Quantum dot ink composition

Abstract

To provide a quantum dot ink composition excellent in both dispersion stability and landing properties of quantum dots.SOLUTION: Provided is a quantum dot ink composition including quantum dots, and a mixed solvent containing at least a solvent (a) and a solvent (b), the ink composition having a surface tension of 30 mN / m or more and 40 mN / m or less. Solvent (a) is a cycloalkane compound having a linear C4 to C16 alkyl group. Solvent (b) is an aromatic hydrocarbon compound having a linear C2 to C12 alkyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a quantum dot ink composition. [Background technology]

[0002] In recent years, organic electroluminescence elements (hereinafter referred to as organic EL elements or OLEDs) have been actively researched and developed as thin-film, lightweight, and low-power-consumption display and lighting elements.

[0003] An organic EL element is a light-emitting element that has a thin film of organic compounds, several nanometers to several hundred nanometers thick, between an anode and a cathode, and is made up of multiple organic materials, such as a hole transport layer, a light-emitting layer, and an electron transport layer.

[0004] The light-emitting materials used in the light-emitting layer include fluorescent materials and phosphorescent materials. Compared to fluorescent materials, phosphorescent materials are expected to have approximately four times the luminous efficiency, but there is a demand for materials with longer life and higher luminous efficiency. In addition, RGB light sources require a sharp emission spectrum to cover a wide color gamut, but it is difficult to obtain materials that satisfy this requirement.

[0005] One way to solve this problem is to use quantum dots as the material for the light-emitting layer. Quantum dots have an inorganic core, making them highly durable and providing a sharp emission spectrum. Furthermore, in recent years, progress has been made in developing quantum dots that do not contain toxic elements such as cadmium (Cd) and lead (Pb).

[0006] Quantum dot electroluminescent devices (hereinafter also referred to as QDLEDs) using quantum dots as the light-emitting layer material can be fabricated by a wet coating method, and can have high productivity compared to existing OLEDs. Recently, development of ink compositions containing quantum dots for use in manufacturing such QDLEDs has progressed (see Patent Documents 1 to 4 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Chinese Patent Application Publication No. 109306207 [Patent Document 2] International Publication No. 2019 / 225782 [Patent Document 3] Japanese Patent Application Publication No. 2019-81868 [Patent Document 4] Japanese Patent Application Publication No. 2020-41079 [Non-patent literature]

[0008] [Non-Patent Document 1] Yang Lie et al., ACS Applied Materials & Interfaces 9, 25506-25512(2017). Summary of the Invention [Problem to be solved by the invention]

[0009] When preparing a quantum dot-containing layer using a wet coating method, particularly an inkjet method, it is necessary to prevent aggregation of the quantum dots in the ink, increase dispersion stability, and improve light-emitting properties. Furthermore, it is also necessary to spray the ink at a precise location in a precise amount. However, the techniques described in Patent Documents 1 to 4 and Non-Patent Document 1 are insufficient in at least one of the dispersion stability and the elasticity of the quantum dots, and therefore are unable to meet the above requirements.

[0010] Therefore, an object of the present invention is to provide a quantum dot ink composition that has excellent dispersion stability and elasticity of quantum dots. [Means for solving the problem]

[0011] The above-mentioned problems of the present invention can be solved by the following means.

[0012] That is, the present invention provides a quantum dot ink composition comprising quantum dots and a mixed solvent containing at least the following solvent a and the following solvent b, and having a surface tension of 30 mN / m or more and 40 mN / m or less: Solvent a: a cycloalkane compound having a linear alkyl group having 4 to 16 carbon atoms Solvent b: an aromatic hydrocarbon compound having a linear alkyl group having 2 to 12 carbon atoms. [Effects of the Invention]

[0013] According to the present invention, a quantum dot ink composition having excellent dispersion stability and adhesiveness of quantum dots can be provided. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing a quantum dot electroluminescence element according to one embodiment of the present invention. [Figure 2] 10 is a diagram showing the cross-sectional shape profiles of a bank substrate, after ink has landed in Example 1, and after ink has landed in Comparative Example 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. Furthermore, unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (20°C or higher and 25°C or lower) and relative humidity of 40% RH or higher and 50% RH or lower.

[0016] [Quantum dot ink composition] One aspect of the present invention is a quantum dot ink composition comprising quantum dots and a mixed solvent containing at least the following solvent a and the following solvent b, and having a surface tension of 30 mN / m or more and 40 mN / m or less: Solvent a: a cycloalkane compound having a linear alkyl group having 4 to 16 carbon atoms Solvent b: an aromatic hydrocarbon compound having a linear alkyl group having 2 to 12 carbon atoms.

[0017] By having such a constitution, the quantum dot ink composition of the present invention is an ink composition that has excellent dispersion stability of the quantum dots and excellent adhesiveness.

[0018] The present inventors presume that the mechanism by which the quantum dot ink composition of the present invention (hereinafter also simply referred to as "ink composition" or "ink") solves the above problems is as follows.

[0019] Generally, quantum dots contain organic ligands such as oleic acid and have high dispersion stability in aliphatic hydrocarbon solvents. However, aliphatic hydrocarbon solvents have low viscosity and surface tension, which means that satellite droplets, which are small droplets that separate from the main droplet of ink ejected from the nozzle and land in a different position from the main droplet, are likely to form. Therefore, inks containing quantum dots and aliphatic hydrocarbon solvents have the problem of easily losing their adhesion elasticity.

[0020] On the other hand, solvents with high surface tension, which are commonly used in inkjet inks, improve adhesion, but when mixed with quantum dots, they cause the quantum dots to aggregate, making them difficult to eject from the nozzle. Furthermore, because the emission color of quantum dots depends on their size, aggregation of quantum dots can cause a change in emission color and also lead to a deterioration in emission characteristics, such as a decrease in quantum yield.

[0021] As a result of extensive research into these problems, the present inventors have found that the above-mentioned problems can be solved by a quantum dot ink composition containing quantum dots and a mixed solvent containing at least the following two solvents: Solvent a: a cycloalkane compound having a linear alkyl group having 4 to 16 carbon atoms Solvent b: an aromatic hydrocarbon compound having a linear alkyl group having 2 to 12 carbon atoms.

[0022] The solvent a maintains the dispersibility of the quantum dots, and the solvent b effectively exerts the effect of solvent a. In addition, the ink composition of the present invention has a high surface tension of 30 mN / m or more and 40 mN / m or less. This allows the ink composition of the present invention to efficiently exert both the effects of solvent a, which provides excellent quantum dot dispersion stability, and ink adhesion suitable for inkjet printing. This makes it possible to achieve both excellent quantum dot dispersion stability and excellent ink adhesion, which were not possible with conventional quantum dot ink compositions.

[0023] The above mechanism is based on speculation, and its correctness does not affect the technical scope of the present invention. Similarly, the correctness of other speculations in this specification does not affect the technical scope of the present invention.

[0024] The composition of the quantum dot ink composition of the present invention will be described in detail below.

[0025] [Quantum dots] Quantum dots (semiconductor nanoparticles) are semiconductor nanoparticles of a certain size that exhibit quantum confinement effects.

[0026] Quantum dots (semiconductor nanoparticles) can be synthesized by wet chemical processes, metalorganic chemical vapor deposition processes, molecular beam epitaxy processes, or other similar processes. Among these, wet chemical processes involve growing particles by adding precursor materials to an organic solvent.

[0027] In the wet chemical process, the organic solvent naturally coordinates with the surface of the quantum dot crystals as they grow, acting as a dispersant and regulating the growth of the crystals. Therefore, the wet chemical process allows for easier and lower cost control of the growth of semiconductor nanoparticles than gas phase deposition methods such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE).

[0028] By adjusting the size of quantum dots (semiconductor nanoparticles), the energy band gap can be adjusted, allowing light of various wavelengths to be obtained in the light-emitting layer (quantum dot light-emitting layer). Therefore, using quantum dots of different sizes enables displays that emit (or emit) light of multiple wavelengths. The size of quantum dots can be selected to emit red, green, and blue light, allowing the construction of color displays. In addition, quantum dot sizes can be combined to emit various colored lights to emit white light.

[0029] As quantum dots (semiconductor nanoparticles), semiconductor materials selected from the group consisting of II-VI group semiconductor compounds; III-V group semiconductor compounds; IV-VI group semiconductor compounds; IV group elements or compounds; and combinations thereof can be used.

[0030] The II-VI semiconductor compound is not particularly limited, but may be selected from the group consisting of binary compounds selected from the group consisting of CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, and mixtures thereof; ternary compounds selected from the group consisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnTeSe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, and mixtures thereof; and quaternary compounds selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof.

[0031] The III-V semiconductor compound is not particularly limited, and may be selected from the group consisting of binary compounds selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; ternary compounds selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and mixtures thereof; and quaternary compounds selected from the group consisting of GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof.

[0032] The IV-VI semiconductor compound is not particularly limited, and may be selected from the group consisting of binary compounds selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof; ternary compounds selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof; and quaternary compounds selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof.

[0033] The Group IV element or compound is not particularly limited, but may be selected from the group consisting of mono-element compounds selected from the group consisting of Si, Ge, and mixtures thereof; and bi-element compounds selected from the group consisting of SiC, SiGe, and mixtures thereof.

[0034] Quantum dots may be composed of one type of compound or two or more types of compounds. They may also have a core-shell structure, for example, with a core made of a semiconductor compound and a shell made of a different semiconductor compound. The luminous efficiency of quantum dots can be improved by using a semiconductor compound constituting the shell with a higher band gap than the semiconductor compound constituting the core, so that excitons are confined in the core. Examples of core-shell structures (core / shell) with such a large-small band gap relationship include CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, CuInS / ZnS, ZnTeSe / ZnSe / ZnS, and InP / ZnSe / ZnS.

[0035] However, from the viewpoint of toxicity, it is preferable that the quantum dots do not contain Cd (cadmium) and Pb (lead) as constituent elements.

[0036] The particle size of quantum dots can be adjusted appropriately depending on the material that makes up the quantum dots so that light of the desired wavelength can be obtained. As the particle size of quantum dots decreases, the energy band gap increases. In other words, as the crystal size decreases, the emission of quantum dots shifts toward the blue side, i.e., toward higher energy. Therefore, by changing the size of quantum dots, the emission wavelength can be adjusted across the wavelength ranges of the ultraviolet, visible, and infrared regions of the spectrum.

[0037] For example, the average particle size (average diameter) of quantum dots (semiconductor nanoparticles) is not particularly limited, but is about 1 nm or more and 15 nm or less. From the viewpoint of light-emitting properties and dispersion stability of quantum dots, the particle size is preferably 7 nm or more and 15 nm or less. The average particle size of quantum dots can be obtained by measuring the particle size of quantum dots using TEM, SEM, XRD, etc., and calculating the volume-based average particle size.

[0038] It is also preferable to use quantum dots with organic ligands having coordinating groups coordinated on the surface. By adding organic ligands to the quantum dot raw material solution during quantum dot synthesis, excessive crystal growth can be prevented and quantum dots within the desired particle size range can be obtained. Furthermore, quantum dots having a surface layer composed of organic ligands on their surface can prevent aggregation after synthesis.

[0039] The organic ligand is preferably an organic compound having a coordinating group that bonds to the cation contained in the quantum dot. Examples of the coordinating group include a halogen atom, a carboxyl group, a carboxylic acid anhydride group, an amino group, an ammonium group, a mercapto group, a sulfide group, a sulfoxide group, a phosphine group, a phosphine oxide group, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfonic acid group, a boronic acid group, and a heterocyclic group. Such organic ligands may be used alone or in combination of two or more.

[0040] Examples of halogen atom-containing compounds include halogenated alkyl compounds having a linear or branched alkyl group having from 1 to 30 carbon atoms. Specific examples of such halogenated alkyl compounds include methyl chloride, methyl bromide, methyl iodide, ethyl chloride, ethyl bromide, ethyl iodide, propyl chloride, propyl bromide, propyl iodide, butyl chloride, butyl bromide, butyl iodide, hexyl chloride, hexyl bromide, octyl chloride, octyl bromide, and decyl chloride.

[0041] Examples of carboxy group-containing compounds include linear or branched aliphatic carboxylic acid compounds having from 1 to 30 carbon atoms. Specific examples of such aliphatic carboxylic acid compounds include arachidonic acid, crotonic acid, trans-2-decenoic acid, erucic acid, 3-decenoic acid, cis-4,7,10,13,16,19-docosahexaenoic acid, 4-decenoic acid, allcis-5,8,11,14,17-eicosapentaenoic acid, allcis-8,11,14-eicosatrienoic acid, cis-9-hexadecenoic acid, trans-3-hexenoic acid, trans-2-hexenoic acid, 2-heptenoic acid, 3-heptenoic acid, 2-hexadecenoic acid, linolenic acid, linoleic acid, γ-linolenic acid, 3-nonenoic acid, 2-nonenoic acid, trans-2-octenoic acid, petroselinic acid, elaidic acid, oleic acid, and the like. Examples of suitable acids include carboxylic acid, 3-octenoic acid, trans-2-pentenoic acid, trans-3-pentenoic acid, ricinoleic acid, sorbic acid, 2-tridecenoic acid, cis-15-tetracosenoic acid, 10-undecenoic acid, 2-undecenoic acid, acetic acid, butyric acid, behenic acid, cerotic acid, decanoic acid, arachidic acid, heneicosanoic acid, heptadecanoic acid, heptanoic acid, hexanoic acid, heptacosanoic acid, lauric acid, myristic acid, melissic acid, octacosanoic acid, nonadecanoic acid, nonacosanoic acid, n-octanoic acid, palmitic acid, pentadecanoic acid, propionic acid, pentacosanoic acid, nonanoic acid, stearic acid, lignoceric acid, tricosanoic acid, tridecanoic acid, undecanoic acid, and valeric acid.

[0042] Examples of the amino group-containing compound include aliphatic amine compounds having a linear or branched alkyl group having from 1 to 30 carbon atoms. Specific examples of such aliphatic amine compounds include 1-aminoheptadecane, 1-aminononadecane, heptadecane-9-amine, stearylamine, oleylamine, 2-n-octyl-1-dodecylamine, allylamine, amylamine, 2-ethoxyethylamine, 3-ethoxypropylamine, isobutylamine, isoamylamine, 3-methoxypropylamine, 2-methoxyethylamine, 2-methylbutylamine, neopentylamine, n-propylamine, and the like. amine, methylamine, ethylamine, n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, n-decylamine, n-undecylamine, n-dodecylamine, n-tridecylamine, n-tetradecylamine, n-pentadecylamine, n-hexadecylamine, n-octadecylamine, tri(n-hexyl)amine, tri(n-octyl)amine, tri(n-decyl)amine, and the like.

[0043] Examples of the mercapto group-containing compound include hexyl mercaptan, octyl mercaptan, and lauryl mercaptan.

[0044] Examples of the sulfide group-containing compound include dialkyl sulfides such as dibutyl sulfide.

[0045] Examples of the sulfoxide group-containing compound include dialkyl sulfoxides such as dimethyl sulfoxide and dibutyl sulfoxide.

[0046] Examples of the phosphine group-containing compound include trialkylphosphines such as tripropylphosphine, tributylphosphine, trihexylphosphine, and trioctylphosphine.

[0047] Examples of the phosphine oxide group-containing compound include trialkylphosphine oxides such as tripropylphosphine oxide, tributylphosphine oxide, trihexylphosphine oxide, trioctylphosphine oxide, and tridecylphosphine oxide.

[0048] Examples of heterocyclic group-containing compounds include nitrogen-containing heterocyclic compounds such as pyridine, lutidine, collidine, and quinolines; sulfur-containing heterocyclic compounds such as thiophene; and the like.

[0049] Among these organic ligands, at least one selected from the group consisting of alkyl halide compounds, mercapto group-containing compounds, and aliphatic carboxylic acid compounds is preferred from the viewpoint of dispersion stability and luminescence properties of quantum dots.Moreover, the organic ligand is more preferably at least one selected from the group consisting of oleic acid, heptanoic acid, hexanoic acid, heptacosanoic acid, lauric acid, hexyl mercaptan, octyl mercaptan, and lauryl mercaptan.

[0050] The content of the organic ligand in the quantum dots is not particularly limited, but from the viewpoint of controlling the film thickness after ejection by an inkjet device, it is preferably 0.5% by mass or more and 15% by mass or less, where the total mass of the quantum dots and the organic ligand is 100% by mass.

[0051] Quantum dots having organic ligands having coordinating groups coordinated on the surface can be synthesized by methods described in, for example, J. Am. Chem. Soc., 115, pp. 8706-8715 (1993), J. Phys. Chem., 101, pp. 9463-9475 (1997), Nature volume 575, pp. 634-638 (2019), etc. Commercially available quantum dots can also be suitably used.

[0052] The content of the quantum dots in the ink composition of the present invention is preferably 0.5% by mass or more, more preferably 2.0% by mass or more, and even more preferably 3.0% by mass or more, based on 100% by mass of the total mass of the ink composition. The content of the quantum dots in the ink composition of the present invention is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less, based on 100% by mass of the total mass of the ink composition.

[0053] [Mixed Solvent] The quantum dot ink composition according to the present invention contains a mixed solvent containing at least solvent A and solvent B. The mixed solvent will be described in detail below.

[0054] <Solvent a> Solvent a is a solvent that maintains the dispersion stability of quantum dots and is a cycloalkane compound having a linear alkyl group having 4 to 16 carbon atoms. Solvent a may be used alone or in combination of two or more. Furthermore, solvent a may be a commercially available product or a synthetic product.

[0055] Furthermore, solvent a may exist as various stereoisomers, but the configuration of "solvent a" is not particularly limited, and it may be any of the various stereoisomers alone or a mixture of the various stereoisomers in any ratio.

[0056] Solvent a has a linear alkyl group having 4 to 16 carbon atoms. Examples of such alkyl groups include n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, and n-hexadecyl. Solvent a may have only one alkyl group having 4 to 16 carbon atoms, or may have two or more alkyl groups having 4 to 16 carbon atoms. Furthermore, as long as solvent a has one or more linear alkyl groups having 4 to 16 carbon atoms, it may further have a linear or branched alkyl group having 1 to 3 carbon atoms. Furthermore, as long as solvent a has one or more linear alkyl groups having 4 to 16 carbon atoms, it may further have a branched alkyl group having 4 to 16 carbon atoms.

[0057] The number of carbon atoms in the cycloalkane portion of solvent a is preferably 4 or more and 12 or less, and more preferably 5 or more and 10 or less. Examples of such cycloalkanes include cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, and cyclododecane.

[0058] Specific examples of the solvent a include n-butylcyclobutane, n-pentylcyclobutane, n-hexylcyclobutane, n-heptylcyclobutane, n-octylcyclobutane, n-nonylcyclobutane, n-decylcyclobutane, n-undecylcyclobutane, n-dodecylcyclobutane, n-tridecylcyclobutane, n-tetradecylcyclobutane, n-pentadecylcyclobutane, n-hexadecylcyclobutane, di(n-butyl)cyclobutane, di(n-pentyl)cyclobutane, di(n-hexyl)cyclobutane, and di(n-octyl)cyclobutane; n-Butylcyclopentane, n-pentylcyclopentane, n-hexylcyclopentane, n-heptylcyclopentane, n-octylcyclopentane, n-nonylcyclopentane, n-decylcyclopentane, n-undecylcyclopentane, n-dodecylcyclopentane, n-tridecylcyclopentane, n-tetradecylcyclopentane, n-pentadecylcyclopentane, n-hexadecylcyclopentane, di(n-butyl)cyclopentane, di(n-pentyl)cyclopentane, di(n-hexyl)cyclopentane, di(n-octyl)cyclopentane; n-Butylcyclohexane, n-pentylcyclohexane, n-hexylcyclohexane, n-heptylcyclohexane, n-octylcyclohexane, n-nonylcyclohexane, n-decylcyclohexane, n-undecylcyclohexane, n-dodecylcyclohexane, n-tridecylcyclohexane, n-tetradecylcyclohexane, n-pentadecylcyclohexane, n-hexadecylcyclohexane, di(n-butyl)cyclohexane, di(n-pentyl)cyclohexane, di(n-hexyl)cyclohexane, di(n-octyl)cyclohexane; n-Butylcycloheptane, n-pentylcycloheptane, n-hexylcycloheptane, n-heptylcycloheptane, n-octylcycloheptane, n-nonylcycloheptane, n-decylcycloheptane, n-undecylcycloheptane, n-dodecylcycloheptane, n-tridecylcycloheptane, n-tetradecylcycloheptane, n-pentadecylcycloheptane, n-hexadecylcycloheptane, di(n-butyl)cycloheptane, di(n-pentyl)cycloheptane, di(n-hexyl)cycloheptane, di(n-octyl)cycloheptane; n-Butylcyclooctane, n-pentylcyclooctane, n-hexylcyclooctane, n-heptylcyclooctane, n-octylcyclooctane, n-nonylcyclooctane, n-decylcyclooctane, n-undecylcyclooctane, n-dodecylcyclooctane, n-tridecylcyclooctane, n-tetradecylcyclooctane, n-pentadecylcyclooctane, n-hexadecylcyclooctane, di(n-butyl)cyclooctane, di(n-pentyl)cyclooctane, di(n-hexyl)cyclooctane, di(n-octyl)cyclooctane; n-Butylcyclononane, n-pentylcyclononane, n-hexylcyclononane, n-heptylcyclononane, n-octylcyclononane, n-nonylcyclononane, n-decylcyclononane, n-undecylcyclononane, n-dodecylcyclononane, n-tridecylcyclononane, n-tetradecylcyclononane, n-pentadecylcyclononane, n-hexadecylcyclononane, di(n-butyl)cyclononane, di(n-pentyl)cyclononane, di(n-hexyl)cyclononane, di(n-octyl)cyclononane; n-Butylcyclodecane, n-pentylcyclodecane, n-hexylcyclodecane, n-heptylcyclodecane, n-octylcyclodecane, n-nonylcyclodecane, n-decylcyclodecane, n-undecylcyclodecane, n-dodecylcyclodecane, n-tridecylcyclodecane, n-tetradecylcyclodecane, n-pentadecylcyclodecane, n-hexadecylcyclodecane, di(n-butyl)cyclodecane, di(n-pentyl)cyclodecane, di(n-hexyl)cyclodecane, di(n-octyl)cyclodecane; n-Butylcycloundecane, n-pentylcycloundecane, n-hexylcycloundecane, n-heptylcycloundecane, n-octylcycloundecane, n-nonylcycloundecane, n-decylcycloundecane, n-undecylcycloundecane, n-dodecylcycloundecane, n-tridecylcycloundecane, n-tetradecylcycloundecane, n-pentadecylcycloundecane, n-hexadecylcycloundecane, di(n-butyl)cycloundecane, di(n-pentyl)cycloundecane, di(n-hexyl)cycloundecane, di(n-octyl)cycloundecane; n-Butylcyclododecane, n-pentylcyclododecane, n-hexylcyclododecane, n-heptylcyclododecane, n-octylcyclododecane, n-nonylcyclododecane, n-decylcyclododecane, n-undecylcyclododecane, n-dodecylcyclododecane, n-tridecylcyclododecane, n-tetradecylcyclododecane, n-pentadecylcyclododecane, n-hexadecylcyclododecane, di(n-butyl)cyclododecane, di(n-pentyl)cyclododecane, di(n-hexyl)cyclododecane, di(n-octyl)cyclododecane; etc.

[0059] Among these solvents a, from the viewpoints of viscosity and vapor pressure, at least one selected from the group consisting of n-decylcyclohexane, n-undecylcyclohexane, n-dodecylcyclohexane, and n-tridecylcyclohexane is preferred.

[0060] The content of solvent a in the mixed solvent is preferably 30% by volume or more, where the total volume of solvent a and solvent b is 100% by volume. The content of solvent a is more preferably 40% by volume or more, and even more preferably 50% by volume or more. The content of solvent a is preferably 99% by volume or less, more preferably 90% by volume or less, and even more preferably 85% by volume or less, where the total volume of solvent a and solvent b is 100% by volume. When two or more types of solvent a are used, the content of solvent a refers to the total amount of solvent a.

[0061] That is, the content of solvent a is preferably 30% by volume or more and 99% by volume or less, more preferably 40% by volume or more and 90% by volume or less, and even more preferably 50% by volume or more and 85% by volume or less, where the total volume of solvent a and solvent b is 100% by volume.

[0062] [Solvent b] Solvent b is an aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms. Because solvent b has an alkyl group, it can have an intermolecular interaction with solvent a, allowing solvent a to effectively exhibit its functions. Solvent b may be used alone or in combination of two or more. Furthermore, solvent b may be a commercially available product or a synthetic product.

[0063] Solvent b has a linear alkyl group having from 2 to 12 carbon atoms. Examples of such an alkyl group include an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, and an n-dodecyl group. Solvent b may have only one alkyl group having from 2 to 12 carbon atoms, or may have two or more alkyl groups having from 2 to 12 carbon atoms. Furthermore, as long as solvent b has one or more linear alkyl groups having from 2 to 12 carbon atoms, it may further have a methyl group and / or a branched alkyl group having from 3 to 12 carbon atoms.

[0064] The aromatic hydrocarbon moiety of solvent b preferably has 6 to 12 carbon atoms. The aromatic hydrocarbon moiety may be a monocyclic ring, a condensed polycyclic ring, or a ring assembly. Examples of such aromatic hydrocarbons include benzene, indene, naphthalene, and biphenyl.

[0065] Solvent b is mainly classified into two types: Solvent b-1: Compounds with a surface tension of 32 mN / m or more and 40 mN / m or less Solvent b-2: A compound having a surface tension of 25 mN / m or more and less than 32 mN / m.

[0066] When solvent b-1 is used as solvent b, the mixed solvent contained in the ink composition may contain at least two of solvent a and solvent b-1. In this case, the mixed solvent may contain solvent b-2 and / or solvent c in addition to solvent a and solvent b-1.

[0067] When the above-mentioned solvent b-2 is used as solvent b, the solvent contained in the quantum dot ink composition preferably includes, in addition to solvent a and solvent b-2, at least one of solvent b-1 and solvent c, which are high surface tension compounds.

[0068] Hereinafter, solvent b will be explained separately as solvent b-1 and solvent b-2.

[0069] <Solvent b-1> Solvent b-1 is an aromatic hydrocarbon compound having a linear alkyl group having from 2 to 12 carbon atoms and a surface tension of from 32 to 40 mN / m. This solvent b-1 effectively exhibits the function of solvent a, which provides dispersion stability for the quantum dots, while also ensuring the surface tension of the entire ink composition. The surface tension of solvent b-1 is preferably 33 mN / m or more, and more preferably 35 mN / m or more. The upper limit of the surface tension of solvent b-1 is typically 40 mN / m or less. In this specification, the surface tensions of the solvents and ink compositions are values ​​measured by the methods described in the Examples.

[0070] The solvent b-1 may be used alone or in combination of two or more kinds. The solvent b-1 may be a commercially available product or a synthetic product.

[0071] Specific examples of solvent b-1 include 1-ethylnaphthalene, 2-ethylnaphthalene, 1-n-propylnaphthalene, 2-n-propylnaphthalene, 1-n-butylnaphthalene, 2-n-butylnaphthalene, 1-n-pentylnaphthalene, 2-n-pentylnaphthalene, 1-n-hexylnaphthalene, 2-n-hexylnaphthalene, 1-n-heptylnaphthalene, 1-n-octylnaphthalene, 1-n-nonylnaphthalene, 1-n-decylnaphthalene, 1-n-undecylnaphthalene, 1-n-dodecylnaphthalene, 1,4-diethylnaphthalene, 1,4-di(n-propyl)naphthalene, 1,4-di(n-butyl)naphthalene, 1,4-di(n-pentyl)naphthalene, 1,4-di(n-hexyl)naphthalene; Examples thereof include 2-ethylbiphenyl, 3-ethylbiphenyl, 4-ethylbiphenyl, 2-n-propylbiphenyl, 3-n-propylbiphenyl, 4-n-propylbiphenyl, 2-n-butylbiphenyl, 3-n-butylbiphenyl, 4-n-butylbiphenyl, 2-n-pentylbiphenyl, 3-n-pentylbiphenyl, 4-n-pentylbiphenyl, 2-n-hexylbiphenyl, 3-n-hexylbiphenyl, 4-n-hexylbiphenyl, 4-n-heptylbiphenyl, and 4-n-octylbiphenyl.

[0072] Among these solvents b-1, from the viewpoints of viscosity and vapor pressure, at least one selected from the group consisting of 1-ethylnaphthalene, 2-ethylnaphthalene, 1-n-propylnaphthalene, 2-n-propylnaphthalene, 1-n-butylnaphthalene, 2-n-butylnaphthalene, 1-n-pentylnaphthalene, and 2-n-pentylnaphthalene is preferred.

[0073] <Solvent b-2> Solvent b-2 is an aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms and a surface tension of 25 to 32 mN / m. Such solvent b-2 can effectively exert the function of solvent a, which provides dispersion stability for quantum dots. The surface tension of solvent b-2 is preferably 31 mN / m or less, and more preferably 30 mN / m or less. The lower limit of the surface tension of solvent b-1 is usually 25 mN / m or more.

[0074] The solvent b-2 may be used alone or in combination of two or more kinds. In addition, the solvent b-2 may be a commercially available product or a synthesized product.

[0075] Specific examples of solvent b-2 include ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, n-hexylbenzene, n-heptylbenzene, n-octylbenzene, n-nonylbenzene, n-decylbenzene, n-undecylbenzene, n-dodecylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 1,2-di(n-propyl)benzene, 1,3-di(n-propyl)benzene, 1, 4-di(n-propyl)benzene, 1,2-di(n-butyl)benzene, 1,3-di(n-butyl)benzene, 1,4-di(n-butyl)benzene, 1,4-di(n-pentyl)benzene, 1,4-di(n-hexyl)benzene, 1,4-di(n-heptyl)benzene, 1,4-di(n-octyl)benzene, 1,4-di(n-nonyl)benzene, 1,4-di(n-decyl)benzene, 1,4-di(n-undecyl)benzene, 1,4-di(n-dodecyl)benzene; 1-ethylindene, 2-ethylindene, 3-ethylindene, 4-ethylindene, 5-ethylindene, 6-ethylindene, 7-ethylindene, 1-n-propylindene, 2-n-propylindene, 3-n-propylindene, 4-n-propylindene, 5-n-propylindene, 6-n-propylindene, 7-n-propylindene, 1-n-butylindene, 2-n-butylindene, 3-n-butylindene, 4-n-butylindene, 5-n-butylindene, 6-n-butylindene, 7-n-butylindene; etc.

[0076] Among the above solvents b-2, at least one selected from the group consisting of n-hexylbenzene, n-heptylbenzene, n-octylbenzene, n-nonylbenzene, and n-decylbenzene is preferred from the viewpoints of viscosity and vapor pressure.

[0077] As described above, when solvent b-1 is used as solvent b, the mixed solvent may contain at least solvent a and solvent b-1. In this case, the mixed solvent may contain at least one of solvent b-2 and solvent c, as necessary. When solvent b-2 is used as solvent b, the mixed solvent preferably contains at least one of solvent b-1 and solvent c, which are high surface tension compounds, in addition to solvent a and solvent b-2.

[0078] The content of solvent b in the mixed solvent is preferably 1.0% by volume or more, where the total volume of solvent a and solvent b is 100% by volume. The content of solvent b is more preferably 10% by volume or more, and even more preferably 15% by volume or more. The content of solvent b is preferably 70% by volume or less, more preferably 60% by volume or less, and even more preferably 50% by volume or less, where the total volume of solvent a and solvent b is 100% by volume. When two or more solvents b are used, the content of solvent b refers to the total amount of solvent b. When solvent b-1 and solvent b-2 are used together, the content of solvent b refers to the total amount of solvent b-1 and solvent b-2.

[0079] That is, the content of solvent b is preferably 1.0 vol% or more and 70 vol% or less, more preferably 10 vol% or more and 60 vol% or less, and even more preferably 15 vol% or more and 50 vol% or less, where the total volume of solvent a and solvent b is 100 vol%.

[0080] Furthermore, when solvent b-1 and solvent b-2 are used together as solvent b, the volume ratio of solvent b-1 to solvent b-2 (solvent b-1 / solvent b-2) is preferably 80 / 20 to 20 / 80, and more preferably 35 / 75 to 75 / 35.

[0081] <Solvent c> The mixed solvent according to the present invention may further contain solvent c. Solvent c is an aromatic compound other than solvent b-1, having a surface tension of 32 mN / m or more, and is capable of imparting high surface tension to the ink. The surface tension of solvent c is preferably 33 mN / m or more, and more preferably 35 mN / m or more. The upper limit of the surface tension of solvent c is not particularly limited, but is usually 50 mN / m or less. Solvent c may be used alone or in combination of two or more types. Furthermore, solvent c may be a commercially available product or a synthetic product.

[0082] The solvent c may be a compound having an aromatic hydrocarbon ring or a compound having an aromatic heterocycle.

[0083] The compound having an aromatic hydrocarbon ring includes an aromatic compound having a functional group selected from a halogen group, an alkyl group, an alkoxy group, an alkenyl group, an aldehyde group, a ketone group, an ether group, a carboxy group, an ester group, a nitro group, and an amide group. The compound having an aromatic heterocycle includes a compound having an oxygen-containing aromatic heterocycle, a nitrogen-containing aromatic heterocycle, or a sulfur-containing aromatic heterocycle.

[0084] More specific examples of solvent c include 1-methylnaphthalene, 2-methylnaphthalene, 1,2-dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 1,6-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1-phenylnaphthalene, and 1-vinylnaphthalene. Ethyl 4-methylbenzoate, methyl 4-tert-butylbenzoate, n-propyl benzoate, n-butyl benzoate, n-pentyl benzoate, n-hexyl benzoate, isopentyl benzoate, 2-ethylhexyl benzoate, ethyl 2-methylbenzoate, 2-ethoxyethyl benzoate, benzyl benzoate; Examples of suitable esters include N,N-dimethylbenzamide, N,N-dimethyl-3-methylbenzamide, N,N-dimethyl-2,3-dimethylbenzamide, N-methoxy-N-methylbenzamide, 2-methylbenzophenone, 3-methylbenzophenone, thiophene, 3,4-ethylenedioxythiophene, 2-methyl-2,3-dihydrothieno[3,4-b]-1,4-dioxine, 2-ethyl-2,3-dihydrothieno[3,4-b]-1,4-dioxine, diphenyl ether, dibenzyl ether, dimethyl phthalate, diethyl phthalate, 1'-acetonaphthone, 1-methoxy-4-methylnaphthalene, methyl-1-naphthalene acetate, ethyl-1-naphthalene acetate, and 2-methylbenzo[e]indene.

[0085] Among these solvents c, at least one selected from the group consisting of 1-phenylnaphthalene, benzyl benzoate, n-butyl benzoate, 1-methylnaphthalene, 2-methylbenzophenone, 3-methylbenzophenone, and 1′-acetonaphthone is preferred.

[0086] When the mixed solvent contains solvent c, the content of solvent c is preferably 5% by volume or more, more preferably 10% by volume or more, and even more preferably 15% by volume or more, based on the total volume of solvent a, solvent b, and solvent c being 100% by volume. When solvent c is contained, the content of solvent c is preferably 40% by volume or less, more preferably 35% by volume or less, and even more preferably 30% by volume or less, based on the total volume of solvent a, solvent b, and solvent c being 100% by volume. When two or more solvents c are used, the content of solvent c refers to the total amount of solvent c.

[0087] That is, the content of solvent c is preferably 5% by volume or more and 40% by volume or less, more preferably 10% by volume or more and 35% by volume or less, and even more preferably 15% by volume or more and 30% by volume or less, where the total volume of solvent a, solvent b, and solvent c is 100% by volume.

[0088] [Solubility parameter] From the viewpoint of further improving the dispersion stability of the quantum dots, it is preferable that the solubility parameter of the mixed solvent contained in the ink composition is close to the solubility parameter of the organic ligand. Specifically, the absolute value of the difference between the solubility parameter of the mixed solvent and the solubility parameter of the organic ligand [(solubility parameter of the mixed solvent) - (solubility parameter of the organic ligand)] is 1.5 (cal / cm 3 ) 1 / 2 It is preferable that the value is 1.0 (cal / cm 3 ) 1 / 2 More preferably, it is 0.7 (cal / cm 3 ) 1 / 2 It is more preferable that the absolute value of the difference is equal to or less than 0.

[0089] In this specification, the solubility parameter of a solvent is a value calculated by the Fedors' estimation method. Specifically, based on Fedors, Polym. Eng. Sci., 14(2), pp. 147-154 (1974), the solubility parameter of a single solvent is calculated by the following formula (unit: (cal / cm)) with reference to Δei and Δvi related to the structure of the solvent. 3 ) 1 / 2 ).

[0090]

number

[0091] The solubility parameter of the mixed solvent is calculated by weighting the SP values ​​of the individual solvents calculated above based on the volume fraction of each solvent in the mixed solvent and adding them together.

[0092] The solubility parameter of the mixed solvent can be controlled by appropriately selecting the types of each solvent contained in the mixed solvent, the content ratio of each solvent, and the like.

[0093] In addition, in this specification, the "solubility parameter of an organic ligand" refers to the solubility parameter when the organic ligand is coordinated to the quantum dot surface, and specifically, is a value calculated from the structure of the organic ligand excluding the substituents adsorbed on the quantum dot surface.

[0094] [Additives] The ink composition of the present invention may contain various additives as needed, such as a host material used in the light-emitting layer, an antioxidant, a leveling agent, a plasticizer, a surfactant, an antifoaming agent, a silane coupling agent, an ultraviolet absorber, and an adhesion promoter.

[0095] Examples of the host material include a compound having a carbazole skeleton, a compound having a diarylamine skeleton, a compound having a pyridine skeleton, a compound having a pyrazine skeleton, a compound having a triazine skeleton, and a compound having an arylsilane skeleton.

[0096] The amount of the additives added can be determined appropriately depending on the application, within a range that does not impair the object of the present invention.

[0097] Furthermore, the ink composition of the present invention may further contain other solvents in addition to the above-described mixed solvent, provided that the object of the present invention is not impaired. Examples of such other solvents include 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol, (+)-limonene, ethylene glycol monobutyl ether, α-terpineol, propylene carbonate, dimethyl sulfoxide, N,N-dimethylformamide, 1-bromooctane, 1-bromononane, 1-bromodecane, and 1-bromododecane. The content of these other solvents is preferably 10 parts by volume or less, and more preferably 5 parts by volume or less, per 100 parts by volume of the mixed solvent. In particular, it is preferable that the content of the other solvent is 0 parts by volume, i.e., no other solvent is included.

[0098] [Method of manufacturing ink composition] The method for producing the quantum dot ink composition of the present invention is not particularly limited. For example, quantum dots, solvent a, solvent b, and other components added as needed may be mixed all at once, or each component may be mixed sequentially. However, from the viewpoint of further improving the dispersibility of the quantum dots, a method is preferred in which a mixed solvent is prepared by mixing solvent a, solvent b, and solvent c in advance, and the resulting mixed solvent is added to the quantum dots prepared separately, followed by mixing and stirring. The temperature during mixing is not particularly limited, but is typically in the range of 20°C to 30°C. The mixing time is also not particularly limited, but is typically in the range of 0.1 to 1 hour.

[0099] [Physical properties of ink composition] The surface tension of the ink composition of the present invention having the above-mentioned configuration is 30 mN / m or more and 40 mN / m or less. If the surface tension is less than 30 mN / m, satellite droplets are likely to form and the landing elasticity is reduced. Furthermore, if the surface tension of the ink composition exceeds 40 mN / m, the flatness after landing within the bank is reduced, which may cause a decrease in element efficiency. The lower limit of the surface tension of the ink composition is preferably 31 mN / m or more, and more preferably 32 mN / m or more. Furthermore, the upper limit of the surface tension of the ink composition is preferably 39 mN / m or less, and more preferably 38 mN / m or less.

[0100] That is, the surface tension of the ink composition according to one embodiment of the present invention may be 31 mN / m or more and 39 mN / m or less, or 32 mN / m or more and 38 mN / m or less.

[0101] The surface tension of the ink composition can be controlled by appropriately selecting the types of solvents contained in the mixed solvent, the content ratio of each solvent, and the like.

[0102] From the viewpoint of improving ejection stability during continuous ejection, the viscosity of the quantum dot ink composition of the present invention is preferably 4 mPa·s or more and 10 mPa·s or less, and more preferably 4.5 mPa·s or more and 7.0 mPa·s or less. The viscosity of the quantum dot ink composition is a value measured by the method described in the examples.

[0103] The quantum dot ink composition of the present invention having the above-described configuration preferably has a photoluminescence quantum yield (PLQY) of 85% or more and 100% or less, more preferably 90% or more and 100% or less, and even more preferably 95% or more and 100% or less. If the PLQY is within the above range, the dispersion stability of the quantum dots is excellent. The PLQY is a value measured by the method described in the Examples.

[0104] [Application] The use of the ink composition according to the present invention is not particularly limited, and it can be used, for example, to form a quantum dot-containing layer of various optical components used in display devices, etc. Furthermore, the ink composition according to the present invention is a composition suitable for forming a quantum dot-containing layer by an inkjet method, and can be preferably used for inkjet printing. Examples of optical components include semiconductor optical components such as light conversion components and light-emitting components.

[0105] In particular, the quantum dot ink composition according to the present invention is suitably used for forming a light-emitting layer of a quantum dot electroluminescence device. That is, according to another aspect of the present invention, there is provided a quantum dot electroluminescence device including a light-emitting layer formed from the quantum dot ink composition according to the present invention.

[0106] This quantum dot electroluminescence device will be described in detail below.

[0107] [Quantum dot electroluminescence device] The quantum dot electroluminescent element according to this embodiment will be described in detail with reference to Fig. 1. Fig. 1 is a schematic diagram showing the quantum dot electroluminescent element according to this embodiment. In this specification, "quantum dot electroluminescent element" may be abbreviated as "QLED."

[0108] As shown in FIG. 1, the QLED 100 of this embodiment includes a substrate 110, a first electrode 120 disposed on the substrate 110, a hole injection layer 130 disposed on the first electrode 120, a hole transport layer 140 disposed on the hole injection layer 130, an emissive layer 150 disposed on the hole transport layer 140, an electron transport layer 160 disposed on the emissive layer 150, an electron injection layer 170 disposed on the electron transport layer 160, and a second electrode 180 disposed on the electron injection layer 170.

[0109] There are no particular limitations on the method for forming layers other than the light-emitting layer 150. Layers other than the light-emitting layer 150 may be formed by, for example, a vacuum deposition method or a solution coating method. Examples of solution coating methods include spin coating, casting, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, and ink jet printing.

[0110] When a layer other than the light-emitting layer 150 is formed by a solution coating method, examples of the solvent used include toluene, xylene, ethylbenzene, diethylbenzene, methylene, propylbenzene, cyclohexylbenzene, dimethoxybenzene, anisole, ethoxytoluene, phenoxytoluene, isopropylbiphenyl, dimethylanisole, phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, cyclohexane, etc. The amount of solvent used in the coating solution is not particularly limited.

[0111] A substrate used in a general EL device can be used as the substrate 110. For example, the substrate 110 may be a glass substrate, a semiconductor substrate such as a silicon substrate, or a transparent plastic substrate.

[0112] A first electrode 120 is formed on the substrate 110. Specifically, the first electrode 120 is an anode and is formed from a metal, alloy, or conductive compound with a large work function. For example, the first electrode 120 may be formed as a transmissive electrode from indium tin oxide (In2O3-SnO2:ITO), indium zinc oxide (In2O3-ZnO), tin oxide (SnO2), zinc oxide (ZnO), or the like, which have excellent transparency and conductivity. The first electrode 120 may also be formed as a reflective electrode by laminating magnesium (Mg), aluminum (Al), or the like on the transparent conductive film. After the first electrode 120 is formed on the substrate 110, cleaning and UV-ozone treatment may be performed, if necessary.

[0113] A hole injection layer 130 is formed on the first electrode 120. The hole injection layer 130 is a layer that facilitates the injection of holes from the first electrode 120, and may be formed to a thickness of 10 nm or more and 1000 nm or less, more specifically, 20 nm or more and 300 nm or less (dry film thickness; the same applies below).

[0114] The hole injection layer 130 can be formed of a known hole injection material. Examples of known hole injection materials for forming the hole injection layer 130 include poly(ether ketone)-containing triphenylamine (TPAPEK), 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (PPBI), N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine (DNTPD), copper phthalocyanine (copper phthalocyanine), and the like. phthalocyanine), 4,4',4"-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), 4,4',4"-tris(diphenylamino)triphenylamine (TDATA), 4,4',4"-tris(N,N-2-naphthylphenylamino)triphenylamine (2-TNATA), polyaniline / dodecylbenzenesulphonic acid acid), poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) (poly(3,Examples include poly(4-ethylenedioxythiophene) / poly(4-styrenesulfonate):PEDOT / PSS), and polyaniline / 10-camphorsulfonic acid.

[0115] The hole transport layer 140 is formed on the hole injection layer 130. The hole transport layer 140 is a layer having a function of transporting holes, and may be formed to a thickness of, for example, 10 nm or more and 150 nm or less, more specifically, 20 nm or more and 50 nm or less.

[0116] The hole transport layer 140 may be formed of a known hole transport material. Examples of known hole transport materials include carbazole derivatives such as 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N-phenylcarbazole, and polyvinylcarbazole, N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'-diamine (TPD), 4,4',4"-tris(N-carbazolyl)triazole, and 4,4',4"-tris(N-carbazolyl)triazole. Examples of hole transport materials include triphenylamine (4,4',4"-tris(N-carbazolyl)triphenylamine: TCTA), N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine: NPB), and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine):TFB]. These hole transport materials may be used alone or in combination of two or more.

[0117] The light-emitting layer 150 is formed on the hole transport layer 140. The light-emitting layer 150 includes quantum dots and is preferably formed using an inkjet method, as described above. The light-emitting layer 150 may be formed to a thickness of, for example, 10 nm to 60 nm, more specifically, 20 nm to 50 nm.

[0118] The ink composition according to the present invention has high viscosity and high surface tension, and therefore the light-emitting layer formed therefrom has excellent flatness. For example, the flatness is preferably 55% or more, and more preferably 60% or more. The upper limit of the flatness is 100%. That is, according to one embodiment of the present invention, the flatness of the light-emitting layer may be 55% or more and 100% or less, or may be 60% or more and 100% or less. The flatness is measured by the method described in the examples.

[0119] An electron transport layer 160 is formed on the light-emitting layer 150. The electron transport layer 160 is a layer having a function of transporting electrons, and is formed using a vacuum deposition method, a spin coating method, an inkjet method, or the like. The electron transport layer 160 may be formed to a thickness of, for example, 15 nm or more and 50 nm or less.

[0120] The electron transport layer 160 may be formed using a known electron transport material. The electron transport material may be an organic material or an inorganic material. Examples of known organic electron transport materials include (8-quinolinolato)lithium (lithium quinolate) (Liq), tris(8-quinolinolato)aluminum (Alq3), and compounds having a nitrogen-containing aromatic ring. Specific examples of the compound having a nitrogen-containing aromatic ring include a compound containing a pyridine ring such as 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene, a compound containing a triazine ring such as 2,4,6-tris(3'-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine, and a compound containing a triazine ring such as 2-(4-(N-phenylbenzoinidazolyl-1-yl-phenyl)-9,10-dinaphthylanthracene). Examples of known inorganic electron transport materials include, but are not limited to, oxides such as TiO2, ZnO, ZnMgO, SiO2, SnO2, WO3, Ta2O3, BaTiO3, BaZrO3, ZrO2, HfO2, Al2O3, YO3, and ZrSiO4.

[0121] The electron transport material may be one type alone or a mixture of two or more types.

[0122] The electron injection layer 170 is formed on the electron transport layer 160. The electron injection layer 170 is a layer that facilitates the injection of electrons from the second electrode 180. The electron injection layer 170 is formed using a vacuum deposition method or the like. The electron injection layer 170 may be formed to a thickness of 0.1 nm to 5 nm, more specifically, 0.3 nm to 2 nm. Any known material can be used to form the electron injection layer 170. For example, the electron injection layer 170 may be formed using a lithium compound such as (8-quinolinolato)lithium (lithium quinolate) (Liq) and lithium fluoride (LiF), sodium chloride (NaCl), cesium fluoride (CsF), lithium oxide (LiO), or barium oxide (BaO).

[0123] The second electrode 180 is formed on the electron injection layer 170. The second electrode 180 is formed by vacuum deposition or the like. Specifically, the second electrode 180 is a cathode and is formed of a metal, alloy, or conductive compound with a small work function. For example, the second electrode 180 may be formed as a reflective electrode using a metal such as lithium (Li), magnesium (Mg), aluminum (Al), or calcium (Ca), or an alloy such as aluminum-lithium (Al-Li), magnesium-indium (Mg-In), or magnesium-silver (Mg-Ag). The second electrode 180 may be formed to a thickness of 10 nm to 200 nm, more specifically, 50 nm to 150 nm. Alternatively, the second electrode 180 may be formed as a transmissive electrode using a thin film of the above metal material, a transparent conductive film such as indium tin oxide (In2O3-SnO2), or indium zinc oxide (In2O3-ZnO), etc., with a thickness of 20 nm or less.

[0124] The layered structure of the QLED 100 according to this embodiment is not limited to the above example. The QLED 100 according to this embodiment may be formed using other known layered structures. For example, the QLED 100 may omit one or more of the hole injection layer 130, the hole transport layer 140, the electron transport layer 160, and the electron injection layer 170, or may include other layers in addition. Each layer of the QLED 100 may be formed as a single layer or as multiple layers.

[0125] For example, the QLED 100 may be configured to prevent excitons or holes from diffusing into the electron transport layer 160. To prevent hole transport, a hole blocking layer may be further provided between the hole transport layer 140 and the light emitting layer 150. The hole blocking layer can be formed of, for example, an oxadiazole derivative, a triazole derivative, or a phenanthroline derivative. [Example]

[0126] The present invention will be described in more detail using the following examples and comparative examples, but the technical scope of the present invention is not limited to the following examples.

[0127] The physical properties were measured by the following methods.

[0128] <Calculation of solubility parameter (SP value)> The solubility parameter (SP value) of the solvent was calculated by the Fedors' estimation method. Specifically, referring to Fedors, Polym. Eng. Sci., 14(2), pp. 147-154 (1974), the solubility parameter of the solvent itself was calculated using the following formula, with reference to Δei and Δvi related to the solvent structure. The solubility parameter of a mixed solvent containing solvent a, solvent b, and, if necessary, solvent c, was calculated by weighting the SP value of the solvent itself calculated above based on the volume fraction of each solvent (unit: cal / cm 3 ) 1 / 2 ).

[0129]

number

[0130] <Viscosity> Viscosity η is expressed by the following equation, which is related to shear stress τ and shear rate D: η=τ / D The viscosity of the ink composition was measured at 25°C using Anton Paar's Physica MCR300 (measuring jig: cone plate PP50). -1 ) was kept constant, and the gap between the cone plate and the base was set to 0.05 mm, and the shear stress τ was measured at 25°C. The viscosity measurement range was calibrated using three standard solutions in the ink viscosity range expected from viscometer calibration standard solutions JS2.5, JS5, JS10, JS20, and JS50 (manufactured by Nippon Grease Co., Ltd.), and the viscosity of the ink composition was calculated using the calibration curve.

[0131] <Surface tension> The surface tension of the solvent and the ink composition was measured at room temperature (20°C or higher and 25°C or lower) using a DMs-400 manufactured by Kyowa Interface Science Co., Ltd. The needle used for the measurement was a 15G (inner diameter Φ1.3 mm) fluorine-coated needle.

[0132] The measurement method was the hanging drop method using the above-mentioned device. The surface tension was calculated by fitting a Young-Laplace theoretical curve to the contour shape and density difference of the droplets formed from the needle tip using image processing, and the average value of the surface tension obtained from 10 consecutive images was used as the surface tension of the ink composition. The images taken 1000 ms after droplet formation were used. Details of the principles of surface tension measurement are in accordance with Y. Rotenberg, J. Colloid Interface Sci., 93, 169 (1983) and Colloid Science IV: Colloid Science Experimental Methods, p. 138 (edited by the Chemical Society of Japan, Tokyo Kagaku Dojin, 1996).

[0133] Example 1 A quantum dot dispersion was prepared by referring to the "Synthesis of InP cores" and "Synthesis of InP / ZnSe / ZnS QDs" sections in the "Methods" section of Nature volume 575, pp 634-638 (2019). (Core species: InP, shell species: ZnSe / ZnS, quantum dot content in dispersion: 3% by mass, maximum quantum dot emission wavelength: 627 nm, organic ligand for quantum dots: oleic acid (SP value when coordinated to the quantum dot surface: 8.1 (cal / cm)). 3 ) 1 / 2 (Quantum dot particle size: 10 nm, see below for an outline of the structure.) Ethanol was added to the resulting quantum dot dispersion to form a precipitate, which was then centrifuged and the supernatant was removed to obtain the precipitate.

[0134] [ka]

[0135] Separately, mixed solvent 1 was prepared by mixing n-dodecylcyclohexane (solvent a), n-decylbenzene (solvent b-2), and benzyl benzoate (solvent c) in a volume ratio of 70:15:15.

[0136] To the precipitate obtained above, 3 mL of the mixed solvent 1 prepared above was added, and the mixture was stirred using a shaker (mixing temperature: 25°C, mixing time: 10 minutes) to disperse the precipitate in the mixed solvent 1, thereby obtaining quantum dot ink composition 1 (hereinafter also referred to as ink 1). The viscosity of ink 1 was 5.7 mPa s, and the surface tension of ink 1 was 33 mN / m. The SP value of mixed solvent 1 was 8.7, and the concentration of quantum dots (InP / ZnSe / ZnS) in ink 1 was 3.0 mass%.

[0137] Example 2 Quantum dot ink composition 2 (hereinafter also referred to as ink 2) was prepared in the same manner as in Example 1, except that mixed solvent 2 was used, in which n-octylbenzene (solvent b-2) was used instead of n-decylbenzene and n-butyl benzoate (solvent c) was used instead of benzyl benzoate.

[0138] The viscosity of ink 2 was 5.0 mPa·s, and the surface tension of ink 2 was 30 mN / m. The SP value of mixed solvent 2 was 8.6 (cal / cm 3 ) 1 / 2 It was.

[0139] Example 3 Quantum dot ink composition 3 (hereinafter also referred to as ink 3) was prepared in the same manner as in Example 1, except that mixed solvent 3 using 1-ethylnaphthalene (solvent b-1) instead of benzyl benzoate was used.

[0140] The viscosity of ink 3 was 5.1 mPa·s, and the surface tension of ink 3 was 31 mN / m. The SP value of mixed solvent 3 was 8.6 (cal / cm 3 ) 1 / 2 It was.

[0141] Example 4 Quantum dot ink composition 4 (hereinafter also referred to as ink 4) was prepared in the same manner as in Example 1, except that mixed solvent 4 using 1-phenylnaphthalene was used instead of benzyl benzoate.

[0142] The viscosity of ink 4 was 6.2 mPa·s, and the surface tension of ink 4 was 31 mN / m. The SP value of mixed solvent 4 was 8.7 (cal / cm 3 ) 1 / 2 It was.

[0143] Example 5 Quantum dot ink composition 5 (hereinafter also referred to as ink 5) was prepared in the same manner as in Example 1, except that mixed solvent 5 was used, in which the ratio of n-dodecylcyclohexane (solvent a), n-decylbenzene (solvent b-2), and benzyl benzoate (solvent c) was changed to 70:20:10 (volume ratio).

[0144] The viscosity of Ink 5 was 4.6 mPa·s, and the surface tension of Ink 5 was 31 mN / m. The SP value of Mixed Solvent 5 was 8.4 (cal / cm3 ) 1 / 2 It was.

[0145] Example 6 Quantum dot ink composition 6 (hereinafter also referred to as ink 6) was prepared in the same manner as in Example 1, except that a mixed solvent 6 was used in which the ratio of n-dodecylcyclohexane (solvent a), n-decylbenzene (solvent b-2), and benzyl benzoate (solvent c) was changed to 70:10:20 (volume ratio).

[0146] The viscosity of ink 6 was 5.8 mPa·s, and the surface tension of ink 6 was 30 mN / m. The SP value of mixed solvent 6 was 8.9 (cal / cm 3 ) 1 / 2 It was.

[0147] Example 7 Quantum dot ink composition 7 (hereinafter also referred to as ink 7) was prepared in the same manner as in Example 1, except that mixed solvent 7 was used, in which n-octylbenzene (solvent b-2) was used instead of n-decylbenzene.

[0148] The viscosity of ink 7 was 5.2 mPa·s, and the surface tension of ink 7 was 32 mN / m. The SP value of mixed solvent 7 was 8.8 (cal / cm 3 ) 1 / 2 It was.

[0149] Example 8 Quantum dot ink composition 8 (hereinafter also referred to as ink 8) was prepared in the same manner as in Example 7, except that a mixed solvent 8 was used in which the ratio of n-dodecylcyclohexane (solvent a), n-octylbenzene (solvent b-2), and benzyl benzoate (solvent c) was changed to 70:10:20.

[0150] The viscosity of ink 8 was 5.8 mPa·s, and the surface tension of ink 8 was 32 mN / m. The SP value of mixed solvent 8 was 8.4 (cal / cm 3 ) 1 / 2 It was.

[0151] Example 9 Quantum dot ink composition 9 (hereinafter also referred to as ink 9) was prepared in the same manner as in Example 1, except that a mixed solvent 9 was used in which the ratio of n-dodecylcyclohexane (solvent a), n-decylbenzene (solvent b-2), and benzyl benzoate (solvent c) was changed to 30:35:35 (volume ratio).

[0152] The viscosity of ink 9 was 5.0 mPa·s, and the surface tension of ink 9 was 31 mN / m. The SP value of mixed solvent 9 was 9.4 (cal / cm 3 ) 1 / 2 It was.

[0153] Example 10 A quantum dot ink composition 10 (hereinafter also referred to as ink 10) was prepared in the same manner as in Example 1, except that a mixed solvent 10 in which the ratio of n-dodecylcyclohexane (solvent a) and 1-ethylnaphthalene (solvent b-1) was changed to 60:40 (volume ratio) was used.

[0154] The viscosity of ink 10 was 5.2 mPa·s, and the surface tension of ink 10 was 32 mN / m. The SP value of mixed solvent 10 was 8.9 (cal / cm 3 ) 1 / 2 It was.

[0155] Example 11 Quantum dot ink composition 11 (hereinafter also referred to as ink 11) was prepared in the same manner as in Example 1, except that a mixed solvent 11 was used in which the ratio of n-tridecylcyclohexane (solvent a), n-dodecylcyclohexane (solvent a), n-octylbenzene (solvent b-2), and benzyl benzoate (solvent c) was changed to 35:35:15:15 (volume ratio).

[0156] The viscosity of the ink 11 was 5.3 mPa·s, and the surface tension of the ink 11 was 33 mN / m. The SP value of the mixed solvent 11 was 8.8 (cal / cm 3 ) 1 / 2 It was.

[0157] Example 12 Quantum dot ink composition 12 (hereinafter also referred to as ink 12) was prepared in the same manner as in Example 1, except that a mixed solvent 12 was used in which the ratio of n-dodecylcyclohexane (solvent a), 1-ethylnaphthalene (solvent b-1), and 1-phenylnaphthalene was changed to 45:30:25 (volume ratio).

[0158] The viscosity of the ink 12 was 6.8 mPa·s, and the surface tension of the ink 12 was 32 mN / m. The SP value of the mixed solvent 12 was 9.3 (cal / cm 3 ) 1 / 2 It was.

[0159] (Comparative Example 1) Comparative quantum dot ink composition 1 (hereinafter also referred to as comparative ink 1) was prepared in the same manner as in Example 1, except that only n-octylcyclohexane (solvent a) (hereinafter also referred to as comparative solvent 1) was used as the solvent.

[0160] The viscosity of Comparative Ink 1 was 3.2 mPa·s, and the surface tension of Comparative Ink 1 was 28 mN / m. The SP value of Comparative Solvent 1 was 8.2 (cal / cm 3 ) 1 / 2 It was.

[0161] (Comparative Example 2) Comparative quantum dot ink composition 2 (hereinafter also referred to as comparative ink 2) was prepared in the same manner as in Example 1, except that comparative solvent 2, which was a mixture of n-dodecylcyclohexane (solvent a) and n-decylbenzene (solvent b-2) in a volume ratio of 85:15, was used.

[0162] The viscosity of Comparative Ink 2 was 6.0 mPa·s, and the surface tension of Comparative Ink 2 was 29 mN / m. The SP value of Comparative Solvent 2 was 8.4 (cal / cm 3 ) 1 / 2 It was.

[0163] (Comparative Example 3) Comparative quantum dot ink composition 3 (hereinafter also referred to as comparative ink 3) was prepared in the same manner as in Example 1, except that comparative solvent 3, which was a 50:50 (volume ratio) mixture of n-dodecylcyclohexane (solvent a) and benzyl benzoate (solvent c), was used.

[0164] The viscosity of Comparative Ink 3 was 7.3 mPa·s, and the surface tension of Comparative Ink 3 was 31 mN / m. The SP value of Comparative Solvent 3 was 9.6 (cal / cm 3 ) 1 / 2 It was.

[0165] Comparative Example 4 Comparative quantum dot ink composition 4 (hereinafter also referred to as comparative ink 4) was prepared in the same manner as in Example 1, except that comparative solvent 4, which was a 50:50 (volume ratio) mixture of n-octylcyclohexane and 4-methylcyclohexanol, was used.

[0166] The viscosity of Comparative Ink 4 was 10.6 mPa·s, and the surface tension of Comparative Ink 4 was 28 mN / m. The SP value of Comparative Solvent 4 was 9.7 (cal / cm 3 ) 1 / 2 It was.

[0167] (Comparative Example 5) Comparative quantum dot ink composition 5 (hereinafter also referred to as comparative ink 5) was prepared in the same manner as in Example 1, except that comparative solvent 5, which was a mixture of n-dodecylcyclohexane (solvent a) and benzyl benzoate (solvent c) in a volume ratio of 70:30, was used.

[0168] The viscosity of Comparative Ink 5 was 6.1 mPa·s, and the surface tension of Comparative Ink 5 was 29 mN / m. The SP value of Comparative Solvent 5 was 9.1 (cal / cm 3 ) 1 / 2 It was.

[0169] (Comparative Example 6) Comparative quantum dot ink composition 6 (hereinafter also referred to as comparative ink 6) was prepared in the same manner as in Example 1, except that comparative solvent 6, which was a mixture of n-dodecylcyclohexane (solvent a), n-tetradecane, and benzyl benzoate (solvent c) in a volume ratio of 70:15:15, was used.

[0170] The viscosity of Comparative Ink 6 was 5.9 mPa·s, and the surface tension of Comparative Ink 6 was 29 mN / m. The SP value of Comparative Solvent 6 was 8.6 (cal / cm 3 ) 1 / 2 It was.

[0171] (Comparative Example 7) Comparative quantum dot ink composition 7 (hereinafter also referred to as comparative ink 7) was prepared in the same manner as in Example 1, except that comparative solvent 7, which was a mixture of n-dodecylcyclohexane (solvent a), 1-phenylnaphthalene (solvent c), and benzyl benzoate (solvent c) in a volume ratio of 70:15:15, was used.

[0172] The viscosity of Comparative Ink 7 was 9.5 mPa·s, and the surface tension of Comparative Ink 7 was 31 mN / m. The SP value of Comparative Solvent 7 was 9.0 (cal / cm 3 ) 1 / 2 It was.

[0173] (Comparative Example 8) Comparative quantum dot ink composition 8 (hereinafter also referred to as comparative ink 8) was prepared in the same manner as in Example 1, except that comparative solvent 8, which was a mixture of n-dodecylcyclohexane (solvent a), n-decylbenzene (solvent b-2), and ethyl laurate in a volume ratio of 70:15:15, was used.

[0174] The viscosity of comparative ink 8 was 5.1 mPa·s, and the surface tension of comparative ink 8 was 28 mN / m. The SP value of comparative solvent 8 was 8.4 (cal / cm 3 ) 1 / 2 It was.

[0175] Comparative Example 9 An attempt was made to prepare comparative quantum dot ink composition 9 (hereinafter also referred to as comparative ink 9) in the same manner as in Example 1, except that comparative solvent 9, a 50:50 (volume ratio) mixture of n-decylbenzene (solvent b-2) and benzyl benzoate (solvent c), was used. However, suspension and precipitation occurred when the components were mixed, and an ink composition could not be obtained.

[0176] The composition of the mixed solvents in each of the Examples and Comparative Examples is shown in Table 1 below.

[0177] [Table 1]

[0178] [evaluation] (PLQY (Photoluminescence Quantum Yield) Measurement) Each ink composition was diluted 1000 times with n-hexane, and the PLQY was measured at a detection wavelength of 610 to 640 nm using a Quantaurus-QY C11347-01 manufactured by Hamamatsu Photonics K.K. If this value is 85% or higher, it means that the dispersion stability of the quantum dots is excellent and the ink is suitable for practical use.

[0179] (Measurement of impact accuracy) The inks of each example and comparative example were printed on the surface of ITO glass at a discharge rate of 10 pL / dot and 100 dpi using a material printer DMP-2850 manufactured by FUJIFILM Dimatix, Inc. The evaluation method involved a continuous discharge test using an inkjet device, and results were evaluated as passing if all ink droplets landed within an error range of a 10 μm radius from the target point, and failing if they did not.

[0180] The evaluation results of the ink compositions of each example and each comparative example are shown in Table 2 below.

[0181] [Table 2]

[0182] As is clear from the results in Table 2 above, the quantum dot ink composition according to the present invention was found to be excellent in both the dispersion stability and adhesiveness of the quantum dots. The ink composition of Comparative Example 9 suffered from suspension and precipitation, making it impossible to evaluate the properties.

[0183] (Evaluation of flatness of light-emitting layer) The flatness evaluation sample was prepared by forming a hole injection layer (HIL for inkjet printing) and a hole transport layer (Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)](TFB)) in that order on a fluorine-containing bank substrate, and then ejecting ink onto them. The ink that had landed inside the bank was dried at room temperature under reduced pressure for 15 minutes using an oil diffusion pump, and then heated and dried at 120°C for 30 minutes in a nitrogen atmosphere.

[0184] The cross-sectional shape was measured using a micro-shape measuring instrument (ET200, manufactured by Kosaka Laboratory Co., Ltd.), and the average film thickness within a width of ±30% from the center was calculated. 5 nm was added to this film thickness, and the width within this range was divided by the bank width to determine the flatness.

[0185] The ink of Example 1 and the ink of Comparative Example 2 were each ejected into the bank and dried, and the flatness was evaluated. As a result, the flatness was 61% when the ink of Example 1 was used, and the flatness was 45% when the ink of Comparative Example 2 was used.

[0186] Figure 2 shows the cross-sectional profile of the bank substrate after the ink of Example 1 has landed, and after the ink of Comparative Example 2 has landed. As shown in Figure 2, it was found that the ink of Example 1 was less likely to adhere to the bank side surface than the ink of Comparative Example 2, and thus the flatness was improved.

[0187] The present invention has been described above with reference to embodiments and examples, but the present invention is not limited to the specific embodiments and examples, and various modifications and changes are possible within the scope of the invention described in the claims. [Explanation of symbols]

[0188] 100 quantum dot electroluminescent devices (QLEDs), 110 board, 120 first electrode, 130 hole injection layer, 140 hole transport layer, 150 luminescent layer, 160 electron transport layer, 170 electron injection layer, 180 Second electrode.

Claims

1. Quantum dots and Contains the following solvent a and the following solvent b-1, containing the following solvent a, the following solvent b-2, and the following solvent b-1, or a mixed solvent containing the following solvent a, the following solvent b-2, the following solvent b-1, and the following solvent c; Including, A quantum dot ink composition having a surface tension of 30 mN / m or more and 40 mN / m or less: Solvent a: at least one of n-dodecylcyclohexane and n-tridecylcyclohexane Solvent b-1: an aromatic hydrocarbon compound having a linear alkyl group having from 2 to 12 carbon atoms and having a surface tension of from 32 to 40 mN / m, such as 1-ethylnaphthalene, 2-ethylnaphthalene, 1-n-propylnaphthalene, 2-n-propylnaphthalene, 1-n-butylnaphthalene, 2-n-butylnaphthalene, 1-n-pentylnaphthalene, 2-n-pentylnaphthalene, 1-n-hexylnaphthalene, 2-n-hexylnaphthalene, at least one selected from the group consisting of 1,4-diethylnaphthalene, 1,4-di(n-propyl)naphthalene, 1,4-di(n-butyl)naphthalene, 1,4-di(n-pentyl)naphthalene, and 1,4-di(n-hexyl)naphthalene; Solvent b-2: an aromatic hydrocarbon compound having a linear alkyl group having from 2 to 12 carbon atoms and having a surface tension of from 25 to 32 mN / m, such as ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, n-hexylbenzene, n-heptylbenzene, n-octylbenzene, n-nonylbenzene, n-decylbenzene, n-undecylbenzene, n-dodecylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 1,2-di(n-propyl)benzene, 1,3-di(n-propyl)benzene, 1,4-di(n-propyl)benzene, 1,2-di(n-butyl)benzene, 1,3-di(n-butyl)benzene, 1,4-di(n-butyl)benzene, 1,4-di(n-pentyl)benzene, 1,4-di(n-hexyl)benzene, 1,4 at least one selected from the group consisting of 1,4-di(n-heptyl)benzene, 1,4-di(n-octyl)benzene, 1,4-di(n-nonyl)benzene, 1,4-di(n-decyl)benzene, 1,4-di(n-undecyl)benzene, 1,4-di(n-dodecyl)benzene, 1-ethylindene, 2-ethylindene, 3-ethylindene, 4-ethylindene, 5-ethylindene, 6-ethylindene, 7-ethylindene, 1-n-propylindene, 2-n-propylindene, 3-n-propylindene, 4-n-propylindene, 5-n-propylindene, 6-n-propylindene, 7-n-propylindene, 1-n-butylindene, 2-n-butylindene, 3-n-butylindene, 4-n-butylindene, 5-n-butylindene, 6-n-butylindene, and 7-n-butylindene; Solvent c: an aromatic compound other than solvent b-1, having a surface tension of 32 mN / m or more and 50 mN / m or less, such as 1-methylnaphthalene, 2-methylnaphthalene, 1,2-dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 1,6-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1-phenylnaphthalene, 1-vinylnaphthalene, ethyl 4-methylbenzoate, methyl 4-tert-butylbenzoate, n-propyl benzoate, n-butyl benzoate, n-pentyl benzoate, n-hexyl benzoate, isopentyl benzoate, 2-ethylhexyl benzoate, ethyl 2-methylbenzoate, 2-ethoxyethyl benzoate, benzyl benzoate, N,N-dimethylbenzamide, N,N-dimethyl-3-methylbenzoate, At least one selected from the group consisting of ethylbenzamide, N,N-dimethyl-2,3-dimethylbenzamide, N-methoxy-N-methylbenzamide, 2-methylbenzophenone, 3-methylbenzophenone, thiophene, 3,4-ethylenedioxythiophene, 2-methyl-2,3-dihydrothieno[3,4-b]-1,4-dioxin, 2-ethyl-2,3-dihydrothieno[3,4-b]-1,4-dioxin, diphenyl ether, dibenzyl ether, dimethylphthalate, diethylphthalate, 1'-acetonaphthone, 1-methoxy-4-methylnaphthalene, methyl-1-naphthalene acetate, ethyl-1-naphthalene acetate, and 2-methylbenzo[e]indene.

2. the solvent a is at least one of n-dodecylcyclohexane and n-tridecylcyclohexane, the solvent b-1 is at least one selected from the group consisting of 1-ethylnaphthalene, 2-ethylnaphthalene, 1-n-propylnaphthalene, 2-n-propylnaphthalene, 1-n-butylnaphthalene, 2-n-butylnaphthalene, 1-n-pentylnaphthalene, and 2-n-pentylnaphthalene; the solvent b-2 is at least one selected from the group consisting of n-hexylbenzene, n-heptylbenzene, n-octylbenzene, n-nonylbenzene, and n-decylbenzene; 2. The quantum dot ink composition according to claim 1, wherein the solvent c is at least one selected from the group consisting of 1-phenylnaphthalene, benzyl benzoate, n-butyl benzoate, 1-methylnaphthalene, 2-methylbenzophenone, 3-methylbenzophenone, and 1′-acetonaphthone.

3. The quantum dot ink composition according to claim 1 , wherein the average particle size of the quantum dots is 7 nm or more and 15 nm or less.

4. The quantum dot ink composition according to any one of claims 1 to 3, wherein the quantum dots are free of cadmium (Cd) and lead (Pb).

5. The quantum dot ink composition according to any one of claims 1 to 4, wherein the surface of the quantum dots is coordinated with at least one organic ligand selected from the group consisting of alkyl halide compounds, mercapto group-containing compounds, and aliphatic carboxylic acid compounds.

6. 6. The quantum dot ink composition according to claim 5, wherein the content of the organic ligand in the quantum dots is 0.5% by mass or more and 15% by mass or less, where the total mass of the quantum dots and the organic ligand is 100% by mass.

7. The absolute value of the difference between the solubility parameter of the mixed solvent and the solubility parameter of the organic ligand [(solubility parameter of the mixed solvent) - (solubility parameter of the organic ligand)] is 1.5 (cal / cm ３ ) １／２ 7. The quantum dot ink composition according to claim 5 or 6, wherein:

8. The quantum dot ink composition according to any one of claims 1 to 7, wherein the photoluminescence quantum yield is 90% or more and 100% or less.

9. A quantum dot electroluminescence device comprising a light-emitting layer formed from the quantum dot ink composition according to any one of claims 1 to 8.

10. 10. The quantum dot electroluminescence device according to claim 9, wherein the flatness of the light-emitting layer is 60% or more and 100% or less.

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