JP2021096947A - Electroluminescent device - Google Patents

Abstract

To provide an electroluminescent device with excellent luminescence efficiency, in which the passage of charge through a light-emitting layer at the interface is suppressed.SOLUTION: The above problem is solved by an electroluminescent device having, on a substrate, an anode, a light-emitting portion having at least two successive light-emitting layers, and a cathode, in that order, and the light-emitting portion has a light-emitting layer (EML1) containing quantum dots (A1), which are semiconductor nanoparticles surface-treated with a ligand having no aromatic ring, and a light-emitting layer (EML2) containing quantum dots (A2), which are semiconductor nanoparticles surface-treated with a ligand having an aromatic ring.SELECTED DRAWING: None

Description

The present invention relates to an electroluminescent device having an anode, a light emitting portion having at least two continuous light emitting layers, and a cathode in this order, and having excellent luminous efficiency.

Electroluminescent devices (EL, Electroluminescence) are attracting attention as surface-emitting devices that are lightweight, thin, consume less power, and have an excellent degree of freedom in shape. Such an electroluminescent element has many excellent features such as high-intensity light emission, high-speed response, wide viewing angle, thinness and light weight, and high resolution, and its application to flat panel displays and lighting is being studied. The use of quantum dots is attracting attention as one of the electroluminescent devices.

Quantum dots are small nanoscale semiconductor particles that exhibit intermediate behavior between atomic or molecular behavior and macroscopic solid (bulk form) behavior. Nanoscale materials (semiconductor nanoparticles) in which charge carriers and excitons are confined in all three-dimensional directions are called quantum dots, and the effective bandgap increases as the size decreases. That is, as the size of the quantum dot becomes smaller, its absorption and emission shift to the shorter wavelength side, in other words, from the red direction to the blue direction. Further, by controlling the composition and size of the quantum dots in combination, a wide spectrum from the infrared region to the ultraviolet region can be obtained, and by further controlling the size distribution, the half-value width is narrow and the color purity is narrow. Excellent spectrum can be obtained. Therefore, in recent years, a quantum dot type organic EL device using quantum dots made of semiconductor nanocrystals as a light emitting material has been proposed by taking advantage of these characteristics.

Semiconductor nanocrystals are generally protected by organic ligands. Most of the organic ligands have a structure having an adsorbing group at the end of a long-chain alkyl group. The organic ligand enhances the chemical stability of the surface of the semiconductor nanocrystal to improve its durability. In addition, the organic ligand enhances the dispersibility in an organic solvent or water, and improves the dispersion stability of quantum dots composed of semiconductor nanocrystals in the composition.
Further, in recent years, ligand designs have been made for the purpose of improving the electrical characteristics of quantum dots such as charge injection. For example, Patent Documents 1 to 3 describe hole-transporting ligands and electron-transporting ligands. It has been shown that the characteristics of the electroluminescent element can be improved by surface-treating the quantum dots in combination.

Special Table 2005-502176 Japanese Unexamined Patent Publication No. 2008-214363 JP-A-2010-209141

However, both the hole-transporting ligand and the electron-transporting ligand described in Patent Documents 1 to 3 have an aromatic ring structure, and the light emitting layer having quantum dots coated with the ligand is from an adjacent layer. The charge reception and charge transfer in the light emitting layer are good, and it is excellent from the viewpoint of reducing the driving voltage. On the other hand, the overlap at the interface between the aromatic ring structures causes the charge to pass through the light emitting layer. , There is a problem that the light emission efficiency tends to decrease.
In particular, when a hole injection layer is provided between the anode and the light emitting layer, the aromatic ring structure contained in the hole injection layer and the aromatic ring structure contained in the hole transporting ligand or the electron transporting ligand in the light emitting layer. However, due to the overlap at the interface, the electrons injected from the cathode side are likely to escape to the anode side.
An object of the present invention is to provide an electroluminescent device having excellent luminous efficiency in which the passage of electric charges at an interface is suppressed.

As a result of diligent studies to solve the above problems, it was found that the above problems can be solved by the following embodiments, and the present invention has been completed.

An embodiment of the present invention is an electroluminescent device having an anode, a light emitting portion having at least two continuous light emitting layers, and a cathode in this order on a substrate.
The light emitting portion is a light emitting layer (EML1) containing quantum dots (A1) which are semiconductor nanoparticles surface-treated with a ligand having no aromatic ring, and semiconductor nanoparticles surface-treated with a ligand having an aromatic ring. The present invention relates to an electroluminescent device having a light emitting layer (EML2) containing quantum dots (A2).

Another embodiment of the present invention relates to the electroluminescent device having a hole injection layer between the anode and the light emitting portion.

Another embodiment of the present invention relates to the electroluminescent device in which light emitting layers are arranged in the order of (EML1) and (EML2) from the anode side.

Another embodiment of the present invention relates to the electroluminescent device in which the ligand having an aromatic ring has hole transporting property or electron transporting property.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an electroluminescent device having excellent luminous efficiency in which the passage of electric charges at an interface is suppressed.

The electroluminescent device of the present invention is an electroluminescent device having an anode, a light emitting portion having at least two continuous light emitting layers, and a cathode in this order, and the light emitting portion is an aromatic ring. It contains a light emitting layer (EML1) containing quantum dots (A1) which are semiconductor nanoparticles surface-treated with a ligand which does not have an aromatic ring, and quantum dots (A2) which are semiconductor nanoparticles surface-treated with a ligand having an aromatic ring. It has a light emitting layer (EML2) and exhibits low drive voltage maintenance, excellent light emission efficiency, and high durability.
Hereinafter, the present invention will be described in detail.

<Semiconductor nanoparticles>
As the material of the semiconductor nanoparticles, a single element of Group IV of the periodic table such as carbon (C) (atypical carbon, graphite, graphene, carbon nanotubes, etc.), silicon (Si), germanium (Ge), tin (Sn), etc. A single element of Group V of the periodic table such as phosphorus (P) (black phosphorus); a single element of Group VI of the periodic table such as selenium (Se) and tellurium (Te); tin oxide (IV), boron nitride (BN) ), Boron phosphide (BP), Boron arsenide (BAs), Aluminum nitride (AlN), Aluminum phosphide (AlP), Aluminum arsenide (AlAs), Aluminum antimonized (AlSb), Gallium nitride (GaN), Gallium phosphide Group III elements of the Periodic Table such as (GaP), gallium arsenide (GaAs), gallium antimonized (GaSb), indium nitride (InN), indium phosphate (InP), indium arsenide (InAs), and indium antimonized (InSb). Compounds of Group V elements of the Periodic Table; Aluminum (Al ₂ S ₃ ), Aluminum _{Serene (Al 2} Se ₃ ), Gallium Sulfide (Ga ₂ S ₃ ), Gallium Selenium (Ga Se _{, Ga 2 Se 3} ) Gallium tellalide (GaTe, Ga ₂ Te ₃ ), indium oxide (In ₂ O ₃ ), indium sulfide (In ₂ S ₃ , In S), indium selenium (In ₂ Se ₃ ), indium tellurate (In ₂ Te ₃₎ ) And other compounds of Group III elements of the Periodic Table and Group VI elements of the Periodic Table; Zinc oxide (ZnO), Zinc sulfide (ZnS), Zinc selenium (ZnSe), Zinc telluride (ZnTe), Cadmium oxide (CdO) ), Cadmium sulfide (CdS), Cadmium selenium (CdSe), Cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenium (HgSe), mercury (HgTe) periodic table, etc. the compounds of the periodic table VI elements; copper (I) oxide compound of _(Cu 2 O) of the periodic table I group element and periodic table group VI elements such as; copper chloride (I) (CuCl), bromide Compounds of Group I elements of the Periodic Table and Group VII elements of the Periodic Table such as copper (I) (CuBr), copper (I) (CuI), silver chloride (AgCl), silver bromide (AgBr), etc. These two or more types may be used in combination if necessary. These semiconductors may contain elements other than the constituent elements. For example, taking Group III-V as an example, an alloy system such as InGaP or InGaN may be used. Further, semiconductor nanoparticles doped with a rare earth element or a transition metal element can be used in the above materials, and examples thereof include ZnS: Mn, ZnS: Tb, ZnS: Ce, and LaPO ₄ : Ce.

Among these, silicon (Si), germanium (Ge), gallium sulfide (GaN), gallium arsenide (GaP), gallium arsenide (GaAs), indium nitride (InN), indium sulfide (InP), indium arsenide (InAs), Gallium arsenide (GaSe, Ga ₂ Se ₃ ), indium sulfide (In ₂ S ₃ , InS), zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc tellurate (ZnTe), oxidation Alloy systems such as cadmium (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), InGaP, and InGaN are preferably used, and in particular, indium sulphide (InP) and cadmium selenide (InP) and cadmium selenide ( CdSe), zinc sulfide (ZnS), and zinc selenium (ZnSe) are particularly preferably used. In particular, it is preferable to use InP as the core and ZnS and / or ZnSe as the shell.

Further, as the material of the semiconductor nanoparticles, perovskite crystals can also be preferably used. The perovskite crystal has a composition represented by the following formula (I) and has a three-dimensional crystal structure.
Formula (I): AQX ₃
[In formula (I), A is a monovalent cation of at least one amine compound selected from the group consisting of _{methylammonium (CH 3} NH ₂ ) and formamidinium (NH _{2 CHNH), or rubidium (} It is a monovalent cation of an alkali metal element which is at least one selected from the group consisting of Rb), cesium (Ce) and franciu (Fr), and Q is from the group consisting of lead (Pb) and tin (Sn). It is a divalent cation of at least one metal element selected, and X is a monovalent anion of at least one halogen element selected from the group consisting of iodine (I), bromine (Br) and chlorine (Cl). It is an ion. ]

As the semiconductor nanoparticles, core-shell type semiconductor nanoparticles having a core-shell structure are preferable. The core-shell type semiconductor nanoparticles have a structure having a core and a shell in which the core is coated with a material different from the material forming the core. By selecting a semiconductor with a large bunt gap for the shell, excitons (electron-hole pairs) generated by photoexcitation are confined in the core. As a result, the probability of non-radiative transition on the particle surface is reduced, and the quantum yield of emission and the stability of fluorescence characteristics are improved. Further, the shell may have a plurality of layers. Further, the boundary between the core and the shell and between one shell and the other shell may be a clear gradient structure or a gradient structure in which the core and the shell are gradually joined with a concentration gradient. Further, the shell may cover only a part of the core or the whole core.

The average particle size of the semiconductor nanoparticles including the core and the shell is usually 0.5 nm to 100 nm, preferably 1 to 50 nm, and more preferably 1 to 15 nm.
Here, the average particle size refers to a value obtained by observing semiconductor nanoparticles with a transmission electron microscope, randomly measuring 30 sizes, and adopting the average value. At this time, the semiconductor nanoparticles are accompanied by an organic ligand described later. On the other hand, by using a scanning transmission electron microscope accompanied by energy dispersive X-ray analysis, semiconductor nanoparticles excluding the organic ligand are specified and the particle size is measured. The semiconductor nanoparticles are identified by utilizing the fact that the semiconductor nanoparticles are imaged darker than the organic ligand due to the difference in electron density in the transmission electron microscope image. The shape of the semiconductor nanoparticles is not limited to a spherical shape, and may be a rod shape, a disk shape, or any other shape.

<Ligand>
The ligand covers at least a part of the surface of the semiconductor nanoparticles and is used for surface treatment of semiconductor nanoparticles. A ligand having no aromatic ring structure is a dispersible ligand, and a ligand having an aromatic ring structure is a charge transporting property. Sometimes abbreviated as ligand.

[Ligand without aromatic ring]
The ligand having no aromatic ring structure is not particularly limited, and preferably has an adsorption site to semiconductor nanoparticles and a non-aromatic chain site.
Examples of the adsorption site include 1 to 3 valent groups, and examples of the monovalent group include a carboxyl group (-COOH), an amino group (-NH ₂ ), a phosphino group (-PH ₂ ), and a sulfanyl group. (-SH); Examples of the divalent group include a carbonyl group (> (C = O)); Examples of the trivalent group include a phosphoroso group (> (P = O)-); It is a monovalent group, more preferably at least one group selected from the group consisting of a carboxyl group and a sulfanyl group.

Ligands having no aromatic ring and a nonaromatic chain moiety and adsorptive group described above, for ^{_{example, R i COOH, R i NH}} 2, R i 2 NH, R i SH, R i H 2 PO, R ^{_{i 2 HPO, R i 3 PO}} , R i H 2 P, R i 2 HP, R i 3 P, include at least one selected from R i PO _{(OH) 2,} and the group consisting of ^R _i 2 POOH. Here, ^Ri is a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aliphatic heterocyclic group, or a substituted or unsubstituted alkoxy group. If a molecule has multiple ^Ris , they may be the same or different.

Examples of the aliphatic hydrocarbon group substituted or unsubstituted in the R ^i, include aliphatic hydrocarbon group having 1 to 18 carbon atoms, for example, an alkyl group, an alkenyl group, an alkynyl group or a cycloalkyl group.

Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a hexyl group, a heptyl group and an octyl group. Examples thereof include alkyl groups having 1 to 18 carbon atoms such as a decyl group, a dodecyl group, a pentadecyl group or an octadecyl group.

Examples of the alkenyl group include a vinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a 1-octenyl group, a 1-decenyl group or 1 -An alkenyl group having 2 to 18 carbon atoms such as an octadecenyl group can be mentioned.

Examples of the alkynyl group include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a 1-butynyl group, a 2-butynyl group, a 3-butynyl group, a 1-octynyl group, a 1-decynyl group or a 1-octadecynyl group. Examples of the alkynyl group having 2 to 18 carbon atoms.

Examples of the cycloalkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclooctadecyl group, a 1-adamantyl group or a 2-adamantyl group having 3 to 18 carbon atoms. Cycloalkyl groups can be mentioned.

The aliphatic heterocyclic group substituted or unsubstituted in the R ^i, for example, 2-Pirazorino group, piperidino group, aliphatic heterocyclic group of 3 to 18 carbon atoms such as a morpholino group or a 2-morpholinyl group.

Examples of the alkoxy group substituted or unsubstituted in the R ^i, for example, a methoxy group, an ethoxy group, a propoxy group, n- butoxy group, sec- butoxy group, tert- butoxy group, pentyloxy group, hexyloxy group, 2-ethylhexyl Examples thereof include an oxy group, a stearyloxy group and a trifluoromethoxy group.

Examples of the substituent R ⁱ may have each independently represent a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aliphatic heterocyclic group, a substituted or unsubstituted alkoxy group, or Halogen atom can be mentioned. A substituted or unsubstituted aliphatic hydrocarbon group, the substituted or unsubstituted aliphatic heterocyclic group and a substituted or unsubstituted alkoxy group include those described as substituents of R ^i, as the halogen atom, Examples include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

Specific examples of ligands that do not have an aromatic ring include methanethiol, ethanethiol, propanethiol, butanethiol, pentanthiol, hexanethiol, octanethiol, dodecanethiol, hexadecanethiol, octadecanethiol; methaneamine, ethaneamine, propaneamine, and butylamine. , Pentylamine, hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine; methaneic acid, ethaneic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, hepanoic acid, Octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid; substituted or unsubstituted methylphosphine (eg, trimethylphosphine, etc.), substituted or unsubstituted ethylphosphine (eg, triethylphosphine, etc.), substituted or unsubstituted Phosphines such as propylphosphine, substituted or unsubstituted butylphosphine, substituted or unsubstituted pentylphosphine, substituted or unsubstituted octylphosphine (eg, trioctylphosphine (TOP)); substituted or unsubstituted methylphosphine oxide (eg). : Trimethylphosphine oxide, methyldihexylphosphine oxide, etc.), substituted or unsubstituted ethylphosphine oxide (eg, triethylphosphine oxide, etc.), substituted or unsubstituted propylphosphine oxide, substituted or unsubstituted butylphosphine oxide, substituted or Examples include unsubstituted octylphosphine oxide (eg, phosphine oxide such as trioctylphosphine oxide (TOPO); phosphonic acid).

The ligand having no aromatic ring preferably has an aliphatic structure from the viewpoint of quantum dot dispersibility, more preferably has an alkyl group having 1 to 18 carbon atoms, and further preferably has 3 to 18 carbon atoms. It has an alkyl group of 5 to 18, and particularly preferably an alkyl group having 5 to 18 carbon atoms (however, it does not have an ether bond or an imino bond).

Furthermore, another preferred group of dispersible ligands of the present invention are compounds having a chain structure containing 1 to 6 oxygen atoms or 1 to 6 nitrogen atoms. Among them, those having an ether bond or an imino bond are preferable, and among them, those having a repeating structure by any one of an oxyethylene bond, an oxypropylene bond and an iminoethylene bond are preferable from the viewpoint of dispersibility. Further, the ligand may further have an ester bond, an amide bond, or a ketone structure.

Specific examples of another group of ligands having no aromatic ring structure of the present invention will be described below, but these are not limited to the present invention.
Dispersible ligands include, for example, 3- (2-methoxyethoxy) propionic acid, 3- (2-methoxypropoxy) ethanethiol, 3,6-dioxadecanoic acid, 3,6,9-trioxadecanoic acid, 3, 6,9,12-Tetraoxatridecanoic acid, 2- [2- (2-methoxyethoxy) ethoxy] ethaneamine, 2- (2-methoxyethoxy) ethaneamine, 2- [2- (2-methoxyethoxy) ethoxy] Esterthiol, 2- [2- (2-dimethylaminoethylmethylamino) ethylmethylamino] propionic acid, 3,6,9,12-tetraoxatridecaneamine, 3,6,9,12-tetraoxatridecane Thiol, 3,6,9,12,15,18-hexaoxanonadecanethiol, 3,6-dioxa-3-mercaptooctane-1-ol, thiol-PEG2-t-butyl ester, thiol-PEG3-t- Butyl ester, thiol-PEG2-carboxylic acid, thiol-PEG3-carboxylic acid, thiol-PEG4-alcohol, 3- [2- (2-methoxyethoxy) ethoxy] propionic acid, 3- (2-aminoethoxy) propionic acid, Amino-PEG1-t-butyl ester, amino-PEG2-t-butyl ester, amino-PEG5-t-butyl ester and the like can be mentioned.
(In the above, the number after PEG represents the number of repetitions of the oxyethylene bond.)

[Ligand with aromatic ring]
The charge-transporting ligand having an aromatic ring structure is not particularly limited as long as it has an adsorption site for semiconductor nanoparticles and an aromatic ring site.
Since the aromatic ring has a π electron that is easier to move than a σ electron in a conjugated form, it is easy to transfer carriers such as holes and electrons. Therefore, the ligand having an aromatic ring has charge transporting property, and examples of the charge transporting property include hole transporting property and / or electron transporting property. Whether the charge transport property is hole transport property or electron transport property is determined by the skeleton and the ionization potential.
In the present invention, the ligand having an aromatic ring may be either a hole-transporting ligand having a hole-transporting property or an electron-transporting ligand having an electron-transporting property, and has both hole-transporting property and electron-transporting property. It may be a ligand. The ligand having both hole transporting property and electron transporting property is included in both the hole transporting ligand and the electron transporting ligand.
The hole-transporting ligand and the electron-transporting ligand will be described below.

[Hole-transporting ligand]
The hole-transporting ligand has an adsorption site on the surface of semiconductor nanoparticles and a hole-transporting site having a hole-transporting function. The adsorption site and the hole transporting site do not have to be completely separated. For example, a part of the hole transporting site may be an adsorption site.

Examples of the adsorption site include a carboxyl group (-COOH), an amino group (-NH ₂ ), a phosphino group (-PH ₂ ), a sulfanyl group (-SH), and the like as monovalent groups. Examples of the divalent group include a carbonyl group (> (C = O)) and the like, and examples of the trivalent group include a phosphoroso group (> (P = O) −) and the like. Further, a 2,2'-bipyridine skeleton, an 8-quinolinol skeleton, or the like can also be used as an adsorption site.

Examples of the hole-transporting moiety include a moiety having a structure composed of a known hole-transporting compound used as an organic electroluminescent element material and a derivative thereof, and are not particularly limited, but for example, a tertiary aromatic amine and thiophene. Oligomers, thiophene polymers, pyrrole oligomers, pyrrol polymers, phenylene vinylene oligomers, phenylene vinylene polymers, vinyl carbazole oligomers, vinyl carbazole polymers, fluorene oligomers, fluorene polymers, phenylene ethine oligomers, phenylene ethine polymers, phenylene oligomers, phenylene polymers Examples thereof include acetylene polymers, phthalocyanines, phthalocyanine derivatives, porphyrins, and porphyrin derivatives. In addition, the compounds shown below and their derivatives can also be used as hole transporting sites.

Further, as a preferable structure of the hole transporting ligand, a compound represented by the following general formula (1), general formula (2) or general formula (3) can be mentioned.

General formula (1)

[In the general formula (1), X ¹ is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, or an acyl group which may have a substituent. , R ^{1 to} R ⁸ are independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, and a substitution. An aryloxy group which may have a group, an acyl group which may have a substituent, an amino group which may have a substituent, a (poly) organosiloxane group which may have a substituent, and a carboxyl group. Alternatively, it is a sulfanyl group, and ^{at least one of X 1} and R ^{1 to} R ⁸ is a group having a carboxyl group or a group having a sulfanyl group. ]

General formula (2)

[In the general formula (2), R ^{11 to} R ²⁵ each independently have a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, and a substituent. May have an alkoxy group, an aryloxy group which may have a substituent, an acyl group which may have a substituent, a (poly) organosiloxane group which may have a substituent, a nitro group, and a substituent. It is an amino group, a carboxyl group or a sulfanyl group which may have ^{, and at least one of R 11 to} R ²⁵ is a group having a carboxyl group or a group having a sulfanyl group. ]

General formula (3)

[In the general formula (3), X ² has a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent (excluding a phenyl group), or a substituent. The acyl groups may be, and R ^{26 to} R ³⁵ each independently have a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, and a substituent. It has an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a (poly) organosiloxane group which may have a substituent, an amino group which may have a substituent, and a substituent. It is also a good acyl group, carboxyl group or sulfanyl group, and ^{at least one of X 2} and R ^{26 to} R ³⁵ is a group having a carboxyl group or a group having a sulfanyl group. ]
The substituents in the general formulas (1) to (3) will be described below.

The alkyl group is a linear, branched or cyclic alkyl group, and some hydrogen atoms may be shed to form a double bond or a triple bond. From the viewpoint that the content of semiconductor nanoparticles in the composition can be increased, the molecular weight of the treatment agent is preferably small, and the number of carbon atoms of the alkyl group is preferably 1 to 30.
Examples of the alkyl group include a linear alkyl group such as a methyl group, an ethyl group, a hexyl group, a dodecyl group and an eicosyl group; a branched alkyl group such as a 2-ethylhexyl group; and a cyclic group such as a cyclohexyl group and a 3-cyclohexylpropyl group. Alkyl group; alkenyl group such as ethenyl group and dodecenyl group; alkynyl group such as 1-propynyl group and propargyl group can be mentioned.

Aryl groups are residues in which one hydrogen atom is formally removed from an aromatic ring, and preferably a residue in which one hydrogen atom is formally removed from an aromatic ring having 6 to 30 carbon atoms.
Examples of the aromatic ring include a benzene ring, a naphthalene ring, a pyrene ring, a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a quinoline ring, a furan ring, a pyrrol ring, a thiophene ring, an imidazole ring, a pyrazole ring, an oxazole ring, and a thiazole ring. , Indol ring, benzimidazole ring, benzofuran ring, purine ring, aclysin ring, phenothiazine ring, biphenyl group, or terphenyl group.

The alkoxy group is a functional group to which an alkyl group is bonded via an ether bond, and the alkyl group is synonymous with the alkyl group in the above general formulas (1) to (3).

The aryloxy group is a functional group to which an aryl group is bonded via an ether bond, and the aryl group is synonymous with the aryl group in the above-mentioned general formulas ((1) to (3)).

The acyl group is a functional group to which an alkyl group or an aryl group is bonded via a carbonyl group, and the alkyl group and the aryl group are synonymous with the alkyl group and the aryl group in the above general formulas (1) to (3). Is.

The (poly) organosiloxane group is a residue obtained by formally removing one hydrogen atom from the siloxane compound, and the silicon of the siloxane compound may be substituted with an alkyl group. The alkyl group which may be substituted is synonymous with the alkyl group in the above general formulas (1) to (3). Examples of siloxane compounds include pentamethyldisiloxane, heptaethyltrisiloxane, undecamethyltetrasiloxane, trimethylsiloxydimethylsilanol, 1,1,3,3, tetramethyl-1,3-dihydroxydisiloxane or 1 , 1,3,3,5,5-hexamethyl-1,5-dihydroxy-trisiloxane and the like.
From the viewpoint that the content of semiconductor nanoparticles in the composition can be increased, the molecular weight of the ligand is preferably small, and the number of repeated siloxane bonds is preferably 4 or less.

The amino group which may have a substituent includes an amino group and a substituted amino group, and examples of the substituent of the substituted amino group include an alkyl group, an aryl group and an acyl group. The alkyl group, aryl group and acyl group are synonymous with the alkyl group, aryl group or acyl group in the above general formulas (1) to (3).

The alkyl group, aryl group, alkoxy group, amino group, aryloxy group and acyl group in the general formulas (1) to (3) may have a substituent.
Examples of the substituent that may be possessed include a halogeno group, a cyano group, a hydroxy group, a nitro group, an alkoxy group, an alkyl group, an aralkyl group, an aryl group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, and an acyloxy group. , Carbamoyloxy group, alkoxycarbonyloxy group, aryloxycarbonyloxy, amino group (including anilino group), acylamino group, aminocarbonylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfamoylamino group, alkyl And arylsulfonylamino groups, sulfanyl groups, alkylthio groups, arylthio groups, heterocyclic thio groups, alkyl and arylsulfinyl groups, alkyl and arylsulfonyl groups, acyl groups, aryloxycarbonyl groups, alkoxycarbonyl groups, carbamoyl groups, imide groups, Examples thereof include a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a silyl group, a group containing a siloxane bond, and the like.
Further, the substituents that may be possessed in the present invention include the above-mentioned monovalent substituent and, if necessary, an alkylene group, an alkenylene group, an arylene group, a heteroarylene group, an ether bond, an ester bond, a sulfide bond and a carbonyl group. It may be a monovalent group in which a group, an imino group, or a divalent linking group in which they are combined is combined.

A group having a carboxyl group or a sulfanyl group is an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an amino group, or a (poly) organo having a carboxyl group or a sulfanyl group as a substituent in addition to the carboxyl group and the sulfanyl group. Contains a siloxane group or an acyl group. Here, in addition to the carboxyl group and the sulfanyl group, the alkyl group, the aryl group, the alkoxy group, the aryloxy group, the (poly) organosiloxane group, the acyl group or the nitro group having a carboxyl group or a sulfanyl group as a substituent are described above. It is synonymous with the group in the general formulas (1) to (3) of.

Examples of the alkyl group having a carboxyl group or the aryl group having a carboxyl group include, for example, a 2-carbosixyl ethyl group, a 2,2-dicarboxyethyl group, a 2-carbosixyl ethenyl group, and a 2-cyano-. Examples thereof include 2-carbosixyl ethenyl group, 2-trifluoromethyl-2-carbosixyl ethenyl group, 2-fluoro-2-carbosixyl ethenyl group and the like.

Examples of the alkyl group having a sulfanyl group, the aryl group having a sulfanyl group, or the acyl group having a sulfanyl group include [(3-sulfanylpropanoyl) oxy] ethyl group and [(2-sulfanylacetyl) oxy] ethyl group. , 4- (Sulfanylmethyl) phenyl group, [(3-sulfanylpropanoyl) oxy] propyl group, 3-sulfanyl [(3-sulfanylpropanoyl) oxy] ethyl group, or {[(2-sulfanylethoxy) propanoyl] Oxy} ethyl group and the like can be mentioned.

Specific examples of the ligands represented by the general formulas (1) to (3) are shown below, but the present invention is not limited thereto. In the following structural formula, when cis-type and trans-type geometric isomers are present, either cis-type or trans-type may be used, and a mixture of cis-type and trans-type isomers may be used. The same applies to the thin-anti geometric isomerism.

[Electron-transporting ligand]
The electron-transporting ligand has an adsorption site on the surface of semiconductor nanoparticles and an electron-transporting site having an electron-transporting function. The adsorption site and the electron transporting site do not have to be completely separated. For example, a part of the electron transporting site may be an adsorption site. Examples of the adsorption site include those described in the section on hole-transporting ligands.

Examples of the electron-transporting moiety include a moiety having a structure composed of a known electron-transporting compound used as an organic electric field light emitting element material and a derivative thereof, and are not particularly limited, but for example, oxadiazole, oxadiazole derivative, and oxazole. , Oxazole derivative, isoxazole, isooxazole derivative, thiazole, thiazole derivative, isothiazole, isothiazole derivative, thiaxazole, thiazazole derivative, 1,2,3-triazole, 1,2,3-triazole derivative, 1,3,5 -Triazine, 1,3,5-triazine derivative, quinoxalin, quinoxalin derivative, pyrrole oligomer, pyrrol polymer, phenylene vinylene oligomer, phenylene vinylene polymer, vinyl carbazole oligomer, vinyl carbazole polymer, fluorene oligomer, fluorene polymer, phenylene ethine oligomer, phenylene Examples thereof include ethine polymers, phenylene oligomers, phenylene polymers, thiophene oligomers, thiophene polymers, acetylene polymers, and acetylene oligomer derivatives. In addition, the following compounds and their derivatives can also be used as electron transporting sites.

The hole-transporting site and the electron-transporting site described above contain the same structure, because they can be both an electron-transporting site and a hole-transporting site. Whether the ligand behaves as hole-transporting or electron-transporting depends on the relative HOMO-LUMO relationship between the hole-transporting ligand and the electron-transporting ligand, and relative to other compounds used in electroluminescent devices. The HOMO and LUMO are determined by the specific HOMO-LUMO relationship, and even if the structure is specific, the HOMO and LUMO are changed by the presence of an electron-withdrawing or electron-donating substituent. For the above reasons, some structures can be both hole-transporting and electron-transporting sites and are therefore described in both.

In the hole-transporting ligand and the electron-transporting ligand, the hole-transporting site and the adsorption site, or the electron-transporting site and the adsorption site may be directly bonded to each other, or a linking group such as an alkylene group may be used. It may be connected via. Examples of the alkylene group in this case include a branched or linear alkylene group, and a linear alkylene group is preferable. The alkylene group preferably has about 1 to 5 carbon atoms, and specific examples thereof include a methylene group, an ethylene group, an n-propylene group, an n-butylene group, and an n-pentylene group.

Specific examples of the hole-transporting ligand and the electron-transporting ligand are shown below, but the present invention is not limited thereto.

In the above-mentioned charge transporting ligand, HOMO and LUMO are important from the viewpoint of charge injection property and charge transport property. HOMO electrons are the most reactive and involved in reactivity. When receiving an electron, LUMO is involved in the reaction. That is, HOMO is a molecular orbital that emits electrons, LUMO is a molecular orbital that accepts electrons, and in an electroluminescent device, HOMO plays a role of transferring holes, and LUMO plays a role of transferring electrons.
The HOMO energy level of the hole transporting ligand is preferably -6, 5 eV or more and -4.6 eV or less, and more preferably -6.1 eV or more and -5.1 eV or less. The LUMO energy level of the electron transporting ligand is preferably −4.5 eV or more and −2.5 eV or less, and more preferably −4.0 eV or more and −3.0 eV or less. When the HOMO and / or LUMO of the hole-transporting ligand and the electron-transporting ligand satisfy the above conditions, the transport of electrons and holes in the electroluminescent device and the injection of electrons and holes into the semiconductor nanoparticles are performed. Quantum dots (A2) surface-treated with this ligand are preferable because they can be excellent and can obtain a high-performance electric field light emitting device.

<Light emitting part>
The light emitting portion in the present invention has at least two continuous light emitting layers, a light emitting layer (EML1) containing quantum dots (A1) which are semiconductor nanoparticles surface-treated with a ligand having no aromatic ring, and an aromatic. It has a light emitting layer (EML2) containing quantum dots (A2), which are semiconductor nanoparticles surface-treated with a ring-bearing ligand.
Here, the at least two continuous light emitting layers represent a state in which at least two light emitting layers (EML1) and (EML2) are laminated.

When the light emitting portion is laminated with light emitting layers in the order of (EML1) and (EML2) from the anode side, the hole injection layer and the hole transport layer, which are lower layers during film formation, are dispersed in a solvent that is difficult to erode. Since the ink composition of the formed quantum dots (A1) is applied first, and then the ink composition of the quantum dots (A2) having high charge transportability is applied, good lamination is performed without eroding the lower layer. It is possible to obtain a film and to achieve both luminous efficiency and durability of the element.
Further, even when laminating from the electron injection layer, if the material is an organic compound, a high-performance element can be similarly obtained by laminating in the order of (EML1) / (EML2).

As for the semiconductor nanoparticles contained in the quantum dots (A1) and (A2) in the light emitting portion of the present invention, it is generally preferable to use those having the same composition, particle size, etc., because color deviation due to lamination does not occur. .. As a surface treatment method for quantum dots, a method in which quantum dots are once synthesized with a ligand for synthesis and then treated with each ligand to obtain (A1) or (A2), and synthesis is relatively easy (A1). ) Is prepared first and treated with a ligand having an aromatic ring to obtain (A2). Further, in order to obtain light emission of a neutral color, semiconductor nanoparticles having different compositions and particle sizes may be intentionally used.

The thicknesses of the light emitting layers (EML1) and (EML2) in the present invention are preferably in the range of 1 nm to 500 nm, respectively, but are preferably in the range of 5 nm to 100 nm because both low driving voltage and high luminous efficiency can be achieved. The thickness of (EML1) is preferably about 5 nm to 50 nm, more preferably about 5 to 20 nm. Within this range, it is possible to prevent the solvent that disperses (A2) from passing through (EML1) and affecting the lower layer, which is preferable. Further, it is preferable that the thickness of (ELM2) is larger than the thickness of (ELM1) in order to achieve both element characteristics such as drive voltage and high luminous efficiency and durability.

The light emitting layer constituting the light emitting portion can be formed by applying or printing a composition in which each of the quantum dots (A1) and (A2) is dispersed in a solvent (hereinafter referred to as an ink composition). ..

<Ink composition>
The ink composition contains quantum dots and a solvent, and may further contain other components if necessary. The ink composition consists of a composition in which quantum dots (A1), which are semiconductor nanoparticles surface-treated with a ligand having no aromatic ring, are dispersed, and quantum dots, which are semiconductor nanoparticles surface-treated with a ligand having an aromatic ring. There are at least two types of compositions in which (A2) is dispersed, and by adjusting the composition to match the properties of quantum dots, especially the surface-treated ligand, dispersion stability, coatability, and (lamination) of the ink composition can be obtained. It is possible to improve all items such as film forming property and light emitting characteristics and durability of the element. Hereinafter, each component contained in the ink composition will be described. The semiconductor nanoparticles that are the light emitting materials are as described above.

[solvent]
The solvent can be appropriately selected from the solvents capable of dispersing the semiconductor nanoparticles, depending on the site of use of the ink composition in the light emitting device and the like. Specific examples of the solvent include aromatic hydrocarbons such as toluene, o-xylene, m-xylene, p-xylene, methicylene, cyclohexylbenzene and tetraline; halogenated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene and trichlorobenzene. Hydrogen; 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetol, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, 2,4-dimethylanisole, etc. Aromatic ethers; aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, n-butyl benzoate; ketones having an alicyclic such as cyclohexanone and cyclooctanone; methylethylketone, dibutyl Aromatic ketones such as ketones; alcohols having an alicyclic such as cyclohexanol and cyclooctanol; aliphatic alcohols such as butanol and hexanol; ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol-1-monomethyl ether acetate (PGMEA) And other aliphatic ethers; ethyl acetate, n-butyl acetate, ethyl lactate, n-butyl lactate and other aliphatic esters; n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2, Aromatic or alicyclic hydrocarbons such as 3-dimethylbutane, n-heptane, n-decane, 2,2,4-trimethylpentane, cyclohexane, methylcyclohexane, mineral spirit; It may be mixed and used.

The solvent is preferably one in which the semiconductor nanoparticles can be dispersed in an amount of 1% by mass or more at 25 ° C. Since it can be dispersed in an amount of 1% by mass or more, it is possible to prevent the ink composition from coagulating and settling over time, and further to suppress coagulation and non-uniformity in the coating and drying steps. More preferably, it is dispersible in an amount of 5% by mass or more. However, in the present invention, the concentration of semiconductor nanoparticles in the ink composition when actually used is not limited to the above values, and is appropriately determined depending on the properties of the ink composition and the film thickness after film formation. It is possible to select.

Of the above solvents, n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, n-heptane, n-octane, n-decane, 2,2,4 An aliphatic hydrocarbon solvent such as −trimethylpentane; an alicyclic hydrocarbon solvent such as cyclohexane and methylcyclohexane; is an aliphatic hydrocarbon-based ligand having no aromatic ring structure, particularly an aliphatic hydrocarbon having 1 to 18 carbon atoms. Since quantum dots surface-treated with a ligand having a hydrogen chain are well dispersed, they can be suitably used as a solvent for an ink composition. When the light emitting device of the present invention has a hole injection layer or a hole transport layer made of an organic compound in the lower layer, the solvent is poorly soluble in the organic compound constituting the lower layer, so that the lower layer is coated without erosion. A film can be formed. This makes it possible to obtain an electroluminescent element having further excellent low drive voltage, high luminous efficiency, and high durability.

Among the solvents, aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA); ethyl acetate, n-butyl acetate, ethyl lactate, n-butyl lactate and the like. Non-aromatic solvents containing ether or ester bonds such as the aliphatic esters of; have ligands having a chain structure containing 1 to 6 oxygen or nitrogen atoms in the chain, particularly ether or imino bonds. Since the quantum dots surface-treated with the chain ligand having the ester are dispersed well, it can be suitably used as a solvent for the ink composition. When the light emitting device of the present invention has a hole injection layer or a hole transport layer made of an organic compound in the lower layer, the solvent has poor solubility of the organic compound constituting the lower layer, so that the lower layer is not eroded. Can be applied and formed into a film. This makes it possible to obtain an electroluminescent element having further excellent low drive voltage, high luminous efficiency, and high durability.

On the other hand, among the solvents, aromatic hydrocarbons such as toluene, o-xylene, m-xylene, p-xylene, methicylene, cyclohexylbenzene and tetraline; and halogenated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene and trichlorobenzene; Aromatic compounds such as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, solvent anisole, phenetol, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole. Group ethers; aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, n-butyl benzoate; aromatic ketones such as acetophenone and propiophenone; aromatic solvents such as Can be suitably used as a solvent for an ink composition because it satisfactorily disperses quantum dots (A2) which are semiconductor nanoparticles surface-treated with a ligand having an aromatic ring. This makes it possible to obtain an electroluminescent element having a low drive voltage, high luminous efficiency, and high durability.

The content ratio of the semiconductor nanoparticles in the ink composition may be appropriately adjusted according to the use of the ink composition and the like. The ratio of the semiconductor nanoparticles to the total amount of the ink composition is preferably 0.001% by mass or more and 50% by mass or less, and more preferably 0.01% by mass or more and 10% by mass or less. When the ratio of the semiconductor nanoparticles is not more than the above upper limit value, the dispersion stability of the semiconductor nanoparticles is excellent.

The ink composition may contain other components as long as the object of the present invention is not impaired. Examples of other components include light emitting materials other than semiconductor nanoparticles described later, various additives, and the like. Examples of the additive include an antifoaming agent, a leveling agent, a thickener and the like.

Examples of the method for obtaining a printed matter from the ink composition include known wet film forming methods, for example, a coating method, an inkjet method, a dip coating method, a die coating method, a spray coating method, a spin coating method, a roll coater method, and a wet coating method. Examples include a screen printing method, a flexographic printing method, a screen printing method, and an LB method.

<Electroluminescent element>
The electroluminescent device of the present invention has at least a substrate, an anode, a light emitting layer, and a cathode, and may be a single-layer electroluminescent device composed of an anode, a light emitting layer, and a cathode, and is necessary. It may have other layers depending on the situation. In general, a multilayer electroluminescent device including a layer other than the light emitting layer is preferably selected from the viewpoint of improving element characteristics such as luminous efficiency.

Other layers include a hole injection layer for the purpose of facilitating the injection of holes and electrons into the light emitting layer and facilitating the recombination of holes and electrons in the light emitting layer. , Hole transport layer, hole blocking layer, electron injection layer and the like. Further, as another layer, it exists between the light emitting layer and the anode adjacent to the light emitting layer, and separates the light emitting layer and the anode, or the light emitting layer from the hole injection layer or the hole transport layer. The target interlayer layer and the like can be mentioned.
Typical layer configurations of the multi-layer electric field light emitting element include (1) anode / hole injection layer / light emitting layer / cathode, (2) anode / hole injection layer / hole transport layer / light emitting layer / cathode, and (1) 3) anode / hole injection layer / light emitting layer / electron injection layer / cathode, (4) anode / hole injection layer / hole transport layer / light emitting layer / electron injection layer / cathode, (5) anode / hole injection Layer / light emitting layer / hole blocking layer / electron injection layer / cathode, (6) anode / hole injection layer / hole transport layer / light emitting layer / hole blocking layer / electron injection layer / cathode, (7) anode / Light emitting layer / hole blocking layer / electron injection layer / cathode, (8) anode / light emitting layer / electron injection layer / cathode (9) anode / hole injection layer / hole transport layer / interlayer layer / light emitting layer / cathode , (10) Electron / hole injection layer / interlayer layer / light emitting layer / electron injection layer / cathode, (11) anode / hole injection layer / hole transport layer / interlayer layer / light emitting layer / electron injection layer / Examples include a cathode.

Each of the above-mentioned layers may be formed by a layer structure of two or more layers, or several layers may be repeatedly laminated. As such an example, in recent years, for the purpose of improving the light extraction efficiency, an element configuration called "multi-photon emission" in which a part of the above-mentioned multi-layer electroluminescent layers is multi-layered has been proposed. In an electroluminescent device composed of a glass substrate / anode / hole transport layer / electron transporting light emitting layer / electron injection layer / charge generating layer / light emitting layer / cathode, there are a plurality of charge generating layer / light emitting layer units. It includes a layered structure and the like.

The electroluminescent device of the present invention has a light emitting layer (EML1) containing semiconductor nanoparticles surface-treated with a ligand having no aromatic ring and a light emitting layer (EML2) containing semiconductor nanoparticles surface-treated with a ligand having an aromatic ring. ) And the ligand that does not have an aromatic ring prevents the injected charge from moving to the opposite film or electrode, while the ligand that has an aromatic ring provides sufficient emission characteristics of the quantum dots. It becomes possible to pull out to.
In particular, in the case of a configuration in which a hole injection layer containing a compound having an aromatic ring is provided between the anode and the light emitting portion, the light emitting portion is formed by arranging the light emitting layers in the order of (EML1) and (EML2) from the anode side. When, the overlap at the interface between the aromatic ring structures is eliminated, and the holes move from the hole injection layer to the light emitting layer, but the electrons are blocked by the light emitting layer (EML1), and while maintaining the low voltage drive, Since it is possible to obtain an element having excellent luminous efficiency and durability, it is very preferable as an element configuration.

[Hole injection layer]
As the hole injection layer, a hole injection material that exhibits an excellent hole injection effect on the light emitting layer and can form a hole injection layer having excellent adhesion to the anode interface and thin film formation is used. Further, when such a material is laminated in multiple layers and a material having a high hole injection effect and a material having a high hole transport effect are laminated in multiple layers, the materials used for each are referred to as a hole injection material and a hole transport material. Sometimes. These hole injection materials and hole transport materials need to have a large hole mobility and a small ionization energy of usually 5.5 eV or less. As such a hole injection layer, a material that transports holes to the light emitting layer with a lower electric field strength is preferable, and further ^{, when an electric field with a hole mobility of, for example, 10 4} to 10 ⁶ V / cm is applied, at least ^{It is preferably 10-6} cm ² / V · sec. The hole injection material and the hole transport material are not particularly limited as long as they have the above-mentioned preferable properties, and are conventionally used as a hole charge transport material in an optical transmission material or an organic EL device. Any known material used for the hole injection layer can be selected and used.

Examples of such hole injection materials and hole transport materials include triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, and amino-substituted chalcones. Examples thereof include derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilben derivatives, silazane derivatives, polysilane-based, aniline-based copolymers, aromatic dimethylidene-based compounds, conductive polymer oligomers, and particularly thiophene oligomers.

The hole injection material and the hole transport material are preferably porphyrin compounds, aromatic tertiary amine compounds, styrylamine compounds and the like, and for example, 4,4'- having two fused aromatic rings in the molecule. Bis (N- (1-naphthyl) -N-phenylamino) biphenyl and 4,4', 4 "-tris (N- (3-methylphenyl)" in which three triphenylamine units are linked in a starburst form. -N-Phenylamino) Triphenylamine can be mentioned, and preferred hole injection materials include phthalocyanine derivatives such as copper phthalocyanine and hydrogen phthalocyanine.

Materials that can be used for the hole injection layer include inorganic semiconductor compounds such as p-type Si and p-type SiC, molybdenum oxide (MnO _x ), vanadium oxide (VO _x ), ruthenium oxide (RuO _x ), and copper oxide (CuO). _x), tungsten oxide _(WO x), an inorganic oxide such as iridium oxide (IrO _x) and their doped products thereof.

Specific examples of the aromatic tertiary amine compound include, for example, N, N'-diphenyl-N, N'-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine, N, N, N', N'-(4-methylphenyl) -1,1'-phenyl-4,4'-diamine, N, N, N', N'-(4-methylphenyl) -1,1' -Biphenyl-4,4'-diamine, N, N'-diphenyl-N, N'-dinaphthyl-1,1'-biphenyl-4,4'-diamine, N, N'-(methylphenyl) -N, N'-(4-n-butylphenyl) -phenanthrene-9,10-diamine, N, N-bis (4-di-4-tolylaminophenyl) -4-phenyl-cyclohexane, N, N'-bis ( 4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine, N, N'-bis (4'-diphenylamino-4-phenyl) -N, N'-diphenylbenzidine, N, N'- Bis (4'-diphenylamino-4-phenyl) -N, N'-di (1-naphthyl) benzidine, N, N'-bis (4'-phenyl (1-naphthyl) amino-4-phenyl) -N , N'-diphenylbenzidine, N, N'-bis (4'-phenyl (1-naphthyl) amino-4-phenyl) -N, N'-di (1-naphthyl) benzidine and the like. It can be used as both a hole injection material and a hole transport material.

Tables 1 and 2 show particularly preferable examples of the hole injection material.

To form the hole injection layer, the above-mentioned compound is thinned by a known method such as a vacuum deposition method, a spin coating method, a casting method, or a Langmuir-Bloget method (LB method). The thickness of the hole injection layer is not particularly limited, and is usually 5 nm to 5 μm.

Examples of the material used for the interlayer layer include polyvinylcarbazole and its derivatives, polyarylene derivatives having aromatic amines in the side chain or main chain, arylamine derivatives, and polymers containing aromatic amines such as triphenyldiamine derivatives. Further, as a method of forming an interlayer layer, when a high molecular weight material is used, a method of forming a film from a solution is exemplified.

For the film formation of the interlayer layer from the solution, known wet film forming methods such as spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, etc. A coating method such as a dip coating method, a spray coating method, a screen printing method, a flexo printing method, an offset printing method, an inkjet printing method, a capillary coating method, or a nozzle coating method can be used.

The optimum value of the thickness of the interlayer layer differs depending on the material used, and it may be selected so that the driving voltage and the luminous efficiency are appropriate values. It is usually 1 nm to 1 μm, preferably 2 to 500 nm, and more preferably. Is 5 to 200 nm.

[Electron injection layer]
As the electron injection layer, an electron injection material that exhibits an excellent electron injection effect on the light emitting layer and can form an electron injection layer having excellent adhesion to the cathode interface and thin film formation is used. Examples of such electron-injected materials include metal complex compounds, nitrogen-containing five-membered ring derivatives, fluorenone derivatives, anthracinodimethane derivatives, diphenoquinone derivatives, thiopyrandioxide derivatives, perylenetetracarboxylic acid derivatives, fleolenilidenemethane. Examples thereof include derivatives, antron derivatives, silol derivatives, triarylphosphine oxide derivatives, polyquinolin and its derivatives, polyquinoxalin and its derivatives, polyfluorene and its derivatives, calcium acetylacetonate, sodium acetate and the like. Inorganic / organic composite materials in which a metal such as cesium is doped with vasophenanthroline (Proceedings of the Society of Polymer Science, Vol. 50, No. 4, p. 660, published in 2001) and the 50th Joint Lecture on Applied Physics. Proceedings of the lecture, No. BCP, TPP, T5MPyTZ, etc. described on page 3, 1402, published in 2003 are also mentioned as examples of electron injection materials, but can form a thin film necessary for device fabrication, inject electrons from a cathode, and transport electrons. As long as it is a material, it is not particularly limited to these.

Among the electron-injected materials, preferred ones include a metal complex compound, a nitrogen-containing five-membered ring derivative, a siror derivative, and a triarylphosphine oxide derivative. As a preferable metal complex compound, a metal complex of 8-hydroxyquinoline or a derivative thereof is suitable. Specific examples of the metal complex of 8-hydroxyquinolin or a derivative thereof include tris (8-hydroxyquinolinate) aluminum, tris (2-methyl-8-hydroxyquinolinate) aluminum, and tris (4-methyl-8-). Hydroxyquinolinate) Aluminum, Tris (5-methyl-8-Hydroxyquinolinate) Aluminum, Tris (5-phenyl-8-Hydroxyquinolinate) Aluminum, Bis (8-Hydroxyquinolinate) (1-naphtholate) ) Aluminum, bis (8-hydroxyquinolinate) (2-naphtholate) Aluminum, bis (8-hydroxyquinolinate) (phenolate) aluminum, bis (8-hydroxyquinolinate) (4-cyano-1-naphtholate) ) Aluminum, bis (4-methyl-8-hydroxyquinolinate) (1-naphtholate) aluminum, bis (5-methyl-8-hydroxyquinolinate) (2-naphtholate) aluminum, bis (5-phenyl-8) -Hydroxyquinolinate) (phenolate) aluminum, bis (5-cyano-8-hydroxyquinolinate) (4-cyano-1-naphtholate) aluminum, bis (8-hydroxyquinolinate) chloroaluminum, bis (8) -Aluminum complex compounds such as hydroxyquinolinate (o-cresolate) aluminum, tris (8-hydroxyquinolinate) gallium, tris (2-methyl-8-hydroxyquinolinate) gallium, tris (4-methyl- 8-Hydroxyquinolinate) gallium, tris (5-methyl-8-hydroxyquinolinate) gallium, tris (2-methyl-5-phenyl-8-hydroxyquinolinate) gallium, bis (2-methyl-8) -Hydroxyquinolinate) (1-naphtholate) gallium, bis (2-methyl-8-hydroxyquinolinate) (2-naphtholate) gallium, bis (2-methyl-8-hydroxyquinolinate) (phenolate) gallium , Bis (2-methyl-8-hydroxyquinolinate) (4-cyano-1-naphtholate) gallium, bis (2,4-dimethyl-8-hydroxyquinolinate) (1-naphtholate) gallium, bis (2) , 5-Dimethyl-8-Hydroxyquinolinate) (2-naphtholate) gallium, bis (2-methyl-5-phenyl-8-hydroxyquinolinate) (phenolate) gallium, bis (2-methyl-5-si) Anno-8-hydroxyquinolinate) (4-cyano-1-naphtholate) gallium, bis (2-methyl-8-hydroxyquinolinate) chlorogallium, bis (2-methyl-8-hydroxyquinolinate) ( In addition to gallium complex compounds such as o-cresolate gallium, 8-hydroxyquinolinate lithium, bis (8-hydroxyquinolinate) copper, bis (8-hydroxyquinolinate) manganese, bis (10-hydroxybenzo [h] ] Kinolinate) Metal complex compounds such as beryllium, bis (8-hydroxyquinolinate) zinc, and bis (10-hydroxybenzo [h] quinolinate) zinc can be mentioned.

Further, preferred examples of the nitrogen-containing five-membered ring derivative include an oxadiazole derivative, a thiazole derivative, an oxadiazole derivative, a thiadiazole derivative, and a triazole derivative. Specifically, 2,5-bis (1-phenyl) -1, 3,4-Oxadiazole, 2,5-bis (1-phenyl) -1,3,4-thiazole, 2,5-bis (1-phenyl) -1,3,4-oxadiazole, 2- (4) '-Tert-butylphenyl) -5- (4 "-biphenyl) 1,3,4-oxadiazole, 2,5-bis (1-naphthyl) -1,3,4-oxadiazole, 1,4 -Bis [2- (5-phenyloxadiazolyl)] benzene, 1,4-bis [2- (5-phenyloxadiazolyl) -4-tert-butylbenzene], 2- (4'-tert-butyl Phenyl) -5- (4 "-biphenyl) -1,3,4-thiadiazole, 2,5-bis (1-naphthyl) -1,3,4-thiadiazole, 1,4-bis [2- (5- (5-) Phenylthiaizolyl)] Benzene, 2- (4'-tert-butylphenyl) -5- (4 "-biphenyl) -1,3,4-triazole, 2,5-bis (1-naphthyl) -1, Examples thereof include 3,4-triazole and 1,4-bis [2- (5-phenyltriazolyl)] benzene.

Further, examples of the material that can be used for the electron injection layer include _{inorganic oxides such as zinc oxide (ZnO x} ) and titanium oxide (TiO _x ), and doped materials thereof.

Specific examples of particularly preferable oxadiazole derivatives, triazole derivatives and siror derivatives are shown in Tables 3 to 5. In addition, Ph in the table represents a phenyl group.

(Oxadiazole derivative)

(Triazole derivative)

(Siror derivative)

Further, as one kind of electron injection layer, there is a hole blocking layer which prevents holes passing through the light emitting layer from reaching the electron injection layer and has excellent thin film forming property. For this, a hole blocking material whose hole transport property is significantly inferior to that of electron transport property is used. Examples of such hole blocking materials include aluminum complex compounds such as bis (8-hydroxyquinolinate) (4-phenylphenolate) aluminum and bis (2-methyl-8-hydroxyquinolinate) ( Examples thereof include gallium complex compounds such as 4-phenylphenolate) gallium and nitrogen-containing condensed aromatic compounds such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).

[Light emitting layer]
As the light emitting layer of the electroluminescent element, one having the following functions is preferable.
Injection function: A function that can inject holes from the anode or hole injection layer when an electric field is applied, and can inject electrons from the cathode or electron injection layer. Transport function; electric charge (electrons and holes) injected Light emitting function; a function that provides a field for recombination of electrons and holes and connects them to light emission. However, there is a difference between the ease of hole injection and the ease of electron injection. Also, the transport capacity represented by the mobility of holes and electrons may be large or small.

It is preferable that at least two consecutive layers of the light emitting layer constituting the electroluminescent device of the present invention contain specific semiconductor nanoparticles, and the light emitting layer is formed from the ink composition. Further, the light emitting layer may contain a known light emitting material in addition to the semiconductor nanoparticles.
Known light-emitting materials that may be added to the ink composition include fluorescent whitening agents such as benzothiazole, benzimidazole, and benzoxazole, and metal chelating of tris (8-quinolinol) aluminum, dilithiumepintridione, and the like. Oxinoid compounds, styrylbenzene compounds, distyrylpyrazine compounds, polyphenyl compounds and the like can be used.

Further, as the light emitting material other than the semiconductor nanoparticles, in addition to the above-mentioned fluorescent whitening agent, metal chelating oxynoid compound, styrylbenzene compound and the like, for example, 12-phthaloperinone, 1,4-diphenyl-1,3-butadiene, 1,1,4,4-Tetraphenyl-1,3-butadiene, naphthalimide derivative, perylene derivative, oxadiazole derivative, aldazine derivative, pyrazirin derivative, cyclopentadiene derivative, pyrolopyrrole derivative, styrylamine derivative, coumarin compound , 9, 9', 10, 10'-tetraphenyl-2,2'-biantrasen, PPV (polyparaphenylene vinylene) derivative, polyfluorene derivative and their copolymers and the like.

Further, as preferred examples of the metal chelated oxinoid compound, bis (2-methyl-8-quinolinolate) (para-phenylphenolate) aluminum (III), bis (2-methyl-8-quinolinolate) (1-naphtholate) aluminum. (III), bis (2-methyl-8-quinolinolate) (para-phenylphenolate) gallium (III) and the like can be mentioned.

In the present invention, the proportion of the light emitting material other than the semiconductor nanoparticles in the total light emitting material is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less.

The light emitting layer for obtaining white light emission is not particularly limited, but the following can be used. The energy level of each layer of the organic EL laminated structure is defined, and light is emitted by using tunnel injection, the light emitting layer has a two-layer structure, and the light emitting layer is divided into a plurality of materials each having a different emission wavelength. The blue light emitting body (fluorescence peak 380 to 480 nm) and the green light emitting body (480 to 580 nm) are laminated, and the red phosphor is further contained, and the blue light emitting layer contains a blue fluorescent dye. , A structure in which the green light emitting layer has a region containing a red fluorescent dye and further contains a green fluorescent substance, and the like, and a part or all of these fluorescent substances are replaced with the semiconductor nanoparticles of the present invention. A white light emitting element can be obtained by using the semiconductor nanoparticles of the present invention in combination with the phosphor.

[anode]
As the material used for the anode, a metal having a large work function (4 eV or more), an alloy, an electrically conductive compound, or a mixture thereof as an electrode material is preferably used. Specific examples of such an electrode material include metals such as Au and conductive materials such as _{CuI, ITO, SnO 2, and ZnO.} In order to form this anode, these electrode materials can be formed into a thin film by a method such as a vapor deposition method or a sputtering method. When the light emitted from the light emitting layer is taken out from the anode, it is desirable that the anode has a property that the transmittance of the anode with respect to the light emitted is larger than 10%. Further, the sheet resistance of the anode is preferably several hundreds of Ω / □ or less. The thickness of the anode depends on the material, but is usually selected in the range of 10 nm to 1 μm, preferably 10 to 200 nm.

[cathode]
As the material used for the cathode, a metal having a small work function (4 eV or less), an alloy, an electrically conductive compound, or a mixture thereof is used as an electrode material. Specific examples of such electrode materials include sodium, sodium-potassium alloys, magnesium, lithium, magnesium / silver alloys, aluminum / aluminum oxide, aluminum / lithium alloys, indium, rare earth metals and the like. This cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. Here, when the light emitted from the light emitting layer is taken out from the cathode, the transmittance of the cathode with respect to the light emitted is preferably larger than 10%. The sheet resistance of the cathode is preferably several hundred Ω / □ or less, and the thickness of the cathode is usually 10 nm to 1 μm, preferably 50 to 200 nm.

As for the method for producing the electroluminescent device, the anode, the light emitting layer, the hole injection layer if necessary, and the electron injection layer if necessary may be formed by the above materials and methods, and finally the cathode may be formed. .. Further, the electroluminescent device can be manufactured from the cathode to the anode in the reverse order of the above.

The electroluminescent device is made on a translucent substrate. The translucent base material is a substrate that supports an electroluminescent element, and its translucency is preferably such that the light transmittance in the visible region of 400 to 700 nm is 50% or more, preferably 90% or more. It is preferable to use a smoother base material.

These base materials are not particularly limited as long as they have mechanical and thermal strength and are transparent, and may be a flexible film or sheet-like base material. As the base material, for example, a glass plate or a synthetic resin plate is preferably used. Examples of the glass plate include plates formed of soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, quartz and the like. Examples of the synthetic resin plate include a plate such as a polycarbonate resin, an acrylic resin, a polyethylene terephthalate resin, a polyether sulfide resin, and a polysulfon resin.

As a method for forming each layer of the electroluminescent element, either a dry film deposition method such as vacuum deposition, electron beam irradiation, sputtering, plasma, or ion plating, or a wet film deposition method such as spin coating, dipping, or flow coating. Method can be applied. In addition, the special table 2002-534782 and S.A. T. Lee, et al. , Proceedings of SID'02, p. The LITI (Laser Induced Thermal Imaging) method described in 784 (2002), printing (offset printing, flexographic printing, gravure printing, screen printing), inkjet and the like can also be applied. However, the light emitting layer is limited to the film formation by the wet film formation method.

The organic layer is particularly preferably a molecular deposition film. Here, the molecular deposition film is a thin film deposited and formed from a material compound in a gas phase state, or a film solidified and formed from a material compound in a solution state or a liquid phase state, and is usually this molecular deposition film. Can be classified by the difference in aggregated structure and higher-order structure from the thin film (molecular cumulative film) formed by the LB method, and the functional difference caused by the difference. Further, as disclosed in Japanese Patent Application Laid-Open No. 57-57181, a binder such as a resin and a material compound are dissolved in a solvent to prepare a solution, which is then thinned by a spin coating method or the like. , An organic layer can be formed. The film thickness of each layer is not particularly limited, but if the film thickness is too thick, a large applied voltage is required to obtain a constant light output, resulting in inefficiency. On the contrary, if the film thickness is too thin, pinholes, etc. Is generated, and it becomes difficult to obtain sufficient emission brightness even when an electric field is applied. Therefore, the film thickness of each layer is preferably in the range of 1 nm to 1 μm, but more preferably in the range of 10 nm to 0.2 μm.

Further, in order to improve the stability of the electroluminescent element with respect to temperature, humidity, atmosphere and the like, a protective layer may be provided on the surface of the element, or the entire element may be coated or sealed with a resin or the like. In particular, when coating or sealing the entire device, a photocurable resin that is cured by light is preferably used.

The current applied to the electroluminescent element is usually direct current, but pulse current or alternating current may be used. The current value and voltage value are not particularly limited as long as they do not destroy the element, but considering the power consumption and life of the element, it is desirable to efficiently emit light with as little electric energy as possible.

The electroluminescent element can be driven not only by the passive matrix method but also by the active matrix method. Further, as a method of extracting light from the organic EL element of the present invention, it can be applied not only to a method of bottom emission which extracts light from the anode side but also to a method of top emission which extracts light from the cathode side. These methods and techniques are described in Junji Kido, "All about Organic EL", Nihon Jitsugyo Publishing Co., Ltd. (published in 2003).

The main methods of the full-color electroluminescent element are a three-color painting method, a color conversion method, and a color filter method. Examples of the three-color painting method include a vapor deposition method using a shadow mask, an inkjet method, and a printing method. In addition, the special table 2002-534782 and S.A. T. Lee, et al. , Proceedings of SID'02, p. The laser thermal transfer method described in 784 (2002) (also referred to as Laser Induced Thermo Imaging, LITI method) can also be used. The color conversion method is a method of converting from blue to green and red having a longer wavelength than blue through a color conversion (CCM) layer in which a fluorescent dye is dispersed by using a light emitting layer that emits blue light. In the color filter method, an organic EL element that emits white light is used to extract light of the three primary colors through a color filter for liquid crystal. In addition to these three primary colors, a part of white light is extracted as it is and used for light emission. As a result, the luminous efficiency of the entire element can be increased.

Further, the electroluminescent element may adopt a microcavity structure. This is because the organic EL element has a structure in which a light emitting layer is sandwiched between an anode and a cathode, and the emitted light causes multiple interference between the anode and the cathode, but the reflectance and transmission of the anode and the cathode are transmitted. It is a technology that positively utilizes the multiple interference effect and controls the emission wavelength extracted from the element by appropriately selecting the optical characteristics such as the rate and the thickness of the organic layer sandwiched between them. .. This also makes it possible to improve the emission chromaticity. Regarding the mechanism of this multiple interference effect, J. AM-LCD Digital Papers by Yamada et al., OD-2, p. 77-80 (2002).

As described above, the electroluminescent device of the present invention can obtain stable light emission with little change in efficiency for a long time at a low drive voltage. Therefore, this organic EL element can be used as a flat panel display such as a wall-mounted television, various flat light emitters, a light source such as a copier or a printer, a light source such as a liquid crystal display or an instrument, a display board, an indicator light, or the like. Can be applied.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples do not limit the scope of rights of the present invention. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples represent "parts by mass" and "% by mass".

<Manufacture of quantum dot (A1) dispersion liquid containing semiconductor nanoparticles surface-treated with a ligand that does not have an aromatic ring>
(Quantum dot dispersion liquid: QD-1)
1.35 parts of indium acetate, 1.30 parts of zinc octanate, 4.65 parts of stearic acid, and 92.7 parts of 1-octadecene were placed in a flask and heated to 100 ° C. Then, after distilling under reduced pressure at that temperature, the inside of the flask was filled with argon gas and heated to 300 ° C. Separately, 23 parts of a hexane solution containing 1.16 parts of tris (trimethylsilyl) phosphine prepared in a waterless glove box was injected, reacted at 280 ° C. for 9 minutes, and then rapidly cooled to obtain a solution.
15 parts of the obtained solution, 46 parts of 1-octadecene and 11.5 parts of oleylamine were placed in a flask, and the mixture was stirred for 15 minutes, and then 4.3 parts of zinc dibenzyldithiocarbamate was added. The inside of the reaction flask was replaced with argon, the temperature was raised to 170 ° C. for 45 minutes, the temperature was kept at 170 ° C. for 2 hours, the mixture was cooled, acetone was added, and the mixture was separated by centrifugal sedimentation to obtain a precipitated paste.
The precipitated paste was dispersed in toluene, 3.7 parts of dodecanethiol was added as a treatment agent, the mixture was stirred at room temperature for 24 hours, concentrated under reduced pressure, acetone was added, and the paste was separated by centrifugation to obtain a precipitated paste.
Again, the precipitated paste is dispersed in octane, adjusted to a solid content concentration of 10%, and contains quantum dots, which are semiconductor nanoparticles surface-treated with dodecanethiol (DL1) having no aromatic ring, in a quantum dot dispersion QD. I got -1. The semiconductor nanoparticles have an InP core and a ZnS shell.

(Quantum dot dispersion liquid: QD-2)
The quantum dot dispersion liquid QD-1 was diluted with toluene to a solid content concentration of 0.5%.
Next, trioctylphosphine oxide is dissolved in toluene to prepare a ligand solution having a solid content concentration of 1.0%, and the ligand solution is added to the quantum dot dispersion QD-1 in an amount of 5 times by mass for 12 hours. Stirred. Semiconductor nanoparticles prepared by reprecipitation method using hexane and ethanol, adjusted to a solid content concentration of 10% using methylcyclohexane, and surface-treated with trioctylphosphine oxide (DL2) having no aromatic ring. A quantum dot dispersion QD-2 containing quantum dots, which are particles, was obtained.

(Quantum dot dispersion liquid: QD-3)
The quantum dot dispersion liquid QD-1 was diluted with toluene to a solid content concentration of 0.5%.
Next, 3,6,9,12-tetraoxatridecaneamine is dissolved in toluene to prepare a ligand solution having a solid content concentration of 1.0%, and the ligand solution is mass-based with respect to the quantum dot dispersion QD-1. 5 times the amount was added, and the mixture was stirred for 12 hours. After purification by the reprecipitation method using hexane and ethanol, the solid content was adjusted to 10% using propylene glycol-1-monomethyl ether acetate, and 3,6,9,12 having no aromatic ring. A quantum dot dispersion QD-3 containing quantum dots, which are semiconductor nanoparticles surface-treated with tetraoxatridecaneamine (DL3), was obtained.

(Quantum dot dispersion liquid: QD-4)
The quantum dot dispersion liquid QD-1 was diluted with toluene to a solid content concentration of 0.5%.
Next, 2- [2- (2-dimethylaminoethylmethylamino) ethylmethylamino] propionic acid is dissolved in toluene to prepare a ligand solution having a solid content concentration of 1.0%, and the ligand solution is used as a quantum dot dispersion. To QD-1, 5 times the amount was added on a mass basis, and the mixture was stirred for 12 hours. After purification by the reprecipitation method using hexane and ethanol, the solid content concentration is adjusted to 10% using n-butyl lactate, and 2- [2- (2-dimethylaminoethylmethyl) having no aromatic ring is used. A quantum dot dispersion QD-4 containing quantum dots, which are semiconductor nanoparticles surface-treated with amino) ethylmethylamino] propionic acid (DL4), was obtained.

Table 6 shows a list of ligands that do not have an aromatic ring used.

<Manufacture of quantum dot (A2) dispersion liquid containing semiconductor nanoparticles surface-treated with a ligand having an aromatic ring>
(Quantum dot dispersion liquid: QD-5)
The quantum dot dispersion liquid QD-1 was diluted with toluene to a solid content concentration of 0.5%.
Next, the hole-transporting ligand (CL1) shown in Table 6 was dissolved in toluene to prepare a ligand solution having a solid content concentration of 1.0%, and the ligand solution was mass-based with respect to the quantum dot dispersion QD-1. 5 times the amount was added, and the mixture was stirred for 12 hours. Quantum dots, which are semiconductor nanoparticles prepared by a reprecipitation method using hexane and ethanol, adjusted to a solid content concentration of 10% using toluene, and surface-treated with a ligand (CL1) having an aromatic ring. A quantum dot dispersion QD-5 containing the above was obtained.

(Quantum dot dispersion liquid: QD-6)
A quantum dot dispersion QD-6 was obtained in the same manner as the quantum dot dispersion QD-5, except that the electron transport ligand (CL2) shown in Table 6 was used instead of the hole transport ligand (CL1). ..

(Quantum dot dispersion liquid: QD-7)
The quantum dot dispersion liquid QD-1 was diluted with toluene to a solid content concentration of 0.5%.
Next, a ligand solution having a solid content concentration of 1.0% was dissolved in toluene so that the mass ratio of the hole-transporting ligand (CL1) and the electron-transporting ligand (CL2) shown in Table 6 was 1: 1. Was adjusted, and the ligand solution was added in an amount of 5 times the mass of the quantum dot dispersion QD-1 on a mass basis and stirred for 12 hours. Semiconductor nanoparticles prepared by reprecipitation method using hexane and ethanol, adjusted to a solid content concentration of 10% using toluene, and surface-treated with ligands (CL1) and (CL2) having an aromatic ring. A quantum dot dispersion liquid QD-7 containing the above-mentioned quantum dots was obtained.

(Quantum dot dispersion liquid: QD-8)
A quantum dot dispersion QD-8 was obtained in the same manner as the quantum dot dispersion QD-5, except that the hole transport ligand (CL3) shown in Table 6 was used instead of the hole transport ligand (CL1). It was.

(Quantum dot dispersion liquid: QD-9)
A quantum dot dispersion QD-9 was obtained in the same manner as the quantum dot dispersion QD-5, except that the electron transport ligand (CL4) shown in Table 6 was used instead of the hole transport ligand (CL1). ..

(Quantum dot dispersion liquid: QD-10)
Quantum dot dispersion liquid except that the hole transporting ligand (CL3) and the electron transporting ligand (CL4) shown in Table 7 were used instead of the hole transporting ligand (CL1) and the electron transporting ligand (CL2). A quantum dot dispersion QD-10 was obtained in the same manner as QD-7.

(Quantum dot dispersion liquid: QD-11)
A quantum dot dispersion QD-11 was obtained in the same manner as the quantum dot dispersion QD-5, except that the hole transport ligand (CL5) shown in Table 7 was used instead of the hole transport ligand (CL1). It was.

(Quantum dot dispersion liquid: QD-12)
A quantum dot dispersion QD-12 was obtained in the same manner as the quantum dot dispersion QD-5, except that the hole transport ligand (CL6) shown in Table 6 was used instead of the hole transport ligand (CL1). It was.

(Quantum dot dispersion liquid: QD-13)
A quantum dot dispersion QD-13 was obtained in the same manner as the quantum dot dispersion QD-5, except that the hole transport ligand (CL7) shown in Table 6 was used instead of the hole transport ligand (CL1). It was.

(Quantum dot dispersion liquid: QD-14)
A quantum dot dispersion QD-14 was obtained in the same manner as the quantum dot dispersion QD-5, except that the hole transport ligand (CL8) shown in Table 6 was used instead of the hole transport ligand (CL1). It was.

(Quantum dot dispersion liquid: QD-15)
Quantum dot dispersion liquid except that the hole transporting ligand (CL7) and the electron transporting ligand (CL2) shown in Table 6 were used instead of the hole transporting ligand (CL1) and the electron transporting ligand (CL2). A quantum dot dispersion QD-15 was obtained in the same manner as QD-7.

(Quantum dot dispersion liquid: QD-16)
Quantum dot dispersion liquid except that the hole transporting ligand (CL5) and the electron transporting ligand (CL4) shown in Table 6 were used instead of the hole transporting ligand (CL1) and the electron transporting ligand (CL2). A quantum dot dispersion QD-16 was obtained in the same manner as QD-7.

Table 7 shows a list of ligands having an aromatic ring used.

<Manufacturing of electroluminescent elements>
Unless otherwise specified, an electroluminescent element was produced using a 25 mm × 25 mm glass plate with an ITO electrode patterned in advance in a 2 mm wide band shape so that the area of the light emitting portion was 2 mm × 2 mm. The vapor deposition (vacuum vapor deposition) was ^{carried out in a vacuum of 10 -4} Pa under the condition that the temperature was not controlled such as heating and cooling of the substrate.

[Example 1]
PEDOT / PSS (poly (3,4-ethylenedioxy) -2,5-thiophene / polystyrene sulfonic acid, Heraeus CLEVIOS® PVP CH8000) on a washed glass plate with an ITO electrode as an anode. ) Was coated by a spin coating method and dried at 110 ° C. for 20 minutes to obtain a hole injection layer having a film thickness of 35 nm.
Next, poly (N-vinylcarbazole) was dissolved in monochlorobenzene at a concentration of 1.0% by mass, coated by a spin coating method, dried at 110 ° C. for 20 minutes, and holes having a film thickness of 35 nm. A transport layer was formed.
Next, on the hole transport layer, the quantum dot dispersion liquid QD-1 was diluted 35-fold with the solvent used for dispersion and used as an ink composition for forming a light emitting layer, and after spin coating, it was dried at 60 ° C. for 10 minutes. A 10 nm light emitting layer (EML1) was formed.
Next, a 30 nm light emitting layer (EML2) was formed on the light emitting layer (EML1) by spin-coating and drying using the quantum dot dispersion liquid QD-5 in the same manner as in the quantum dot dispersion liquid QD-1.
Next, an isopropanol dispersion of zinc oxide manufactured by Avantama N-10 was applied onto the light emitting layer (EML2) by a spin coating method, and heat-dried on a hot plate at 80 ° C. for 20 minutes to generate electrons at 80 nm. A transport layer was formed.
Finally, aluminum (Al) was vapor-deposited on the electron transport layer in a strip shape having a width of 2 mm at 200 nm to form a cathode to obtain an electroluminescent device.
The electroluminescent device had a peak wavelength of 610 nm and a full width at half maximum of 25 nm.
The results of the obtained electroluminescent device are shown in Table 8 together with the results of other examples and comparative examples.

[Examples 2 to 16, Comparative Examples 1 to 4]
The electroluminescent devices of Examples 2 to 16 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that the quantum dot dispersion liquid shown in Table 8 was used to form the light emitting layer layer structure shown in Table 8. It was.
<Evaluation of electroluminescent element>
The following evaluation was performed on the obtained electroluminescent device having an area of 2 mm × 2 mm. For various evaluations of the elements, a PC-controlled Advantest 6243 source meter and a Konica Minolta luminance meter CS-100A or a spectral radiance system CS-1000 were used. The results are shown in Table 8.

[Drive voltage (V)]
The drive voltage (V) when driven at a current density of 10 (mA / cm ^{2) was measured.}

[External quantum efficiency (%)]
The external quantum efficiency (%) when driven at a current density of 10 (mA / cm ^{2) was calculated.} External quantum efficiency (%) = number of photons emitted to the outside of the electroluminescent element / number of electrons passed through the electroluminescent element × 100, and was calculated by a brightness conversion method based on the measurement results of the spectral radiance system CS-1000.

[Relative brightness]
The relative luminance (= (luminance after 100 hours) / (initial luminance)) after continuous driving for 100 hours under the condition of initial luminance 500 (cd / m ^{2) in an environment of 80 ° C. was measured.}

From the evaluation results in Table 8, as the light emitting part, a light emitting layer (EML1) containing quantum dots (A1) which are semiconductor nanoparticles surface-treated with a ligand having no aromatic ring, and at least one kind of ligand having an aromatic ring. The electroluminescent device having a light emitting layer (EML2) containing quantum dots (A2), which are semiconductor nanoparticles surface-treated with the above, exhibited excellent light emission efficiency and high durability at a low driving voltage.

Comparing Examples 1 to 16 with Comparative Examples 1 to 4, the examples were equal to or better than those of the comparative examples in all the evaluations. Specifically, compared to the element of the comparative example having a light emitting layer of only quantum dots surface-treated with a ligand having no aromatic ring, the element of the example has significantly improved drive voltage and quantum efficiency, and further, the element. The relative brightness, which indicates the degree of deterioration of, has also been improved. Further, for the element of the comparative example having a light emitting layer having only quantum dots surface-treated with a ligand having an aromatic ring, the quantum efficiency is improved and the relative brightness is greatly improved while maintaining a low driving voltage. did.
Further, comparing Examples 1 and 3 with Comparative Examples 3 and 4, the elements of the Comparative Example composed of the quantum dot light emitting layer having both the hole transporting ligand and the electron transporting ligand tend to have various characteristics. On the contrary, it improved in the examples.
From these results, the electroluminescent element of the present invention is obtained by laminating a light emitting layer made of quantum dots surface-treated with a ligand having no aromatic ring and a light emitting layer made of quantum dots surface-treated with a ligand having an aromatic ring. Therefore, it is presumed that the quantum efficiency and the relative brightness are improved by suppressing the escape of the injected charge in the opposite direction. Furthermore, by selecting the solvent contained in the composition containing the quantum dots surface-treated with a ligand having no aromatic ring, the interface between the lower layer and the light emitting layer becomes smoother, and the mixing of the materials is suppressed. It is considered that the drive voltage, quantum efficiency, and relative brightness were further improved.

Claims (4)

An electroluminescent device having an anode, a light emitting portion having at least two continuous light emitting layers, and a cathode in this order on a substrate.
The light emitting portion is a light emitting layer (EML1) containing quantum dots (A1) which are semiconductor nanoparticles surface-treated with a ligand having no aromatic ring, and semiconductor nanoparticles surface-treated with a ligand having an aromatic ring. An electroluminescent device having a light emitting layer (EML2) containing quantum dots (A2). The electroluminescent device according to claim 1, further comprising a hole injection layer between the anode and the light emitting portion. The electroluminescent device according to claim 1 or 2, wherein light emitting layers are arranged in the order of (EML1) and (EML2) from the anode side. The electroluminescent device according to any one of claims 1 to 3, wherein the ligand having an aromatic ring has hole transporting property or electron transporting property.