Quantum dot ink composition

Abstract

This invention provides a quantum dot ink composition that exhibits excellent dispersion stability and deposition elasticity of quantum dots. [Solution] A quantum dot ink composition comprising quantum dots and a mixed solvent containing at least the following solvent a and the following solvent b, wherein the surface tension is 30 mN / m or more and 40 mN / m or less: Solvent a: Cycloalkane compound having a linear alkyl group with 4 to 16 carbon atoms Solvent b: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms.

Description

[Technical Field]

[0001] This invention relates to quantum dot ink compositions. [Background technology]

[0002] In recent years, organic electroluminescent elements (hereinafter also referred to as organic EL elements or OLEDs) have been the subject of active research and development as thin-film, lightweight, and low-power display and lighting elements.

[0003] Organic light-emitting diodes (OLEDs) are light-emitting devices that have a thin film of an organic compound with a thickness of several nanometers to several hundred nanometers between the anode and the cathode, and consist of multiple organic materials such as a hole transport layer, an emissive layer, and an electron transport layer.

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

[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 giving them a sharp emission spectrum. In recent years, there has also been progress in developing quantum dots that do not contain toxic substances such as cadmium (Cd) and lead (Pb).

[0006] Quantum dot electroluminescent devices (hereinafter also referred to as QDLEDs), which use quantum dots as the light-emitting layer material, can be manufactured using a wet coating method and may have higher productivity than existing OLEDs. Recently, progress has been made in developing ink compositions containing quantum dots for use in the manufacture of such QDLEDs (see Patent Documents 1-4 and Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Document

[0008]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] When producing a quantum dot-containing layer by a wet coating method, particularly an inkjet method, it is required to prevent aggregation of quantum dots in the ink, enhance dispersion stability, and improve luminescence characteristics. Also, landing elasticity for spraying the ink in an accurate amount at an accurate position is required. However, in the technologies described in Patent Documents 1 to 4 and Non-Patent Document 1 above, at least one of the dispersion stability and landing elasticity of quantum dots is insufficient and cannot meet the above requirements. .

[0010] Therefore, an object of the present invention is to provide a quantum dot ink composition excellent in both the dispersion stability and landing elasticity of quantum dots.

Means for Solving the Problems

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

[0012] In other words, 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, wherein the surface tension is 30 mN / m or more and 40 mN / m or less: Solvent a: Cycloalkane compound having a linear alkyl group with 4 to 16 carbon atoms Solvent b: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms. [Effects of the Invention]

[0013] According to the present invention, a quantum dot ink composition can be provided that exhibits excellent dispersion stability and deposition elasticity of quantum dots. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic cross-sectional view showing a quantum dot electroluminescent device according to one embodiment of the present invention. [Figure 2] This figure shows the cross-sectional profile of the bank substrate, the substrate after ink deposition in Example 1, and the substrate after ink deposition in Comparative Example 2. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below. However, the present invention is not limited to the embodiments described below. Unless otherwise specified, operations and measurements of physical properties will be performed under conditions of room temperature (20°C to 25°C) and relative humidity of 40%RH to 50%RH.

[0016] [Quantum dot ink composition] One embodiment 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, wherein the surface tension is 30 mN / m or more and 40 mN / m or less: Solvent a: Cycloalkane compound having a linear alkyl group with 4 to 16 carbon atoms Solvent b: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms.

[0017] Having such a configuration, the quantum dot ink composition of the present invention is an ink composition that exhibits excellent dispersion stability and deposition elasticity of quantum dots.

[0018] The inventors of the present invention hypothesize the following 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.

[0019] Generally, quantum dots have organic ligands such as oleic acid and exhibit high dispersion stability in aliphatic hydrocarbon solvents. However, because aliphatic hydrocarbon solvents have low viscosity and surface tension, they tend to separate from the main droplet of ink ejected from the nozzle, forming satellite droplets that land at a different location than the main droplet. Therefore, inks containing quantum dots and aliphatic hydrocarbon solvents have the problem of reduced adhesion elasticity.

[0020] On the other hand, solvents with high surface tension, commonly used in inkjet inks, While this improves the elasticity of the material, mixing it with quantum dots causes aggregation of the quantum dots, making them difficult to extrude from the nozzle. Furthermore, since the emission color of quantum dots depends on their size, aggregation of quantum dots can cause changes in emission color, and can also lead to a decrease in emission properties such as a reduction in quantum yield.

[0021] In response to these problems, the inventors have diligently conducted research and have found that a quantum dot ink composition comprising quantum dots and a mixed solvent containing at least the following two solvents can solve the above problems: Solvent a: Cycloalkane compound having a linear alkyl group with 4 to 16 carbon atoms Solvent b: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms.

[0022] Solvent a is a solvent that maintains the dispersibility of quantum dots, and solvent b plays a role in effectively exerting the effects of solvent a. In addition, the ink composition of the present invention has a high surface tension of 30 mN / m to 40 mN / m. As a result, both the excellent dispersion stability of quantum dots possessed by solvent a and the ink's adhesion elasticity suitable for inkjet printing are efficiently exhibited. This makes it possible to achieve both excellent dispersion stability of quantum dots and excellent ink adhesion elasticity, which could not be obtained with conventional quantum dot ink compositions.

[0023] It should be noted that the above mechanism is based on speculation, and its accuracy does not affect the technical scope of the present invention. Similarly, the accuracy 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 predetermined size that exhibit quantum constraint effects.

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

[0027] In wet chemical processes, as crystals grow, organic solvents naturally coordinate to the surface of quantum dot crystals, acting as dispersants and regulating crystal growth. Therefore, wet chemical processes allow for easier and lower-cost control of semiconductor nanoparticle growth compared to vapor deposition methods such as metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE).

[0028] Quantum dots (semiconductor nanoparticles) can have their energy bandgap adjusted by controlling their size, allowing them to produce light in a variety of wavelengths in their light-emitting layer (quantum dot light-emitting layer). Therefore, using multiple quantum dots of different sizes enables displays that emit (or emit) light of multiple wavelengths. The size of the quantum dots can be selected to emit red, green, and blue light, allowing for the construction of color displays. Alternatively, the sizes of the quantum dots can be combined to emit white light from a variety of colors.

[0029] Quantum dots (semiconductor nanoparticles) include: Group II-VI semiconductor compounds; Group III-V semiconductor compounds; Group IV-VI semiconductor compounds; Group IV elements or compounds; and combinations thereof. A semiconductor material selected from the group consisting of combinations can be used.

[0030] The group II-VI semiconductor compounds are not particularly limited, but include, for example, two-element compounds selected from the group consisting of CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, and mixtures thereof; three-element 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 four-element compounds selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof.

[0031] III-V semiconductor compounds are not particularly limited, but include, for example, two-element compounds selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; three-element 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 four-element 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 compounds are not particularly limited, but can be selected from, for example, two-element compounds selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof; three-element compounds selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof; and four-element compounds selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof.

[0033] The Group IV elements or compounds are not particularly limited, but include, for example, mono-element compounds selected from the group consisting of Si, Ge, and mixtures thereof; and di-element compounds selected from the group consisting of SiC, SiGe, and mixtures thereof.

[0034] A quantum dot may consist of one compound or two or more compounds. Furthermore, it may have a core-shell structure, for example, comprising a core made of a semiconductor compound and a shell made of a different semiconductor compound. The luminescence efficiency of the quantum dot can be increased by using a semiconductor compound with a higher band gap than the core-forming semiconductor compound as the semiconductor compound constituting the shell, so that excitons are confined to the core. Examples of core-shell structures (core / shell) with such band gap relationships include CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, CuInS / ZnS, ZnTeSe / ZnSe / ZnS, and InP / ZnSe / ZnS.

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

[0036] The particle size (size) of the quantum dot is determined to ensure that light of the desired wavelength is obtained. The appropriate adjustments can be made depending on the material being used. 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 towards the blue side, that is, towards higher energy. Therefore, by changing the size of the quantum dots, the emission wavelength can be adjusted across the wavelength range of the ultraviolet, visible, and infrared spectra.

[0037] For example, the average particle size (average diameter) of quantum dots (semiconductor nanoparticles) is not particularly limited, but is generally between 1 nm and 15 nm. From the viewpoint of luminescence characteristics and dispersion stability of quantum dots, a particle size between 7 nm and 15 nm is preferred. 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 average particle size based on volume.

[0038] Furthermore, it is preferable to use quantum dots in which organic ligands having coordinating groups are coordinated to the surface. By adding organic ligands to the raw material solution of the quantum dots during synthesis, excessive crystal growth can be prevented, and quantum dots within the desired particle size range can be obtained. In addition, quantum dots having a surface layer composed of organic ligands on their surface can be prevented from agglomerating 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 coordinating groups include halogen atoms, carboxyl groups, carboxylic acid anhydride groups, amino groups, ammonium groups, mercapto groups, sulfide groups, sulfoxide groups, phosphine groups, phosphine oxide groups, phosphoric acid groups, phosphonic acid groups, phosphinic acid groups, sulfonic acid groups, boronic acid groups, heterocyclic groups, etc. Such organic ligands may be used individually or in combination of two or more.

[0040] Examples of halogen atom-containing compounds include alkyl halides having linear or branched alkyl groups with 1 to 30 carbon atoms. Specific examples of such alkyl halides 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 carboxyl group-containing compounds include linear or branched aliphatic carboxylic acid compounds having 1 to 30 carbon atoms. Specific examples of such aliphatic carboxylic acid compounds include, for example, 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-nonenic acid, 2-nonenic acid, trans-2-octenoic acid, petroseric acid, elaidic acid, and oleic acid. Examples include octanoic 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, valeric acid, etc.

[0042] Examples of amino group-containing compounds include aliphatic amine compounds having a linear or branched alkyl group with 1 to 30 carbon atoms. Specific examples of such aliphatic amine compounds include, for example, 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 Examples include 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, and tri(n-decyl)amine.

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

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

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

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

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

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

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

[0050] The content of organic ligands in quantum dots is not particularly limited. However, from the viewpoint of controlling the film thickness after ejection in an inkjet device, it is preferable that the total mass of quantum dots and organic ligands be 0.5% by mass or more and 15% by mass or less, with the total mass of quantum dots and organic ligands being 100% by mass.

[0051] Quantum dots with organic ligands having coordinating groups coordinated to their surface can be synthesized by methods described, for example, in J.Am.Chem.Soc.,115,pp8706-8715(1993), J.Phys.Chem.,101,pp9463-9475(1997), Nature volume 575,pp634-638(2019), etc. Commercially available products can also be used as suitable alternatives.

[0052] The quantum dot content 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. Furthermore, the quantum dot content 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 comprises 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 with 4 to 16 carbon atoms. Solvent a may be used alone or as a mixture of two or more. Furthermore, solvent a may be a commercially available product or a synthesized product.

[0055] Furthermore, while solvent a may contain various stereoisomers, its stereoconfiguration is not particularly limited; it may consist of individual stereoisomers or a mixture of various stereoisomers in any proportion.

[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 groups. Solvent a may have only one alkyl group having 4 to 16 carbon atoms, or it may have two or more. Furthermore, if solvent a has one or more linear alkyl groups having 4 to 16 carbon atoms, it may further have linear or branched alkyl groups having 1 to 3 carbon atoms. Furthermore, if solvent a has one or more linear alkyl groups having 4 to 16 carbon atoms, it may further have branched alkyl groups having 4 to 16 carbon atoms.

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

[0058] Specific examples of solvent a include, for example, 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 Ntan, 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; These are some examples.

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

[0060] The content of solvent a in the mixed solvent is preferably 30% by volume or more, with the total volume of solvent a and solvent b being 100% by volume. More preferably, the content of solvent a is 40% by volume or more, and even more preferably 50% by volume or more. Furthermore, 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, with the total volume of solvent a and solvent b being 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] In other words, the content of solvent a is preferably 30% to 99% by volume, more preferably 40% to 90% by volume, and even more preferably 50% to 85% by volume, with the total volume of solvent a and solvent b being 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 interact with solvent a through intermolecular interactions and effectively enhance the function of solvent a. Solvent b may be used alone or as a mixture of two or more. Furthermore, solvent b may be a commercially available product or a synthesized product.

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

[0064] Furthermore, the number of carbon atoms in the aromatic hydrocarbon portion of solvent b is preferably 6 to 12. The aromatic hydrocarbon portion may be a monocyclic, polycyclic, or ring-assembled structure. Examples of such aromatic hydrocarbons include benzene, indene, naphthalene, and biphenyl.

[0065] Solvent b is mainly classified into the following two types: Solvent b-1: Compound with a surface tension of 32 mN / m or more and 40 mN / m or less. Solvent b-2: A compound with 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 only needs to contain at least two types of solvents: solvent a and solvent b-1. In this case, the mixed solvent may also contain solvent b-2 and / or solvent c in addition to solvent a and solvent b-1.

[0067] When solvent b-2 is used as solvent b, it is preferable that the solvent included in the quantum dot ink composition 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] Below, solvent b will be explained by dividing it into solvent b-1 and solvent b-2.

[0069] <Solvent b-1> Solvent b-1 is an aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms and a surface tension of 32 mN / m to 40 mN / m. Such solvent b-1 plays a role in effectively enabling solvent a to exhibit its function in providing dispersion stability for quantum dots, and also in ensuring the surface tension of the entire ink composition. The surface tension of solvent b-1 is preferably 33 mN / m or higher, and more preferably 35 mN / m or higher. The upper limit of the surface tension of solvent b-1 is usually 40 mN / m or lower. In this specification, the surface tension of the solvent and the ink composition is the value obtained by the method described in the examples.

[0070] Solvent b-1 may be used alone or as a mixture of two or more types. Furthermore, solvent b-1 may be a commercially available product or a synthesized product.

[0071] Specific examples of solvent b-1 include, for example, 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, and 1,4-di(n-hexyl)naphthalene; Examples 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, 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 from the viewpoint of viscosity and vapor pressure.

[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 mN / m or more and less than 32 mN / m. Such solvent b-2 can effectively exert the function of solvent a that 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] Solvent b-2 may be used alone or as a mixture of two or more types. Furthermore, 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; These are some examples.

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

[0077] As described above, when solvent b-1 is used as solvent b, the mixed solvent should contain at least solvent a and solvent b-1. In this case, the mixed solvent may optionally contain at least one of solvent b-2 and solvent c. When solvent b-2 is used as solvent b, it is preferable that the mixed solvent 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 vol% or more, based on the total volume of solvent a and solvent b being 100 vol%. More preferably, the content of solvent b is 10 vol% or more, and even more preferably 15 vol% or more. Furthermore, the content of solvent b is preferably 70 vol% or less, more preferably 60 vol% or less, and even more preferably 50 vol% or less, based on the total volume of solvent a and solvent b being 100 vol%. When two or more types of solvent b are used, the above content of solvent b refers to the total amount of solvent b. When solvent b-1 and solvent b-2 are used together, the above content of solvent b refers to the total amount of solvent b-1 and solvent b-2.

[0079] In other words, the content of solvent b is preferably 1.0% to 70% by volume, more preferably 10% to 60% by volume, and even more preferably 15% to 50% by volume, with the total volume of solvent a and solvent b being 100% by volume.

[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 can impart 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. There is no particular upper limit to the surface tension of solvent c, but it is usually 50 mN / m or less. Solvent c may be a single type or a mixture of two or more types. It may be used. Furthermore, solvent c may be a commercially available product or a synthesized product.

[0082] Solvent c may be a compound having an aromatic hydrocarbon ring, or it may be a compound having an aromatic heterocycle.

[0083] Compounds having an aromatic hydrocarbon ring include aromatic compounds having a functional group selected from halogen groups, alkyl groups, alkoxy groups, alkenyl groups, aldehyde groups, ketone groups, ether groups, carboxyl groups, ester groups, nitro groups, and amide groups. Compounds having an aromatic heterocycle include compounds having an oxygen-containing aromatic heterocycle, a nitrogen-containing aromatic heterocycle, or a sulfur-containing aromatic heterocycle.

[0084] Further 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 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-dioxin, 2-ethyl-2,3-dihydrothieno[3,4-b]-1,4-dioxin, diphenyl ether, dibenzyl ether, dimethylphthalic acid, diethylphthalic acid, 1'-acetonaphthone, 1-methoxy-4-methylnaphthalene, methyl-1-naphthalate, 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 solvents a, b, and c being 100% by volume. Furthermore, when solvent c is included, 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 solvents a, b, and c being 100% by volume. Note that when two or more types of solvent c are used, the above content of solvent c refers to the total amount of solvent c.

[0087] In other words, the content of solvent c is preferably 5% to 40% by volume, more preferably 10% to 35% by volume, and even more preferably 15% to 30% by volume, based on the total volume of solvent a, solvent b, and solvent c being 100% by volume.

[0088] [Solubility parameters] From the viewpoint of further improving the dispersion stability of 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 difference between the solubility parameter of the mixed solvent and the solubility parameter of the organic ligand. The absolute value of [(solubility parameter of mixed solvent) - (solubility parameter of organic ligand)] is 1.5 (cal / cm³). 3 ) 1 / 2 Preferably, it is 1.0 (cal / cm³). 3 ) 1 / 2 It is more preferable that the following conditions be met: 0.7 (cal / cm³) 3 ) 1 / 2 It is even more preferable that the following conditions are met. Note that the lower limit of the absolute value of the difference is 0.

[0089] In this specification, the solubility parameters of solvents are those calculated using Fedors' estimation method. Specifically, based on RFFedors, Polym. Eng. Sci., 14(2), pp147-154 (1974), the solubility parameters of individual solvents are calculated using the following formula, referencing Δei and Δvi related to the solvent structure (unit: cal / cm³). 3 ) 1 / 2 ).

[0090]

number

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

[0092] The solubility parameters of a mixed solvent can be controlled by appropriately selecting the types of solvents included in the mixed solvent, their respective content ratios, and other factors.

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

[0094] [Additives] The ink composition of the present invention may optionally contain various additives. Examples of additives include, for example, host materials used in the light-emitting layer, antioxidants, leveling agents, plasticizers, surfactants, defoamers, silane coupling agents, ultraviolet absorbers, adhesion promoters, and the like.

[0095] Examples of the host materials mentioned above include compounds having a carbazole skeleton, a diarylamine skeleton, a pyridine skeleton, a pyrazine skeleton, a triazine skeleton, and an arylsilane skeleton.

[0096] The amount of the above-mentioned additive can be appropriately determined according to the application, as long as it does not impair the objective of the present invention.

[0097] Furthermore, the ink composition of the present invention may further contain other solvents in addition to the mixed solvent described above, as long as it does not impair the objective of the present invention. 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, 1-bromododecane, and the like. 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 other solvents is 0 parts by volume, i.e., that no other solvents are included.

[0098] [Method for manufacturing ink composition] The method for producing the quantum dot ink composition of the present invention is not particularly limited. For example, the quantum dots, solvent a, solvent b, and other components to be added as needed may be mixed together. Alternatively, the components may be mixed sequentially. However, from the viewpoint of further improving the dispersibility of the quantum dots, it is preferable to prepare a mixed solvent by mixing solvent a, solvent b, and solvent c in advance, and then add the resulting mixed solvent to the separately prepared quantum dots and mix and stir. The temperature during mixing is not particularly limited, but is usually in the range of 20°C to 30°C. Similarly, the mixing time is not particularly limited, but is usually in the range of 0.1 hours to 1 hour.

[0099] [Physical properties of ink compositions] The surface tension of the ink composition of the present invention having the above 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 adhesion elasticity decreases. Also, if the surface tension of the ink composition exceeds 40 mN / m, the flatness after adhesion to the bank decreases, which can 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. Also, 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] In other words, 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] Furthermore, the surface tension of the ink composition can be controlled by appropriately selecting the types of solvents included in the mixed solvent, the content ratio of each solvent, and so on.

[0102] The viscosity of the quantum dot ink composition of the present invention is preferably 4 mPa·s to 10 mPa·s, and more preferably 4.5 mPa·s to 7.0 mPa·s, from the viewpoint of improving ejection stability during continuous ejection. The viscosity of the quantum dot ink composition is the 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% to 100%, more preferably 90% to 100%, and even more preferably 95% to 100%. When the PLQY is within the above range, the dispersion stability of the quantum dots is excellent. The PLQY value used is the value measured by the method described in the examples.

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

[0105] In particular, the quantum dot ink composition according to the present invention is suitably used to form a light-emitting layer in a quantum dot electroluminescent element. That is, according to another embodiment of the present invention, a quantum dot electroluminescent element is provided which comprises a light-emitting layer formed from the quantum dot ink composition of the present invention.

[0106] The following provides a detailed explanation of this quantum dot electroluminescent device.

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

[0108] As shown in Figure 1, the QLED 100 according to this embodiment comprises 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, a light-emitting layer 150 disposed on the hole transport layer 140, an electron transport layer 160 disposed on the light-emitting 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] The method for forming layers other than the light-emitting layer 150 is not particularly limited. Layers other than the light-emitting layer 150 may be formed by, for example, vacuum deposition or by solution coating. 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 inkjet printing.

[0110] When forming layers other than the luminescent layer 150 by a solution coating method, examples of solvents that can be used include toluene, xylene, ethylbenzene, diethylbenzene, methylene, propylbenzene, cyclohexylbenzene, dimethoxybenzene, anisole, ethoxytoluene, phenoxytoluene, isopropyl biphenyl, 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] The substrate 110 can be a substrate commonly used in EL elements. 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 high work function. For example, the first electrode 120 may be formed as a transmissive electrode using indium tin oxide (In2O3-SnO2:ITO), indium zinc oxide (In2O3-ZnO), tin oxide (SnO2), zinc oxide (ZnO), etc., which have excellent transparency and conductivity. Alternatively, the first electrode 120 may be formed as a reflective electrode by laminating magnesium (Mg), aluminum (Al), etc., onto the transparent conductive film. Furthermore, after forming the first electrode 120 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 with a thickness of 10 nm to 1000 nm, more specifically, 20 nm to 300 nm (dry film thickness; the same applies hereinafter).

[0114] The hole injection layer 130 can be formed using known hole injection materials. Examples of known hole injection materials for forming the hole injection layer 130 include poly(ether ketone)-containing triphenylamine (TPAPEK) and 4-isopropyl-4'-methyldiphenyliodon. 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 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 / dodecylbenzenesulfonic acid Examples include poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate):PEDOT / PSS, and polyaniline / 10-camphorsulfonic acid.

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

[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), and 4,4',4”-tris(N-carbazolyl) Examples include 4,4',4”-tris(N-carbazolyl)triphenylamine (TCTA), 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 individually or as a mixture of two or more.

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

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

[0119] An electron transport layer 160 is formed on the light-emitting layer 150. The electron transport layer 160 is a layer that has the function of transporting electrons and is formed using methods such as vacuum deposition, spin coating, or inkjet. The electron transport layer 160 may be formed with a thickness of, for example, 15 nm to 50 nm.

[0120] The electron transport layer 160 may be formed using a known electron transport material. This electron transport material may be an organic material or an inorganic material. Examples of known organic electron transport materials include (8-quinolinato)lithium (lithium quinolate) (Liq), tris(8-quinolinato)aluminium (tris(8-quinolinato)aluminium:Alq3), and compounds having a nitrogen-containing aromatic ring. Specific examples of compounds containing nitrogen-containing aromatic rings include, for example, compounds containing a pyridine ring such as 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene, compounds containing a triazine ring such as 2,4,6-tris(3'-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine, and 2-(4-(N-phenylbenzoinidazolyl-1-ylphenyl)-9,10-dinaphthylanthracene Examples of compounds containing an imidazole ring include N-phenylbenzoimidazolyl-1-yl-phenyl)-9,10-dinaphthylanthracene and 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene (TPBI). Furthermore, known inorganic electron transport materials are not particularly limited, but examples include oxides of TiO2, ZnO, ZnMgO, SiO2, SnO2, WO3, Ta2O3, BaTiO3, BaZrO3, ZrO2, HfO2, Al2O3, Y2O3, and ZrSiO4.

[0121] The above-mentioned electron transport material may be a single material or a mixture of two or more materials.

[0122] An 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 method such as vacuum deposition. The electron injection layer 170 may be formed with 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 lithium compounds such as (8-quinolinato)lithium (lithium quinolate) ((8-quinolinato)lithium:Liq) and lithium fluoride (LiF), sodium chloride (NaCl), cesium fluoride (CsF), lithium oxide (Li2O), or barium oxide (BaO).

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

[0124] Note that the stacked structure of the QLED 100 according to this embodiment is not limited to the above illustration. The QLED 100 according to this embodiment may be formed with other known stacked structures. For example, in the QLED 100, 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 may be omitted, or additional other layers may be provided. Also, each layer of the QLED 100 may be formed of a single layer or a plurality of layers, respectively.

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

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 only to the following examples.

[0127] Each physical property was measured by the following method.

[0128] <Calculation of solubility parameter (SP value)> The solubility parameter (SP value) of the solvent was calculated by Fedors' estimation method. Specifically, referring to R.F. Fedors, Polym. Eng. Sci., 14(2), pp147-154(1974), and referring to Δei and Δvi related to the structure of the solvent, the solubility parameter of the single solvent was calculated by the following formula. The solubility parameter of a mixed solvent containing solvent a, solvent b, and, if necessary, solvent c was obtained by weighting the SP value of the single solvent obtained 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, based on the relationship between shear stress τ and shear rate D: η = τ / D The viscosity of the ink composition was measured at 25°C using an Anton Paar Physica MCR300 (measurement jig: cone plate PP50). Specifically, the viscosity was measured at a shear rate of 1000 s. -1 The shear stress τ was measured at 25°C with a constant temperature and a distance of 0.05 mm between the cone plate and the base. The viscosity measurement range was estimated from the viscometer calibration standard solutions JS2.5, JS5, JS10, JS20, and JS50 (manufactured by Nippon Grease Co., Ltd.). The viscosity of the ink composition was calculated using a calibration curve obtained by calibrating with three standard solutions within the ink viscosity range.

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

[0132] The measurement method was performed using the suspension droplet method with the above-described apparatus. Surface tension was calculated by fitting the Young-Laplace theoretical curve to the contour shape and density difference values ​​of droplets created from the needle tip using image processing, and the average value of the surface tension obtained from 10 consecutive images was taken as the surface tension of the ink composition. Furthermore, the images used were those taken 1000 ms after droplet formation. For details of the principle of surface tension measurement, please refer to Y. ROTENBERG, J. Colloid Interface Sci., 93, 169 (1983), and Colloid Science IV Colloid Science Experimental Methods, p138, (edited by The Chemical Society of Japan, Tokyo Kagaku Dojin, 1996).

[0133] (Example 1) A quantum dot dispersion was prepared by referring to the sections "Synthesis of InP cores" and "Synthesis of InP / ZnSe / ZnS QDs" in the "Methods" section of Nature volume 575, pp634-638 (2019) (core species: InP, shell species: ZnSe / ZnS, quantum dot content in dispersion: 3% by mass, maximum emission wavelength of quantum dots: 627 nm, organic ligand of quantum dots: oleic acid (SP value when coordinated to the quantum dot surface: 8.1 (cal / cm²)). 3 ) 1 / 2 (Quantum dot particle size: 10 nm; see below for a schematic of the structure). Ethanol was added to the obtained quantum dot dispersion to generate a precipitate and perform centrifugation. 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 stirred with a shaker (mixing temperature: 25°C, mixing time: 10 minutes) to disperse the precipitate in the mixed solvent 1 to obtain 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: It was 3.0% by 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, which consisted of n-octylbenzene (solvent b-2) instead of n-decylbenzene and n-butyl benzoate (solvent c) 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 / cm²). 3 ) 1 / 2 That was the case.

[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) was used instead of benzyl benzoate.

[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 / cm²). 3 ) 1 / 2 That was the case.

[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 / cm²). 3 ) 1 / 2 That was the case.

[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 / cm²). 3 ) 1 / 2 That was the case.

[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 / cm²). 3 ) 1 / 2 That was the case.

[0147] (Example 7) A quantum dot ink composition 7 (hereinafter also referred to as ink 7) was prepared in the same manner as in Example 1, except that a mixed solvent 7 using 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 / cm²). 3 ) 1 / 2 That was the case.

[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 / cm²). 3 ) 1 / 2 That was the case.

[0151] (Example 9) A 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 / cm²). 3 ) 1 / 2 That was the case.

[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 was used in which the ratio of n-dodecylcyclohexane (solvent a) and 1-ethylnaphthalene (solvent b-1) was changed to 60:40 (volume ratio).

[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 the mixed solvent 10 was 8.9 (cal / cm²). 3 ) 1 / 2 That was the case.

[0155] (Example 11) A 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 ink 11 was 5.3 mPa·s, and the surface tension of ink 11 was 33 mN / m. The SP value of the mixed solvent 11 was 8.8 (cal / cm²). 3 ) 1 / 2 That was the case.

[0157] (Example 12) A 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 ink 12 was 6.8 mPa·s, and the surface tension of ink 12 was 32 mN / m. The SP value of the mixed solvent 12 was 9.3 (cal / cm²). 3 ) 1 / 2 That was the case.

[0159] (Comparative Example 1) A comparative quantum dot ink composition 1 (hereinafter referred to as,) 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. We created a comparative ink (also known as comparative ink 1).

[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 / cm²). 3 ) 1 / 2 That was the case.

[0161] (Comparative Example 2) A 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 was used, which was a mixture of n-dodecylcyclohexane (solvent a) and n-decylbenzene (solvent b-2) in a volume ratio of 85:15.

[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 / cm²). 3 ) 1 / 2 That was the case.

[0163] (Comparative Example 3) A 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 mixture of n-dodecylcyclohexane (solvent a) and benzyl benzoate (solvent c) in a 50:50 (volume ratio), 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 / cm²). 3 ) 1 / 2 That was the case.

[0165] (Comparative Example 4) A 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 mixture of n-octylcyclohexane and 4-methylcyclohexanol in a 50:50 (volume ratio), 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 / cm²). 3 ) 1 / 2 That was the case.

[0167] (Comparative Example 5) A 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 / cm²). 3 ) 1 / 2 That was the case.

[0169] (Comparative Example 6) A 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 was used, which was a mixture of n-dodecylcyclohexane (solvent a), n-tetradecane, and benzyl benzoate (solvent c) in a volume ratio of 70:15:15.

[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 / cm²). 3 ) 1 / 2 That was the case.

[0171] (Comparative Example 7) A comparative quantum dot ink composition 7 (hereinafter referred to as "comparative ink") was prepared in the same manner as in Example 1, except that comparative solvent 7 was used, 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. He created the (also known as Ku7)

[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 / cm²). 3 ) 1 / 2 That was the case.

[0173] (Comparative Example 8) A 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 was used, 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.

[0174] The viscosity of comparative ink 8 was 5.1 mPa·s, and the surface tension of comparative ink 8 was 28 mN / m. Furthermore, the SP value of comparative solvent 8 was 8.4 (cal / cm²). 3 ) 1 / 2 That was the case.

[0175] (Comparative Example 9) An attempt was made to prepare a 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 was used, which was a mixture of n-decylbenzene (solvent b-2) and benzyl benzoate (solvent c) in a 50:50 (volume ratio). 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 example and comparative example 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 Hamamatsu Photonics K.K. Using the Quantaurus-QY C11347-01, PLQY was measured at detection wavelengths of 610-640 nm. A value of 85% or higher indicates excellent dispersion stability of the quantum dot, making it practical for real-world use.

[0179] (Measurement of bullet impact precision) Using a FUJIFILM Dimatix DMP-2850 material printer, the inks for each example and comparative example were printed onto the surface of ITO glass under ejection conditions of 10 pl / dot and 100 dpi. The evaluation method involved continuous ejection testing with the inkjet device. Prints were deemed acceptable if all impact points were within a 10 μm radius of the target point, and unacceptable if they did not meet this criterion.

[0180] The evaluation results of the ink compositions for each example and 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 have excellent dispersion stability and deposition elasticity of quantum dots. The ink composition of Comparative Example 9 experienced suspension and precipitation, making it impossible to perform these evaluations.

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

[0184] The cross-sectional shape was measured using a micro-shape measuring machine (ET200, manufactured by Kosaka Research Institute Co., Ltd.), and the middle The average film thickness within ±30% of the center was determined, 5 nm was added to that film thickness, and the flatness was calculated by dividing the width within that range by the bank width.

[0185] The inks from Example 1 and Comparative Example 2 were dispensed into a printing bank and dried, and their flatness was evaluated. As a result, the flatness when using the ink from Example 1 was 61%, and the flatness when using the ink from Comparative Example 2 was 45%.

[0186] Furthermore, Figure 2 shows the cross-sectional profiles of the bank substrate, the ink of Example 1 after deposition, and the ink of Comparative Example 2 after deposition. As shown in Figure 2, it was found that the ink of Example 1 exhibited suppressed adhesion to the bank side surface and improved flatness compared to the ink of Comparative Example 2.

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

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

Claims

1. Quantum dots and A mixed solvent containing at least the following solvent a and solvent b, Includes, A quantum dot ink composition having a surface tension of 30 mN / m or more and 40 mN / m or less: Solvent a: Cycloalkane compound having a linear alkyl group with 4 to 16 carbon atoms Solvent b: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms.

2. The mixed solvent comprises solvent a and solvent b-1 described below, or The quantum dot ink composition according to claim 1, comprising solvent a, solvent b-2 below, and at least one of solvent b-1 below and solvent c below: Solvent b-1: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms and a surface tension of 32 mN / m to 40 mN / m. Solvent b-2: An aromatic hydrocarbon compound having a linear alkyl group with 2 to 12 carbon atoms and a surface tension of 25 mN / m or more and less than 32 mN / m. 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.

3. The quantum dot ink composition according to claim 1 or 2, 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 do not contain 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 dot 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. The quantum dot ink composition according to claim 5, wherein the content of the organic ligand in the quantum dot is 0.5% by mass or more and 15% by mass or less, with the total mass of the quantum dot and the organic ligand being 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 / cm³). ３ ) １／２ The quantum dot ink composition according to claim 5 or 6, which is as follows:

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

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

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