JP7567267B2 - Quantum dots, ink composition, electroluminescent element, and photoelectric conversion element - Google Patents

Description

The present invention relates to quantum dots, which are semiconductor particles that have been surface-treated with a compound having an aliphatic heterocyclic group containing a sulfur atom and a charge transport group, an ink composition containing the quantum dots, an electroluminescent device, and a photoelectric conversion device.

Quantum dots are extremely small particles (dots) formed to confine electrons in a tiny space in order to express unique optical properties according to quantum mechanics. The size of a single quantum dot is 1 nm to several tens of nm in diameter, and it is composed of approximately 10,000 atoms or less. Quantum dots have attracted attention in recent years because the wavelength of the emitted fluorescence can be continuously controlled by the size of the particle, and because they can produce sharp light emission with a highly symmetric wavelength distribution of the fluorescence intensity. Since the fluorescence can be adjusted to a wavelength that easily penetrates the human body and can be delivered to any part of the body, quantum dots are being considered for use as luminescent materials for bioimaging, as solar cells as wavelength conversion materials without the risk of fading, and as vivid luminescent materials or wavelength conversion materials for electronics and photonics.

On the other hand, one of the properties required for the above applications is the quantum yield of fluorescence. Non-Patent Document 1 describes the use of quantum dots in which semiconductor particles are coated with benzenethiol, an aromatic thiol, to improve the quantum yield of fluorescence.

Nanotechnology 27(24):245203

However, the quantum dots coated with benzenethiol described in Non-Patent Document 1 have a problem with stability over time because the coating material, benzenethiol, itself is relatively easily oxidized. As a result, a composition in which the quantum dots are mixed with a solvent or binder component has insufficient stability over time, and there is a problem that the quantum dots aggregate or precipitate. In addition, there is a problem that the quantum yield maintenance rate of fluorescence is significantly reduced.
Therefore, an object of the present invention is to provide a quantum dot and an ink composition that are excellent in stability over time and can maintain a high fluorescence quantum yield even after aging. Another object of the present invention is to provide a highly reliable electroluminescent device using quantum dots that can maintain a high fluorescence quantum yield even after aging.

Another object of the present invention is to provide a photoelectric conversion element with excellent durability.

The present invention relates to the following inventions.
[1] A quantum dot which is a semiconductor fine particle surface-treated with a compound represented by the following general formula (1):

［一般式（１）中、Ｑは硫黄原子を含有する脂肪族複素環基であり、Ｘは直接結合又は２
価の連結基であり、Ａは電荷輸送性基である。］ General formula (1)

[In the general formula (1), Q is an aliphatic heterocyclic group containing a sulfur atom, and X is a direct bond or
A is a charge transporting group.

[2] The quantum dot according to [1], wherein the semiconductor particles are compound semiconductors.

[3] The quantum dot according to [1] or [2], wherein the semiconductor particles are of a core-shell type.

[4] The quantum dot according to any one of [1] to [3], wherein the charge transport group is a hole transport group.

[5] An ink composition comprising the quantum dots described in any one of [1] to [4] and a solvent.

[6] The ink composition according to [5], which is used in an inkjet system.

[7] An electroluminescent device comprising an anode, a light-emitting layer, and a cathode on a substrate, the light-emitting layer including the quantum dots described in any one of [1] to [5].

[8] A photoelectric conversion element having a photoelectric conversion layer between a pair of electrodes, the photoelectric conversion layer containing the quantum dots described in any one of [1] to [5].

The present invention can provide quantum dots and ink compositions that have excellent stability over time and can maintain a high fluorescence quantum yield even after aging. The present invention can also provide a highly reliable electroluminescent device using quantum dots that can maintain a high fluorescence quantum yield even after aging.

The present invention also makes it possible to provide a photoelectric conversion element with excellent durability.

<Quantum dots>
The quantum dots of the present invention are semiconductor particles surface-treated with a compound represented by general formula (1). "Surface-treated" means that at least a part of the surface of the semiconductor particles has the compound, and the compound present on the surface of such semiconductor particles is also called a ligand. The compound represented by general formula (1) has an aliphatic heterocyclic group containing a sulfur atom and a charge transport group. The aliphatic heterocyclic group containing a sulfur atom has high oxidation resistance and can exist stably on the surface of the quantum dot even over time. As a result, the quantum dots of the present invention exhibit excellent stability over time in addition to charge transportability. As a result, compared to conventional quantum dots coated with benzenethiol, etc., they do not precipitate and have excellent stability over time, and further have a high fluorescence quantum yield maintenance rate, making them suitable as light-emitting materials.
The present invention will be described in detail below. Unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass".

<Semiconductor particles>
Examples of materials for the semiconductor fine particles include simple substances of elements in Group IV of the periodic table, such as carbon (C) (amorphous carbon, graphite, graphene, carbon nanotubes, etc.), silicon (Si), germanium (Ge), and tin (Sn); simple substances of elements in Group V of the periodic table, such as phosphorus (P) (black phosphorus); simple substances of elements in 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), and aluminum nitride (AlN); Compounds of elements in Group III of the periodic table and elements in Group V of the periodic table, such as aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), and indium antimonide (InSb); _2S3 ), aluminum selenide ( _Al2Se3 ), gallium sulfide _{( Ga2S3} ), gallium selenide ( _GaSe , _Ga2Se3 ), gallium telluride _{(GaTe, Ga2Te3), indium oxide (In2O3), indium sulfide (In2S3 , InS ) , indium selenide ( In2Se3 )} , indium _telluride ( _In2Te3 compounds of elements in Group III of the periodic table and elements in Group VI of the periodic table, such as zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), and mercury telluride (HgTe); compounds of elements in Group II of the periodic table and elements in Group VI of the periodic table, such as copper oxide (I) (Cu ₂ O), copper sulfide (I) (Cu ₂ S), copper selenide (I) (Cu ₂ Se), silver sulfide (I) (Ag ₂ S), silver selenide (I) (Ag ₂ Se), and silver telluride (I) (Ag ₂ compounds of elements of Group I and Group VI of the periodic table, such as gold(I) sulfide (Au ₂ S), gold(I) selenide (Au ₂ Se), and gold(I) telluride (Au ₂ Te); compounds of elements of Group I and Group VII of the periodic table, such as copper(I) chloride (CuCl), copper(I) bromide (CuBr), copper(I) iodide (CuI), silver chloride (AgCl), and silver bromide (AgBr); compounds of elements of Group IV and Group VI of the periodic table, such as tin(II) sulfide (SnS), tin(II) selenide (SnSe), tin(II) telluride (SnTe), lead(II) sulfide (PbS), lead(II) selenide (PbSe), and lead(II) telluride (PbTe); compounds of elements of Group VI and Group IV of the periodic table, such as antimony(III) sulfide (Sb ₂ Compounds of Group V elements and Group VI elements of the _periodic table, such as bismuth (III) sulfide (Bi 2 S ₃ ), and bismuth ( _III ) sulfide (Bi ₂ S ₃ ); compounds of Group VIII elements and Group VI elements of the periodic table, such as iron sulfide (FeS ₂ ), iron selenide (FeSe 2 ), and iron telluride (FeTe 2 ); compounds of lanthanoid elements and Group VI elements of the periodic table, such as europium sulfide (EuS), europium selenide (EuSe), and europium telluride (EuTe), and the like, may be used in combination of two or more of these, if necessary. These semiconductors may contain elements other than the constituent elements. For example, in the III-V group, alloys such as InGaP and InGaN may be used, and alloys such as CuInS ₂ , CuInSe ₂ , and CuInTe ₂ containing elements of multiple groups may be used. Furthermore, semiconductor particles 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.

Furthermore, perovskite crystals can also be suitably used as the material for the semiconductor fine particles. Perovskite crystals have a composition represented by the following formula (I) and have a three-dimensional crystal structure.
Formula (I): _AQX3
[In formula (I), A is [ _CH3NH3 ] ⁺ , [ _NH3CHNH ] ⁺ , Rb ⁺ , Cs ⁺ or Fr ⁺ , Q is Pb2 ⁺ or _Sn2 ⁺ , and X is I- ^{, Br-} , ^Cl- or ^F- .]

Semiconductor particles used in electroluminescent devices include silicon (Si), germanium (Ge), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), gallium selenide (GaSe, _Ga2Se3 ), and indium _{sulfide (In2S3 ) .} , InS), zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), InGaP, InGaN, and other alloy systems are preferably used, and indium phosphide (InP), cadmium selenide (CdSe), zinc sulfide (ZnS), and zinc selenide (ZnSe) are particularly preferably used. In particular, it is preferable to use InP for the core and ZnS and/or ZnSe for the shell.

The semiconductor particles used in the photoelectric conversion element are preferably capable of absorbing electromagnetic waves with wavelengths of 700 to 2500 nm, and examples thereof include compound semiconductors having a perovskite crystal structure and metal chalcogenides (e.g., oxides, sulfides, selenides, tellurides, etc.). Specific examples of compound semiconductors having _{a perovskite crystal} structure include _{CH3NH3PbF3 , CH3NH3PbCl3} , _CH3NH3PbBr3 , _CH3NH3PbI3 , _CsPbF3 , CsPbCl3 _{, CsPbBr3} , _CsPbI3 , _RbPbF3 , _RbPbCl3 , _{RbPbBr3 , RbPbI3 , KPbF3} , _KPbCl3 , _KPbBr3 , _{KPbI3 , etc.} Specific examples of metal chalcogenides include _PbS , PbSe, PbTe, CdS, CdSe, CdTe _{, Sb2S3} , _Bi2S3 , _Ag2S , _Ag2Se , _Ag2Te , Au2S, _Au2Se , _Au2Te , _Cu2S , Cu2Se, Cu2Te, _Fe2S , _Fe2Se , _Fe2Te , _In2S3 , SnS, SnSe, SnTe, _CuInS2 , _CuInSe2 , _CuInTe2 , EuS, _EuSe , _EuTe , etc. Among these, PbS, PbSe, and _Ag2S are preferred _.

Semiconductor particles used in electroluminescent devices are preferably core-shell type semiconductor particles having a core-shell structure. Core-shell type semiconductor particles have a structure having a core and a shell that is coated with a material made of a component different from the material that forms the core. By selecting a semiconductor with a large band gap for the shell, excitons (electron-hole pairs) generated by photoexcitation are confined within the core. As a result, the probability of non-radiative transitions on the particle surface is reduced, improving the quantum yield of light emission and the stability of the fluorescent properties. The shell may also have multiple layers. Furthermore, the boundaries between the core and the shell, and between one shell and another shell may be clear, or a gradient structure in which the shells are gradually joined with a concentration gradient may be provided. Furthermore, the shell may cover only a part of the core, or the entire core.

The average particle size of the semiconductor particles, including the core and shell, is usually 0.5 nm to 100 nm, preferably 1 to 50 nm, and more preferably 1 to 15 nm.

The average particle size here refers to the value obtained by observing semiconductor particles with a transmission electron microscope, measuring the sizes of 30 particles at random, and adopting the average value. In this case, the semiconductor particles are accompanied by organic ligands, which will be described later. In contrast, a scanning transmission electron microscope equipped with energy dispersive X-ray analysis is used to identify the semiconductor particles excluding the organic ligands and measure their particle size. The semiconductor particles are identified by utilizing the fact that in transmission electron microscope images, the semiconductor particle portion appears darker than the organic ligand due to differences in electron density. The shape of the semiconductor particles is not limited to spherical, but may be rod-like, disk-like, or other shapes.

<Ligand: Compound represented by formula (1)>
The compound represented by the general formula (1) covers at least a part of the surface of the semiconductor fine particles, and is used for surface treatment of the semiconductor fine particles.

［一般式（１）中、Ｑは硫黄原子を含有する脂肪族複素環基であり、Ｘは直接結合又は２価の連結基であり、Ａは電荷輸送性基である。］ General formula (1)

[In general formula (1), Q is an aliphatic heterocyclic group containing a sulfur atom, X is a direct bond or a divalent linking group, and A is a charge transporting group.]

The aliphatic heterocyclic group containing a sulfur atom is an aliphatic heterocycle containing at least one sulfur atom as a ring-constituting heteroatom, and is preferably, for example, an aliphatic heterocyclic group containing a sulfur atom and having 2 to 30 carbon atoms. Specific examples of the aliphatic heterocyclic group containing a sulfur atom include an ethylene sulfide ring, a trimethylene sulfide ring, a tetrahydrothiophene ring, a thiane ring, a thiepane ring, a thiocane ring, a thionan ring, a thiazolidine ring, a 1,2-dithiane ring, a 1,3-dithiane ring, a 1,4-dithiane ring, and a thiomorpholine ring.

The aliphatic heterocyclic group may contain a heteroatom other than a sulfur atom in the ring structure, or may contain a sulfur atom and at least one atom selected from a nitrogen atom and an oxygen atom as ring-constituting heteroatoms. The aliphatic heterocyclic group is more preferably one containing a sulfur atom and a nitrogen atom as ring-constituting heteroatoms.
The number of ring members in the aliphatic heterocyclic group is preferably a 3- to 8-membered ring, and more preferably a 5- or 6-membered ring.

Examples of divalent linking groups include divalent hydrocarbon groups, oxygen atoms, amide groups, carbonyl groups, ester groups, imide groups, azomethine groups, azo groups, sulfide groups, sulfone groups, and divalent linking groups formed by combining these.

Examples of divalent hydrocarbon groups include alkylene groups, cycloalkylene groups, and arylene groups. Of these, alkylene groups having 1 to 12 carbon atoms, cycloalkylene groups having 5 to 12 carbon atoms, and arylene groups having 6 to 12 carbon atoms are preferred. Specific examples include methylene groups, ethylene groups, propylene groups, hexylene groups, dodecylene groups, cyclohexylene groups, and phenylene groups. X is preferably a direct bond.

Charge transporting groups include hole transporting groups and electron transporting groups. Hole transporting groups are primarily responsible for transporting holes, and therefore require stability against holes, i.e., oxidation stability, while electron transporting groups are responsible for transporting electrons, and therefore require stability against electrons, i.e., reduction stability.
As the hole transporting group, for example, a group containing a unit such as a tertiary aromatic amine, such as triphenylamine or diphenylamine, carbazole, or thiophene can be used.
As the electron transporting group, for example, a group containing a unit such as oxadiazole, triazine, triazole, oxazole, isoxazole, thiazole, isothiazole, thiadiazole, or quinoxaline can be used.
These charge transporting groups may have a substituent within the range that does not impair the charge transporting property. Examples of the substituent that may be possessed include an alkyl group, an alkoxy group, a carbonyl group, a cyano group, a trifluoromethyl group, and a trimethylsilyl group.

The charge transport group is preferably a hole transport group, and more preferably a group containing a tertiary aromatic amine or carbazole unit.

Therefore, the compound represented by the general formula (1) is preferably a compound in which Q is an aliphatic heterocyclic group containing a sulfur atom and a nitrogen atom as ring atoms, X is a direct bond, and A is a charge-transporting residue containing a tertiary aromatic amine or carbazole unit.

Furthermore, preferred structures of the compound represented by general formula (1) include compounds represented by the following general formulas (2) to (11).

[In general formula (2), R ¹ to R ¹⁴ each independently represent a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ¹ represents a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ¹ represents an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (3), R ¹⁵ to R ²⁴ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ² is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ² is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (4), R ²⁵ to R ³² are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ² is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ³ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (5), R ³³ to R ⁴⁰ each independently represent a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ⁴ represents a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ⁴ represents an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (6), R ⁴¹ to R ⁴³ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a thio group, or a trimethylsilyl group; X ⁵ is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ⁵ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (7), R ⁴⁴ to R ⁴⁶ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ⁶ is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ⁶ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In the general formula (8), R ⁴⁷ and R ⁴⁸ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ⁷ is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ⁷ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In the general formula (9), R ⁴⁹ and R ⁵⁰ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ⁸ is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ⁸ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (10), R ⁵¹ to R ⁵⁵ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ⁹ is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ⁹ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

[In general formula (11), R ⁵⁶ and R ⁵⁷ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted alkoxy group, an optionally substituted amino group, an optionally substituted alkylthio group, a cyano group, a nitro group, or a trimethylsilyl group; X ¹⁰ is a direct bond, an optionally substituted alkylene group, an optionally substituted alkyleneoxycarbonyl group, an optionally substituted arylene group, or an azomethine group; and Q ¹⁰ is an optionally substituted thiazolidinyl group, an optionally substituted thiomorpholinyl group, an optionally substituted tetrahydrothiopyranyl group, or an optionally substituted 1,3-dithianyl group.]

The groups in general formulas (2) to (11) are explained below.

An alkyl group is a monovalent residue formed by formally removing one hydrogen atom from an alkane, and may be linear or branched. Specific examples of alkyl groups include linear alkyl groups such as methyl, ethyl, hexyl, and dodecyl groups, and branched alkyl groups such as 2-ethylhexyl groups. The number of carbon atoms in the alkyl group is preferably 1 to 6.

An alkoxy group is a group to which an alkyl group is bonded via an ether bond, and examples of the alkyl group include the alkyl groups listed above.

An amino group is a monovalent residue formed by formally removing one hydrogen atom from ammonia.

An alkylthio group is a group in which an alkyl group is bonded via a sulfide bond, and examples of the alkyl group include the alkyl groups listed above.

R ¹ , R ² , R ⁴ to R ⁷ , R ⁹ to R ¹⁶ , R ¹⁸ to R ²¹ , R ²³ to R ²⁶ , and R to R ⁵⁷ are preferably hydrogen atoms. R ³ , R ⁸ , ^{R 17 ,} and R ²² are preferably hydrogen atoms, alkyl groups, or alkoxy groups, and more preferably hydrogen atoms, methyl groups, or methoxy groups. R ²⁷ is preferably a hydrogen atom or an alkyl group, and more preferably an ethyl group.

An alkylene group is a divalent residue formed by formally removing two hydrogen atoms from an alkane, and may be linear or branched. Specific examples of alkylene groups include linear alkylene groups such as methylene, 1,2-ethylene, 1,6-hexylene, and 1,12-dodecylene, and branched alkylene groups such as 2-ethyl-1,6-hexylene. The number of carbon atoms in the alkylene group is preferably 1 to 6, and more preferably 1 or 2.

An arylene group is a divalent residue formed by formally removing two hydrogen atoms from an aromatic hydrocarbon. Specific examples of arylene groups include a 1,2-phenylene group, a 1,3-phenylene group, a 1,4-phenylene group, a 1,4-naphthylene group, and a 2,6-pyrenyl group. The number of carbon atoms in the aryl group is preferably 6 to 10, and more preferably 6.

The azomethine group is a divalent residue represented by --CR ⁶¹ .dbd.N--, where R ⁶¹ is a hydrogen atom or the above-mentioned alkyl group. R ⁶¹ is preferably a hydrogen atom.

An alkyleneoxycarbonyl group is a divalent residue represented by the formula --R ⁶² O(C.dbd.O)--, where R ⁶² is an alkylene group as defined above.

A thiazolidinyl group is a monovalent residue formed by formally removing one hydrogen atom from thiazolidine, and examples of such groups include the 2-thiazolidinyl group, the 3-thiazolidinyl group, the 4-thiazolidinyl group, and the 5-thiazolidinyl group. The 2-thiazolidinyl group is preferred.

A thiomorpholinyl group is a monovalent residue formed by formally removing one hydrogen atom from thiomorpholine, and examples of such groups include the 2-thiomorpholinyl group, the 3-thiomorpholinyl group, the 4-thiomorpholinyl group, the 5-thiomorpholinyl group, and the 6-thiomorpholinyl group. The 4-thiomorpholinyl group is preferred.

A tetrahydrothiopyranyl group is a monovalent residue formed by formally removing one hydrogen atom from tetrahydropyran, and examples of such groups include the 2-tetrahydrothiopyranyl group, the 3-tetrahydrothiopyranyl group, the 4-tetrahydrothiopyranyl group, the 5-tetrahydrothiopyranyl group, and the 6-tetrahydrothiopyranyl group. The 4-tetrahydrothiopyranyl group is preferred.

The 1,3-dithiane ring group is a monovalent residue formed by formally removing one hydrogen atom from 1,3-dithiane, and examples of such groups include the (1,3-dithianyl)-2-yl group, the (1,3-dithianyl)-4-yl group, the (1,3-dithianyl)-5-yl group, and the (1,3-dithianyl)-6-yl group. The (1,3-dithianyl)-2-yl group is preferred.

Tables 1 to 4 show specific examples of compounds represented by general formula (1), but are not limited to these.

The quantum dots of the present invention may be surface-treated with another known ligand in addition to the compound represented by general formula (1). Quantum dots surface-treated with a known ligand other than the compound represented by general formula (1) may also be used in combination. Examples of known ligands that can be used include dodecanethiol, oleic acid, oleylamine, trioctylphosphine, and trioctylphosphine oxide.

<Ink composition>
The ink composition of the present invention contains the quantum dots according to the present invention and a solvent, and may further contain other components as necessary. The ink composition of the present invention contains highly stable quantum dots, and therefore has excellent stability over time and fluorescence quantum yield.
Each component contained in the ink composition will be described below.

[solvent]
In the ink composition, the solvent can be appropriately selected from solvents capable of dispersing the semiconductor fine particles, depending on the application of the ink composition, etc. Specific examples of the solvent include 1,2,3-trichloropropane, 1,3-butylene glycol, 1,3-butylene glycol diacetate, 1,4-dioxane, 2-heptanone, 2-methyl-1,3-propanediol, 3,5,5-trimethyl-2-cyclohexen-1-one, 3,3,5-trimethylcyclohexanone, 3-ethoxyethylpropionate, 3-methyl-1,3-butanediol, 3-methoxy-3-methyl-1-butanediol, 3-methyl-1,3 ... ethanol, 3-methoxy-3-methylbutyl acetate, 3-methoxybutanol, 3-methoxybutyl acetate, 4-heptanone, m-xylene, m-diethylbenzene, m-dichlorobenzene, N,N-dimethylacetamide, N,N-dimethylformamide, n-butyl alcohol, n-butylbenzene, n-propyl acetate, N-methylpyrrolidone, toluene, octane, nonane, hexane, o-xylene, o-chlorotoluene, o-diethylbenzene, o-dichlorobenzene, p-chlorotoluene, p-diethylbenzene, sec-butylbenzene, tert-butylbenzene, γ-butyrolactone, water, methanol, ethanol, isopropyl alcohol, tert-tert-butyl ethanol, isobutyl alcohol, isophorone, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monotertiary butyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monopropyl ether, ethylene glycol monohexyl ether, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, diisobutyl ketone, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether, cyclohexanol, cyclohexanol acetate, cyclohexanone, dipropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diacetone alcohol, triacetin, tripropylene glycol mono Examples of the solvent include butyl ether, tripropylene glycol monomethyl ether, propylene glycol diacetate, propylene glycol phenyl ether, propylene glycol monoethyl ether, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether propionate, benzyl alcohol, methyl isobutyl ketone, methylcyclohexanol, n-amyl acetate, n-butyl acetate, isoamyl acetate, isobutyl acetate, propyl acetate, and dibasic acid esters. These solvents can be used alone or in combination of two or more in any ratio as required.

<Inkjet ink>
The ink composition of the present invention can be used as an inkjet ink for use in an inkjet system by adjusting the viscosity using a solvent, a resin component or a polymerizable monomer described below, etc. When used as an inkjet ink, it is preferable to adjust the viscosity at 25° C. to 3 to 50 mPa·s.

In the case of preparing an inkjet ink, the solvent is selected in terms of solubility in the resin, swelling action on device components, viscosity, and drying property of the ink in the nozzle, and it is preferable that the solvent contains one or more organic solvents having a boiling point of 135° C. or higher at 760 mmHg selected from the group consisting of the following solvents (A-1), (A-2), and (A-3).
Solvent (A-1): R ¹ -(O-C ₂ H ₄ )m-O-C(=O)-CH ₃
[wherein R ¹ is an alkyl group having 1 to 8 carbon atoms, C ₂ H ₄ is a linear or branched ethylene chain, and 1≦m≦3.]
Solvent (A-2): R ² -(O-C ₃ H ₆ )p-O-C(=O)-CH ₃
[wherein ^R2 is an alkyl group having 1 to 8 carbon atoms, _C3H6 is a linear or branched propylene chain, and 1≦ _p ≦3.]
Solvent (A-3): An organic solvent having two or more acetate structures.

Specific examples of the solvents (A-1) to (A-3) include, but are not limited to, propylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol diacetate, 1,3-butylene glycol diacetate, 1,6-hexanediol diacetate, triacetin, etc. Among these, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol methyl ether acetate, and 1,3-butylene glycol diacetate are preferred from the viewpoint of ejection stability.
From the viewpoints of ejection stability and drying properties of the ink in the nozzles, it is preferable that the content of the solvent having a boiling point of 135° C. or higher at 760 mmHg is 60% by mass or more based on the total amount of the solvent.

<Other ingredients>
The ink composition of the present invention may contain a resin, a crosslinking agent, a polymerizable monomer, a photosensitive substance, a heat-sensitive substance, a photopolymerization initiator, a photoacid generator, a photobase generator, a sensitizer, etc., depending on the performance required for the application to which it is used. These components may be used alone or in combination of two or more, and the content thereof is preferably 0 to 100 parts by mass relative to 1 part by mass of the quantum dots. If the content exceeds 100 parts by mass, the content of the quantum dots in the ink composition becomes low, and sufficient fluorescence intensity may not be obtained.
Furthermore, by containing a photosensitive substance or a polymerizable monomer, the ink composition of the present invention can be made into a positive or negative resist that can be patterned by a photolithography method.

[resin]
The resin may be a thermoplastic resin or a thermosetting resin, such as a petroleum-based resin, a maleic acid resin, a nitrocellulose, a cellulose acetate butyrate, a cyclized rubber, a chlorinated rubber, an alkyd resin, an acrylic resin, a polyester resin, an amino resin, a vinyl resin, or a butyral resin. The resin may be appropriately selected depending on the substrate on which the ink composition is printed.

[Crosslinking agent]
The crosslinking agent is preferably a thermally crosslinkable crosslinking agent, and at least one selected from the group consisting of a melamine compound, a benzoguanamine compound, an acrylate monomer, a carbodiimide compound, an epoxy compound, an oxetane compound, a phenol compound, a benzoxazine compound, a blocked carboxylic acid compound, a blocked isocyanate compound, and a silane coupling agent is suitably used from the viewpoint of excellent heat resistance.

[Polymerizable monomer]
The polymerizable monomer includes a monomer or oligomer that is cured by ultraviolet light, heat, or the like to form a resin, and these can be used alone or in combination of two or more kinds.
Examples of the polymerizable monomer include methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, cyclohexyl (meth)acrylate, β-carboxyethyl (meth)acrylate, polyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, neopentyl glycol modified trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, 1,6-hexanediol diglycidyl ether di(meth)acrylate, and bisphenol. Examples of the acrylic acid esters and methacrylic acid esters such as A diglycidyl ether di(meth)acrylate, neopentyl glycol diglycidyl ether di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, tricyclodecanyl (meth)acrylate, ester acrylate, (meth)acrylic acid ester of methylol melamine, epoxy (meth)acrylate, urethane acrylate, (meth)acrylic acid, styrene, vinyl acetate, hydroxyethyl vinyl ether, ethylene glycol divinyl ether, pentaerythritol trivinyl ether, (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-vinylformamide, acrylonitrile, etc., are not necessarily limited thereto. These may be used alone or in a mixture of two or more kinds at any ratio as required.

[Heat-sensitive substances, light-sensitive substances]
Examples of the heat-sensitive substance include a thermal polymerization initiator, and specifically, an organic peroxide initiator, an azo initiator, etc. Examples of the light-sensitive substance include a photopolymerization initiator, a photoacid generator, or a photobase generator.

[Photopolymerization initiator, photoacid generator]
Examples of the photopolymerization initiator include acetophenone-based compounds, benzoin-based compounds, benzophenone-based compounds, thioxanthone-based compounds, triazine-based compounds, oxime ester-based compounds, phosphine-based compounds, quinone-based compounds, borate-based compounds, carbazole-based compounds, imidazole-based compounds, and titanocene-based compounds.
Examples of the photoacid generator include sulfonium salts, tetrahydrothiophenium salts, and N-sulfonyloxyimide compounds.

The amount of the photopolymerization initiator and/or photoacid generator is preferably 0.01 to 20 parts by mass per 100 parts by mass of the polymerizable monomer. This is preferable because sufficient curing properties are obtained and coloring and deterioration of other physical properties do not occur within the above range.

[Photobase Generator]
Examples of the photobase generator include heterocyclic group-containing photobase generators, 2-nitrobenzylcyclohexylcarbamate, [[(2,6-dinitrobenzyl)oxy]carbonyl]cyclohexylamine, bis[[(2-nitrobenzyl)oxy]carbonyl]hexane-1,6-diamine, triphenylmethanol, o-carbamoylhydroxylamide, o-carbamoyloxime, hexaamminecobalt(III) tris(triphenylmethylborate), and the like.

[Sensitizer]
Examples of the sensitizer include polymethine dyes such as chalcone derivatives, unsaturated ketones typified by dibenzalacetone, 1,2-diketone derivatives typified by benzil and camphorquinone, benzoin derivatives, fluorene derivatives, naphthoquinone derivatives, anthraquinone derivatives, xanthene derivatives, thioxanthene derivatives, xanthone derivatives, thioxanthone derivatives, coumarin derivatives, ketocoumarin derivatives, cyanine derivatives, merocyanine derivatives, and oxonol derivatives, acridine derivatives, azine derivatives, thiazine derivatives, oxazine derivatives, indoline derivatives, azulene derivatives, azulenium derivatives, squarylium derivatives, porphyrin derivatives, tetraphenylporphyrin derivatives, triarylmethane derivatives, tetrabenzoporphyrin derivatives, and tetrapyrazinoporphyrazine. derivatives, phthalocyanine derivatives, tetraazaporphyrazine derivatives, tetraquinoxalyloporphyrazine derivatives, naphthalocyanine derivatives, subphthalocyanine derivatives, pyrylium derivatives, thiopyrylium derivatives, tetraphylline derivatives, annulene derivatives, spiropyran derivatives, spirooxazine derivatives, thiospiropyran derivatives, metal arene complexes, organic ruthenium complexes, or Michler's ketone derivatives, α-acyloxy esters, acylphosphine oxides, methylphenyl glyoxylates, benzyl, 9,10-phenanthrenequinone, camphorquinone, ethyl anthraquinone, 4,4'-diethylisophthalophenone, 3,3', or 4,4'-tetra(t-butylperoxycarbonyl)benzophenone, 4,4'-diethylaminobenzophenone, and the like.

The ink composition of the present invention may contain other components in addition to those described above, provided that the object of the present invention is not impaired. Examples of other components include defoamers, leveling agents, thickeners, etc.

The substrate for forming a quantum dot-containing layer using the ink composition of the present invention is not particularly limited, and examples thereof include plastic substrates such as polycarbonate, hard PVC, soft PVC, polystyrene, polystyrene foam, PMMA, polypropylene, polyethylene, and PET, or mixtures or modified products thereof, paper substrates such as fine paper, art paper, coated paper, and cast-coated paper, glass substrates, and metal substrates such as stainless steel. The substrate can be appropriately selected depending on the application of the ink composition. In addition, examples of a method for forming a quantum dot-containing layer on a substrate using the ink composition of the present invention include a method in which the ink composition is applied and then the solvent is dried to form a quantum dot-containing layer, and a method in which the ink composition is applied and then irradiated with ultraviolet light to form a cured film.

<Light Wavelength Conversion Layer>
The quantum dot-containing layer can be used as a light wavelength conversion layer. The light wavelength conversion layer can convert excitation light into fluorescence on the long wavelength side and emit it, and is not particularly limited as long as it can maintain the relationship between the excitation light wavelength and the emitted fluorescence wavelength. For example, blue or ultraviolet light can be used as excitation light to obtain green or red fluorescence, or ultraviolet or visible light can be used as excitation light to obtain fluorescence in the near infrared region. The thickness of the light wavelength conversion layer is preferably 1 to 500 μm, more preferably 1 to 50 μm, and even more preferably 1 to 10 μm. A thickness of 1 μm or more is preferable because a high wavelength conversion effect can be obtained. In addition, a thickness of 500 μm or less is preferable because the light source unit can be made thinner when incorporated into the light source unit.

<Light Wavelength Conversion Member>
The above-mentioned light wavelength conversion layer can also be used as a light wavelength conversion member.
The light wavelength conversion member is a substrate having a light wavelength conversion layer formed on at least one side thereof. The substrate is not particularly limited, but may be, for example, a plastic substrate such as polycarbonate, hard PVC, soft PVC, polystyrene, polystyrene foam, PMMA, polypropylene, polyethylene, PET, or a mixture or modified product thereof, a paper substrate such as fine paper, art paper, coated paper, cast coated paper, or a metal substrate such as glass or stainless steel. The substrate may be appropriately selected depending on the application. For example, in the case of a prepaid card or a pass card, a plastic substrate or a mixture or modified product thereof is preferred from the viewpoint of durability. In the case of a one-dimensional barcode, a two-dimensional barcode, or a QR code (registered trademark) (matrix type two-dimensional code) as an information recording medium, a plastic substrate or a paper substrate is preferred. In addition, in the case of a wavelength conversion color filter, a transparent substrate is preferred.

<Electroluminescent Device>
The electroluminescent element of the present invention is characterized in that it comprises an anode, a light-emitting layer, and a cathode on a substrate, and the light-emitting layer contains the quantum dots according to the present invention as a light-emitting material. The electroluminescent element of the present invention has excellent reliability because the light-emitting layer contains the quantum dots according to the present invention, which have excellent stability. The electroluminescent element of the present invention has at least a substrate, an anode, a light-emitting layer, and a cathode, and may further have other layers as necessary. In addition, the light-emitting layer may be a single layer or a multilayer, and when there are two or more light-emitting layers, at least one layer may contain the light-emitting material according to the present invention.

That is, the electroluminescent element of the present invention includes a single-layer electroluminescent element consisting of an anode, a light-emitting layer, and a cathode, and a multi-layer electroluminescent element including other layers. In addition to the light-emitting layer, other layers constituting the multi-layer electroluminescent element include a hole injection layer, a hole transport layer, a hole blocking layer, an electron injection layer, etc., which are intended to facilitate the injection of holes and electrons into the light-emitting layer and to facilitate the recombination of holes and electrons in the light-emitting layer. Other layers include an interlayer layer, which is adjacent to the light-emitting layer between the light-emitting layer and the anode and has the role of isolating the light-emitting layer from the anode, or the light-emitting layer from the hole injection layer or the hole transport layer.

Representative layer configurations of multi-layer electroluminescent elements include: (1) anode/hole injection layer/light-emitting layer/cathode; (2) anode/hole injection layer/hole transport layer/light-emitting layer/cathode; (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) anode/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/cathode, etc.

Each of the above-mentioned layers may be formed of two or more layers, or several layers may be repeatedly stacked. In recent years, an element structure called "multi-photon emission" has been proposed in which some of the layers of the above-mentioned multi-layered electroluminescence are multi-layered in order to improve the light extraction efficiency. For example, an electroluminescence element composed of a glass substrate/anode/hole transport layer/electron transporting luminescent layer/electron injection layer/charge generation layer/luminescent layer/cathode may have multiple units of charge generation layer/luminescent layer stacked.

[Hole injection layer]
The hole injection layer is made of a hole injection material that exhibits excellent hole injection effect in the light emitting layer, and can form a hole injection layer that has excellent adhesion to the anode interface and excellent thin film forming properties. In addition, when such materials are laminated in multiple layers, and a material with a high hole injection effect and a material with a high hole transport effect are laminated in multiple layers, the materials used for each layer may be called hole injection material and hole transport material. These hole injection materials and hole transport materials must have a large hole mobility and a small ionization energy, usually 5.5 eV or less. As such a hole injection layer, a material that transports holes to the light emitting layer at a lower electric field strength is preferable, and further, a material that has a hole mobility of at least 10 ^-6 cm ² /V·sec when an electric field of, for example, 10 ⁴ to 10 ⁶ V/cm is applied is preferable. The hole injection material and the hole transport material are not particularly limited as long as they have the above-mentioned preferable properties, and any material may be selected and used from those conventionally used as charge transport materials for holes in photoconductive materials and known materials used in the hole injection layer of an organic EL element.

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, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, polysilane-based and aniline-based copolymers, and conductive polymer oligomers (particularly thiophene oligomers) disclosed in JP-A-1-211399.

In addition, porphyrin compounds, aromatic tertiary amine compounds, and styrylamine compounds can also be used as hole injection materials and hole transport materials. For example, 4,4'-bis(N-(1-naphthyl)-N-phenylamino)biphenyl, which has two condensed aromatic rings in the molecule, as described in U.S. Pat. No. 5,061,569, and 4,4',4"-tris(N-(3-methylphenyl)-N-phenylamino)triphenylamine, in which three triphenylamine units are linked in a starburst configuration, as described in Japanese Patent Laid-Open No. 4-308688, can be mentioned. In addition, phthalocyanine derivatives such as copper phthalocyanine and hydrogen phthalocyanine can also be used as hole injection materials and hole transport materials. Furthermore, aromatic dimethylidene compounds, p-type Si, p-type SiC, and other inorganic compounds can also be used as hole injection materials and hole transport materials.

Additionally, materials that can be used for the hole injection layer include inorganic oxides such as molybdenum oxide ( _MnOx ), vanadium oxide ( _VOx ), ruthenium oxide ( _RuOx ), copper oxide ( _CuOx ), tungsten oxide ( _WOx ), iridium oxide ( _IrOx ), and doped versions thereof.

Specific examples of aromatic tertiary amine compounds 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, and N,N-bis(4-di-4-tolylaminophenyl)-4-phenyl-cyclo Examples include hexane, 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, which can be used as both a hole injection material and a hole transport material.

To form the hole injection layer, the above-mentioned compound is formed into a thin film by a known method such as vacuum deposition, spin coating, casting, or the Langmuir-Blodgett method (LB method). There are no particular limitations on the thickness of the hole injection layer, but it is usually 5 nm to 5 μm.

Examples of materials used for the interlayer layer include polyvinylcarbazole and its derivatives, polyarylene derivatives having aromatic amines in the side chain or main chain, arylamine derivatives, triphenyldiamine derivatives, and other polymers containing aromatic amines. In addition, examples of the method for forming the interlayer layer include a method of forming a film from a solution when a high molecular weight material is used.

To form the interlayer layer from a solution, known wet film formation methods can be used, such as spin coating, casting, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, inkjet printing, capillary coating, and nozzle coating.

The optimum thickness of the interlayer layer varies depending on the material used, and can be selected so that the driving voltage and luminous efficiency are adequate. The thickness is usually 1 nm to 1 μm, preferably 2 to 500 nm, and more preferably 5 to 200 nm.

[Electron injection layer]
For the electron injection layer, an electron injection material is used that can form an electron injection layer that exhibits excellent electron injection effect for the light emitting layer and has excellent adhesion to the cathode interface and excellent thin film formability. Examples of such electron injection materials include metal complex compounds, nitrogen-containing five-membered ring derivatives, fluorenone derivatives, anthraquinodimethane derivatives, diphenoquinone derivatives, thiopyran dioxide derivatives, perylene tetracarboxylic acid derivatives, fluorenylidenemethane derivatives, anthrone derivatives, silole derivatives, triarylphosphine oxide derivatives, polyquinoline and its derivatives, polyquinoxaline and its derivatives, polyfluorene and its derivatives, calcium acetylacetonate, sodium acetate, etc. In addition, inorganic/organic composite materials in which a metal such as cesium is doped into bathophenanthroline (Proceedings of the Society of Polymer Science, Vol. 50, No. 4, p. 660, published in 2001) and Proceedings of the 50th Joint Conference of Applied Physics, No. No. 3, p. 1402, published in 2003, BCP, TPP, T5MPyTZ, and the like are given as examples of the electron injection material, but the material is not particularly limited to these, so long as it can form a thin film necessary for element production, can inject electrons from the cathode, and can transport electrons.

Among the above electron injection materials, preferred are metal complex compounds, nitrogen-containing five-membered ring derivatives, silole derivatives, and triarylphosphine oxide derivatives. Preferred metal complex compounds are metal complexes of 8-hydroxyquinoline or its derivatives. Specific examples of metal complexes of 8-hydroxyquinoline or derivatives thereof include tris(8-hydroxyquinolinato)aluminum, tris(2-methyl-8-hydroxyquinolinato)aluminum, tris(4-methyl-8-hydroxyquinolinato)aluminum, tris(5-methyl-8-hydroxyquinolinato)aluminum, tris(5-phenyl-8-hydroxyquinolinato)aluminum, bis(8-hydroxyquinolinato)(1-naphtholate)aluminum, bis(8-hydroxyquinolinato)(2-naphtholate)aluminum, bis(8-hydroxyquinolinato)(phenolate)aluminum, and bis(8-hydroxyquinolinato)(4-cyano-1-naphtholate)aluminum. aluminum complex compounds such as 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, and bis(8-hydroxyquinolinate)(o-cresolate)aluminum; tris(8-hydroxyquinolinate)gallium, tris(2-methyl-8-hydroxyquinolinate)gallium, and tris(4-methyl-8-hydroxyquinolinate ) gallium, tris(5-methyl-8-hydroxyquinolinato)gallium, tris(2-methyl-5-phenyl-8-hydroxyquinolinato)gallium, bis(2-methyl-8-hydroxyquinolinato)(1-naphtholate)gallium, bis(2-methyl-8-hydroxyquinolinato)(2-naphtholate)gallium, bis(2-methyl-8-hydroxyquinolinato)(phenolate)gallium, bis(2-methyl-8-hydroxyquinolinato)(4-cyano-1-naphtholate)gallium, bis(2,4-dimethyl-8-hydroxyquinolinato)(1-naphtholate)gallium, bis(2,5-dimethyl-8-hydroxyquinolinato)(2-naphtholate)gallium, bis(2-methyl- In addition to gallium complex compounds such as 5-phenyl-8-hydroxyquinolinate) (phenolate), bis(2-methyl-5-cyano-8-hydroxyquinolinate) (4-cyano-1-naphtholate) gallium, bis(2-methyl-8-hydroxyquinolinate) chlorogallium, and bis(2-methyl-8-hydroxyquinolinate) (o-cresolate) gallium, metal complex compounds such as 8-hydroxyquinolinate lithium, bis(8-hydroxyquinolinate) copper, bis(8-hydroxyquinolinate) manganese, bis(10-hydroxybenzo[h]quinolinate) beryllium, bis(8-hydroxyquinolinate) zinc, and bis(10-hydroxybenzo[h]quinolinate) zinc are also included.

Preferable nitrogen-containing five-membered ring derivatives include oxazole derivatives, thiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, and triazole derivatives. Specific examples include 2,5-bis(1-phenyl)-1,3,4-oxazole, 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- butylphenyl)-5-(4"-biphenyl)-1,3,4-thiadiazole, 2,5-bis(1-naphthyl)-1,3,4-thiadiazole, 1,4-bis[2-(5-phenylthiadiazolyl)]benzene, 2-(4'-tert-butylphenyl)-5-(4"-biphenyl)-1,3,4-triazole, 2,5-bis(1-naphthyl)-1,3,4-triazole, 1,4-bis[2-(5-phenyltriazolyl)]benzene, etc.

Additionally, materials that can be used for the electron injection layer include inorganic oxides such as zinc oxide (ZnO _x ), titanium oxide (TiO _x ), and doped versions thereof.

Furthermore, the hole blocking layer uses a hole blocking material that can prevent holes that have passed through the light emitting layer from reaching the electron injection layer and form a layer with excellent thin film formability. Examples of such hole blocking materials include aluminum complex compounds such as bis(8-hydroxyquinolinato)(4-phenylphenolato)aluminum, gallium complex compounds such as bis(2-methyl-8-hydroxyquinolinato)(4-phenylphenolato)gallium, and nitrogen-containing condensed aromatic compounds such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).

[Light-emitting layer]
The light-emitting layer of the electroluminescent device preferably has the following functions:
Injection function: the ability to inject holes from the anode or hole injection layer when an electric field is applied, and the ability to inject electrons from the cathode or electron injection layer. Transport function: the ability to move injected charges (electrons and holes) by the force of an electric field. Light-emitting function: the ability to provide a site for the recombination of electrons and holes, leading to light emission. However, there may be differences in the ease with which holes and electrons are injected, and there may also be differences in the transport ability, which is represented by the mobility of holes and electrons.

At least one of the light-emitting layers constituting the electroluminescent device of the present invention contains a light-emitting material consisting of the quantum dots of the present invention. The light-emitting layer containing the light-emitting material is preferably formed from the ink composition of the present invention. The light-emitting layer may contain a known light-emitting material in addition to the quantum dots of the present invention. Known light-emitting materials that may be added to the ink composition of the present invention include fluorescent brighteners such as benzothiazoles, benzimidazoles, and benzoxazoles, metal chelated oxinoid compounds, and styrylbenzene compounds. Specific examples of these compounds include the compounds disclosed in JP-A-59-194393. Other useful compounds are listed in Chemistry of Synthetic Dyes (1971), pages 628-637 and 640.

Suitable examples of the metal chelated oxinoid compound include 8-hydroxyquinoline-based metal complexes such as tris(8-quinolinol)aluminum, and dilithium epitridione.

In addition, as the styrylbenzene-based compound, distyrylpyrazine derivatives or polyphenyl-based compounds can also be used as materials for the light-emitting layer.

In addition to the above-mentioned fluorescent brightening agents, metal chelated oxinoid compounds and styrylbenzene compounds, for example, 12-phthaloperinone, 1,4-diphenyl-1,3-butadiene, 1,1,4,4-tetraphenyl-1,3-butadiene, naphthalimide derivatives, perylene derivatives, oxadiazole derivatives, aldazine derivatives, pyrazirine derivatives, cyclopentadiene derivatives, pyrrolopyrrole derivatives, styrylamine derivatives, coumarin compounds, and those described in International Publication WO90/13148 and Appl. Phys. Lett. , vol. 58, 18, p. 1982 (1991), 9,9',10,10'-tetraphenyl-2,2'-bianthracene, PPV (polyparaphenylenevinylene) derivatives, polyfluorene derivatives and copolymers thereof, for example, those having structures of the following general formulas (12) to (14).

[In general formula (12), R ^x1 and R ^x2 each independently represent a monovalent aliphatic hydrocarbon group, and n1 represents an integer of 3 to 100.]

[In general formula (13), R ^x3 and R ^x4 each independently represent a monovalent aliphatic hydrocarbon group, and n2 and n3 each independently represent an integer of 3 to 100.]

[In general formula (14), ^R and ^R each independently represent a monovalent aliphatic hydrocarbon group, n and n each independently represent an integer of 3 to 100, and Ph represents a phenyl group.]

Further, compounds represented by the general formula (Rs-Q) ₂ -Al-O-L3 (wherein L3 is a hydrocarbon having 6 to 24 carbon atoms containing a phenyl moiety, O-L3 is a phenolate ligand, Q is a substituted 8-quinolinate ligand, and Rs is an 8-quinolinate ring substituent selected so as to sterically prevent more than two substituted 8-quinolinate ligands from bonding to the aluminum atom) described in JP-A-5-258862 etc. are also included. Specific examples include bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III), bis(2-methyl-8-quinolinolato)(1-naphtholate)aluminum(III), etc.

[anode]
The material used for the anode of the electroluminescent device is preferably a metal, alloy, electrically conductive compound, or a mixture thereof having a large work function (4 eV or more). Specific examples of such electrode materials include metals such as Au, and conductive materials such as CuI, ITO, SnO ₂ , and ZnO. To form the anode, these electrode materials can be formed into a thin film by a method such as deposition or sputtering. When light emitted from the light-emitting layer is taken out from the anode, it is desirable for the anode to have a characteristic such that the transmittance of the anode for light emission is greater than 10%. In addition, the sheet resistance of the anode is preferably several hundred Ω/□ or less. Furthermore, the film thickness of the anode is usually selected in the range of 10 nm to 1 μm, preferably 10 to 200 nm, depending on the material.

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

The method for producing an electroluminescent device is to form an anode, a light-emitting layer, a hole injection layer if necessary, and an electron injection layer if necessary, using the above-mentioned materials and methods, and finally to form a cathode. It is also possible to produce an electroluminescent device in the reverse order from the cathode to the anode.

The electroluminescent element is fabricated on a light-transmitting substrate. The light-transmitting substrate is a substrate that supports the electroluminescent element, and its light transmittance in the visible region of 400 to 700 nm is desirably 50% or more, preferably 90% or more. It is also preferable to use a smooth substrate.

These substrates are not particularly limited as long as they have mechanical and thermal strength and are transparent, and may be flexible film or sheet-like substrates. For example, glass plates, synthetic resin plates, etc. are preferably used as substrates. Examples of glass plates include plates made of soda-lime glass, barium-strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, quartz, etc. Examples of synthetic resin plates include plates made of polycarbonate resin, acrylic resin, polyethylene terephthalate resin, polyether sulfide resin, polysulfone resin, etc.

The layers of the electroluminescent device can be formed by dry deposition methods such as vacuum deposition, electron beam irradiation, sputtering, plasma, and ion plating, or wet deposition methods such as spin coating, dipping, and flow coating. Laser Induced Thermal Imaging (LITI), printing (offset printing, flexographic printing, gravure printing, and screen printing), inkjet printing, and other methods can also be used. However, it is preferable that the light-emitting layer is formed by a wet deposition method.

The organic layer is preferably a molecular deposition film. A molecular deposition film is a thin film formed by deposition from a material compound in a gas phase state, or a film formed by solidifying a material compound in a solution or liquid phase state. Usually, this molecular deposition film can be distinguished from a thin film (molecular stacked film) formed by the LB method by differences in aggregation structure, higher-order structure, and functional differences resulting therefrom. In addition, an organic layer can also be formed by dissolving a binder such as a resin and a material compound in a solvent to form a solution, and then thinning the solution by a spin coating method or the like. The thickness of each layer is not particularly limited, but if the thickness is too thick, a large applied voltage is required to obtain a certain light output, resulting in poor efficiency, and conversely, if the thickness is too thin, pinholes and the like will occur, making it difficult to obtain sufficient luminescence brightness even when an electric field is applied. Therefore, the thickness of each layer is suitable to be in the range of 1 nm to 1 μm, but more preferably in the range of 10 nm to 0.2 μm.

In addition, in order to improve the stability of the electroluminescent element against temperature, humidity, atmosphere, etc., a protective layer may be provided on the surface of the element, or the entire element may be covered or sealed with a resin or the like. In particular, when covering or sealing the entire element, a photocurable resin that hardens when exposed to light is preferably used.

The current applied to an electroluminescent element is usually direct current, but pulse current or alternating current may also be used. There are no particular limitations on the current and voltage values as long as they are within a range that does not destroy the element, but considering the power consumption and lifespan of the element, it is desirable to emit light efficiently with as little electrical energy as possible.

The electroluminescent element can be driven not only by the passive matrix method but also by the active matrix method. In addition, the method of extracting light from the electroluminescent element of the present invention can be not only bottom emission, in which light is extracted from the anode side, but also top emission, in which light is extracted from the cathode side.

The main methods for full-coloring electroluminescent elements include the three-color coating method, the color conversion method, and the color filter method. The three-color coating method includes deposition using a shadow mask, the inkjet method, and the printing method. Laser thermal transfer can also be used. The color conversion method uses a blue-emitting light-emitting layer and converts it into green and red, which have longer wavelengths than blue, through a color conversion (CCM) layer in which fluorescent dyes are dispersed. The color filter method uses a white-emitting organic EL element to extract the three primary colors of light through a liquid crystal color filter, but in addition to these three primary colors, some white light can also be extracted and used for light emission, which can increase the luminous efficiency of the entire element.

Furthermore, electroluminescent elements may adopt a microcavity structure. This is a technology in which an 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 cathode. However, by appropriately selecting the optical characteristics such as the reflectance and transmittance of the anode and cathode, and the film thickness of the organic layer sandwiched between them, the multiple interference effect can be actively utilized to control the emission wavelength extracted from the element. This also makes it possible to improve the chromaticity of the emitted light.

As described above, the electroluminescent element using the quantum dots of the present invention has excellent fluorescence quantum yield and reliability. Therefore, the electroluminescent element can be used as a flat panel display such as a wall-mounted television, or as a variety of flat light emitters. It can also be used as a light source for copying machines and printers, a light source for liquid crystal displays and instruments, display boards, marker lights, etc.

<Photoelectric conversion element>
The photoelectric conversion element of the present invention has the photoelectric conversion layer between a pair of electrodes. The photoelectric conversion element of the present invention can be configured as a known photoelectric conversion element. The photoelectric conversion element of the present invention can be manufactured by known methods except for the photoelectric conversion layer.

Here, we will explain in detail the photoelectric conversion element that can be created using the ink composition of the present invention. Generally, a photoelectric conversion element using semiconductor particles is composed of at least a pair of electrodes and a photoelectric conversion layer. With the aim of improving photoelectric conversion efficiency, various types of element structures have been proposed, such as by matching the energy between the electrodes and the semiconductor particles and by using a method for producing a photoelectric conversion layer made of semiconductor particles. For example, a photoelectric conversion element having the known configuration shown below can be produced using the ink composition of the present invention.

1. Schottky-type photoelectric conversion element This is a photoelectric conversion element that obtains photovoltaic power by utilizing a Schottky barrier formed at the interface between an electron-donating (p-type) or electron-accepting (n-type) semiconductor particle and an electrode. For example, when a p-type photoelectric conversion layer is used, a Schottky barrier is formed at the interface with the electrode having the smaller work function of the pair of electrodes, and charge separation occurs at the interface to perform photoelectric conversion.

2. Bilayer heterojunction photoelectric conversion element This is a photoelectric conversion element in which electron-donating (p-type) and electron-accepting (n-type) semiconductor particles or other semiconductor materials are individually formed between a pair of electrodes, and photoinduced charge separation occurs at the pn junction interface to obtain a photocurrent.

3. Bulk heterojunction photoelectric conversion element An organic semiconductor layer is formed by mixing electron-donating (p-type) and electron-accepting (n-type) semiconductor particles and other semiconductor materials in any ratio between a pair of electrodes. In this case, the p-type and n-type materials may be uniformly or non-uniformly dispersed. Since photocharge separation occurs at the interface formed by the individual p-type and n-type materials, a wider pn junction can be formed than in the bilayer heterojunction type.

<Electrodes>
At least one of the pair of electrodes constituting the photoelectric conversion element is preferably light-transmitting. Specific examples include conductive metal oxides such as tin oxide, zinc oxide, indium oxide, and indium tin oxide (ITO), metals such as gold, silver, platinum, chromium, nickel, lithium, indium, aluminum, calcium, and magnesium, and mixtures or laminates of these metals and conductive metal oxides.

The electrodes are generally flat in shape, but may be wavy, pyramidal, comb-shaped, etc., to improve energy conversion efficiency. These electrodes can be formed using general electrode formation methods, such as vacuum deposition, sputtering, ion plating, and other PVD methods, CVD, chemical reaction methods (sol-gel method, etc.), casting, spray coating, inkjet, and spin coating.

The photoelectric conversion element may have a layer other than the photoelectric conversion layer between the pair of electrodes, and may have the hole injection layer, hole transport layer, electron transport layer, and/or electron injection layer.

The photoelectric conversion element may include other components in addition to the layers described above. For example, it may include an optical film (filter) that blocks ultraviolet light. Ultraviolet light has high energy and is one of the causes of deterioration of organic materials. Blocking this ultraviolet light can extend the life of the element.

A protective film may be provided to protect the photoelectric conversion layer against external impact. The protective film may be composed of, for example, a polymer film such as styrene resin, epoxy resin, acrylic resin, polyurethane, polyimide, polyvinyl alcohol, polyvinylidene fluoride, or polyethylene-polyvinyl alcohol copolymer; an inorganic oxide film or nitride film such as silicon oxide, silicon nitride, or aluminum oxide; a metal plate or foil such as aluminum; or a laminate film of these. Note that only one type of material may be used for these protective films, or two or more types may be used.

It is generally said that semiconductor particles deteriorate due to moisture and oxygen in the air. To prevent this, a barrier film may be provided. For example, metals or inorganic oxides are preferred, such as Ti, Al, Mg, Zr, silicon oxide, aluminum oxide, silicon oxynitride, aluminum oxynitride, magnesium oxide, zinc oxide, indium oxide, tin oxide, yttrium oxide, boron oxide, and calcium oxide. There is no particular order in which these various functional films are stacked, and a functional film that combines these functions may be used.

The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the scope of the invention. Unless otherwise specified, "parts" and "%" in the examples and comparative examples represent "parts by mass" and "% by mass". The mass average molecular weight (Mw) is a value measured using GPC and calculated in terms of polystyrene.

<Synthesis of compound represented by general formula (1)>
(Synthesis of Compound 1)
80 parts of methanol, 5.5 parts of 4-(N,N-diphenylamino)benzaldehyde, and 1.8 parts of 2-aminoethanethiol were added to a recovery flask and then heated under reflux for 3 hours. Methanol was distilled off under reduced pressure, and the resulting crude product was collected by filtration and washed with methanol. The resulting solid was dried under reduced pressure to obtain Compound 1. The yield was 99%.

(Synthesis of Compound 2)
80 parts of methanol, 6.6.0 parts of 4-(N,N-di-p-tolylamino)benzaldehyde, and 1.8 parts of 2-aminoethanethiol were added to a recovery flask and then heated under reflux for 3 hours. Methanol was distilled off under reduced pressure, and the resulting crude product was collected by filtration and washed with methanol. The resulting solid was dried under reduced pressure to obtain compound 2. The yield was 88%.

(Synthesis of Compound 3)
To a recovery flask were added 80 parts of methanol, 6.7 parts of 4-(bis(p-methoxyphenyl)amino)benzaldehyde, and 1.8 parts of 2-aminoethanethiol, and the mixture was heated under reflux for 3 hours. Methanol was distilled off under reduced pressure, and the resulting crude product was collected by filtration and washed with methanol. The resulting solid was dried under reduced pressure to obtain compound 3. The yield was 93%.

(Synthesis of Compound 4)
80 parts of methanol, 5.2 parts of 9-ethyl-3-carbazolecarboxaldehyde, and 1.8 parts of 2-aminoethanethiol were added to a recovery flask and then heated under reflux for 3 hours. Methanol was distilled off under reduced pressure, and the resulting crude product was collected by filtration and washed with methanol. The resulting solid was dried under reduced pressure to obtain compound 4. The yield was 95%.

The obtained compounds 1 to 4 and the compounds 0 and 19 used in the comparative examples are shown in Table 5.

<Production of Resin>
[Preparation of resin solution 1]
A separable 4-neck flask was fitted with a thermometer, a cooling tube, a nitrogen gas inlet tube, and a stirrer. 70 parts of mesitylene was charged into the reaction vessel, which was then heated to 80°C. The atmosphere in the reaction vessel was replaced with nitrogen, and a mixture of 18 parts of n-butyl methacrylate, 12 parts of methyl methacrylate, and 0.4 parts of 2,2'-azobisisobutyronitrile was dripped from the drip tube over 2 hours. After the dripping was completed, the reaction was continued for another 3 hours to obtain a solution of an acrylic resin having a mass average molecular weight (Mw) of 26,000. After cooling to room temperature, about 2 g of the resin solution was sampled and dried by heating at 180°C for 20 minutes to measure the nonvolatile content, and mesitylene was added to the resin solution previously synthesized so that the nonvolatile content was 30% by mass, to prepare acrylic resin solution 1.

[Preparation of resin solution 2]
A separable 4-neck flask was fitted with a thermometer, a cooling tube, a nitrogen gas inlet tube, and a stirrer to prepare a reaction vessel. Diethylene glycol monobutyl ether acetate (DBCA) 70 parts was charged and heated to 80 ° C., and the inside of the reaction vessel was replaced with nitrogen. A mixture of 14 parts of n-butyl methacrylate, 10 parts of methyl methacrylate, 6 parts of styrene, and 0.4 parts of 2,2'-azobisisobutyronitrile was dripped from the drip tube over 2 hours. After dripping was completed, the reaction was continued for another 3 hours to obtain a solution of an acrylic resin having a mass average molecular weight (Mw) of 26,000. After cooling to room temperature, about 2 g of the resin solution was sampled and dried at 180 ° C. for 20 minutes to measure the nonvolatile content, and diethylene glycol monobutyl ether acetate was added to the resin solution previously synthesized so that the nonvolatile content was 30% by mass, to prepare an acrylic resin solution 2.

[Preparation of resin solution 3]
200 parts of norbornene, 50 parts of cyclopentene, 180 parts of 1-hexene, and 750 parts of toluene were charged into a nitrogen-substituted reaction vessel and heated to 60° C. To this, 0.62 parts of a toluene solution of triethylaluminum (1.5 mol/l) and 3.7 parts of a WCl ₆ solution (concentration: 0.05 mol/l) modified with tert-C ₄ H ₉ OH/CH ₃ OH (tert-C ₄ H ₉ OH/CH ₃ OH/WCl ₆ = 0.35/0.3/1; molar ratio) were added, and the mixture was heated and stirred at 80° C. for 3 hours to carry out a ring-opening polymerization reaction and a hydrogenation reaction. Then, the nonvolatile content was adjusted to 30% using trimethylbenzene, and cyclopentadiene resin solution 3 was obtained.

<Preparation of quantum dots PbS-0>
First, 0.40 parts of elemental sulfur and 6.0 parts of oleylamine were heated to 120°C in a reaction vessel under a nitrogen atmosphere to obtain a homogeneous solution, and then cooled to 25°C. Next, 0.32 parts of lead chloride and 6.0 parts of oleylamine were heated to 120°C in a separate reaction vessel under a nitrogen atmosphere to obtain a lead source solution. After that, the lead source solution was prepared at 40°C, and 1.8 parts of the above sulfur source solution were added at once. After reacting for 30 seconds, the vessel was immersed in an ice bath to rapidly cool, and then diluted with 13 parts of hexane. After centrifuging (4000 rpm, 5 minutes) to remove unreacted raw materials, 12 parts of a mixture consisting of butanol:methanol = 2:1 (volume ratio) was added to precipitate the quantum dots, and centrifuging (4000 rpm, 5 minutes) was performed to recover the quantum dots. Then, 24 parts of a mixture of hexane and oleic acid (volume ratio: 1:2) was added, stirred for 30 minutes, centrifuged, and the supernatant was collected. The quantum dots were precipitated, redispersed, and impurity precipitated twice more, and finally the quantum dots were precipitated and dried in vacuum. The solid content was adjusted to 5% using n-octane to obtain quantum dots PbS-0 (average particle size: 3.5 nm).

<Synthesis of quantum dots PbSe-0>
As a lead source solution, 0.22 parts of lead oxide, 0.73 parts of oleic acid, and 10 parts of 1-octadecene were heated to 150°C in a reaction vessel under a nitrogen atmosphere. Then, a mixture consisting of 2.5 parts of 1M-trioctylphosphine-selenium solution and 0.028 parts of diphenylphosphine was quickly added, and the reaction solution was heated to 180°C, kept at 160°C, reacted for 2 minutes, and then quenched. After dilution with 10 parts of hexane, the solution was precipitated with acetone. The precipitate was washed five times with acetone and dried in vacuum to obtain quantum dots PbSe-0 (average particle size 2.7 nm).

<Synthesis of quantum dots Ag ₂ S-0>
0.04 parts of silver oleate, 8 parts of octanethiol, and 4 parts of dodecylamine were heated in a reaction vessel under an Ar atmosphere at 200° C. for 0.5 hours. After the solution was cooled to room temperature, 40 parts of absolute ethanol were added. The resulting mixture was centrifuged and vacuum dried to obtain quantum dots Ag ₂ S-0 (average particle size 2.5 nm).

<Manufacturing of quantum dots>
[Comparative Example 0] (Quantum dot QD-0)
0.55 parts of anhydrous zinc acetate, 7.0 parts of dodecanethiol (compound 0), and 5.0 parts of oleylamine were heated and dissolved to prepare an additive solution. Separately, 0.22 parts of indium chloride and 8.25 parts of octylamine were placed in a reaction vessel, and heated to 165°C while performing nitrogen bubbling. After the indium chloride was dissolved, 0.86 parts of diethylaminophosphine were injected in a short time and controlled at 165°C for 20 minutes. Then, it was quenched and cooled to 40°C. The above additive solution was injected, heated at 240°C for 2 hours, and then allowed to cool to room temperature. After allowing to cool, purification was performed by reprecipitation using hexane and ethanol. The precipitate was collected and dried under reduced pressure to obtain quantum dots QD-0 in which core-shell type semiconductor fine particles with InP cores and ZnS shells were surface-treated with dodecanethiol (compound 0).

[Example 1] (Quantum dot QD-1)
The quantum dots QD-0 were dispersed in toluene to a solid concentration of 1%. The diluted solution was mixed with a 5% toluene solution of compound 1 in the same amount as the diluted solution and stirred for 12 hours. Purification was performed by reprecipitation using toluene and methanol. The precipitate was collected and dried under reduced pressure to obtain quantum dots QD-1 surface-treated with compound 1.

[Examples 2 to 4, Comparative Example 1] (Quantum dots QD-2 to 5)
Quantum dots QD-2 to QD-5 were prepared in the same manner as QD-1, except that the compounds were changed to compounds 2 to 4 and 19 shown in Table 6.

<Preparation of Ink Composition>
[Example 101] (Ink composition 1)
2 parts of quantum dots (QD-1) and 38 parts of n-hexane were mixed in a sealable container, which was then sealed and stirred, and filtered using a membrane filter with a pore size of 1 μm to obtain ink composition 1.

[Examples 102 to 104, Comparative Example 101] (Ink compositions 2 to 4, 9)
Ink compositions 2 to 4 and 9 were prepared in the same manner as ink composition 1, except that the quantum dots and solvent were weighed in that order in the formulation shown in Table 7 into a sealable container.

[Example 105] (Ink composition 5)
In a sealable container, 2 parts of quantum dots (QD-1), 60 parts of resin solution 1, and 68 parts of diethylene glycol monobutyl ether acetate (DBCA) were mixed, then the mixture was sealed and stirred, and filtered using a membrane filter with a pore size of 1 μm to obtain ink composition 5.

[Examples 106 to 108] (Ink compositions 6 to 8)
Ink compositions 6 to 8 were prepared in the same manner as ink composition 5, except that the quantum dots, resin solution, and solvent were weighed in that order in a sealable container according to the formulation shown in Table 7.

<Evaluation of Ink Composition>
The resulting ink compositions were subjected to the following evaluations, and the results are shown in Table 7.

[Stability over time]
The stability over time was evaluated by visually observing the appearance of the ink composition after storing it in an environment at 40° C. for 7 days and according to the following criteria.
A: No sediment (usable)
C: Sediment present (unusable)

[Fluorescence quantum yield (QY) maintenance rate]
First, the ink composition after storage for 7 days in a 40°C environment used in the evaluation of stability over time was used to coat a transparent film (Lumirror 75S10 polyester film manufactured by Toray Industries, Inc.) substrate with a bar coater so that the thickness after drying would be 6.0 μm, and then dried at 100°C for 10 minutes to obtain a printed matter. Next, the fluorescence quantum yield of the ink composition and the printed matter was measured under the following conditions. The ratio of the fluorescence quantum yield of the printed matter to the fluorescence quantum yield of the ink composition taken as 1 was taken as the fluorescence quantum yield maintenance rate, and was evaluated according to the following criteria. The fluorescence quantum yield maintenance rate is preferably closer to 1, and a rate of 0.6 or higher is practically usable.
A: Fluorescence quantum yield maintenance rate is 0.6 or more (usable)
C: Fluorescence quantum yield maintenance rate is less than 0.6 (unusable)
<Fluorescence quantum yield measurement conditions>
Measuring instrument: Quantum efficiency measuring system QE-2000 manufactured by Otsuka Electronics Co., Ltd. Excitation wavelength: 400 nm, integral range 375-425 nm
Fluorescence integration range: 430-800 nm

[Ejection properties]
A discharge test was carried out on the ink composition using an inkjet printer (Fujifilm Dimatix Materials Printer "DMP-2831", cartridge: Dimatix Materials Cartridges, 10 pL). In the discharge test, the ink composition was continuously discharged for 30 seconds. The discharge head of the inkjet printer had 16 nozzles, and the dischargeability was evaluated based on the number of nozzles capable of continuous discharge according to the following criteria.
A: Continuous ejection possible with 10 or more nozzles (ejection possible)
C: The number of nozzles capable of continuous ejection is 9 or less (ejection failure)

<Manufacture of electroluminescent device>
[Example 201]
(Fabrication of electroluminescent device)
Unless otherwise specified, deposition (vacuum deposition) was performed in a vacuum of ^10-6 Torr without temperature control such as heating or cooling of the substrate. The light-emitting characteristics of the element were measured using an electroluminescent element having a light-emitting element area of 2 mm x 2 mm.
On a washed glass plate with an ITO electrode, PEDOT/PSS (poly(3,4-ethylenedioxy)-2,5-thiophene/polystyrenesulfonic acid, CLEVIOS (registered trademark) P VP CH8000 manufactured by Heraeus) was applied by spin coating, and dried at 110° C. for 20 minutes to obtain a hole injection layer with a thickness of 35 nm. Next, poly(N-vinylcarbazole) was dissolved in monochlorobenzene at a concentration of 1.0 mass%, applied by spin coating, and dried at 110° C. for 20 minutes to form a hole transport layer with a thickness of 35 nm. The obtained ink composition 1 was diluted 35 times and applied thereon by spin coating, and the mixture was dried by holding it in a nitrogen atmosphere at room temperature for 5 minutes to form a light-emitting layer with a thickness of 20 nm. An isopropanol dispersion liquid N-10 of zinc oxide manufactured by Avantama was applied thereon by spin coating, and the applied layer was dried by heating on a hot plate at 80°C for 20 minutes to form an electron transport layer of 80 nm. Finally, an electrode was formed by depositing aluminum to a thickness of 200 nm to obtain an electroluminescent device. When the obtained electroluminescent device was driven at a current density of 10 (mA/ ^cm2 ), it was confirmed that the device emitted green light.

<Preparation of Ink Composition>
<Example 301>
The quantum dot PbS-0 was prepared as a toluene solution with a solid content concentration of 1%. One part of the prepared solution was mixed with one part of a 5% toluene solution of compound 1, and then stirred for 12 hours. Purification was performed by a reprecipitation method using toluene and ethanol. The precipitate was vacuum dried, and octane was added to prepare a 5% solution in octane, thereby preparing an ink composition PbS-1.

<Examples 302 to 306, Comparative Examples 301 to 303>
PbS-2 to 4, PbSe-1, and Ag ₂ S-1 were each prepared in the same manner as in Example 301, except that compound 1 was changed to the compound shown in Table 8. Of these, PbS-2 to 4, PbSe-1, and Ag ₂ S-1 are ink compositions of the present invention, and PbS-5, PbSe-2, and Ag ₂ S-2 are compositions that are not ink compositions of the present invention.

<Example 401>
(Fabrication of photoelectric conversion element)
The preparation and evaluation of the photoelectric conversion element will be described below. The deposition was performed in a vacuum of 10 ^-6 Torr under conditions where temperature control such as heating or cooling of the substrate was not performed. The element was evaluated using a photoelectric conversion element with an element area of 2 mm x 2 mm. First, PEDOT/PSS (poly(3,4-ethylenedioxy)-2,5-thiophene/polystyrene sulfonic acid, CLEVIOS (registered trademark) PVP CH8000 manufactured by Heraeus) was applied by spin coating on a washed glass plate with an ITO electrode, and dried at 110°C for 20 minutes to obtain a hole injection layer with a thickness of 35 nm. On the hole injection layer, the ink composition PbS-1 was applied by spin coating to form a photoelectric conversion layer with a thickness of 150 nm. Next, ZnO dispersion N-10 manufactured by Avantama was spin coated on the photoelectric conversion layer to form a film with a thickness of 50 nm. Next, aluminum (hereinafter, referred to as Al) was evaporated onto the electron transport layer to form an electrode having a thickness of 200 nm, thereby obtaining a photoelectric conversion element.

(Evaluation of photoelectric conversion element)
The durability of the obtained element was evaluated by the method shown below. The IV curves of the element were measured before and after storage, and the ratio of these measured values (measured value after storage/measured value before storage) was calculated to calculate the durability. The IV curve of the cell was measured using a xenon lamp white light source (PEC-L01, manufactured by Peccell Technologies, Inc.) with a light intensity (100 mW/cm ² ) equivalent to sunlight (AM1.5) under a mask with a light irradiation area of 0.0363 cm ² (2 mm square) using an IV characteristic measuring device (PECK2400-N, manufactured by Peccell Technologies, Inc.) under the conditions of a scanning speed of 0.1 V/sec (0.01 Vstep), a waiting time after voltage setting of 50 msec, a measurement integration time of 50 msec, a starting voltage of -0.1 V, and an end voltage of 1.1 V. The durability was calculated by measuring the I-V curves of the photoelectric conversion element before storage (immediately after the element was fabricated) and after storage for 4 days under conditions of light-shielded, 25°C, and 60% humidity, and calculating the ratio of the conversion efficiency after storage to the conversion efficiency before storage (immediately after the element was fabricated).
(Evaluation Criteria)
◎: Ratio is 95% or more: Good ○: Ratio is 90% or more but less than 95%: Usable for practical use △: Ratio is 80% or more but less than 90%: Unusable for practical use ×: Ratio is less than 80%: Poor

<Examples 402 to 406>
Photoelectric conversion elements were prepared and evaluated in the same manner as in Example 401, except that PbS-2 to 4, PbSe-1, and Ag ₂ S-1 were used instead of PbS-1 used in Example 401. The results are shown in Table 9.

<Comparative Examples 401 to 403>
Photoelectric conversion elements were fabricated and evaluated in the same manner as in Example 401, except that PbS-5, PbSe-2, and Ag ₂ S-2 were used instead of PbS-1 used in Example 301. The results are shown in Table 9.

In Table 7, the ink composition of the present invention using quantum dots surface-treated with a ligand having an aliphatic heterocyclic moiety containing a sulfur atom and a charge transporting moiety exhibited excellent stability over time and fluorescence quantum yield maintenance rate, and showed high reliability. Also in Table 9, the photoelectric conversion element using quantum dots surface-treated with a ligand having an aliphatic heterocyclic moiety containing a sulfur atom and a charge transporting moiety showed high durability.
Although the mechanism of action of the above results is unclear, it is speculated that the sulfur-containing aliphatic heterocyclic group has better oxidation resistance than the alkylthio group in benzenethiol in the comparative example, and thus the ligand is prevented from peeling off from the quantum dots, resulting in the above effects. Ligand peeling reduces the dispersibility of quantum dots, which leads to reduced sedimentation stability, defects on the quantum dot surface, and reduced fluorescence quantum yield due to oxidation, so it is speculated that suppressing ligand peeling suppresses these decreases.
In addition, since the quantum dots have good stability, the ink composition has ink-jet ejection properties and can be used as an ink-jet ink. Furthermore, the quantum dots of the present invention can be used as an electroluminescent device.

Claims (8)

A quantum dot is a semiconductor particle having a compound represented by the following general formula (1) on its surface:
General formula (1)
[In general formula (1), Q is an aliphatic heterocyclic group containing a sulfur atom and a nitrogen atom as ring atoms , X is a direct bond, and A is a charge transporting group containing a tertiary aromatic amine or carbazole unit .] The quantum dot of claim 1, wherein the semiconductor particles include a compound semiconductor. The quantum dot according to claim 1 or 2, wherein the semiconductor particles are of a core-shell type. The quantum dot according to any one of claims 1 to 3, wherein the charge transport group is a hole transport group. An ink composition comprising the quantum dots according to any one of claims 1 to 4 and a solvent. The ink composition according to claim 5, which is used in an inkjet system. An electroluminescent device comprising an anode, a light-emitting layer, and a cathode on a substrate, the light-emitting layer including the quantum dots according to any one of claims 1 to 4. A photoelectric conversion element having a photoelectric conversion layer between a pair of electrodes, the photoelectric conversion layer comprising the quantum dot according to any one of claims 1 to 4.