The hole transporting compound is preferably a compound having an ionization potential of 4.5 eV or more and 6.0 eV or less from the viewpoint of a charge injection barrier from the anode to the second organic layer. From this point of view, examples of hole transporting compounds include aromatic amine compounds, phthalocyanine derivatives, porphyrin derivatives, oligothiophene derivatives, polythiophene derivatives, benzylphenyl compounds, compounds in which tertiary amines are linked by a fluorene group, hydrazone compounds, Examples include silazane compounds, silanamine derivatives, phosphamine derivatives, quinacridone compounds, and phthalocyanine derivatives.

  Among these, an aromatic amine compound is preferable from the viewpoint of being amorphous and a visible light transmittance, and an aromatic tertiary amine compound is particularly preferable. Here, the aromatic tertiary amine compound is a compound having an aromatic tertiary amine structure, and includes a compound having a group derived from an aromatic tertiary amine. The kind of the aromatic tertiary amine compound is not particularly limited, but from the viewpoint of uniform light emission due to the surface smoothing effect, a polymer compound having a weight average molecular weight of 1,000 or more and 1,000,000 or less (a polymer in which repeating units are linked) is more preferable.

  Preferable examples of the aromatic tertiary amine polymer compound include a polymer compound having a repeating unit represented by the following formula (3).

(In Formula (3), Ar ⁵ and Ar ⁶ each independently represent an aromatic hydrocarbon group that may have a substituent, or an aromatic heterocyclic group that may have a substituent. Ar ^{7 to} Ar ⁹ each independently represents a divalent aromatic hydrocarbon group which may have a substituent, or a divalent aromatic heterocyclic group which may have a substituent. X ¹ represents a linking group selected from the following group of linking groups, and among Ar ^{5 to} Ar ⁹ , two groups bonded to the same N atom are bonded to each other to form a ring. You may do it.)

(In said each formula, Ar < ¹⁰ > -Ar < ¹⁴ >, Ar < ¹⁶ > -Ar < ¹⁹ > may each independently have the aromatic hydrocarbon ring group which may have a substituent, or a substituent. Represents an aromatic heterocyclic group, and Ar ¹⁵ and Ar ²⁰ each independently represents an aromatic hydrocarbon ring group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. R ¹⁰ and R ¹¹ each independently represents a hydrogen atom or an arbitrary substituent.
Ar ^{5 to} Ar ²⁰ each independently represents an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. These may be the same or different from each other. Moreover, these groups may further have a substituent. The molecular weight of the substituent is usually 400 or less, and preferably 250 or less.

Ar ⁵ and Ar ⁶ are each independently a benzene ring, naphthalene ring, phenanthrene ring, thiophene ring, pyridine, from the viewpoint of the solubility, heat resistance, hole injection / transport properties of the aromatic tertiary amine polymer compound A group derived from a ring is preferable, and a phenyl group (a group derived from a benzene ring) and a naphthyl group (a group derived from a naphthalene ring) are more preferable.
Moreover, as Ar < ⁷ > -Ar < ⁹ >, the group derived from a benzene ring, a naphthalene ring, a triphenylene ring, and a phenanthrene ring is each independently preferable from the point of hole injection | pouring and transport property including heat resistance and oxidation-reduction potential, A phenylene group (a group derived from a benzene ring), a biphenylene group (a group derived from a benzene ring), and a naphthylene group (a group derived from a naphthalene ring) are more preferable.

Specific examples of the aromatic tertiary amine polymer compound having a repeating unit represented by the formula (3) include those described in WO 2005/089024 pamphlet.
In addition, the hole transportable compound may contain any 1 type and may contain 2 or more types. In the case of containing two or more kinds of hole transporting compounds, the combination is arbitrary, but one or more kinds of aromatic tertiary amine polymer compounds and one or two kinds of other hole transporting compounds. It is preferable to use the above in combination.

The concentration of the hole transporting compound (including the arylamine polymer of the present invention) in the second organic layer forming composition is arbitrary as long as the effects of the present invention are not significantly impaired. In this respect, it is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.5% by weight or more, usually 70% by weight or less, preferably 60% by weight or less, more preferably 50% by weight. % By weight or less. If the concentration is too low, defects may occur in the formed second organic layer, and if the concentration is too high, film thickness unevenness may occur.

(Electron-accepting compound)
The second organic layer preferably contains an electron accepting compound, and therefore the second organic layer forming composition preferably also contains an electron accepting compound. As the electron-accepting compound, a compound having an oxidizing power and an ability to accept one electron from the above-described hole-transporting compound is preferable. Specifically, a compound having an electron affinity of 4 eV or more is preferable, and a compound of 5 eV or more is more preferable.

Examples of the electron-accepting compound include a triaryl boron compound, a metal halide, a Lewis acid, an organic acid, an onium salt, a salt of an arylamine and a metal halide, and a salt of an arylamine and a Lewis acid. 1 type, or 2 or more types of compounds etc. chosen from are mentioned. More specifically, an onium salt substituted with an organic group such as 4-isopropyl-4′-methyldiphenyliodonium tetrakis (pentafluorophenyl) borate or triphenylsulfonium tetrafluoroborate (WO 2005/089024) High-valent inorganic compounds such as iron (III) chloride (Japanese Patent Laid-Open No. 11-251067) and ammonium peroxodisulfate; cyano compounds such as tetracyanoethylene, tris (pendafluorophenyl) borane (Japanese Patent Laid-Open No. 2003-31365) Aromatic boron compounds; fullerene derivatives; iodine and the like. In addition, only 1 type may be used for an electron-accepting compound, and 2 or more types may be used together by arbitrary combinations and arbitrary ratios.

Since these electron-accepting compounds oxidize the hole-transporting compound, the conductivity of the second organic layer can be improved.
The content of the electron-accepting compound with respect to the hole-transporting compound is usually 0.1 mol% or more, preferably 1 mol% or more. However, it is usually 100 mol% or less, preferably 40 mol% or less.

At least one of the solvents contained in the second composition for forming an organic layer is preferably a solvent that can dissolve the material of the second organic layer.
Moreover, the boiling point of a solvent is 110 degreeC or more normally, Preferably it is 140 degreeC or more, More preferably, it is 200 degreeC or more, and is 400 degrees C or less normally, Preferably it is 300 degrees C or less. If the boiling point of the solvent is too low, the drying rate of the formed film is high and the film quality may deteriorate. Moreover, if the boiling point of the solvent is too high, the temperature of the drying process increases, which may adversely affect other layers 2 and the substrate 1 (for example, a glass substrate).

Examples of the solvent include ether solvents, ester solvents, aromatic hydrocarbon solvents, amide solvents and the like. Specifically, 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, 1,3- And aromatic ethers such as dimethoxybenzene, anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole. Examples of the ester solvent include aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate. Furthermore, examples of the aromatic hydrocarbon solvent include toluene, xylene, cyclohexylbenzene, 3-iropropylbiphenyl, 1,2,3,4-tetramethylbenzene,
Examples include 1,4-diisopropylbenzene, cyclohexylbenzene, methylnaphthalene and the like. Examples of the amide solvent include N, N-dimethylformamide, N, N-dimethylacetamide, and the like. In addition, dimethyl sulfoxide and the like can also be used as a solvent.

Among the solvents described above, a solvent having a high ability to dissolve the material of the second organic layer (dissolution ability) or a high affinity with the material is preferable. This is because the concentration of the second organic layer forming composition can be arbitrarily set to prepare a composition having a concentration excellent in the efficiency of the film forming process.
In addition, 1 type may be used for a solvent and it may use 2 or more types together by arbitrary combinations and arbitrary ratios.

  As a material of the second organic layer, other components may be further contained in addition to the hole transporting compound and the electron accepting compound as long as the effects of the present invention are not significantly impaired. Examples of other components include various light emitting materials, electron transporting compounds, binder resins, and coating property improving agents. In addition, 1 type may be used for another component and it may use 2 or more types together by arbitrary combinations and arbitrary ratios.

  After preparing the composition for forming the second organic layer, the composition is applied onto a layer (usually an anode) corresponding to the lower layer of the second organic layer by a wet film-forming method, and dried. Two organic layers are formed. After the application, it is usually dried by heating or the like. The heating means used in the heating step is not limited as long as the effects of the present invention are not significantly impaired. Examples of the heating means include a clean oven, a hot plate, infrared rays, a halogen heater, and microwave irradiation. Among them, a clean oven and a hot plate are preferable in order to uniformly apply heat to the entire film. However, when the 2nd composition for organic layer formation contains the arylamine polymer of this invention, it is made to perform bridge | crosslinking after application | coating.

In the case of forming a layer by a vacuum deposition method, first, one or more materials (hole transporting compound, electron accepting compound, etc.) are put in a crucible installed in a vacuum vessel (two or more types). When using the material, put it in each crucible), and evacuate the inside of the vacuum vessel to about 10 ⁻⁴ Pa with an appropriate vacuum pump. Then, the crucible is heated (each crucible is heated when two or more materials are used), and the evaporation amount is controlled to evaporate (when two or more materials are used, the evaporation amount is controlled independently). Evaporate) to form a second organic layer on the anode of the substrate placed facing the crucible. In addition, when using 2 or more types of materials, they can also be put into a crucible, can be heated and evaporated, and can be used for formation of a 2nd organic layer.

The film thickness of the second organic layer is usually 5 nm or more, preferably 10 nm or more, and usually 1000 nm or less, preferably 500 nm or less. If the film thickness is too thin, the hole injection ability may be insufficient, and if it is too thick, the resistance may be increased.
The second organic layer may be composed of a single layer, or may be composed of a plurality of layers. In the latter case, the plurality of layers may be layers made of the same material or layers made of different materials.

As the electron-accepting compound, a compound having an oxidizing power and an ability to accept one electron from the above-described hole-transporting compound is preferable. Specifically, a compound with an electron affinity of 4 eV or more is preferable, and a compound with a compound of 5 eV or more is more preferable.
Examples of the electron-accepting compound include onium salts substituted with an organic group such as 4-isopropyl-4′-methyldiphenyliodonium tetrakis (pentafluorophenyl) borate, iron (III) chloride (Japanese Patent Laid-Open No. 11-251067). Publication), high valence inorganic compounds such as ammonium peroxodisulfate, cyano compounds such as tetracyanoethylene, aromatic boron compounds such as tris (pentafluorophenyl) borane (Japanese Patent Laid-Open No. 2003-31365), fullerene derivatives, iodine Etc.

Of the above-mentioned compounds, an onium salt substituted with an organic group, a high-valence inorganic compound, and the like are preferable because they have strong oxidizing power. In addition, an onium salt substituted with an organic group, a cyano compound, an aromatic boron compound, or the like is preferable because it is highly soluble in various solvents and can be applied to form a film by a wet film formation method.
Specific examples of onium salts substituted with organic groups, cyano compounds, and aromatic boron compounds suitable as electron-accepting compounds include those described in WO 2005/089024, and preferred examples thereof are also the same. is there. Examples thereof include compounds represented by the following structural formulas, but are not limited thereto.

In addition, an electron-accepting compound may be used individually by 1 type, and may use 2 or more types by arbitrary combinations and a ratio.
The content of the electron-accepting compound in the first organic layer forming composition is usually 0.01% by weight or more, preferably 0.05% by weight or more, usually 20% by weight or less, preferably 10% by weight or less. is there. The first charge transport layer forming composition may contain two or more types of electron accepting compounds, and in that case, the total of the two or more types is preferably within the above range.

<Measurement method of refractive index>
The refractive index can be measured using various methods. Using a spectroscopic ellipsometer (manufactured by JA Woollam), for example, the phase difference delta and the amplitude ratio psi are set to the wavelengths at incident angles of 70 °, 75 °, and 80 ° with respect to the sample on which the compound is formed on the substrate. Measured as a function of (250 nm to 1320 nm). For a wavelength region where there is no optical absorption by the deposited compound, fitting assuming a Cauchy dispersion relationship is performed, and the refractive index and film thickness are calculated to best fit the measured delta and psi.

<Organic electroluminescent device>
Below, the layer structure of the organic electroluminescent element manufactured with the method of this invention, its general formation method, etc. are demonstrated with reference to FIG.
FIG. 1 is a schematic cross-sectional view showing a structural example of an organic electroluminescent device 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, 5 Represents 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.

In the case of the element shown in FIG. 1, the hole transport layer corresponds to the first organic layer, and the hole injection layer corresponds to the second organic layer. Each layer described below is formed by selecting materials satisfying the above-described conditions as the conditions of the second organic layer, the first organic layer, and the light emitting layer to which they correspond.
(substrate)
The substrate serves as a support for the organic electroluminescence device, and quartz or glass plates, metal plates or metal foils, plastic films, sheets, or the like are used. In particular, a glass plate or a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, polysulfone or the like is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescent element may be deteriorated by the outside air that has passed through the substrate, which is not preferable. For this reason, a method of providing a gas barrier property by providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate is also a preferable method.

(anode)
The anode 2 serves to inject holes into the layer on the light emitting layer side.
This anode 2 is usually made of a metal such as aluminum, gold, silver, nickel, palladium, platinum, a metal oxide such as an oxide of indium and / or tin, a metal halide such as copper iodide,
It is composed of carbon black or a conductive polymer such as poly (3-methylthiophene), polypyrrole, or polyaniline.

  In general, the anode 2 is often formed by a sputtering method, a vacuum deposition method, or the like. When forming the anode 2 using fine metal particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, conductive polymer fine powder, etc., an appropriate binder resin solution It is also possible to form the anode 2 by dispersing it and applying it onto the substrate. Further, in the case of a conductive polymer, a thin film can be directly formed on the substrate by electrolytic polymerization, or the anode 2 can be formed by applying a conductive polymer on the substrate (Appl. Phys. Lett., 60, 2711, 1992).

The anode 2 usually has a single-layer structure, but it can also have a laminated structure made of a plurality of materials if desired.
The thickness of the anode 2 varies depending on the required transparency. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the thickness of the anode 2 is usually 5 nm or more, preferably 10 nm or more, and is usually 1000 nm or less, preferably about 500 nm or less. When it may be opaque, the thickness of the anode 2 is arbitrary, and the anode 2 may be the same as the substrate. Furthermore, it is also possible to laminate different conductive materials on the anode 2 described above.

For the purpose of removing impurities adhering to the anode 2 and adjusting the ionization potential to improve the hole injection property, the surface of the anode 2 is treated with ultraviolet (UV) / ozone, or with oxygen plasma or argon plasma. It is preferable to do.
(Hole injection layer)
The hole injection layer is a layer that transports holes from the anode 2 to the light emitting layer, and is usually formed on the anode 2.
As the material and method for forming the hole injection layer in the present invention, the material and method described in the above section [Second organic layer] can be used. The preferred materials and methods are also the same.

[Hole transport layer]
The hole transport layer is provided on the hole injection layer. The hole transport layer can be formed by the material and the film forming method described in [First organic layer]. The same applies to preferred embodiments of the material and the film formation method.
(Light emitting layer)
When a hole injection layer is provided on the hole injection layer, a light emitting layer is provided on the hole transport layer. The light emitting layer is a layer which is excited by recombination of holes injected from the anode and electrons injected from the cathode between the electrodes to which an electric field is applied, and becomes a main light emitting source.
The light emitting layer can be formed by the material and the film forming method described in [Light emitting layer]. The same applies to preferred embodiments of the material and the film formation method.

(Hole blocking layer)
A hole blocking layer may be provided between the light emitting layer and an electron injection layer described later. The hole blocking layer is a layer stacked on the light emitting layer so as to be in contact with the cathode side interface of the light emitting layer.
The hole blocking layer has a role of blocking holes moving from the anode from reaching the cathode and a role of efficiently transporting electrons injected from the cathode toward the light emitting layer.

  The physical properties required for the material constituting the hole blocking layer include high electron mobility, low hole mobility, large energy gap (difference between HOMO and LUMO), and excited triplet level (T1). It is expensive. Examples of the material for the hole blocking layer that satisfies such conditions include bis (2-methyl-8-quinolinolato) (phenolato) aluminum, bis (2-methyl-8-quinolinolato) (triphenylsilanolato) aluminum, and the like. Mixed-ligand complexes, metal complexes such as bis (2-methyl-8-quinolato) aluminum-μ-oxo-bis- (2-methyl-8-quinolinato) aluminum binuclear metal complexes, distyrylbiphenyl derivatives, etc. Triazole derivatives such as styryl compounds (JP-A-11-242996), 3- (4-biphenylyl) -4-phenyl-5 (4-tert-butylphenyl) -1,2,4-triazole (JP-A-7 -41759), phenanthroline derivatives such as bathocuproine (JP-A-10-79297), and the like. That. Further, a compound having at least one pyridine ring substituted at the 2,4,6-positions described in International Publication No. 2005-022962 is also preferable as a material for the hole blocking layer.

In addition, the material of a hole-blocking layer may use only 1 type, and may use 2 or more types together by arbitrary combinations and ratios.
There is no restriction | limiting in the formation method of a hole-blocking layer. Therefore, it can be formed by a wet film forming method, a vapor deposition method, or other methods.
The thickness of the hole blocking layer 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.

(Electron transport layer)
You may provide an electron carrying layer between a light emitting layer and the below-mentioned electron injection layer.
The electron transport layer is provided for the purpose of further improving the light emission efficiency of the device, and can efficiently transport electrons injected from the cathode between the electrodes to which an electric field is applied in the direction of the light emitting layer. Is formed.

  The electron transporting compound used for the electron transporting layer is usually a compound that has high electron injection efficiency from the cathode or the electron injection layer and has high electron mobility and can efficiently transport the injected electrons. Is used. Examples of the compound satisfying such conditions include metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393), metal complexes of 10-hydroxybenzo [h] quinoline, oxadiazole derivatives , Distyrylbiphenyl derivatives, silole derivatives, 3-hydroxyflavone metal complexes, 5-hydroxyflavone metal complexes, benzoxazole metal complexes, benzothiazole metal complexes, trisbenzimidazolylbenzene (US Pat. No. 5,645,948), quinoxaline compounds ( JP-A-6-207169), phenanthroline derivative (JP-A-5-331459), 2-t-butyl-9,10-N, N'-dicyanoanthraquinonediimine, n-type hydrogenated amorphous silicon carbide , N-type zinc sulfide, n-type zinc Such as emissions of zinc, and the like.

In addition, only 1 type may be used for the material of an electron carrying layer, and 2 or more types may be used together by arbitrary combinations and a ratio.
There is no restriction | limiting in the formation method of an electron carrying layer. Therefore, it can be formed by a wet film forming method, a vapor deposition method, or other methods.
The thickness of the electron transport layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 1 nm or more, preferably 5 nm or more, and usually 300 nm or less, preferably 100 nm or less.

(Electron injection layer)
The electron injection layer plays a role of efficiently injecting electrons injected from the cathode into the light emitting layer. In order to perform electron injection efficiently, the material for forming the electron injection layer 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 film thickness is preferably from 0.1 nm to 5 nm.

  Furthermore, an organic electron transport compound represented by a metal complex such as a nitrogen-containing heterocyclic compound such as bathophenanthroline or an aluminum complex of 8-hydroxyquinoline is doped with an alkali metal such as sodium, potassium, cesium, lithium, or rubidium ( (As described in JP-A-10-270171, JP-A-2002-1000047, JP-A-2002-1000048, etc.), it is possible to improve the electron injection / transport properties and achieve excellent film quality. preferable. In this case, the film thickness is usually 5 nm or more, preferably 10 nm or more, and is usually 200 nm or less, preferably 100 nm or less.

In addition, only 1 type may be used for the material of an electron injection layer, and 2 or more types may be used together by arbitrary combinations and a ratio.
There is no restriction | limiting in the formation method of an electron injection layer. Therefore, it can be formed by a wet film forming method, a vapor deposition method, or other methods.
(cathode)
The cathode plays a role of injecting electrons into a layer (such as an electron injection layer or a light emitting layer) on the light emitting layer side.

  As the material of the cathode, it is possible to use the material used for the anode, but in order to perform electron injection efficiently, a metal having a low work function is preferable, for example, tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy.

In addition, only 1 type may be used for the material of a cathode, and 2 or more types may be used together by arbitrary combinations and a ratio.
The thickness of the cathode is usually the same as that of the anode.
Further, for the purpose of protecting the cathode made of a low work function metal, it is preferable to further stack a metal layer having a high work function and stable to the atmosphere because the stability of the device is increased. For this purpose, for example, metals such as aluminum, silver, copper, nickel, chromium, gold and platinum are used. In addition, these materials may be used only by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

(Other layers)
The organic electroluminescent element according to the present invention may have another configuration without departing from the gist thereof. For example, as long as the performance is not impaired, an arbitrary layer may be provided between the anode and the cathode in addition to the layers described above, and an arbitrary layer may be omitted.
<Electron blocking layer>
Examples of the layer that may be included include an electron blocking layer.

  The electron blocking layer is provided between the hole injecting layer or the hole transporting layer and the light emitting layer, and prevents electrons moving from the light emitting layer from reaching the hole injecting layer. Increases the recombination probability of holes and electrons, and has the role of confining the generated excitons in the light-emitting layer, and the role of efficiently transporting holes injected from the hole injection layer toward the light-emitting layer. . In particular, when a phosphorescent material or a blue light emitting material is used as the light emitting material, it is effective to provide an electron blocking layer.

  The characteristics required for the electron blocking layer include high hole transportability, a large energy gap (difference between HOMO and LUMO), and a high excited triplet level (T1). Furthermore, in the present invention, when the light emitting layer is produced by a wet film formation method, the electron blocking layer is also required to be compatible with the wet film formation. Examples of the material used for such an electron blocking layer include a copolymer of dioctylfluorene and triphenylamine typified by F8-TFB (International Publication No. 2004/084260).

In addition, the material of an electron blocking layer may use only 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
There is no restriction | limiting in the formation method of an electron blocking layer. Therefore, it can be formed by a wet film forming method, a vapor deposition method, or other methods.
Further, at the interface between the cathode and the light emitting layer or the electron transport layer, for example, lithium fluoride (LiF), magnesium fluoride (MgF ₂ ), lithium oxide (Li ₂ O), cesium carbonate (II) (CsCO ₃ ), etc. are formed. It is also an effective method to improve the efficiency of the device by inserting a very thin insulating film (0.1 to 5 nm) (Applied Physics Letters, 1997, Vol. 70, pp. 152; No. 74586; see IEEE Transactions on Electron Devices, 1997, Vol. 44, pp. 1245; SID 04 Digest, pp. 154, etc.).

Moreover, in the layer structure demonstrated above, it is also possible to laminate | stack components other than a board | substrate in reverse order. For example, in the case of the layer configuration of FIG. 1, the other components on the substrate are in the order of cathode, electron injection layer, electron transport layer, hole blocking layer, light emitting layer, hole transport layer, hole injection layer, and anode. It may be provided.
Furthermore, it is also possible to constitute the organic electroluminescent element according to the present invention by laminating components other than the substrate between two substrates, at least one of which is transparent.

Further, a structure in which a plurality of components (light emitting units) other than the substrate are stacked in a plurality of layers (a structure in which a plurality of light emitting units are stacked) may be employed. In that case, instead of the interface layer between the steps (between the light emitting units) (when the anode is ITO and the cathode is Al, these two layers), for example, a charge made of vanadium pentoxide (V ₂ O ₅ ) or the like. When a generation layer (Carrier Generation Layer: CGL) is provided, a barrier between steps is reduced, which is more preferable from the viewpoint of light emission efficiency and driving voltage.

Furthermore, the organic electroluminescent device according to the present invention may be configured as a single organic electroluminescent device, or may be applied to a configuration in which a plurality of organic electroluminescent devices are arranged in an array. You may apply to the structure by which the cathode is arrange | positioned at XY matrix form.
Each layer described above may contain components other than those described as materials unless the effects of the present invention are significantly impaired.

<Organic EL display, organic EL lighting, and organic EL signal device>
The organic electroluminescent element of the present invention is used in organic EL display devices, organic EL lighting devices, and organic EL signal devices. The organic electroluminescent device obtained by the present invention is described in, for example, “Organic EL Display” (Ohm, August 20, 2004, written by Shizushi Tokito, Chiba Adachi, and Hideyuki Murata). An organic EL display device and organic EL illumination can be formed by the method.

  The present invention relates to various fields in which organic electroluminescent elements are used, for example, light sources (for example, light sources of copiers, flat panel displays (for example, for OA computers and wall-mounted televisions) and surface light emitters). It can be suitably used in the fields of liquid crystal displays and backlights of instruments), display panels, indicator lamps and the like.

DESCRIPTION OF SYMBOLS 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

Claims (6)

An anode, a first organic layer, a light emitting layer provided adjacent to the first organic layer, and a cathode in this order;
The first organic layer and the light emitting layer are formed by a wet film formation method,
The first organic layer is a layer formed by insolubilizing a compound having a group represented by the following formula (1) or a dissociating group,
The light emitting layer is an organic electroluminescent element composed of a low molecular weight compound having a molecular weight of 5,000 or less,
An organic electroluminescent element characterized by satisfying the following formula (2).

(The benzocyclobutene ring in the formula (II) may have a substituent. The substituents may be bonded to each other to form a ring.)
0.6 ≦ n ^H / n ^E ≦ 1.4 (2)
(In the formula, n ^H represents the refractive index of the first organic layer, and n ^E represents the refractive index of the light emitting layer.) The organic electroluminescent element according to claim 3, wherein the compound having an insolubilizing group is a compound having a partial structure represented by the following formula (4).

  The organic electroluminescent element according to claim 1, wherein a second organic layer containing an electron-accepting compound is provided between the anode and the first organic layer.   An organic EL display comprising the organic electroluminescent element according to claim 1.   An organic EL illumination comprising the organic electroluminescent element according to claim 1.   An organic EL signal device comprising the organic electroluminescent element according to claim 1.

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