Charge-transporting ink composition and surface-treated metal oxide nanoparticle sol

Abstract

As a charge-transporting ink composition which has improved dispersibility of metal oxide nanoparticles in an organic solvent and which enables the achievement of a film that has charge transport properties and excellent flatness, the present invention provides a charge-transporting ink composition that contains: an organic solvent; and surface-treated metal oxide nanoparticles which each have a core that is composed of a nanoparticle of one or more metal oxides selected from the group consisting of oxides of a metal selected from the group consisting of Ti, Fe, Zr, Sn, Ta, Nb, Y, Mo, W, Pb, In, Bi, and Sr, and composites of at least two of these oxides, wherein the surface of the core is coated with a metal oxide, and the surface of the metal oxide is coated with at least one surface treatment agent.

Description

Charge transport ink composition and surface-treated metal oxide nanoparticle sol

[0001] The present invention relates to a charge transporting ink composition and a surface-treated metal oxide nanoparticle sol.

[0002] Organic electroluminescence (hereinafter referred to as organic EL) elements have attracted attention due to various advantages such as high contrast, energy saving, and flexibility, and are being put to practical use in fields such as displays and lighting. Organic EL elements use multiple functional thin films, one of which is the electron transport layer, which is responsible for the exchange of charges between the cathode and the light-emitting layer and plays an important role in achieving low-voltage operation and high brightness of organic EL elements.

[0003] Methods for manufacturing organic EL devices are broadly divided into dry processes, such as vapor deposition, and wet processes, such as spin coating and inkjet printing. Comparing these processes from the perspective of increasing the area of ​​devices, wet processes can more efficiently produce films with high flatness over large areas than dry processes. Therefore, given the current demand for large-area manufacturing of organic EL devices, it is important to provide electron transport layers and other layers that have excellent functionality and can be formed by wet processes.

[0004] Furthermore, with the recent development of display technology, quantum dot EL devices, which use quantum dot materials as their light-emitting layers, have emerged and are expected to have a wide range of applications. These quantum dot EL devices can be manufactured at low cost using wet processes, and are attracting much attention in fields such as display technology and lighting due to their characteristics such as controllability of emission wavelength, high color purity, high luminous efficiency, and flexibility.

[0005] In such EL devices, it is necessary to laminate an electron transport layer containing metal oxide nanoparticles between the light-emitting layer and the cathode to efficiently inject electrons into the light-emitting layer, and to date, various studies have been conducted on the type and primary particle size of metal oxide nanoparticles in order to improve this efficiency (Patent Documents 1 to 3).

[0006] Furthermore, metal oxide nanoparticles, such as ZnO and SnO2, commonly used in organic EL devices and quantum dot EL devices, have small particle diameters (primary particle diameter: approximately several nm to several tens of nm), resulting in a large specific surface area. The resulting large surface energy makes the metal oxide nanoparticles highly unstable and prone to aggregation. Aggregation of metal oxide nanoparticles affects film-forming properties and the conductivity of the resulting thin film (Patent Document 4). When a functional layer, such as an electron transport layer, is formed by applying an ink containing aggregated metal oxide nanoparticles, stable film formation is not possible, resulting in unevenness and poor flatness.

[0007] As a means for suppressing aggregation of metal oxide nanoparticles, surface treatment of metal oxide nanoparticles (Patent Document 5), addition of binders (Patent Document 6), etc. have been performed, but further improvements are desired to improve the performance of the resulting EL devices.

[0008] International Publication No. WO 2006 / 098540 JP 2010-055900 A International Publication No. WO 2009 / 084273 International Publication No. WO 2019 / 128992 International Publication No. WO 2020 / 121398 International Publication No. WO 2021 / 044634

[0009] The present invention has been made in view of the above background, and aims to provide a charge transporting ink composition that improves the dispersibility of metal oxide nanoparticles in organic solvents and provides a film that has charge transport properties and excellent flatness, and a surface-treated metal oxide nanoparticle sol that has improved dispersibility in the charge transporting ink composition.

[0010] As a result of extensive research, the present inventors have found that, in a charge transport ink composition comprising metal oxide nanoparticles and an organic solvent, the metal oxide nanoparticles have a core made of one or more metal oxide nanoparticles selected from the group consisting of oxides of specific metals and composites of oxides of the above metals, and the surface of the core is coated with a metal oxide, and the surface of the metal oxide is further coated with one or more surface treatment agents, by using surface-treated metal oxide nanoparticles, the surface-treated metal oxide nanoparticles are less likely to aggregate and have excellent dispersibility in an organic solvent, and they have also found that a charge transport thin film obtained from the charge transport ink composition has practical conductivity and excellent flatness, thereby completing the present invention.

[0011] That is, the present invention provides the following charge transport ink composition and surface-treated metal oxide nanoparticle sol: 1. A charge transport ink composition comprising surface-treated metal oxide nanoparticles having a core composed of one or more metal oxide nanoparticles selected from the group consisting of oxides of a metal selected from the group consisting of Ti, Fe, Zr, Sn, Ta, Nb, Y, Mo, W, Pb, In, Bi, and Sr, and composites of at least two of these metal oxides, the surfaces of which are coated with a metal oxide and further coated with one or more surface treatment agents, and an organic solvent. 2. The charge transport ink composition of 1, in which the metal oxide nanoparticles are one or more metal oxide nanoparticles selected from the group consisting of oxides of a metal selected from the group consisting of Ti, Zr, and Sn, and composites of at least two of these metal oxides. 3. The charge transport ink composition of 2, in which the metal oxide nanoparticles are SnO2 or a SnO2-TiO2-ZrO2 composite. 4. The charge transport ink composition of any one of 1 to 3, wherein the metal oxide is at least one selected from the group consisting of In2O3, Sb2O5, SiO2, SnO2, TiO2, WO3, ZnO, ZrO2, and complexes of at least two of these. 5. The charge transport ink composition of 4, wherein the metal oxide is at least one selected from the group consisting of Sb2O5, SiO2, SnO2, TiO2, ZnO, and complexes of at least two of these. 6. The charge transport ink composition of 5, wherein the metal oxide is at least one selected from the group consisting of Sb2O5, SiO2, SnO2, and complexes of at least two of these. 7. The charge transport ink composition of 6, wherein the metal oxide is Sb2O5 or a SnO2-SiO2 complex. 8. The charge transport ink composition of any one of 1 to 7, wherein the surface treatment agent is at least one selected from the group consisting of compounds represented by the following formulas (S1) to (S9): (In formula (S1), R 1are each independently an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond; R 2 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and a represents an integer of 1 to 3. In formulas (S2) and (S3), R 3 and R 5 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 4 and R 6 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, Y represents an alkylene group, an NH group, or an oxygen atom, b represents an integer of 1 to 3, c is 0 or 1, and d represents an integer of 1 to 3. In formula (S4), R 7 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and e represents 1 or 2. 8 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 9 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 10 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 11represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 12 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 13 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and Z represents an oxygen atom or a sulfur atom. 14 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and f represents 1 or 2. 9. The charge transporting ink composition of 8, wherein the surface treatment agent is at least one selected from the group consisting of compounds represented by the following formulas (S1) to (S3): (R 1 ~R 6 , a, b, c and d have the same meanings as above.) 10. In the compound represented by (S1) above, R 1 are each independently an alkyl group or an alkyl group substituted with a mercapto group, and R 1 at least one of R is an alkyl group substituted with a mercapto group; 2is an alkoxy group, and a is an integer of 1 to 3. 11. A charge transporting ink composition according to any one of claims 1 to 10. 12. An electronic device comprising the charge transporting thin film of claim 11. 13. An electronic device according to claim 12, wherein the charge transporting thin film is an electron transport layer. 14. An electronic device according to claim 13, wherein the electronic device is an organic EL device or a quantum dot EL device. 15. A surface-treated metal oxide nanoparticle sol comprising surface-treated metal oxide nanoparticles having a core made of one or more metal oxide nanoparticles selected from the group consisting of SnO2 and SnO2-TiO2-ZrO2 composites, the surface of the core being coated with a SnO2-SiO2 composite, and the surface of the SnO2-SiO2 composite being further coated with at least one surface treating agent selected from the group consisting of compounds represented by the following formulas (S1) to (S9), and a solvent: (In formula (S1), R 1 are each independently an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond; R 2 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and a represents an integer of 1 to 3. In formula (S2), R 3 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 4 each independently represents an alkoxy group, an acyloxy group, or a halogen atom; Y represents an alkylene group, an NH group, or an oxygen atom; b represents an integer of 1 to 3; and c is 0 or 1. In formula (S3), R 5 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 6 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and d represents an integer of 1 to 3. In formula (S4), R 7each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and e represents 1 or 2. 8 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 9 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 10 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 11 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 12 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 13 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and Z represents an oxygen atom or a sulfur atom. 14each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and f represents 1 or 2.

[0012] By using the charge-transporting ink composition of the present invention, a charge-transporting thin film with excellent flatness can be obtained, which can be suitably used as a thin film for electronic devices such as organic EL devices and quantum dot EL devices.

[0013] The present invention will be described in more detail below. The charge transport ink composition of the present invention comprises surface-treated metal oxide nanoparticles having a core composed of one or more metal oxide nanoparticles selected from the group consisting of oxides of metals selected from the group consisting of Ti, Fe, Zr, Sn, Ta, Nb, Y, Mo, W, Pb, In, Bi, and Sr, and composites of at least two of these metal oxides, the surface of which is coated with a metal oxide, and the surface of the metal oxide is further coated with one or more surface treatment agents; and an organic solvent. In the present invention, the term "solid content" in connection with the charge transport ink composition of the present invention refers to components contained in the composition other than the solvent. Furthermore, the term "charge transportability" in the present invention is synonymous with both electrical conductivity and electron transportability. The charge transport ink composition of the present invention may have charge transportability itself, or a solid film obtained using the composition may have charge transportability.

[0014] The charge transport ink composition of the present invention contains a core (hereinafter sometimes referred to as a "core particle") made of one or more metal oxide nanoparticles selected from the group consisting of oxides of metals selected from the group consisting of Ti, Fe, Zr, Sn, Ta, Nb, Y, Mo, W, Pb, In, Bi, and Sr, and composites of at least two of these metals. The core surface is coated with a metal oxide (particles at this stage are sometimes referred to as "metal oxide-coated nanoparticles"), and the surface of the metal oxide is further coated with one or more surface treatment agents. The term "nanoparticles" refers to fine particles whose average primary particle diameter is on the order of nanometers (typically 500 nm or less). The particle diameter can be measured by methods such as transmission electron microscopy or dynamic light scattering (DLS).

[0015] The core particles are composed of one or more metal oxide nanoparticles selected from the group consisting of metal oxides selected from the group consisting of Ti, Fe, Zr, Sn, Ta, Nb, Y, Mo, W, Pb, In, Bi, and Sr, and composites of at least two of these metal oxides. As the metal oxide, an oxide of a metal having a valence of 2 to 6 is preferred.

[0016] Specific examples of the oxides of the above metals include TiO2, Fe2O3, ZrO2, SnO2, Ta2O5, Nb2O5, Y2O3, MoO3, WO3, PbO, In2O3, Bi2O3, SrO, SrTiO3, BaTiO3, a SnO2-WO3 composite, a SnO2-ZrO2 composite, a SnO2-TiO2 composite, and a SnO2-TiO2-ZrO2 composite. In the present invention, among these, from the viewpoint of charge transportability, TiO2, ZrO2, SnO2, a SnO2-ZrO2 composite, a SnO2-TiO2 composite, and a SnO2-TiO2-ZrO2 composite are preferred, SnO2 and a SnO2-TiO2-ZrO2 composite are more preferred, and a SnO2-TiO2-ZrO2 composite is even more preferred.

[0017] In the surface-treated metal oxide nanoparticles, the primary particle diameter of the core particles is not particularly limited as long as it is nano-sized. However, in consideration of obtaining a thin film with good reproducibility and excellent flatness, the diameter is preferably 1 to 60 nm, more preferably 2 to 50 nm, and even more preferably 3 to 50 nm.

[0018] As the metal oxide coating the surface of the core particle, from the viewpoint of achieving both dispersibility in organic solvents and charge transportability, at least one selected from the group consisting of In2O3, Sb2O5, SiO2, SnO2, TiO2, WO3, ZnO, ZrO2, and complexes of at least two of these is preferred, at least one selected from the group consisting of Sb2O5, SiO2, SnO2, TiO2, ZnO, and complexes of at least two of these is more preferred, at least one selected from the group consisting of Sb2O5, SiO2, SnO2, and complexes of at least two of these is even more preferred, and Sb2O5 and SnO2-SiO2 complexes are even more preferred.

[0019] When the metal oxide is a SnO2-SiO2 composite, the SiO2 / SnO2 mass ratio is preferably 0.1 to 5.0. An amine compound is preferably bonded to the surface of the metal oxide, and more preferably the amine compound is bonded in a molar ratio of amine compound / (SnO2+SiO2) in the range of 0.001 to 1.0.

[0020] The amine compound may be any of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, propylamine, isopropylamine, butylamine, isobutylamine, amylamine, allylamine, hexylamine, hepitylamine, octylamine, nonylamine, decylamine, dodecylamine, cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine. Examples of secondary amines include dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, diisobutylamine, N-ethyl-1,2-dimethylpropylamine, diamylamine, and diallylamine. Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, triamylamine, and triallylamine. These amine compounds may be used alone or in combination of two or more.

[0021] The amine compound can be bonded to the SnO2-SiO2 composite by a known method, such as that described in Japanese Patent No. 5704345.

[0022] The primary particle size of the metal oxide is not particularly limited as long as it is large enough to sufficiently cover the surface of the core particle, but from the viewpoint of reliably covering the core particle, it is preferably 1 to 10 nm.

[0023] The mass ratio of the metal oxide nanoparticles to the metal oxide (metal oxide / metal oxide nanoparticles) is preferably 0.01 to 1.00, more preferably 0.03 to 0.30, from the viewpoint of achieving both dispersibility in organic solvents and charge transport properties.

[0024] The surface treatment agent for coating the surface of the metal oxide that coats the surface of the core particle is preferably a compound represented by the following formulas (S1) to (S9). These surface treatment agents may be used alone or in combination of two or more.

[0025]

[0026] In formula (S1), R 1 are each independently an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond; R 2 each independently represents an alkoxy group, an acyloxy group, or a halogen atom; and a represents an integer of 1 to 3.

[0027] In formula (S2), R 3 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 4 each independently represents an alkoxy group, an acyloxy group, or a halogen atom; Y represents an alkylene group, an NH group, or an oxygen atom; b is an integer of 1 to 3; and c is 0 or 1.

[0028] In formula (S3), R 5 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 6 each independently represents an alkoxy group, an acyloxy group, or a halogen atom; and d represents an integer of 1 to 3.

[0029] In formula (S4), R 7 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and e represents 1 or 2.

[0030] In formula (S5), R 8 represents an organic group having an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group.

[0031] In formula (S6), R 9represents an organic group having an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group.

[0032] In formula (S7), R 10 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 11 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group.

[0033] In formula (S8), R 12 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 13 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and Z represents an oxygen atom or a sulfur atom.

[0034] In formula (S9), R 14 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and f represents 1 or 2.

[0035] The alkyl group is preferably an alkyl group having 1 to 18 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and even more preferably an alkyl group having 1 to 8 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a cyclopropyl group, an n-butyl group, an i-butyl group, an s-butyl group, a t-butyl group, a cyclobutyl group, a 1-methyl-cyclopropyl group, a 2-methyl-cyclopropyl group, an n-pentyl group, a 1-methyl-n-butyl group, a 2-methyl-n-butyl group, a 3-methyl-n-butyl group, a 1,1-dimethyl-n-propyl group, a 1,2-dimethyl-n-propyl group, a 2,2-dimethyl-n-propyl group, a 1-ethyl-n-propyl group, a cyclobutyl group, a cyclopropyl ... n-hexyl group, 1-methyl-n-pentyl group, 2-methyl-n-pentyl group, 3-methyl-n-cyclobutyl group, 1,2-dimethyl-cyclopropyl group, 2,3-dimethyl-cyclopropyl group, 1-ethyl-cyclopropyl group, 2-ethyl-cyclopropyl group, n-hexyl group, 1-methyl-n-pentyl group, 2-methyl-n-pentyl group, 3-methyl-n-pentyl group, 4-methyl-n-pentyl group, 1,1-dimethyl-n-butyl group, 1,2-dimethyl-n-butyl group, 1,3-dimethyl-n-butyl group, 2,2-dimethyl-n-butyl group, methyl-n-butyl group, 2,3-dimethyl-n-butyl group, 3,3-dimethyl-n-butyl group, 1-ethyl-n-butyl group, 2-ethyl-n-butyl group, 1,1,2-trimethyl-n-propyl group, 1,2,2-trimethyl-n-propyl group, 1-ethyl-1-methyl-n-propyl group, 1-ethyl-2-methyl-n-propyl group, cyclohexyl group, 1-methyl-cyclopentyl group, 2-methyl-cyclopentyl group, 3-methyl-cyclopentyl group, 1-ethyl-cyclobutyl group, 2-ethyl-cyclobutyl group, 3-ethyl-cyclobutyl group, 1,2-dimethyl-cyclobutyl group, 1,3-dimethyl-cyclobutyl group, 2,2-dimethyl-cyclobutyl group, 2,3-dimethyl-cyclobutyl group, 2,4-dimethyl-cyclobutyl group, 3,3-dimethyl-cyclobutyl group, 1-n-propyl-cyclopropyl group, 2-n-propyl-cyclopropyl group, 1-i-propyl-cyclopropyl group, 2-i-propyl-cyclopropyl group, 1,2,2-trimethyl-cyclopropyl group, 1,2,3-trimethyl-cyclopropyl group, 2,Examples include a 2,3-trimethyl-cyclopropyl group, a 1-ethyl-2-methyl-cyclopropyl group, a 2-ethyl-1-methyl-cyclopropyl group, a 2-ethyl-2-methyl-cyclopropyl group, a 2-ethyl-3-methyl-cyclopropyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group.

[0036] Examples of halogenated alkyl groups include the above-mentioned alkyl groups in which at least one carbon atom is substituted with a halogen group, preferably a halogenated alkyl group having 1 to 18 carbon atoms, more preferably a halogenated alkyl group having 1 to 10 carbon atoms, and even more preferably a halogenated alkyl group having 1 to 8 carbon atoms. Specific examples of the halogenated alkyl group include fluoromethyl, difluoromethyl, trifluoromethyl, bromodifluoromethyl, 2-chloroethyl, 2-bromoethyl, 1,1-difluoroethyl, 2,2,2-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, 2-chloro-1,1,2-trifluoroethyl, pentafluoroethyl, 3-bromopropyl, 2,2,3,3-tetrafluoropropyl, 1,1,2,3,3,3-hexafluoropropyl, 1,1,1,3,3,3-hexafluoropropan-2-yl, 3-bromo-2-methylpropyl, 4-bromobutyl, perfluoropentyl, and 2-(perfluorohexyl)ethyl groups.

[0037] The alkenyl group is preferably an alkenyl group having 2 to 10 carbon atoms, and more preferably an alkenyl group having 2 to 8 carbon atoms. Specific examples of the alkenyl group include ethenyl, 1-propenyl, 2-propenyl, 1-methyl-1-ethenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylethenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-n-propylethenyl, 1-methyl-1-butenyl, 1-methyl-2-butenyl, 1-methyl-3-butenyl, 2-ethyl-2-propenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, 2-methyl-3-butenyl, 3-methyl-4-butenyl, 4-methyl-5-butenyl, 5-methyl-6-butenyl, 5-methyl-7-butenyl, 5-methyl-8-butenyl, 5-methyl-9-butenyl, 5-methyl-10-butenyl, 10-methyl-11-butenyl, 10-methyl-12-butenyl, 10-methyl-13-butenyl, 10-methyl-14-butenyl, 10-methyl-15-butenyl, 10-methyl-16-butenyl, 10-methyl-17-butenyl, 10-methyl-18-butenyl, 10-methyl-19-butenyl, 10-methyl-20-butenyl, 10-methyl-21-butenyl, 10-methyl-22-butenyl, 10-methyl-23-butenyl, 10-methyl-24-butenyl, 10-methyl-25-butenyl, 10-methyl-26-buten 1-methyl-1-butenyl group, 3-methyl-2-butenyl group, 3-methyl-3-butenyl group, 1,1-dimethyl-2-propenyl group, 1-i-propylethenyl group, 1,2-dimethyl-1-propenyl group, 1,2-dimethyl-2-propenyl group, 1-cyclopentenyl group, 2-cyclopentenyl group, 3-cyclopentenyl group, 1-hexenyl group, 2-hexenyl group, 3-hexenyl group, 4-hexenyl group, 5-hexenyl group, 1-methyl-1-pentenyl group, 1-methyl-2-pentenyl group, 1-methyl-3-pentenyl group, 1-methyl-4-pentenyl group, 1-n-butylethenyl group, 2-methyl-1-pentenyl group, 2-methyl-2-pentenyl group, and the like.

[0038] The aryl group is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 10 carbon atoms. Specific examples of the aryl group include a phenyl group, a naphthyl group, an anthracenyl group, and a pyrenyl group.

[0039] The alkoxy group is preferably an alkoxy group having 1 to 10 carbon atoms, and more preferably an alkoxy group having 1 to 8 carbon atoms. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butoxy group, an i-butoxy group, an s-butoxy group, a t-butoxy group, an n-pentyloxy group, a 1-methyl-n-butoxy group, a 2-methyl-n-butoxy group, a 3-methyl-n-butoxy group, a 1,1-dimethyl-n-propoxy group, a 1,2-dimethyl-n-propoxy group, a 2,2-dimethyl-n-propoxy group, a 1-ethyl-n-propoxy group, and an n-hexyloxy group.

[0040] The acyloxy group is preferably an acyloxy group having 2 to 10 carbon atoms, and more preferably an acyloxy group having 2 to 8 carbon atoms. Specific examples of the acyloxy group include, but are not limited to, a methylcarbonyloxy group, an ethylcarbonyloxy group, an n-propylcarbonyloxy group, an i-propylcarbonyloxy group, an n-butylcarbonyloxy group, an i-butylcarbonyloxy group, an s-butylcarbonyloxy group, a t-butylcarbonyloxy group, an n-pentylcarbonyloxy group, a 1-methyl-n-butylcarbonyloxy group, a 2-methyl-n-butylcarbonyloxy group, a 3-methyl-n-butylcarbonyloxy group, a 1,1-dimethyl-n-propylcarbonyloxy group, a 1,2-dimethyl-n-propylcarbonyloxy group, a 2,2-dimethyl-n-propylcarbonyloxy group, a 1-ethyl-n-propylcarbonyloxy group, an n-hexylcarbonyloxy group, a 1-methyl-n-pentylcarbonyloxy group, and a 2-methyl-n-pentylcarbonyloxy group.

[0041] Examples of the alkylene group include alkylene groups derived from the above-mentioned alkyl groups, preferably alkylene groups having 1 to 18 carbon atoms, and more preferably alkylene groups having 1 to 8 carbon atoms. Specific examples of the alkylene group include a methylene group, a methylmethylene group, a dimethylmethylene group, an ethylene group, a 1,2-dimethylethylene group, a tetramethylethylene group, a trimethylene group, a propylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a 1,2-cyclohexylene group, a 1,3-cyclohexylene group, and a 1,4-cyclohexylene group.

[0042] Halogen atoms include fluorine atoms, chlorine atoms, bromine atoms and iodine atoms.

[0043] Examples of organic groups having a polyether group include polyetherpropyl groups having an alkoxy group, such as (CH3O)3SiC3H6(OC2H4). n OCH3, n can be in the range of 1 to 100, or 1 to 10.

[0044] Examples of the organic group having an epoxy group include a 2-(3,4-epoxycyclohexyl)ethyl group and a 3-glycidoxypropyl group.

[0045] The (meth)acryloyl group refers to both an acryloyl group and a methacryloyl group. Examples of organic groups having a (meth)acryloyl group include a 3-methacryloxypropyl group and a 3-acryloxypropyl group.

[0046] Examples of the organic group having a mercapto group include a 3-mercaptopropyl group.

[0047] Examples of organic groups having an amino group include a 2-aminoethyl group, a 3-aminopropyl group, an N-2-(aminoethyl)-3-aminopropyl group, an N-(1,3-dimethyl-butylidene)aminopropyl group, an N-phenyl-3-aminopropyl group, and an N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl group.

[0048] Examples of the organic group having a ureido group include a 3-ureidopropyl group.

[0049] Examples of the organic group having a thioureido group include 3-thioureidopropyl.

[0050] An example of the organic group having a cyano group is a 3-cyanopropyl group.

[0051] In the compound represented by formula (S1), R 1 Preferably, R are each independently an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, or a thioureido group, and are bonded to a silicon atom by a Si—C bond. 2 are each independently preferably an alkoxy group.

[0052] Furthermore, the compound represented by (S1) above includes R 1 are each independently an alkyl group or an alkyl group substituted with a mercapto group, and R 1 at least one of R is an alkyl group substituted with a mercapto group; 2 is an alkoxy group, and a is an integer of 1 to 3.

[0053] Specific examples of the compound represented by formula (S1) include, but are not limited to, compounds represented by the following formulas (S1-1) to (S1-10).

[0054]

[0055] In formula (S2), R 3 are each independently preferably an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 10 carbon atoms. 4 are each independently preferably an alkoxy group or a halogen atom. Y is preferably an alkylene group, an NH group, or an oxygen atom.

[0056] Furthermore, the compound represented by the above formula (2) is preferably a compound capable of forming a trimethylsilyl group or a triethylsilyl group on the surface of silica particles.

[0057] Specific examples of the compound represented by formula (S2) include, but are not limited to, compounds represented by the following formulas (S2-1) to (S2-4). These silane compounds may be commercially available products, and for example, silane compounds manufactured by Shin-Etsu Chemical Co., Ltd. may be used.

[0058]

[0059] In formula (S3), R 5 are each independently preferably an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 10 carbon atoms. 6 are each independently preferably an alkoxy group or a halogen atom.

[0060] Furthermore, the compound represented by formula (S3) above is preferably a compound capable of forming trimethylsilyl or triethylsilyl groups on the surface of silica particles. Examples of such compounds include those represented by the following formulas (S3'-1) to (S3'-2).

[0061]

[0062] In the above formula, R 51 is an alkoxy group, and specific examples thereof include those exemplified above, such as a methoxy group and an ethoxy group. As the silane compound, a commercially available product can be used, and for example, a silane compound manufactured by Shin-Etsu Chemical Co., Ltd. can be used.

[0063] Specific examples of the compound represented by formula (S3) include, but are not limited to, compounds represented by the following formulas (S3-1) to (S3-4).

[0064]

[0065] In formula (S4), R 7 are preferably each independently an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group.

[0066] Specific examples of the compound represented by formula (S4) include, but are not limited to, the compound represented by formula (S4-1) below.

[0067]

[0068] In formula (S5), R 8 As the alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group is preferred.

[0069] In formula (S6), R 9 As the alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group is preferred.

[0070] Specific examples of the compound represented by formula (S6) include, but are not limited to, the compound represented by formula (S6-1) below.

[0071]

[0072] In formula (S7), R 10 R is preferably an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group. 11 As the alkyl group, a hydrogen atom, an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group is preferred.

[0073] In formula (S8), R 12 R is preferably an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group. 13 As the alkyl group, a hydrogen atom, an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group is preferred.

[0074] Specific examples of the compound represented by formula (S8) include, but are not limited to, the compound represented by formula (S8-1) below.

[0075]

[0076] In formula (S9), R 14 are preferably each independently an alkyl group, an alkenyl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, a ureido group, or a thioureido group.

[0077] The surface-treated metal oxide nanoparticles can be produced by coating the surface of colloidal metal oxide nanoparticles (core particles) having a primary particle diameter within the above range with the desired metal oxide (metal oxide-coated nanoparticles), and then coating the surface of the metal oxide with a surface treatment agent. Known methods can be used for producing colloidal metal oxide nanoparticles and for coating the surface of the metal oxide nanoparticles with a metal oxide. Examples of known methods include those described in Japanese Patent Nos. 4,561,955, 4,730,487, and 5,704,345. Known methods can also be used for coating the surface of the metal oxide with a surface treatment agent. Examples of known methods include those described in Japanese Patent No. 5,704,345.

[0078] Furthermore, from the viewpoint of improving the charge transport properties of the resulting thin film, metal oxide-coated nanoparticles in which the surfaces of core particles are coated with a metal oxide are preferably hydrothermally treated metal oxide-coated nanoparticles that have been subjected to hydrothermal treatment in the production process. In the present invention, examples of the hydrothermal treatment method include Methods 1 and 2 below. Method 1: A method in which metal oxide nanoparticles before surface coating are subjected to hydrothermal treatment to obtain hydrothermally treated metal oxide nanoparticles, and the surfaces of the hydrothermally treated metal oxide nanoparticles are coated with a metal oxide. Method 2: A method in which metal oxide-coated nanoparticles obtained by coating the surfaces of metal oxide nanoparticles (not subjected to hydrothermal treatment) with a metal oxide are further subjected to hydrothermal treatment to obtain hydrothermally treated metal oxide-coated nanoparticles.

[0079] When the hydrothermal treatment is carried out, the temperature is preferably 60 to 180° C. The treatment time is preferably 0.1 to 50 hours.

[0080] The surface treatment of the metal oxide-coated nanoparticles with a surface treatment agent can be carried out by adding the surface treatment agent to a dispersion of the metal oxide-coated nanoparticles and heating the mixture at a predetermined temperature. If the dispersion medium of the metal oxide-coated nanoparticles is not suitable for use with the surface treatment agent, it can be replaced with an appropriate solvent.

[0081] The surface treatment can be carried out at a temperature ranging from 20° C. to the boiling point of the dispersion medium, preferably 20 to 100° C. The treatment time is preferably about 0.1 to 48 hours.

[0082] The amount of the surface treatment agent used is preferably 1 to 50% by mass, more preferably 5 to 30% by mass, based on the mass of the metal oxide-coated nanoparticles, from the viewpoint of reliably coating the surfaces of the metal oxide-coated nanoparticles.

[0083] When the compounds (silane compounds) represented by formulae (S1) to (S3) are used as the surface treatment agents, water is required for the hydrolysis of these silane compounds. However, when an aqueous medium is substituted with an organic solvent, the water remaining in the solvent can be used. For example, water present in an amount of 0.01 to 10% by mass can be used. Furthermore, the hydrolysis can be carried out with or without a catalyst.

[0084] The surface-treated metal oxide nanoparticles contained in the charge transport ink composition of the present invention may be of one type alone or two or more types.

[0085] The surface-treated metal oxide nanoparticles contained in the charge transport ink composition of the present invention are preferably uniformly dispersed in the composition.

[0086] The surface-treated metal oxide nanoparticles may contain one or more organic capping groups. The organic capping groups may be reactive or non-reactive. Examples of reactive organic capping groups include organic capping groups that can be crosslinked by ultraviolet light or a radical initiator.

[0087] The primary particle diameter of the surface-treated metal oxide nanoparticles is not particularly limited as long as it is nano-sized, but in consideration of obtaining a thin film with good reproducibility and excellent flatness, it is preferably 2 to 60 nm, more preferably 3 to 40 nm.

[0088] In the charge transport ink composition of the present invention, the content of the surface-treated metal oxide nanoparticles is not particularly limited, but from the viewpoint of suppressing particle aggregation in the charge transport ink composition and obtaining a thin film with excellent flatness and good reproducibility, the content is preferably 10 to 100 mass %, more preferably 20 to 100 mass %, even more preferably 30 to 100 mass %, and most preferably 40 to 100 mass %, of the solid content.

[0089] In particular, in the present invention, by using a surface-treated metal oxide nanoparticle sol in which surface-treated metal oxide nanoparticles are dispersed, a composition in which the surface-treated metal oxide nanoparticles are uniformly dispersed can be prepared with good reproducibility. Such a surface-treated metal oxide nanoparticle sol can be prepared by a known method using a solvent and surface-treated metal oxide nanoparticles that can be contained in the charge-transporting ink composition of the present invention.

[0090] In particular, when preparing the charge-transporting ink composition of the present invention, it is preferable to use a surface-treated metal oxide nanoparticle sol in which surface-treated metal oxide nanoparticles are dispersed in a dispersion medium. The surface-treated metal oxide nanoparticle sol is not particularly limited, as long as the surface-treated metal oxide nanoparticles are stably dispersed in a solvent. In the present invention, a surface-treated metal oxide nanoparticle sol having improved dispersibility in the charge-transporting ink composition may preferably be a surface-treated metal oxide nanoparticle sol containing surface-treated metal oxide nanoparticles having a core composed of one or more metal oxide nanoparticles selected from the group consisting of SnO and SnO-TiO-ZrO composites, the surface of the core being coated with a SnO-SiO composite (metal oxide), and the surface of the SnO-SiO composite being further coated with at least one surface-treating agent selected from the group consisting of compounds represented by the following formulas (S1) to (S9), and a solvent.

[0091] (In formula (S1), R1 are each independently an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and are bonded to a silicon atom by a Si—C bond; R 2 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and a represents an integer of 1 to 3. In formula (S2), R 3 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 4 each independently represents an alkoxy group, an acyloxy group, or a halogen atom; Y represents an alkylene group, an NH group, or an oxygen atom; b represents an integer of 1 to 3; and c is 0 or 1. In formula (S3), R 5 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms, and R 6 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and d represents an integer of 1 to 3. In formula (S4), R 7 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and e represents 1 or 2. 8 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 9 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 10represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 11 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 12 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 13 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and Z represents an oxygen atom or a sulfur atom. 14 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and f represents 1 or 2.

[0092] In formulas (S1) to (S9), R 1 ~R 14 , Y, and Z are the same as those exemplified in the description of the surface-treated metal oxide nanoparticles above.

[0093] The surface-treated metal oxide nanoparticle sol is usually in the form of a dispersion. Examples of the surface-treated metal oxide nanoparticle sol include a dispersion of surface-treated metal oxide nanoparticles in various solvents, such as alcohols, glycols, ketones, esters, ethers, amides, hydrocarbons, or mixtures thereof. Examples of alcohols include methanol, ethanol, n-propanol, i-propanol, n-butanol, 1-octanol, 1-nonanol, 1-decanol, tetrahydrofurfuryl alcohol, and terpineol. Examples of glycols include ethylene glycol, propylene glycol, 2-methyl-2,4-pentanediol, 1,3-octylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, and 3-methyl-1,5-pentanediol. Examples of ketones include acetone, acetylacetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, 4-hydroxy-4-methyl-2-pentanone, 2-heptanone, cyclohexanone, methylcyclopentanone, and isophorone. Examples of the ester include dimethyl carbonate, diethyl carbonate, propylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, dimethyl maleate, diethyl maleate, dipropyl maleate, dibutyl maleate, dimethyl adipate, diethyl adipate, dipropyl adipate, diisopropyl malonate, dimethyl sebacate, diethyl sebacate, and propylene glycol monomethyl ether acetate.Examples of ethers include dimethyl ether, ethyl methyl ether, diethyl ether, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-tert-butyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol butyl ether. Examples of amides include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-ethylpyrrolidone, and 1,3-dimethyl-2-imidazolidinone. Examples of hydrocarbons include n-hexane, n-heptane, n-octane, n-nonane, n-decane, i-octane, i-nonane, i-decane, and toluene.

[0094] In particular, in the present invention, surface-treated metal oxide nanoparticles in which the dispersion medium is methanol, ethanol, n-propanol, i-propanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, propylene carbonate, propylene glycol monomethyl ether acetate, ethyl acetate, butyl acetate, methyl methacrylate, diisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-tert-butyl ether, tripropylene glycol monomethyl ether, tripropylene glycol butyl ether, N,N-dimethylformamide, n-hexane, or toluene are preferred.

[0095] The solids concentration of the surface-treated metal oxide nanoparticle sol of the present invention is appropriately set taking into consideration the saturated solubility in the solvent, storage stability, etc., but is usually about 1 to 60 mass %, preferably about 3 to 55 mass %, and more preferably about 3 to 50 mass %.

[0096] The concentration of the surface-treated metal oxide nanoparticles in the charge-transporting ink composition is set appropriately taking into consideration the viscosity and surface tension of the charge-transporting ink composition, the thickness of the thin film to be produced, etc., but is usually about 0.1 to 30 mass %. If the concentration of the surface-treated metal oxide nanoparticles is high, the surface-treated metal oxide nanoparticles may aggregate depending on the type of solvent contained in the mixture, so this point must be taken into consideration when preparing the composition.

[0097] The charge transporting ink composition of the present invention contains an organic solvent. There are no particular limitations on the organic solvent as long as it disperses or dissolves solids. Specific examples include alcoholic solvents such as methanol, ethanol, n-propanol, i-propanol, n-butanol, 1-octanol, 1-nonanol, 1-decanol, tetrahydrofurfuryl alcohol, terpineol, cyclohexanol, diacetone alcohol, benzyl alcohol, 2-phenoxyethanol, and 2-benzyloxyethanol; ethylene glycol, propylene glycol, 2-methyl-2,4-pentanediol, 1,3-octylene glycol, diethylene glycol, and dipropylene glycol. Glycol-based solvents such as glycerol, triethylene glycol, tripropylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, and 3-methyl-1,5-pentanediol; ketone-based solvents such as acetone, acetylacetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, 4-hydroxy-4-methyl-2-pentanone, 2-heptanone, cyclohexanone, methylcyclopentanone, and isophorone;Dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-hexyl acetate, benzyl acetate, 2-hydroxyethyl acetate, methyl lactate, ethyl lactate, methyl propionate, ethyl propionate, propyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate, dimethyl maleate, diethyl maleate, dipropyl maleate, dibutyl maleate, dimethyl adipate, diethyl adipate, dipropyl adipate, diisopropyl malonate, dimethyl sebacate, diethyl sebacate, methyl benzoate, ethyl benzoate, butyl benzoate, dimethyl phthalate, dioxalate Ester-based solvents such as ethyl acetate, dibutyl oxalate, diethyl fumarate, ethylene glycol monomethyl ether acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, propylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, dipropylene glycol methyl ether acetate, 1,3-butylene glycol diacetate, 1,6-hexanediol diacetate, triacetin, and γ-butyrolactone; ether-based solvents such as dimethyl ether, ethyl methyl ether, diethyl ether, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, anisole, and 4-methoxytoluene;Glycol ether solvents such as ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol diglycidyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-tert-butyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol butyl ether solvents such as amide solvents, N-methylformamide, N-methylacetamide, N-methylformanilide, N,N-dimethylacetamide, N,N-dimethylformamide, N,N-dimethylisobutyramide, N-methyl-2-pyrrolidone, N-ethylpyrrolidone, and 1,3-dimethyl-2-imidazolidinone; aromatic or halogenated aromatic hydrocarbon solvents, such as benzene, toluene, xylene, ethylbenzene, cyclohexylbenzene, chlorobenzene, tetralin, and decylbenzene; aliphatic hydrocarbon solvents, such as n-hexane, n-heptane, n-octane, n-nonane, n-decane, i-octane, i-nonane, and i-decane; halogenated hydrocarbon solvents, such as methylene chloride, dichloromethane, 1,2-dichloroethane, and chloroform; and cyano solvents, such as acetonitrile and 3-methoxypropionitrile.The solvent may be appropriately selected from among sulfoxide solvents such as dimethyl sulfoxide. In the present invention, among these, alcohol solvents, glycol solvents, ketone solvents, ester solvents, and glycol ether solvents are preferred, and methanol, ethanol, 1-octanol, 1-nonanol, 1-decanol, terpineol, ethylene glycol, 2-methyl-2,4-pentanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 3-methyl-1,5-pentanediol, isophorone, propylene carbonate, dibutyl maleate, diethyl sebacate, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-tert-butyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol butyl ether are more preferred. These organic solvents may be used alone or in combination of two or more.

[0098] Furthermore, when forming a thin film using a charge transport ink composition, a composition that will result in a uniform film thickness is required. In particular, when forming a film using an inkjet method, a composition containing only a low-boiling-point solvent can make it difficult to obtain a flat layer depending on the conditions of use. In such cases, the use of a high-boiling-point solvent is thought to suppress solvent evaporation and reduce the rate of ink convection and viscosity increase, thereby resulting in a flat layer. In consideration of this, among the above-mentioned organic solvents, it is preferable to include at least one organic solvent with a boiling point of 200°C or higher, and it is more preferable to include at least one organic solvent with a boiling point of 230°C or higher. The upper limit of the boiling point is not particularly limited, but is usually 330°C or lower. When an organic solvent with a boiling point of 200°C or higher is included, its content is not particularly limited, but is preferably 20% by mass or higher in the organic solvent.

[0099] The charge transport ink composition of the present invention is best prepared using only an organic solvent as the solvent. In this case, "only an organic solvent" means that only an organic solvent is used as the solvent, and does not exclude the presence of trace amounts of water contained in the organic solvent or solids used.

[0100] The charge-transporting ink composition of the present invention contains the above-described surface-treated metal oxide nanoparticles and an organic solvent. In order to further improve the flatness and charge-transporting properties of the resulting thin film, the ink composition may contain a binder resin, as described below, as necessary.

[0101] The binder resin is not particularly limited as long as it disperses or dissolves in at least one solvent used in the charge transport ink composition, and a polymeric material can be used as the binder. By blending surface-treated metal oxide nanoparticles into the binder resin, excellent film-forming properties can be achieved and a stable film can be easily formed. Note that at least one type of binder resin is sufficient, and the number of types is not particularly limited.

[0102] Specific examples of the material that can be used include, but are not limited to, polystyrene, polyimide, polycarbonate, acrylic resin, and inactive resin.

[0103] Furthermore, the binder resin may have charge transport properties, or a charge transport material may be mixed into the binder resin. In these cases, the conductivity of the electron transport layer can be improved compared to when the binder resin is insulating. Although the surface-treated metal oxide nanoparticles themselves have sufficient charge transport properties, when minute nanoparticles are uniformly dispersed in the binder at a low concentration, the charge carried by the nanoparticles may not be transported effectively. Therefore, by using a material with charge transport properties as a material constituting the electron transport layer other than the surface-treated metal oxide nanoparticles, the high charge transport properties of the surface-treated metal oxide nanoparticles can be more effectively utilized.

[0104] When the charge-transporting ink composition of the present invention contains a binder resin, the content thereof is usually about 5 to 95% by mass of the solid content. However, taking into consideration the balance between improving the flatness of the thin film obtained and suppressing a decrease in charge transport properties, the content is preferably about 10 to 90% by mass, more preferably about 20 to 80% by mass, and even more preferably about 30 to 70% by mass.

[0105] The charge transport ink composition of the present invention may contain an organosilane compound or a phosphate ester compound. When a charge transport thin film obtained from the ink composition is used as an electron transport layer in an organic EL device or a quantum dot EL device, the inclusion of such an organosilane compound or a phosphate ester compound in the charge transport ink composition can improve the flatness of the obtained thin film and the electron transport properties to the light-emitting layer provided in contact with the thin film.

[0106] As the organic silane compound, alkoxysilanes are preferred, with trialkoxysilanes and tetraalkoxysilanes being more preferred. Examples of the alkoxysilane include tetraethoxysilane, tetramethoxysilane, tetraisopropoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, dimethyldiethoxysilane, and dimethyldimethoxysilane. Among these, tetraethoxysilane (TEOS), tetramethoxysilane, and tetraisopropoxysilane are preferred for use in the present invention. These organic silane compounds can be used alone or in combination of two or more. Furthermore, these organic silane compounds can be used in combination with the phosphate ester-based compounds described below.

[0107] The phosphate ester compound is preferably a compound represented by the following formulas (1) to (3), and more preferably a polyoxyethylene alkyl ether phosphate represented by the following formula (1). The polyoxyethylene alkyl ether phosphate ester is, for example, a compound represented by the following formula (1) where the terminal alkyl group (Y 1) represents an alkyl group having 6 to 15 carbon atoms. Commercially available phosphate ester compounds include, for example, Phosphanol RA-600, RS-410, RS-610, and RS-710, manufactured by Toho Chemical Industry Co., Ltd. These phosphate ester compounds can be used alone or in combination of two or more. Furthermore, these phosphate ester compounds can be used in combination with an organosilane compound.

[0108]

[0109] In formulas (1) to (3), X 1 , X 2 and X 3 each independently represents an alkylene group having 2 to 20 carbon atoms; f, h, and j each independently represent an integer of 1 to 100; e, g, and i each independently represent an integer of 1 to 3; Y 1 , Y 2 and Y 3 are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, or a (meth)acrylic group.

[0110] The alkylene group having 2 to 20 carbon atoms may be linear, branched, or cyclic, and specific examples include a methylmethylene group, a dimethylmethylene group, an ethylene group, a 1,2-dimethylethylene group, a tetramethylethylene group, a trimethylene group, a propylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a 1,2-cyclohexylene group, a 1,3-cyclohexylene group, and a 1,4-cyclohexylene group.

[0111] The alkyl group having 1 to 20 carbon atoms may be linear, branched, or cyclic, and specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a s-butyl group, a t-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, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadec ...octyl group, an n-pentyl group, an n-hexadecyl group, an n-heptadecyl group, an n-pentyl group, an n-hexadecyl group, an n-heptadecyl group, an n-pentyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadecyl group, an n-hexadec straight-chain or branched-chain alkyl groups having 1 to 20 carbon atoms, such as n-octadecyl, n-nonadecyl, and n-eicosanyl groups; and cyclic alkyl groups having 3 to 20 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, bicyclobutyl, bicyclopentyl, bicyclohexyl, bicycloheptyl, bicyclooctyl, bicyclononyl, and bicyclodecyl groups.

[0112] Examples of alkenyl groups having 2 to 20 carbon atoms include ethenyl, n-1-propenyl, n-2-propenyl, 1-methylethenyl, n-1-butenyl, n-2-butenyl, n-3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylethenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, n-1-pentenyl, n-1-decenyl, and n-1-eicosenyl groups.

[0113] Examples of the aryl group having 6 to 30 carbon atoms include a phenyl group, a tolyl group, a 1-naphthyl group, a 2-naphthyl group, a 1-anthryl group, a 2-anthryl group, a 9-anthryl group, a 1-phenanthryl group, a 2-phenanthryl group, a 3-phenanthryl group, a 4-phenanthryl group, a 9-phenanthryl group, a biphenyl-2-yl group, a biphenyl-3-yl group, and a biphenyl-4-yl group.

[0114] When the charge transport ink composition of the present invention contains an organic silane compound or a phosphate ester-based compound, the content thereof is usually about 0.1 to 50 mass % of the solid content. However, taking into consideration the balance between improving the flatness of the thin film obtained and suppressing a decrease in charge transport properties, the content is preferably about 0.5 to 40 mass %, more preferably about 0.8 to 30 mass %, and even more preferably about 1 to 20 mass %.

[0115] The viscosity of the charge transporting ink composition of the present invention is typically 1 to 50 mPa·s at 25° C., and the surface tension is typically 20 to 50 mN / m at 25° C. The viscosity and surface tension of the charge transporting ink composition of the present invention can be adjusted by changing the types of organic solvents used, their ratios, solids concentration, etc., taking into consideration various factors such as the dispersibility of the surface-treated metal oxide nanoparticles, the coating method used, and the desired film thickness.

[0116] The solids concentration of the charge transport ink composition of the present invention is set appropriately taking into consideration the viscosity and surface tension of the charge transport ink composition, the thickness of the thin film to be formed, and the like. However, it is usually about 0.1 to 30% by mass, and from the viewpoint of suppressing aggregation of the charge transport substance and surface-treated metal oxide nanoparticles in the ink composition, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0117] When preparing the charge-transporting ink composition of the present invention, the surface-treated metal oxide nanoparticles and organic solvent, and optionally, binder resins, organosilane compounds, phosphate ester compounds, etc., can be mixed in any order as long as the solids are uniformly dissolved or dispersed in the solvent. When the other components are included, for example, a method can be used in which previously prepared other components or their solutions are added to a sol of surface-treated metal oxide nanoparticles dispersed in a solvent. The above method can be used as long as the solids are uniformly dissolved or dispersed in the solvent. When using a binder resin, organosilane compound, or phosphate ester compound, these can be dissolved at any time during the above method. Note that the surface-treated metal oxide nanoparticles may aggregate or precipitate when mixed, depending on the type and amount of the components mixed with them. When preparing the charge-transporting ink composition, heating may be performed as appropriate within a range that does not cause decomposition or deterioration of the components.

[0118] In the present invention, the charge transporting ink composition may be filtered using a sub-micrometer filter or the like during the production of the charge transporting ink composition or after all of the components have been mixed, in order to obtain a thin film with higher flatness with good reproducibility.

[0119] The charge transporting ink composition described above can be applied to a substrate and baked to form a charge transporting thin film on the substrate.

[0120] The method for applying the ink composition is not particularly limited, and examples thereof include a dipping method, a spin coating method, a transfer printing method, a roll coating method, a brush coating method, an inkjet method, a spray method, and a slit coating method. It is preferable to adjust the viscosity and surface tension of the ink composition depending on the application method.

[0121] Furthermore, when using the charge transport ink composition of the present invention, the baking atmosphere is not particularly limited; a thin film having a uniform film surface and high charge transport properties can be obtained not only in air but also in an inert gas atmosphere such as nitrogen or in a vacuum. The baking temperature is appropriately set within a range of approximately 80 to 260°C, taking into consideration the application of the resulting thin film, the level of charge transport properties to be imparted to the resulting thin film, the type and boiling point of the solvent, etc. However, when the resulting thin film is used as an electron transport layer in an organic EL device or a quantum dot EL device, a temperature of approximately 100 to 250°C is preferred. During baking, the temperature may be changed in two or more stages to achieve more uniform film formation or to promote a reaction on the substrate. Heating may be performed using appropriate equipment, such as a hot plate, oven, or vacuum oven.

[0122] The thickness of the charge transport thin film is not particularly limited, but when used as a functional layer provided between a cathode and a light-emitting layer, such as an electron injection layer or electron transport layer of an organic EL device or a quantum dot EL device, it is preferably 5 to 300 nm, and more preferably 20 to 200 nm. Methods for changing the film thickness include changing the solids concentration in the charge transport ink composition and changing the amount of solution on the substrate during application.

[0123] The organic EL element or quantum dot EL element of the present invention has a pair of electrodes and a charge transport layer between these electrodes, which is made of the charge transport thin film of the present invention. Typical configurations of organic EL elements or quantum dot EL elements include, but are not limited to, the following (a) to (f). The charge transport ink composition of the present invention can be suitably employed in elements having the configurations (a) to (d) among these. In the configurations described below, an electron blocking layer or the like can be provided between the light-emitting layer and the anode, and a hole blocking layer or the like can be provided between the light-emitting layer and the cathode, as necessary. Furthermore, the hole injection layer, hole transport layer, or hole injection transport layer may also function as an electron blocking layer, and the electron injection layer or electron transport layer may also function as a hole blocking layer. Furthermore, an optional functional layer can be provided between each layer as necessary. (a) anode / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / electron injection layer / cathode (b) anode / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / cathode (c) anode / hole injection transport layer / light-emitting layer / electron transport layer / electron injection layer / cathode (d) anode / hole injection transport layer / light-emitting layer / electron transport layer / cathode (e) anode / hole injection layer / hole transport layer / light-emitting layer / cathode (f) anode / hole injection transport layer / light-emitting layer / cathode

[0124] The terms "hole injection layer," "hole transport layer," and "hole injection transport layer" refer to layers formed between the light-emitting layer and the anode, which have the function of transporting holes from the anode to the light-emitting layer. When only one layer of a hole-transporting material is provided between the light-emitting layer and the anode, it is the "hole injection transport layer." When two or more layers of a hole-transporting material are provided between the light-emitting layer and the anode, the layer closest to the anode is the "hole injection layer," and the remaining layers are "hole transport layers." In particular, the hole injection (transport) layer is a thin film that is excellent not only in the ability to accept holes from the anode but also in the ability to inject holes into the hole transport (light-emitting) layer.

[0125] An "electron injection layer" and an "electron transport layer" are layers formed between the light-emitting layer and the cathode and have the function of transporting electrons from the cathode to the light-emitting layer. When only one layer of an electron-transporting material is provided between the light-emitting layer and the cathode, it is the "electron transport layer." When two or more layers of electron-transporting material are provided between the light-emitting layer and the cathode, the layer closest to the cathode is the "electron injection layer" and the other layers are "electron transport layers." An "light-emitting layer" is a layer having a light-emitting function and may be an organic light-emitting layer or a quantum dot light-emitting layer. Correspondingly, when the light-emitting layer is an organic light-emitting layer EL element, it is an organic EL element, and when the light-emitting layer is a quantum dot light-emitting layer EL element, it is a quantum dot EL element.

[0126] The charge transporting thin film prepared from the charge transporting ink composition of the present invention can be used as a functional layer formed between a cathode and an emitting layer in an organic EL device or a quantum dot EL device, but is suitable as an electron injection layer or an electron transport layer, and is more suitable as an electron transport layer.

[0127] When an EL device is produced using the charge transporting ink composition of the present invention, the materials and production methods used include, but are not limited to, those listed below.

[0128] An example of a method for producing an organic EL device or a quantum dot EL device having an electron transport layer made of a thin film obtained from the charge transport ink composition of the present invention is as follows. It is preferable to previously perform surface treatment on the electrodes, such as cleaning with alcohol, pure water, or the like, or UV ozone treatment, oxygen plasma treatment, or the like, to the extent that the electrode is not adversely affected. A hole injection layer and a hole transport layer are sequentially laminated on an anode substrate by a wet process using a hole injection layer-forming composition or a hole transport layer-forming composition containing a hole transport polymer. Next, an emissive layer is laminated by a wet process using an emissive layer-forming composition containing a light-emitting polymer or a quantum dot material. Furthermore, an electron transport layer is formed by a wet process using the charge transport ink composition of the present invention, and a cathode metal is vapor-deposited thereon. Alternatively, in this method, instead of forming the hole injection layer, hole transport layer, and emissive layer by a wet process, these layers can also be formed by vapor deposition. If necessary, an electron blocking layer may be provided between the emissive layer and the hole transport layer. In the above, an example (forward structure) in which an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode are stacked in this order has been described, but the present invention is not limited thereto, and a reverse structure in which a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an anode are stacked in this order may also be used.

[0129] Examples of anode materials include transparent electrodes such as indium tin oxide (ITO) and indium zinc oxide (IZO), metal anodes such as aluminum, and metal anodes composed of alloys thereof, and those that have undergone planarization treatment are preferred. Polythiophene derivatives and polyaniline derivatives with high charge transport properties can also be used. Other metals that can be used to compose the metal anode include, but are not limited to, gold, silver, copper, indium, and alloys thereof.

[0130] Examples of hole-transporting polymers include poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(N,N'-bis{p-butylphenyl}-1,4-diaminophenylene)], poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N'-bis{p-butylphenyl}-1,1'-biphenylene-4,4-diamine)], poly[(9,9-bis{1'-penten-5'-yl}fluorenyl-2,7-diyl)-co-(N,N'-bis{p-butylphenyl}-1,4-diaminophenylene)], and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine]-endcapped with Examples include, but are not limited to, polysilcisquinoxane, poly[(9,9-didioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)], and the like.

[0131] Examples of the light-emitting polymer include, but are not limited to, polyfluorene derivatives such as poly(9,9-dialkylfluorene) (PDAF), polyphenylenevinylene derivatives such as poly(p-phenylenevinylene) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), polythiophene derivatives such as poly(3-alkylthiophene) (PAT), and polyvinylcarbazole (PVCz).

[0132] The quantum dot material may include at least one semiconductor material selected from the group consisting of II-VI semiconductors, III-V semiconductors, I-III-VI semiconductors, IV semiconductors, and I-II-IV-VI semiconductors. Specific examples of the semiconductor material include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, and CdHgZnT. e, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe; GaN, GaP, GaAs, G aSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, Ga InNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb; SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnS Examples of suitable gallium arsenide include, but are not limited to, Cu ...

[0133] Examples of materials for forming the hole injection layer include copper phthalocyanine, titanium oxide phthalocyanine, platinum phthalocyanine, pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile, N,N,N',N'-tetrakis(4-methoxyphenyl)benzidine, 2,7-bis[N,N-bis(4-methoxy-phenyl)amino]-9,9-spirobifluorene, 2,2'-bis[N,N-bis(4-methoxy-phenyl)amino]-9,9-spirobifluorene, N,N'-diphenyl-N,N'-di[4-(N,N-ditolylamino)phenyl]benzidine, N,N'-diphenyl-N,N'-di[4-(N,N-diphenylamino)phenyl]benzidine, N 4 , N 4 '-(biphenyl-4,4'-diyl)bis(N 4 , N 4 ', N 4 '-triphenylbiphenyl-4,4'-diamine)N 1 , N 1 '-(biphenyl-4,4'-diyl)bis(N 1 -phenyl-N 4 , N 4'-di-m-tolylbenzene-1,4-diamine), WO 2004 / 043117, WO 2004 / 105446, WO 2005 / 000832, WO 2005 / 043962, WO 2005 / 042621, WO 2005 / 107335, WO 2006 / 006459, WO 2006 / 025342, WO 2006 / 137473, WO 2007 / 049631, WO 2007 / 099808, WO 2008 / 010474, WO 2008 / 03 2617, WO 2008 / 032616, WO 2008 / 129947, WO 2009 / 096352, WO 2010 / 041701, WO 2010 / 058777, WO 2010 / 058776, WO 2013 / 042623, WO 2013 / 129249, WO 2014 / 115865, WO 2014 / 132917, WO 2014 / 141998 and WO 2014 / 132834, and the like. However, it is not limited to these.

[0134] Examples of materials for forming the hole transport layer include, but are not limited to, triarylamines such as (triphenylamine) dimer derivatives, [(triphenylamine) dimer] spiro dimer, N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (α-NPD), 4,4',4"-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA), and 4,4',4"-tris[1-naphthyl(phenyl)amino]triphenylamine (1-TNATA), and oligothiophenes such as 5,5"-bis-{4-[bis(4-methylphenyl)amino]phenyl}-2,2':5',2"-terthiophene (BMA-3T).

[0135] Examples of materials for forming the light-emitting layer include, but are not limited to, low-molecular-weight light-emitting materials such as metal complexes (e.g., aluminum complexes of 8-hydroxyquinoline), metal complexes of 10-hydroxybenzo[h]quinoline, bisstyrylbenzene derivatives, bisstyrylarylene derivatives, metal complexes of (2-hydroxyphenyl)benzothiazole, and silole derivatives; and systems in which a light-emitting material and an electron transfer material are mixed with a polymer compound (e.g., poly(p-phenylenevinylene), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], poly(3-alkylthiophene), or polyvinylcarbazole. Furthermore, when the light-emitting layer is formed by vapor deposition, it may be co-deposited with a light-emitting dopant. Examples of light-emitting dopants include, but are not limited to, metal complexes (e.g., tris(2-phenylpyridine)iridium(III) (Ir(ppy)), naphthacene derivatives (e.g., rubrene), quinacridone derivatives, and fused polycyclic aromatic rings (e.g., perylene).

[0136] Cathode materials include, but are not limited to, aluminum, magnesium-silver alloy, aluminum-lithium alloy, etc. Materials for forming the electron blocking layer include, but are not limited to, tris(phenylpyrazole)iridium, etc.

[0137] The materials constituting the anode, cathode, and layers formed therebetween differ depending on whether an element having a bottom emission structure or a top emission structure is manufactured, and therefore, materials are selected appropriately taking this into consideration. Normally, in an element having a bottom emission structure, a transparent anode is used on the substrate side, and light is extracted from the substrate side, whereas in an element having a top emission structure, a reflective anode made of metal is used, and light is extracted from the transparent electrode (cathode) side opposite the substrate. Therefore, for example, in terms of anode materials, when an element having a bottom emission structure is manufactured, a transparent anode such as ITO is used, and when an element having a top emission structure is manufactured, a reflective anode such as an Ag alloy or an Al alloy is used.

[0138] The organic EL element of the present invention may be sealed, if necessary, with a moisture scavenger or the like in accordance with a conventional method in order to prevent deterioration of the characteristics.

[0139] As described above, the charge transport ink composition of the present invention is suitably used for forming a functional layer formed between the cathode and light-emitting layer of an organic EL element or a quantum dot EL element, but it can also be used for forming a charge transport thin film in electronic elements such as organic photoelectric conversion elements, organic thin-film solar cells, organic perovskite photoelectric conversion elements, organic integrated circuits, organic field-effect transistors, organic thin-film transistors, organic light-emitting transistors, organic optical inspectors, organic photoreceptors, organic field quenching elements, light-emitting electrochemical cells, quantum lasers, organic laser diodes, and organic plasmon light-emitting elements. In particular, it can be suitably used in organic EL elements and quantum dot EL elements.

[0140] The improvement in flatness of the charge-transporting thin film can be evaluated by the arithmetic mean surface roughness Ra. Specifically, the charge-transporting thin film formed on the substrate can be measured using a known micro-profile measuring instrument, for example, a Surfcorder ET-4000 manufactured by Kosaka Laboratory Co., Ltd. In the present invention, the arithmetic mean surface roughness Ra (nm) is usually 10.0 nm or less, in a preferred embodiment, 4.0 nm or less, in a more preferred embodiment, 2.0 nm or less, and in an even more preferred embodiment, 1.0 nm or less.

[0141] The present invention will be described in more detail below with reference to Production Examples, Examples, and Comparative Examples, but the present invention is not limited thereto. The apparatuses used in the Examples are as follows.

[0142] (1) Evaluation of primary particle size by transmission electron microscope Apparatus: JEM-1010 transmission electron microscope manufactured by JEOL Ltd. (2) Evaluation of average particle size by dynamic light scattering Apparatus: Zetasizer NanoS manufactured by Malvern Instruments Ltd. (3) Substrate cleaning Apparatus: Substrate cleaning apparatus (low pressure plasma method) manufactured by Choshu Sangyo Co., Ltd. (4) Spin coating Apparatus: Spin Coater MS-A100 manufactured by Mikasa Co., Ltd. (5) Evaluation of flatness of charge transport thin film Apparatus: Surfcorder ET-4000 microprofile measuring instrument manufactured by Kosaka Laboratory Co., Ltd.

[0143] [1] Production of Surface-Treated Metal Oxide Nanoparticle Sol [Reference Example 1] Preparation of Aqueous Dispersion Sol (A) of Core Titanium Oxide-Zirconium Oxide-Tin Oxide Colloidal Particles 104.4 kg (28.6 kg in terms of TiO) of titanium tetrachloride (equivalent to 27.2% by mass in terms of TiO, 32.0% by mass in terms of Cl, manufactured by Sumitomo Sitix Co., Ltd.) and 182.0 kg of water were placed in a reaction vessel equipped with a stirring blade to prepare 286.4 kg of aqueous titanium chloride solution (10.0% by mass in terms of TiO). 10.56 kg (4.4 kg in terms of ZrO) of zirconium carbonate (41.7% by mass in terms of ZrO) was then added to prepare a titanium chloride-zirconium carbonate composite aqueous solution. This aqueous solution was heated to 60°C while stirring in a reaction vessel equipped with a stirring blade. Then, while cooling, 132.1 kg of 35% by mass aqueous hydrogen peroxide (industrial grade) and 80.5 kg of metallic tin powder (manufactured by Yamaishi Metals Co., Ltd., product name AT-Sn, No. 200) were added in portions according to the procedure described below. First, 7.34 kg of aqueous hydrogen peroxide was gradually added, followed by 4.47 kg of metallic tin. After waiting for the reaction resulting from the addition to be complete (15 to 20 minutes), 7.34 kg of aqueous hydrogen peroxide was gradually added, followed by 4.47 kg of metallic tin. This process of adding aqueous hydrogen peroxide followed by metallic tin was repeated 18 times at intervals of 15 to 20 minutes, resulting in 18 separate additions (7.34 kg of aqueous hydrogen peroxide and 4.47 kg of metallic tin). After the separate additions were completed, 9.00 kg of aqueous hydrogen peroxide was added. The mixture was then stirred and heated at 90°C for 3 hours. This step yielded 518.6 kg of an aqueous solution of titanium-zirconium-tin composite salt. 1,091 kg of water was added to 259.3 kg of the obtained aqueous solution of titanium-zirconium-tin composite salt for dilution. Thereafter, 2.00 kg of aqueous hydrogen peroxide was added. This aqueous solution was subjected to hydrolysis at 96 to 98°C for 10 hours to obtain a slurry of aggregates of titanium oxide-zirconium oxide-tin oxide composite colloid. The obtained slurry of aggregates of titanium oxide-zirconium oxide-tin oxide composite colloid was subjected to repeated cycles of concentration using approximately 12,000 L of water, water injection, and concentration, and the excess electrolyte was removed by washing, followed by peptization to obtain 1,298 kg of an acidic aqueous sol of titanium oxide-zirconium oxide-tin oxide composite sol.The obtained sol was a water-dispersed sol (A) of titanium oxide-zirconium oxide-tin oxide composite colloid, and had a total metal oxide concentration (TiO2, ZrO2, and SnO2) of 4.9 mass % and a primary particle diameter of 3 to 10 nm as determined by observation with a transmission electron microscope.

[0144] Reference Example 2 Preparation of Silicon Dioxide-Stannic Oxide Composite Oxide Colloidal Particles (B1) to Be Used as a Coating Material 77.2 g of JIS No. 3 sodium silicate (containing 29.8% by mass, calculated as SiO) was dissolved in 668.8 g of pure water, followed by the dissolution of 20.9 g of sodium stannate NaSnO3·H2O (containing 55.1% by mass, calculated as SnO2). The resulting aqueous solution was passed through a column packed with a hydrogen cation exchange resin. 7.2 g of diisopropylamine was then added to the resulting aqueous sol. The resulting sol was an aqueous dispersion of silicon dioxide-stannic oxide composite oxide colloidal particles (B1), with a total metal oxide concentration (SnO2 and SiO2) of 2.8% by mass and a primary particle size of 1 to 4 nm as determined by observation with a transmission electron microscope.

[0145] Reference Example 3: Preparation of antimony pentoxide colloidal particles (B2) to be used as a coating material. 12.5 kg of antimony trioxide (containing 99.5% by mass as SbO), 66.0 kg of pure water, and 12.5 kg of potassium hydroxide (containing 95% by mass as KOH) were added to a 100 L vessel, and 8.4 kg of 35% by mass hydrogen peroxide was gradually added with stirring. 17.6 kg of the resulting potassium antimonate aqueous solution was diluted to 2.2% by mass and passed through a column packed with hydrogen cation exchange resin. 0.25 kg of diisopropylamine was added to the ion-exchanged antimonic acid solution with stirring. The resulting sol was an aqueous dispersion sol of antimony pentoxide colloidal particles (B2). The SbO concentration was 1.5% by mass, and the primary particle diameter was 1 to 10 nm as observed with a transmission electron microscope.

[0146] Production Example 1 167.8 g of water was added to 272.2 g of the aqueous dispersion sol (A) of the acidic titanium oxide-zirconium oxide-tin oxide composite aqueous sol prepared in Reference Example 1, and the mixture was diluted to a total metal oxide (TiO, ZrO, and SnO) concentration of 3 mass%. 0.39 g of isopropylamine was added to the diluted aqueous sol, and the mixture was passed through a column packed with 450 mL of anion exchange resin (Amberlite IRA-410, manufactured by Organo Corporation) to obtain 559.8 g of an alkaline titanium oxide-zirconium oxide-tin oxide composite aqueous sol. To this alkaline titanium oxide-zirconium oxide-tin oxide composite aqueous sol was added 61.7 g of an aqueous dispersion sol of silicon dioxide-stannic oxide composite oxide colloidal particles (B1) prepared in Reference Example 2 (1.7 g of total metal oxide concentration (SnO2 and SiO2), 15% by mass relative to the core particles), and the mixture was then aged at 95°C for 5 hours to obtain an aqueous dispersion sol (C1) of stannic oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide. The obtained aqueous dispersion sol was then passed through a column packed with a hydrogen cation exchange resin. 0.2 g of tri-n-pentylamine was added to the obtained aqueous dispersion sol, and the mixture was concentrated by ultrafiltration membrane method. The resulting sol was an aqueous dispersion sol (C1) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide, with a total metal oxide (TiO2, ZrO2, SnO2, and SiO2) concentration of 1.78% by mass and an average particle size of 28 nm as measured by dynamic light scattering (DLS). 307 g of the aqueous dispersion sol (C1) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide was evaporated with methanol to obtain a methanol dispersion sol (C2) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide. The resulting sol had a total metal oxide (TiO2, ZrO2, SnO2, and SiO2) concentration of 12.3% by mass and an average particle size of 28 nm as measured by dynamic light scattering (DLS).

[0147] Production Example 2 445 g of water and 255 g of the aqueous dispersion sol of antimony pentoxide colloidal particles (B2) prepared in Reference Example 3 (4.54 g as a total metal oxide concentration (SbO), 7% by mass relative to the core particles) were added to 1,298 g of the aqueous dispersion sol (A) of the acidic titanium oxide-zirconium oxide-tin oxide composite aqueous sol prepared in Reference Example 1 to prepare a mixed slurry. This mixed slurry was passed through a column packed with 450 ml of anion exchange resin (Amberlite IRA-410, manufactured by Organo Corporation), to obtain 2,300 g of an alkaline titanium oxide-zirconium oxide-tin oxide composite aqueous sol mixed with antimony pentoxide colloidal particles. To this alkaline titanium oxide-zirconium oxide-tin oxide composite aqueous sol containing antimony pentoxide colloidal particles, 291 g of the water-dispersed sol of antimony pentoxide colloidal particles (B2) prepared in Reference Example 2 (5.18 g in terms of total metal oxide concentration (SbO), 8% by mass relative to the core particles) was added, and the mixture was then aged at 95°C for 3 hours to obtain a water-dispersed sol (C3) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with antimony pentoxide colloidal particles. The resulting water-dispersed sol was concentrated by ultrafiltration membrane. The resulting sol was a water-dispersed sol of titanium oxide-zirconium oxide-tin oxide colloidal particles (C1) coated with antimony pentoxide colloidal particles, and had a total metal oxide (TiO, ZrO, SnO, and SbO) concentration of 15% by mass and an average particle diameter of 25 nm as measured by dynamic light scattering (DLS). 495 g of the aqueous dispersion sol (C3) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with antimony pentoxide colloidal particles was replaced with methanol using a rotary evaporator to obtain a methanol dispersion sol (C4) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with antimony pentoxide colloidal particles. The resulting sol had a total metal oxide (TiO2, ZrO2, SnO2, and Sb2O5) concentration of 35 mass% and an average particle diameter of 26 nm as measured by dynamic light scattering (DLS).

[0148] [Production Example 3] 7.8 g of methanol was added to 34 g of the methanol-dispersed sol (C2) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide prepared in Production Example 1, and the mixture was diluted to a total metal oxide (TiO2, ZrO2, SnO2, and SiO2) concentration of 10% by mass. 10 g of this diluted methanol-dispersed sol was removed from a reaction vessel. 0.2 g of hexyltrimethoxysilane (Tokyo Chemical Industry Co., Ltd.) was then added to the reaction vessel, followed by heating under reflux and stirring at 65°C for 15 hours. This procedure yielded a methanol-dispersed sol (C5) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide that had been surface-treated with hexyltrimethoxysilane. The resulting sol had an average particle diameter of 24 nm as determined by dynamic light scattering (DLS).

[0149] [Production Examples 4 to 6] Methanol-dispersed sols (C6 to C8) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with silicon dioxide-stannic oxide composite oxide that had been surface-treated with each compound were obtained in the same manner as in Production Example 3, except that [3-(2-methoxyethoxy)propyl]trimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name X-12-641), (3-mercaptopropyl)triethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.), and 3-mercaptopropyl(dimethoxy)methylsilane (manufactured by Tokyo Chemical Industry Co., Ltd.) were used instead of hexyltrimethoxysilane. The average particle diameters of the resulting sols, measured by dynamic light scattering (DLS), were 24 nm, 26 nm, and 23 nm, respectively.

[0150] [Production Example 7] 13 g of the methanol dispersion sol (C4) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with antimony pentoxide colloidal particles prepared in Production Example 2 was diluted with 32.5 g of methanol to a total metal oxide (TiO2, ZrO2, SnO2, and Sb2O5) concentration of 10% by mass. 10 g of this diluted methanol dispersion sol was removed from a reaction vessel. 0.2 g of propionic acid (Kanto Chemical Co., Inc.) was then added to the reaction vessel, followed by heating under reflux and stirring at 65°C for 15 hours. This procedure yielded a methanol dispersion sol (C9) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with antimony pentoxide colloidal particles surface-treated with propionic acid. The resulting sol had an average particle diameter of 25 nm as determined by dynamic light scattering (DLS).

[0151] Production Example 8 A methanol-dispersed sol (C10) of titanium oxide-zirconium oxide-tin oxide colloidal particles coated with antimony pentoxide colloidal particles that had been surface-treated with each compound was obtained in the same manner as in Production Example 3, except that N,N'-diethylthiourea (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of propionic acid. The average particle diameter of the obtained sol was 22 nm as measured by dynamic light scattering (DLS).

[0152] [2] Preparation of Charge-Transporting Ink Composition [Example 1-1] 0.1 g of the C5 sol prepared in Production Example 3 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition.

[0153] Examples 1-2 to 1-8 Charge transporting ink compositions were prepared in the same manner as in Example 1-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0154] Example 2-1 0.1 g of the C6 sol prepared in Production Example 4 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge transporting ink composition.

[0155] Examples 2-2 to 2-8 Charge transporting ink compositions were prepared in the same manner as in Example 2-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0156] Example 3-1 0.1 g of the C7 sol prepared in Production Example 5 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge transporting ink composition.

[0157] Examples 3-2 to 3-8 Charge transporting ink compositions were prepared in the same manner as in Example 3-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0158] Example 4-1 0.1 g of the C8 sol prepared in Production Example 6 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge transporting ink composition.

[0159] Examples 4-2 to 4-8 Charge transporting ink compositions were prepared in the same manner as in Example 4-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0160] Example 5-1 0.1 g of the C9 sol prepared in Production Example 7 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge transporting ink composition.

[0161] Examples 5-2 to 5-8 Charge-transporting ink compositions were prepared in the same manner as in Example 5-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0162] Example 6-1 0.1 g of the C10 sol prepared in Production Example 8 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge transporting ink composition.

[0163] Examples 6-2 to 6-8 Charge transporting ink compositions were prepared in the same manner as in Example 4-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0164] Comparative Example 1-1 0.2 g of the sol A prepared in Reference Example 1 was added to 1.60 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge transporting ink composition.

[0165] Comparative Examples 1-2 to 1-8 Charge-transporting ink compositions were prepared in the same manner as in Example 4-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0166] The dispersion state of the charge transporting ink compositions prepared in Examples 1-1 to 1-8, 2-1 to 2-8, 3-1 to 3-8, 4-1 to 4-8, 5-1 to 5-8, 6-1 to 6-8, and Comparative Examples 1-1 to 1-8 was visually observed and judged based on the following criteria. The results are shown in Tables 1 and 2. <Judgment Criteria> ○: A colorless, transparent liquid or a liquid with a slight colloidal color, judged to have dispersibility ×: A cloudy liquid or a liquid in which particles precipitated, judged to have no dispersibility

[0167]

[0168]

[0169] As shown in Tables 1 and 2, charge transport ink compositions containing surface-treated metal oxide nanoparticles, which have specific metal oxide nanoparticles as nuclei and whose surfaces are coated with metal oxide and further treated with an organic substance, remained colorless and transparent or had a slight colloidal color even after mixing with an organic solvent, demonstrating good dispersibility. On the other hand, charge transport ink compositions containing metal oxide nanoparticles whose surfaces were not coated with metal oxide and further not treated with an organic substance showed cloudiness and precipitation after mixing with an organic solvent, demonstrating poor dispersibility. From the above, a charge transport ink composition with high dispersibility in organic solvents was obtained from the present invention.

[0170] [3] Preparation of Charge-Transporting Thin Film [Example 7-1] 0.50 g of the C5 sol prepared in Production Example 3 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, dried at 120°C for 1 minute, and then the substrate was moved into a glove box and baked at 200°C for 15 minutes under nitrogen to form a charge-transporting thin film with a thickness of 50 nm on the substrate. Note that the ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0171] Examples 7-2 to 7-8 Charge-transporting thin films were formed in the same manner as in Example 7-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0172] Example 8-1: 0.50 g of the C6 sol prepared in Production Example 4 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, then dried at 120°C for 1 minute. The substrate was then moved into a glove box and baked at 200°C for 15 minutes under nitrogen, forming a charge-transporting thin film with a thickness of 50 nm on the substrate. The ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0173] Examples 8-2 to 8-8 Charge-transporting thin films were formed in the same manner as in Example 8-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0174] Example 9-1: 0.50 g of the C7 sol prepared in Production Example 5 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, dried at 120°C for 1 minute, and then the substrate was moved into a glove box and baked at 200°C for 15 minutes under nitrogen to form a charge-transporting thin film with a thickness of 50 nm on the substrate. Note that the ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0175] Examples 9-2 to 9-8 Charge-transporting thin films were formed in the same manner as in Example 9-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0176] Example 10-1: 0.50 g of the C8 sol prepared in Production Example 6 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, dried at 120°C for 1 minute, and then the substrate was moved into a glove box and baked at 200°C for 15 minutes under nitrogen to form a charge-transporting thin film with a thickness of 50 nm on the substrate. Note that the ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0177] Examples 10-2 to 10-8 Charge-transporting thin films were formed in the same manner as in Example 11-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0178] Example 11-1: 0.50 g of the C9 sol prepared in Production Example 7 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, dried at 120°C for 1 minute, and then the substrate was moved into a glove box and baked at 200°C for 15 minutes under nitrogen, forming a charge-transporting thin film with a thickness of 50 nm on the substrate. Note that the ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0179] Examples 11-2 to 11-8 Charge-transporting thin films were formed in the same manner as in Example 12-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0180] Example 12-1: 0.50 g of the C10 sol prepared in Production Example 8 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, dried at 120°C for 1 minute, and then the substrate was moved into a glove box and baked at 200°C for 15 minutes under nitrogen, forming a charge-transporting thin film with a thickness of 50 nm on the substrate. Note that the ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0181] Examples 12-2 to 12-8 Charge-transporting thin films were formed in the same manner as in Example 12-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol.

[0182] Comparative Example 2-1: 1.20 g of the sol A prepared in Reference Example 1 was added to 1.00 g of methanol, stirred, and filtered through a PP syringe filter with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition was applied to an ITO-glass substrate using a spin coater, dried at 120°C for 1 minute, and then the substrate was moved into a glove box and baked at 200°C for 15 minutes under nitrogen, forming a charge-transporting thin film with a thickness of 50 nm on the substrate. Note that the ITO-glass substrate was used after removing impurities from its surface using a plasma cleaning device (150 W, 30 seconds).

[0183] [Comparative Examples 2-2 to 2-8] Charge-transporting ink compositions were prepared in the same manner as in Comparative Example 2-1, except that dipropylene glycol, 2-methyl-2,4-pentanediol, triethylene glycol monomethyl ether, isophorone, propylene carbonate, ethylene glycol, and triethylene glycol dimethyl ether were used instead of methanol. However, when isophorone, propylene carbonate, and triethylene glycol dimethyl ether were used, ink compositions could not be prepared.

[0184] The flatness of the charge transport thin film was evaluated by the following method. The arithmetic mean surface roughness Ra of the charge transport thin film was evaluated using a micro-profile measuring instrument for the spin-coated films obtained in Examples 7-1 to 7-8, 8-1 to 8-8, 9-1 to 9-8, 10-1 to 10-8, 11-1 to 11-8, 12-1 to 12-8, Comparative Examples 2-1 to 2-4, and 2-7. The measurement range of the micro-profile measuring instrument was 0.2 mm (0.05 mm for Example 7-6 only). The results are shown in Tables 3 to 5.

[0185]

[0186]

[0187]

[0188] As shown in Tables 3 to 5, the charge-transporting thin films formed from charge-transporting ink compositions containing surface-treated metal oxide nanoparticles, each of which has a specific metal oxide nanoparticle core and whose surface is coated with a metal oxide and further treated with an organic substance, exhibited small arithmetic mean surface roughness Ra and good flatness. On the other hand, charge-transporting thin films formed from charge-transporting ink compositions containing metal oxide nanoparticles whose surface is not coated with a metal oxide and whose surface is not further treated with an organic substance exhibited significantly poor flatness, such as aggregation and film formation defects. From the above, it was found from the present invention that a highly dispersible charge-transporting ink composition can be used to obtain a highly flat charge-transporting thin film.

[0189] [4] Fabrication of Electron-Only Device (EOD) [Example 13-1] The charge-transporting ink composition used in Example 7-1 was applied to an ITO substrate using a spin coater, and then pre-baked in an air atmosphere at 120°C for 1 minute. The substrate was then moved into a glove box and baked in nitrogen at 200°C for 15 minutes, forming a 40 nm thin film on the ITO substrate. The ITO substrate used was a 25 mm x 25 mm x 0.7 mm glass substrate with a patterned ITO film of 50 nm thickness formed on its surface. Prior to use, impurities on the surface were removed using an O2 plasma cleaning device (150 W, 30 seconds). A vapor deposition device (vacuum degree 1.0 x 10 -5 An 80 nm thick aluminum thin film was formed using a pressure of 1000 kJ / s at a rate of 0.2 nm / sec using a pressure of 1000 kJ / s. The substrate was then sealed with a sealing substrate to prevent deterioration of characteristics due to the effects of oxygen, water, etc. in the air. Sealing was performed using the following procedure. In a nitrogen atmosphere with an oxygen concentration of 2 ppm or less and a dew point of -76°C or less, the ITO substrate was placed between the sealing substrates, and the sealing substrates were bonded together with an adhesive (Moresco Moisture Cut WB90US(P) manufactured by MORESCO Corporation). At this time, a moisture scavenger (HD-071010W-40 manufactured by DYNIC Corporation) was placed inside the sealing substrate together with the ITO substrate. The bonded sealing substrates were irradiated with UV light (wavelength: 365 nm, irradiation dose: 6,000 mJ / cm). 2 After that, the adhesive was cured by annealing at 80° C. for 1 hour, which was used as an electron-only device (EOD).

[0190] [Examples 13-2 to 13-3] Electron-only devices (EODs) were obtained in the same manner as in Example 13-1, except that the charge-transporting ink compositions used in Examples 7-2 and 7-4 were used instead of the charge-transporting ink composition used in Example 7-1.

[0191] Examples 14-1 to 14-3 Electron-only devices (EODs) were obtained in the same manner as in Example 13-1, except that the charge-transporting ink compositions used in Examples 8-1, 8-2, and 8-4 were used instead of the charge-transporting ink composition used in Example 7-1.

[0192] Examples 15-1 to 15-3 Electron-only devices (EODs) were obtained in the same manner as in Example 13-1, except that the charge-transporting ink compositions used in Examples 9-1, 9-2, and 9-4 were used instead of the charge-transporting ink composition used in Example 7-1.

[0193] Examples 16-1 to 16-3 Electron-only devices (EODs) were obtained in the same manner as in Example 13-1, except that the charge-transporting ink compositions used in Examples 11-1, 11-2, and 11-4 were used instead of the charge-transporting ink composition used in Example 7-1.

[0194] For the EODs prepared in Examples 13-1 to 13-3, 14-1 to 14-3, 15-1 to 15-3, and 16-1 to 16-3, a voltage of 1.0 V was applied for 0.01 seconds at room temperature and normal pressure to measure the current density. The results are shown in Table 6.

[0195]

[0196] As shown in Table 6, a charge-transporting thin film formed from a charge-transporting ink composition containing surface-treated metal oxide nanoparticles, each of which has a specific metal oxide nanoparticle as a nucleus, the surface of which is coated with a metal oxide and further treated with an organic substance, was found to have sufficient charge transport properties based on the current density values ​​when a voltage was applied. From the above, the charge-transporting thin film obtained by the present invention is suitable for use as a charge-transporting layer, particularly an electron-transporting layer.

Claims

1. A charge transporting ink composition comprising surface-treated metal oxide nanoparticles having a core made of one or more metal oxide nanoparticles selected from the group consisting of metal oxides selected from the group consisting of metal oxides selected from the group consisting of Ti, Fe, Zr, Sn, Ta, Nb, Y, Mo, W, Pb, In, Bi and Sr, and complexes of at least two of these metal oxides, the surface of the core being coated with a metal oxide, and the surface of the metal oxide being further coated with one or more surface treatment agents, and an organic solvent.

2. The charge transport ink composition according to claim 1, wherein the metal oxide nanoparticles are one or more metal oxide nanoparticles selected from the group consisting of oxides of metals selected from the group consisting of Ti, Zr and Sn, and complexes of at least two of these metals.

3. The charge transport ink composition according to claim 2, wherein said metal oxide nanoparticles are SnO2 or a SnO2-TiO2-ZrO2 composite.

4. The charge transporting ink composition according to claim 1, wherein said metal oxide is at least one selected from the group consisting of In2O3, Sb2O5, SiO2, SnO2, TiO2, WO3, ZnO, ZrO2 and complexes of at least two of these.

5. The charge transporting ink composition according to claim 4, wherein said metal oxide is at least one selected from the group consisting of Sb2O5, SiO2, SnO2, TiO2, ZnO and complexes of at least two of these.

6. The charge transporting ink composition according to claim 5, wherein said metal oxide is at least one selected from the group consisting of Sb2O5, SiO2, SnO2 and complexes of at least two of these.

7. The charge transport ink composition according to claim 6, wherein said metal oxide is Sb2O5 or a SnO2-SiO2 complex.

8. The charge transporting ink composition according to claim 1, wherein the surface treatment agent is at least one selected from the group consisting of compounds represented by the following formulas (S1) to (S9): (In formula (S1), R 1 are each independently an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and are bonded to a silicon atom by a Si-C bond; R 2 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and a represents an integer of 1 to 3. 3 and R 5 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms; R 4 and R 6 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, Y represents an alkylene group, an NH group, or an oxygen atom, b represents an integer of 1 to 3, c represents 0 or 1, and d represents an integer of 1 to 3. In formula (S4), R 7 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and e represents 1 or 2. 8 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 9 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 10 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 11 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 12 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 13 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and Z represents an oxygen atom or a sulfur atom. 14 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and f represents 1 or 2.

9. The charge transporting ink composition according to claim 8, wherein the surface treatment agent is at least one selected from the group consisting of compounds represented by the following formulas (S1) to (S3): (R 1 ~R 6 , a, b, c and d have the same meanings as above.) 10. In the compound represented by (S1) above, R 1 are each independently an alkyl group or an alkyl group substituted with a mercapto group, R 1 At least one of R is an alkyl group substituted with a mercapto group; 2 9. The charge transporting ink composition according to claim 8, wherein: is an alkoxy group; and a is an integer of 1 to 3.

11. A charge transporting thin film obtained from the charge transporting ink composition according to any one of claims 1 to 10.

12. An electronic device comprising the charge transporting thin film according to claim 11.

13. The electronic device according to claim 12, wherein said charge transporting thin film is an electron transporting layer.

14. The electronic device according to claim 13, which is an organic EL device or a quantum dot EL device.

15. A surface-treated metal oxide nanoparticle sol comprising: a core made of one or more metal oxide nanoparticles selected from the group consisting of SnO2 and a SnO2-TiO2-ZrO2 complex, the surface of the core being coated with a SnO2-SiO2 complex, and the surface of the SnO2-SiO2 complex being further coated with at least one surface treating agent selected from the group consisting of compounds represented by the following formulas (S1) to (S9); and a solvent. (In formula (S1), R 1 are each independently an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and are bonded to a silicon atom by a Si-C bond; R 2 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and a represents an integer of 1 to 3. 3 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms; R 4 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, Y represents an alkylene group, an NH group, or an oxygen atom, b is an integer of 1 to 3, and c is 0 or 1. In formula (S3), R 5 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms; R 6 each independently represents an alkoxy group, an acyloxy group, or a halogen atom, and d represents an integer of 1 to 3. 7 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and e represents 1 or 2. 8 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 9 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 10 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 11 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group. 12 represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group; R 13 represents a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and Z represents an oxygen atom or a sulfur atom. 14 each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a thioureido group, or a cyano group, and f represents 1 or 2.

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