Metal element-doped metal oxide dispersion liquid, method for producing same, charge-transporting ink composition, charge-transporting thin film, and electronic element

Abstract

Provided are a metal element-doped metal oxide dispersion liquid and a method for producing the same, the metal element-doped metal oxide dispersion liquid being excellent in dispersibility of the metal element-doped metal oxide particles, and it being possible to satisfy characteristics (flatness, defect amount, PL intensity of quantum dots when laminated as an ETL on a quantum dot layer, charge transport properties, etc.)　The metal element-doped metal oxide dispersion liquid includes metal element-doped metal oxide particles and a solvent as a dispersion medium, and has a metal cation content calculated from Li, Na, K, and Ca included in the solvent of 1 to 2700 ppm, the metal oxide particles being particles having zinc oxide as a main component, the metal element doped into the particles having zinc oxide as a main component including one or more elements selected from Al, Mg, Li, Ca, Ga, and In, and the doped metal element being included in a ratio of 2-20 mol% with respect to elemental zinc.

Description

Metal element-doped metal oxide dispersion and method for producing the same, charge transport ink composition, charge transport thin film, and electronic device

[0001] The present invention relates to a metal element-doped metal oxide dispersion and a method for producing the same, as well as a charge transporting ink composition, a charge transporting thin film, and an electronic device.

[0002] In recent years, with the development of display technology, quantum dot electroluminescence (hereinafter referred to as QDEL) devices, which use quantum dot materials as light-emitting layers, have emerged and are expected to have a wide range of applications. QDEL devices have attracted attention because they use nano-sized semiconductor particles as quantum dot materials, and can control the emission wavelength by adjusting the type and particle size of the semiconductor particles, while also achieving a narrower spectral linewidth than organic light-emitting diodes (OLEDs).

[0003] QDEL technology is also superior in that it has many advantages, such as a narrow emission spectrum that allows for a wide color gamut, high luminance efficiency that contributes to high brightness and low power consumption, a relatively short recombination emission time that provides a fast response speed, and the ability to print on minute areas that contributes to low costs.

[0004] Methods for manufacturing QDEL 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 device area, 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.

[0005] In such QDEL devices, it is necessary to stack 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. To date, various types of metal oxide nanoparticles have been investigated to improve this efficiency.

[0006] For example, Patent Document 1 discloses a nanomaterial having a core-shell structure, wherein the core of the nanomaterial comprises ZnO nanoparticles and a metal element doped into the ZnO nanoparticles, and the shell of the nanomaterial comprises a metal oxide, the metal element doped into the ZnO nanoparticles comprises one or more of Al, Mg, Li, Ca, Ga, In, etc., and the metal element in the metal oxide comprises one or more of Al, Mg, Li, Ca, Ga, In, etc. Also, Patent Document 1 discloses a quantum dot light-emitting diode comprising an anode and a cathode attached to face each other, a quantum dot light-emitting layer attached between the anode and the cathode, and an electron transport layer attached between the cathode and the quantum dot light-emitting layer, wherein the material forming the electron transport layer comprises the nanomaterial.

[0007] Special Publication No. 2023-517364

[0008] The present inventors have conducted extensive research into metal element-doped metal oxide dispersions containing metal oxide particles doped with a specific metal element and a specific solvent, with the aim of achieving excellent electron transport properties, hole blocking properties, and / or inkjet coating suitability when used in the electron transport layer (ETL) of a QDEL device. They have found that, unless certain conditions are met, the dispersions exhibit poor dispersibility and are inferior in the properties required for an electron transport layer (e.g., flatness, defect level, PL intensity of the quantum dots when laminated as an ETL on a quantum dot layer, and charge transport properties). The present invention aims to provide a means for solving these problems.

[0009] The present inventors have conducted extensive research into the above-mentioned problems and have found that a metal-doped metal oxide dispersion containing metal-doped metal oxide particles and a specific solvent has excellent dispersibility when the metal cation content calculated from the Li, Na, K, and Ca contained in the solvent is a specific ratio, and when the ligand molecular length and χ parameter are specific values. Furthermore, they have found that the use of this dispersion satisfies the properties required for an electron transport layer, thereby completing the present invention. Furthermore, the present inventors have conducted extensive research into a method for producing the metal-doped metal oxide dispersion. The method includes a step of mixing a specific organic solvent, a zinc salt, and a salt of the metal element to be doped, and then adding an alkaline solution to the resulting solution to produce an organic solvent dispersion containing metal-doped metal oxide particles. This step then involves washing the organic solvent dispersion to remove the metal cations, thereby obtaining a dispersion with excellent dispersibility. This finding has led to the completion of the present invention.

[0010] That is, the gist of the present invention is as follows, as described in this paragraph. [1] A metal-element-doped metal oxide dispersion comprising metal-element-doped metal oxide particles and a solvent as a dispersion medium, wherein the metal cation content calculated from the Li, Na, K, and Ca contained in the solvent is 1 to 2700 ppm, wherein the metal oxide particles are particles containing zinc oxide as a main component, and the metal element doped into the zinc oxide-based particles comprises one or more elements selected from Al, Mg, Li, Ca, Ga, and In, and the doped metal element is contained in a ratio of 2 to 20 mol % relative to elemental zinc. [2] The metal-element-doped metal oxide dispersion according to [1], wherein the metal-element-doped metal oxide particles have an average primary particle size of 2 to 50 nm. [3] The metal element-doped metal oxide dispersion according to [1], wherein a powder obtained by drying the metal element-doped metal oxide dispersion at 120°C is subjected to a thermal analysis in which the powder is heated in an air atmosphere at a temperature increase rate of 10°C / min, and the DTA curve obtained at measurement temperatures of 200°C to 400°C shows no endothermic peak. [4] The metal element-doped metal oxide particles are coated on their surfaces with a metal oxide layer and / or a metal sulfide layer as a coating layer, and the metal oxide particles are particles containing zinc oxide as a main component, and the coating layer is Al ２ O ３ , MgO, SiO ２ , SnO ２[5] The metal element-doped metal oxide dispersion according to [1], which contains one or more metal oxides and / or metal sulfides selected from the group consisting of ZnS, ZnS, and ZnS. [6] The metal element-doped metal oxide dispersion according to [4], which has a 50% volume average diameter of 2 to 50 nm, a 90% volume average diameter of 2 to 100 nm, and a value obtained by subtracting the 10% volume average diameter from the 90% volume average diameter of 50 nm or less, as measured by dynamic light scattering. [7] The metal element-doped metal oxide dispersion according to [4], which has an absolute quantum yield of 0 to 10%, calculated from the peak top at wavelengths of 500 nm to 600 nm in the emission spectrum when the metal element-doped metal oxide dispersion having a solids content of 0.5 mass % is irradiated with ultraviolet light at a wavelength of 365 nm. [7] The metal element-doped metal oxide dispersion liquid according to [1], wherein the solvent contains one or more organic solvents selected from alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents. [8] The metal element-doped metal oxide dispersion liquid according to [1], further contains a ligand having an amine group, a carboxylic acid group, or a thiol group, and the metal element-doped metal oxide dispersion liquid according to [1], further contains one or more organic solvents selected from alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents. [9] The metal element-doped metal oxide dispersion liquid according to [1], further contains one or more organic solvents selected from alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents.

[10] The metal element-doped metal oxide dispersion liquid according to

[11] , further contains one or more organic solvents selected from alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents.

[11] The metal element-doped metal oxide dispersion liquid according to

[12] , further contains one or more organic solvents selected from alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents.

[12] The metal element-doped metal oxide dispersion liquid according to

[13] , further contains one or more organic solvents selected from alcohols, ３ ], k is the Boltzmann constant [J / K], T is the temperature in the system of the metal element-doped metal oxide dispersion [K], and δs is the Hansen solubility parameter of the solvent [Pa １／２ ], and δm is the Hansen solubility parameter of the ligand [Pa １／２]. The metal element-doped metal oxide dispersion liquid according to [1], wherein the χ parameter calculated from the above equation is 0.34 to 0.50. [9] The metal element-doped metal oxide dispersion liquid according to [8], wherein the amount of the ligand is 1 to 200 mass % relative to the metal element-doped metal oxide particles.

[10] A charge transport ink composition comprising the metal element-doped metal oxide dispersion liquid according to [1] and a solvent.

[11] A charge transport thin film obtained from the charge transport ink composition according to

[10] .

[12] An electronic device comprising the charge transport thin film according to

[11] .

[13] The electronic device according to

[12] , wherein the charge transport thin film is an electron transport layer.

[14] The electronic device according to

[13] , wherein the electronic device is an organic EL device or a quantum dot EL device.

[15] A method for producing a metal element-doped metal oxide dispersion liquid according to [1], comprising the following steps (a) and (b): step (a): adding an alkaline solution to a solution obtained by mixing an organic solvent, a zinc salt, and a salt of the metal element to be doped as raw materials, to produce an organic solvent dispersion liquid containing metal element-doped metal oxide particles, and step (b): washing the organic solvent dispersion liquid to remove metal cations.

[16] A method for producing a metal element-doped metal oxide dispersion liquid according to

[15] , further comprising the following steps (c) and (d): step (c): adding a ligand to the organic solvent dispersion liquid from which the metal cations have been removed, and heating the organic solvent dispersion liquid at 20°C to 150°C for 0.1 to 20 hours, or step (d): adding a high-boiling point organic solvent to the organic solvent dispersion liquid from which the metal cations have been removed, to remove the organic solvent derived from the raw materials, in this order or in reverse order.

[0011] The gist of the present invention is also as follows, as described in this paragraph. [1] A metal-element-doped metal oxide dispersion comprising metal-element-doped metal oxide particles and a solvent as a dispersion medium, wherein the metal cation content calculated from the Li, Na, K, and Ca contained in the solvent is 1 to 2700 ppm. [2] The metal-element-doped metal oxide dispersion according to [1], wherein the metal-element-doped metal oxide particles have an average primary particle size of 2 to 50 nm. [3] The metal-element-doped metal oxide dispersion according to [1], wherein the metal oxide particles are particles containing zinc oxide as a main component. [4] The metal-element-doped metal oxide dispersion according to [3], wherein the metal element doped into the zinc oxide-based particles contains one or more elements selected from Al, Mg, Li, Ca, Ga, and In, and the doped metal element is contained in a ratio of 2 to 20 mol % relative to elemental zinc. [5] The surface of the metal element-doped metal oxide particle is coated with a metal oxide layer and / or a metal sulfide layer as a coating layer, the metal oxide particle is a particle mainly composed of zinc oxide, and the coating layer is Al ２ O ３ , MgO, SiO ２ , SnO ２[6] The metal-element-doped metal oxide dispersion according to [1], which contains one or more metal oxides and / or metal sulfides selected from the group consisting of ZnS, ZnS, and ZnS. [6] The metal-element-doped metal oxide dispersion according to [1], which has a 50% volume average diameter of 2 to 50 nm and a 90% volume average diameter of 2 to 100 nm as measured by dynamic light scattering. [7] The metal-element-doped metal oxide dispersion according to [5], which has an absolute quantum yield of 0 to 10%, calculated from the peak top at wavelengths of 500 to 600 nm in the emission spectrum when the metal-element-doped metal oxide dispersion having a solids content of 0.5 mass % is irradiated with ultraviolet light at a wavelength of 365 nm. [8] The metal-element-doped metal oxide dispersion according to [1], wherein the solvent contains one or more organic solvents selected from alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents. [9] The compound further contains a ligand having an amine group, a carboxylic acid group, or a thiol group, and is expressed by the following formula (1): χ = Vm / kT × (δs - δm)^2 + 0.34 ... formula (1) (Vm is the molecular volume [m ３ ], k is the Boltzmann constant [J / K], T is the temperature in the system of the metal element-doped metal oxide dispersion [K], and δs is the Hansen solubility parameter of the solvent [Pa １／２ ], and δm is the Hansen solubility parameter of the ligand [Pa １／２]. The metal element-doped metal oxide dispersion liquid according to [8], wherein the χ parameter calculated from the above equation is 0.34 to 0.50.

[10] The metal element-doped metal oxide dispersion liquid according to [9], wherein the amount of the ligand is 1 to 200 mass % relative to the metal element-doped metal oxide particles.

[11] A charge transport ink composition comprising the metal element-doped metal oxide dispersion liquid according to [1] and a solvent.

[12] A charge transport thin film obtained from the charge transport ink composition according to

[11] .

[13] An electronic device comprising the charge transport thin film according to

[12] .

[14] The electronic device according to

[13] , wherein the charge transport thin film is an electron transport layer.

[15] The electronic device according to

[14] , wherein the electronic device is an organic EL device or a quantum dot EL device.

[16] A method for producing a metal element-doped metal oxide dispersion liquid according to [1], comprising the following steps (a) and (b): step (a): adding an alkaline solution to a solution obtained by mixing an organic solvent, a zinc salt, and a salt of the metal element to be doped as raw materials, to produce an organic solvent dispersion liquid containing metal element-doped metal oxide particles, and step (b): washing the organic solvent dispersion liquid to remove metal cations.

[17] A method for producing a metal element-doped metal oxide dispersion liquid according to

[16] , further comprising the following steps (c) and (d): step (c): adding a ligand to the organic solvent dispersion liquid from which the metal cations have been removed, and heating the organic solvent dispersion liquid at 20°C to 150°C for 0.1 to 20 hours, or step (d): adding a high-boiling point organic solvent to the organic solvent dispersion liquid from which the metal cations have been removed, to remove the organic solvent derived from the raw materials, in this order or in reverse order.

[0012] The dispersion of the present invention has excellent dispersibility of metal element-doped metal oxide particles, and by using this dispersion, it is possible to obtain a charge transport ink composition, a charge transport thin film, and an electronic device such as an organic EL device or a quantum dot EL device that satisfy the properties required for an electron transport layer (e.g., flatness, defect level, PL intensity of the quantum dots when laminated as an ETL on a quantum dot layer, charge transport property). Furthermore, by using the manufacturing method of the present invention that includes specific steps, it is possible to obtain a dispersion for obtaining a charge transport ink composition, a charge transport thin film, and an electronic device such as an organic EL device or a quantum dot EL device that has excellent dispersibility of metal element-doped metal oxide particles and satisfies the properties required for an electron transport layer.

[0013] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited to the following embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0014] [Metal Element-Doped Metal Oxide Dispersion] In the present invention, the metal element-doped metal oxide dispersion refers to a metal element-doped metal oxide dispersion that contains metal element-doped metal oxide particles and a solvent as a dispersion medium, and has a metal cation content calculated from the Li, Na, K, and Ca contained in the solvent of 1 to 2700 ppm. In consideration of the effects of the present invention, the metal cation content calculated from the Li, Na, K, and Ca contained in the solvent is preferably 1 to 2700 ppm, 1 to 2000 ppm, 1 to 1500 ppm, 1 to 1000 ppm, 1 to 500 ppm, 1 to 200 ppm, or 1 to 100 ppm, more preferably 1 to 50 ppm, and even more preferably 1 to 20 ppm.

[0015] In the present invention, the term "metal element-doped metal oxide particles" refers to metal oxide particles doped with a metal element. Hereinafter, in this specification, the metal element-doped metal oxide particles may be simply referred to as a metal element-doped metal oxide.

[0016] Specific examples of the metal oxide particles include inorganic oxide particles such as cesium carbonate, titanium oxide, tin oxide, and zinc oxide. In the present invention, among these, particles containing zinc oxide as a main component are most preferred from the viewpoints of electron mobility and transparency. The average primary particle diameter of the metal oxide particles is preferably 2 to 50 nm, 2 to 20 nm, or 2 to 15 nm, more preferably 2 to 10 nm, and even more preferably 2 to 7 nm, from the viewpoint of the formation of an electron transport layer (ETL). From the viewpoint of the properties required for the metal oxide particles as an electron transport layer (ETL) (e.g., PL intensity and charge transport properties of quantum dots when laminated as an ETL on a quantum dot layer), it is preferable that the metal oxide particles have no endothermic peak in the DTA curve obtained at measurement temperatures of 200 to 400°C in a thermal analysis in which a metal element-doped metal oxide dispersion liquid is dried at 120°C and heated in an air atmosphere at a heating rate of 10°C / min, and that the metal hydroxide content is low. In particular, Mg(OH) ２ When the content of metal hydroxide, which is an insulating material, is low, particles having excellent charge transport properties can be obtained.

[0017] In the present invention, the metal element doped into the metal oxide (particles) may be one or more elements selected from Al, Mg, Li, Ca, Ga, and In. Furthermore, in the present invention, the metal element doped into the metal oxide (particles) may be one or more elements selected from Mg, Li, Ca, and In. Among these, Mg and Li are preferred, with Mg being more preferred. Such preferred metal elements have an atomic radius not smaller than that of Zn, are less likely to cause oxygen defects, and are more effective than other metal elements in that they can suppress deterioration of PL quenching (reduction in the PL intensity of the PL intensity evaluation element).

[0018] In the present invention, for example, when the metal oxide is mainly composed of zinc oxide, the doped metal element is preferably contained in a ratio of 2 to 50 mol % relative to the zinc element, more preferably 2 to 20 mol %, even more preferably 5 to 15 mol %, and most preferably 10 to 15 mol %. This can be applied in the same ratio even when the metal element constituting the metal oxide is a metal element other than zinc.

[0019] In the present invention, the surface of the metal element-doped metal oxide particle may be coated with a metal oxide layer or a metal sulfide layer as a coating layer, and the metal element-doped metal oxide particle and / or metal element-doped metal sulfide particle serving as the core is called a core particle, and the coating layer is called a shell, and particles of this type can be called core-shell type particles.

[0020] Specific examples of the metal oxide or metal sulfide constituting the metal oxide layer include Al ２ O ３ , MgO, SiO ２ , ZnS, and SnO ２ Examples of suitable metal oxide particles include one or more metal oxides selected from the group consisting of: (a) and (b) above. Forming a metal oxide layer on the surface of the metal-element-doped metal oxide particles improves the stability of the particles when an electron transport layer is formed, improving the LT90 value evaluated below and extending the device operation life. From the viewpoint of device operation life, LT90 is preferably 50 to 1000%, 50 to 700%, 50 to 500%, 50 to 300%, 50 to 150%, or 70 to 150%, more preferably 80 to 150%, and even more preferably 90 to 150%.

[0021] In the present invention, the 50% volume average diameter of the metal element-doped metal oxide dispersion, as measured by dynamic light scattering, is preferably 2 to 50 nm, 5 to 50 nm, 7 to 50 nm, 2 to 40 nm, 5 to 40 nm, or 7 to 40 nm, and the 90% volume average diameter is preferably 2 to 100 nm, 5 to 100 nm, 7 to 100 nm, 2 to 70 nm, 5 to 70 nm, or 7 to 70 nm. From the viewpoint of ink ejection properties, the 50% volume average diameter is more preferably 2 to 20 nm, and even more preferably 2 to 10 nm. Furthermore, from the viewpoint of ETL flatness, the 90% volume average diameter is more preferably 2 to 50 nm, and even more preferably 2 to 20 nm. Furthermore, the value obtained by subtracting the 10% volume average diameter from the 90% volume average diameter (also referred to as particle size distribution: 90% volume average diameter (nm) - 10% volume average diameter (nm)) is preferably 2 to 50 nm, and from the viewpoint of producing a charge-transporting thin film having a high particle packing rate and excellent electrical properties, is more preferably 2 to 30 nm, and even more preferably 2 to 10 nm.

[0022] In the present invention, when the metal element-doped metal oxide dispersion having a solids content of 0.5% by mass is irradiated with ultraviolet light having a wavelength of 365 nm, the absolute quantum yield at a wavelength of 570 nm in the emission spectrum is preferably 0 to 10%, more preferably 0 to 7%, and even more preferably 1 to 10%. From the viewpoint of the luminescence characteristics of the quantum dot layer, the absolute quantum yield is more preferably 0 to 5%, and even more preferably 0 to 3%. By setting the absolute quantum yield to 0 to 10%, the number of defects caused by oxygen defects in the metal element-doped metal oxide particles is small, and when the electron transport layer ETL is formed on the quantum dot layer, excitons in the quantum dots are not trapped in defect levels, and energy loss can be reduced.

[0023] In the present invention, examples of the solvent used as the dispersion medium include one or more organic solvents selected from alcohols such as methanol, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents. Among these, alcohols and ethers are preferred, and methanol, ethanol, dimethyl sulfoxide, glycols, diols, and glycol ethers are more preferred.

[0024] In the present invention, the metal element-doped metal oxide dispersion liquid may further contain a ligand having an amine group, a carboxylic acid group, or a thiol group. In this case, the molecular length of the ligand is 6.5 Å or more, preferably 7.0 Å or more, and the molecular length is expressed by the following formula (1): χ = Vm / kT × (δs - δm)^2 + 0.34 ... formula (1) (Vm is the molecular volume [m ３ ], k is the Boltzmann constant [J / K], T is the temperature in the system of the metal element-doped metal oxide dispersion [K], and δs is the Hansen solubility parameter of the solvent [Pa １／２ ], and δm is the Hansen solubility parameter of the ligand [Pa １／２ ]. The χ parameter, which is a value calculated from

[0000] (1) above, is preferably 0.34 to 0.50, more preferably 0.34 to 0.45, and even more preferably 0.34 to 0.40. In the present invention, the ligand is an organic compound having an amine group, a carboxylic acid group, or a thiol group as a functional group, and the ligand is adsorbed to the particle surface through interaction between the functional group and the hydroxyl groups on the surface of the metal element-doped metal oxide (inorganic oxide) particles. When the molecular length of the ligand is long, the steric repulsion energy between the particles increases, thereby providing the excellent effect of enhancing the dispersion stability of the particles. Furthermore, the adsorption of the ligand enhances the compatibility between the particle surface and the solvent used as the dispersion medium, thereby providing the excellent effect of enhancing the dispersion stability of the particles. The χ parameter is useful in determining such compatibility.

[0025] Specific examples of the ligand include organic compounds such as propylamine, isopropylamine, n-octylamine, acetic acid, isobutyric acid, propionic acid, oleic acid, 1-dodecanethiol, etc. In the present invention, among these, acetic acid, isobutyric acid, propionic acid, and oleic acid, which have a carboxylic acid group, are preferred from the viewpoint of the adsorption of the ligand to the particle surface, and isobutyric acid, propionic acid, and oleic acid are more preferred from the viewpoint of the dispersion stability of the particles.

[0026] The amount of the ligand is preferably 1 to 200% by mass relative to the metal element-doped metal oxide particles, more preferably 1 to 100% by mass, and even more preferably 1 to 50% by mass, from the viewpoint of the electroluminescence characteristics of the QDEL device.

[0027] In the present invention, a charge transporting ink composition may be prepared by adding a solvent to the metal element-doped metal oxide dispersion liquid described above. The solvent may be, but is not limited to, an alcohol, a ketone, an ester, an ether, an amide, a cyano group-containing solvent, or a halogen-containing solvent.

[0028] In the present invention, the charge transport layer ink composition described above can be applied to a substrate and baked to obtain a charge transport thin film.

[0029] 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.

[0030] 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 a QDEL device or the like, a baking temperature of approximately 100 to 250°C is preferred. Note that during baking, the temperature may be changed in two or more stages in order 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.

[0031] 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 an electron transport layer in a QDEL element, the thickness is preferably 5 to 300 nm, and more preferably 20 to 200 nm. Methods for changing the thickness include changing the solids concentration in the charge transport ink composition and changing the amount of solution on the substrate during application.

[0032] 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 a light emitting layer in a QDEL device or the like, but is also suitable as an electron injection layer or an electron transport layer, and is more suitable as an electron transport layer.

[0033] [Organic EL Device and Quantum Dot EL Device] The organic EL device and quantum dot EL device of the present invention have 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 devices and quantum dot EL devices include, but are not limited to, the following (a) to (f). The charge transport ink composition of the present invention can be suitably used in devices having the configurations (a) to (d) in particular. 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

[0034] 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.

[0035] The terms "electron injection layer" and "electron transport layer" refer to layers formed between the light-emitting layer and the cathode, which 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 remaining layers are "electron transport layers." The term "light-emitting layer" refers to 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, the element is an organic EL element, and when the light-emitting layer is a quantum dot light-emitting layer EL element, the element is a quantum dot EL element.

[0036] 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.

[0037] An example of a method for producing a quantum dot EL device having an electron transport layer composed of a thin film obtained from the charge transport ink composition of the present invention is as follows. It is preferable to preliminarily perform surface treatments such as washing with alcohol, pure water, or the like, or UV ozone treatment or oxygen plasma treatment, to the extent that the electrodes are 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 and 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 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, instead of forming the hole injection layer, hole transport layer, and emissive layer by a wet process in this method, these layers can also be formed by vapor deposition. If necessary, an electron blocking layer may be provided between the emissive layer and 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 the layers may be stacked in the reversed order (cathode, electron transport layer, light-emitting layer, hole transport layer, hole injection layer, and anode).

[0038] 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.

[0039] 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.

[0040] 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).

[0041] 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; 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; and quantum dot materials. Furthermore, when forming the light-emitting layer by vapor deposition, the layer 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).

[0042] 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, SnSe, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, SnPbSTe; Si, Ge, SiC, SiGe, AgInSe, CuGaSe, CuInS, CuGaS, CuInSe, AgInS, AgGaSe, AgGaS, C, Si, and Ge.

[0043] 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.

[0044] 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. Typically, 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.

[0045] The organic EL element and quantum dot EL element of the present invention may be sealed with a moisture scavenger or the like, if necessary, according to a standard method, in order to prevent deterioration of the characteristics.

[0046] [Method for Producing Metal Element-Doped Metal Oxide Dispersion] In the present invention, the method for producing a metal element-doped metal oxide dispersion includes the following steps (a) and (b): step (a): adding an alkaline solution to a solution obtained by mixing an organic solvent, a zinc salt, and a salt of the metal element to be doped as raw materials, to produce an organic solvent dispersion containing metal element-doped metal oxide particles, and step (b): washing the organic solvent dispersion to remove metal cations.

[0047] Specific examples of the organic solvent as a raw material include methanol, ethanol, n-propanol, i-propanol, methyl ethyl ketone, n-butanol, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and dimethyl sulfoxide. In the present invention, among these, methanol, ethanol, and dimethyl sulfoxide are preferred, and methanol is more preferred. Note that, when the production method of the present invention further includes step (d) described below, it is preferable to use, as the organic solvent as a raw material, an organic solvent having a boiling point lower than that of the high-boiling-point organic solvent used in step (d).

[0048] Specific examples of the zinc salt include zinc chloride, zinc oxide, zinc acetate, zinc acetate dihydrate, zinc sulfide, zinc citrate, zinc lactate trihydrate, zinc nitrate, zinc nitrate hexahydrate, zinc oxalate dihydrate, zinc sulfate, zinc sulfate heptahydrate, zinc tartrate, zinc stearate, zinc benzoate, zinc ammonium chloride, zinc acetylacetonate, zinc carbonate, etc. Among these, zinc chloride, zinc acetate, zinc acetate dihydrate, zinc oxalate dihydrate, zinc sulfate, zinc sulfate heptahydrate, and zinc carbonate are preferred in the present invention.

[0049] Specific examples of the salt of the metal element to be doped include magnesium chloride, magnesium chloride hexahydrate, magnesium oxide, magnesium acetate, magnesium acetate tetrahydrate, magnesium hydroxide, magnesium phosphate octahydrate, magnesium lactate trihydrate, magnesium nitrate hexahydrate, magnesium oxalate dihydrate, magnesium sulfate, magnesium sulfate heptahydrate, magnesium diethoxide, magnesium oleate, magnesium perchlorate, magnesium stearate, magnesium benzoate trihydrate, lithium chloride, lithium acetate, lithium acetate dihydrate, lithium carbonate, lithium phosphate, lithium lactate, lithium tert-butoxide, lithium citrate tetrahydrate, lithium hydroxide monohydrate, lithium nitrate, lithium oxalate, and lithium sulfate. Examples of calcium carbonate include calcium carbonate monohydrate, lithium tetraborate, lithium tetraborate trihydrate, lithium pyruvate monohydrate, lithium tartrate, lithium stearate, lithium hydroxide, lithium sulfate, calcium carbide, calcium chloride, calcium formate, calcium oxide, calcium acetate monohydrate, calcium bromide dihydrate, calcium carbonate, calcium citrate tetrahydrate, calcium hydroxide, calcium lactate n-hydrate, calcium nitrate tetrahydrate, calcium oxalate monohydrate, calcium sulfate, calcium sulfate dihydrate, calcium gluconate monohydrate, calcium oleate, calcium pyrophosphate, calcium tartrate tetrahydrate, tricalcium phosphate, calcium propionate, calcium stearate, calcium chloride hexahydrate, and calcium perchlorate tetrahydrate.

[0050] Specific examples of the alkaline solution include solutions of alkali metal hydroxides (e.g., lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.), organic base catalysts (e.g., tetramethylammonium (TMAH), tetraethylammonium (TEAH), and ammonia (NH3), ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylguanidine, 3-ethoxypropylamine, dipropylamine, triethylamine), etc. In the present invention, among these, aqueous solutions of sodium hydroxide, potassium hydroxide, TEAH, NH ３ is preferred.

[0051] Specific examples of the metal element-doped metal oxide particles contained in the organic solvent dispersion are the same as those exemplified in the description of the metal element-doped metal oxide dispersion.

[0052] In the above step (a), it is preferable to dissolve the zinc salt and the salt of the metal element to be doped separately in an organic solvent, and then add the solution of the metal element to be doped to the solution of the zinc salt.By preventing uneven particle synthesis reaction resulting from the difference in solubility between the salt of the metal element to be doped and the zinc salt, the metal element to be doped can be uniformly doped into the metal oxide particles.

[0053] In the above step (a), it is preferable to heat the mixed solution after mixing the organic solvent, zinc salt, and salt of the metal element to be doped. From the viewpoint of the electrical properties of the particles, the heating temperature is preferably 20°C to 150°C, more preferably 20°C to 100°C, and even more preferably 20°C to 70°C. From the viewpoint of the progress of particle synthesis and manufacturing aspects, the heating time is preferably 0.1 to 20 hours, more preferably 0.1 to 10 hours, and even more preferably 0.1 to 5 hours. By setting the heating temperature to 20 to 150°C and allowing the particle synthesis reaction to proceed sufficiently, the generation of metal hydroxide, which is an insulating material, is suppressed, and particles with excellent charge transport properties can be synthesized.

[0054] In the step (b), specific examples of the step of washing the organic solvent dispersion to remove metal cations include treatment with an ion exchange resin, treatment with an ion exchange membrane, filtration using an ultramembrane, separation using a centrifuge, decantation, etc. As described in Examples 1 and 2 described below. That is, as long as the target metal cations can be removed, the method of washing the organic solvent dispersion is not particularly limited. For example, the step of adding the dispersion and the organic solvent to an ultrafilter and concentrating until a predetermined particle solid content is reached may be repeated multiple times (e.g., five times), or the step of adding an organic solvent to the precipitate obtained from the dispersion, permeating it, and then centrifuging and removing the supernatant may be repeated multiple times (e.g., five times) to reduce the metal cations. In the present invention, the metal cations to be removed refer to Li, Na, K, and Ca.

[0055] In the present invention, the method for producing a metal element-doped metal oxide dispersion may further include the following steps (c) and (d) in this order or in reverse order: step (c): adding a ligand to the organic solvent dispersion from which the metal cations have been removed, and heating the mixture at 20°C to 150°C for 0.1 to 20 hours; and step (d): adding a high-boiling organic solvent to the organic solvent dispersion from which the metal cations have been removed, and removing the organic solvent derived from the raw material.

[0056] Specific examples of the ligand are the same as those given as examples in the description of the metal element-doped metal oxide dispersion liquid.

[0057] In the step (c), from the viewpoints of efficient adsorption of the ligand onto the particle surface and maintaining particle dispersibility, the heating temperature is preferably 20° C. to 150° C., more preferably 20° C. to 100° C., and even more preferably 20° C. to 70° C. In addition, in the step (c), from the viewpoint of sufficient adsorption of the ligand onto the particle surface, the heating time is preferably 0.1 to 20 hours, more preferably 0.1 to 10 hours, and even more preferably 0.1 to 5 hours.

[0058] In the above step (d), specific examples of the high-boiling organic solvent include alcohols, ketones, esters, ethers, amides, cyano group-containing solvents, and halogen-containing solvents. The alcohol is a monohydric alcohol having 1 to 20 carbon atoms or 1 to 10 carbon atoms, or a polyhydric alcohol having 1 to 20 carbon atoms or 1 to 10 carbon atoms. Examples of the monohydric alcohol include methanol, ethanol, n-propanol, i-propanol, n-butanol, propylene glycol monomethyl ether, isobutanol, n-pentanol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, 1-octanol, 1-nonanol, 1-decanol, benzyl alcohol, 2-phenoxyethanol, 2-benzyloxyethanol, tetrahydrofurfuryl alcohol, and tetradecyl alcohol. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 2,3-butanediol, 1,2-hexanediol, 2,4-diethyl-1,5-pentanediol, etc. As the ketone, an aliphatic ketone can be preferably used as a ketone having 1 to 20 carbon atoms or 1 to 10 carbon atoms. Examples include acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, methyl cyclopentanone, isophorone, 4-hydroxy-4-methyl-2-pentanone, methyl n-propyl ketone, methyl n-butyl ketone, methyl n-amyl ketone, 2-heptanone, and acetylacetone. As the ester, an aliphatic ester can be preferably used as an ester having 1 to 20 carbon atoms or 1 to 10 carbon atoms. For example, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate, dimethyl maleate, diethyl maleate, dipropyl maleate, dimethyl adipate, diethyl adipate, dipropyl adipate, diisopropyl fumarate, propylene glycol monomethyl ether acetate, methyl benzoate, ethyl benzoate, butyl benzoate ethyl, dimethyl phthalate, dibutyl maleate, diethyl oxalate, dibutyl oxalate, hexyl acetate, benzyl acetate, dibutyl fumarate, diethyl decanedioate, 2-phenoxyethyl isobutyrate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethyl maleate, diethyl fumarate, dipropylene glycol methyl ether acetate, 1,3-butylene glycol diacetate, propylene glycol diacetate, 1,6-hexanediol diacetate, triacetin, γ-butyrolactone, ethylene carbonate, propylene carbonate, methyl cellosolve acetate, ethyl cellosolve acetate, diethyl cellosolve acetate, phenyl cellosolve acetate, n-butyl acetate, isobutyl acetate, methyl lactate, ethyl lactate, methyl hydroxyacetate, ethyl hydroxyacetate, butyl hydroxyacetate, methoxymethyl acetate, methoxyethyl acetate, methoxybutyl acetate, ethoxymethyl acetate, ethoxyethyl acetate, methyl 3-hydroxypropionate, ethyl 3-hydroxypropionate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, propyl-2-hydroxypropionate, methyl-2-methoxypropionate, ethyl-2-methoxypropionate, ethyl-2-ethoxypropionate, methyl-2-ethoxypropionate, methyl-2-hydroxy-2-methylpropionate, ethyl-2-hydroxy-2-methylpropionate, methyl-2-methoxy-2-methylpropionate, ethyl-2-ethoxy-2-methylpropionate, 2-hydroxyethylpropionate, 2-hydroxy-2-methylethylpropionate, hydroxyethyl acetate, methyl 2-hydroxy-3-methylbutanoate, ethyl pyruvate, methyl ethyl carbitol, diethyl carbitol, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether acetate, and the like. As the ether, an aliphatic ether having 1 to 20 carbon atoms or 1 to 10 carbon atoms can be preferably used. For example, dimethyl ether, ethyl methyl ether, diethyl ether, tetrahydrofuran, 1,Examples of suitable amides include 4-dioxane, anisole, 4-methoxytoluene, diethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol monophenyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, diethylene glycol butyl methyl ether, diethylene glycol dibutyl ether, dipropylene glycol monobutyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, tripropylene glycol monomethyl ether, 2-(2-isobutoxyethoxy)ethanol, benzyl ethyl ether, etc. Examples of suitable amides include amides having 1 to 20 carbon atoms or 1 to 10 carbon atoms, such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylisobutyramide, 1,3-dimethyl-2-imidazolidinone, N-methylformamide, N-methylformanilide, and N-methylacetamide. Examples of hydrocarbons include paraffinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, and mixtures thereof having 6 to 18 or 6 to 40 carbon atoms. Examples of n-paraffins include n-hexane, n-heptane, n-octane, n-nonane, and n-decane. Examples of i-paraffins include i-octane, i-nonane, and i-decane. Examples of aromatic hydrocarbons include toluene, xylene, tetralin, cyclohexylbenzene, and decylbenzene. Examples of cyano group-containing solvents include acetonitrile and 3-methoxypropionitrile. Examples of halogen-containing solvents include chloroform and chlorobenzene. Examples of sulfonyl group-containing solvents include dimethyl sulfoxide. Examples of carboxyl group-containing solvents include formic acid, acetic acid, acrylic acid, methacrylic acid, oleic acid, linoleic acid, linolenic acid, lactic acid, and caproic acid. In the present invention, among these, alcohol-based and ether-based solvents are preferred from the viewpoint of dispersibility of nanoparticles, and glycols, diols, and glycol ethers are more preferred from the viewpoint of solvent resistance of the quantum dot light-emitting layer.

[0059] In the step (d), the method for removing the organic solvent derived from the raw materials is not particularly limited, and examples thereof include a method in which the organic solvent is reduced while maintaining the high-boiling organic solvent in a dispersion liquid by heating under reduced pressure using an evaporator.

[0060] The present invention will be described in more detail below based on Production Examples, Examples and Comparative Examples, but the present invention is not limited to these Examples in any way.

[0061] The physical properties of the dispersion and the coating film prepared using the dispersion were determined by the following measurement methods.

[0062] [Measurement of 10% Volume Average Diameter, 50% Volume Average Diameter, and 90% Volume Average Diameter] The organic solvent dispersion or the metal element-doped metal oxide dispersion was diluted with a dispersion solvent, and measurement was performed using a Zetasizer Nano ZS (trade name, manufactured by Malvern Instruments Ltd.) using parameters of the particles in the dispersion and the solvent.

[0063] [Measurement of Metal Cation Content] A measurement sample was prepared by adding ultrapure water to a mixed solution of 0.1 g of the organic solvent dispersion or the metal element-doped metal oxide dispersion, 1.0 mL of 63% nitric acid, and 0.5 mL of concentrated sulfuric acid so that the total amount was 10 g. The amounts of metals (Li, Na, K, and Ca) were measured using an ICP-OES (product name Optima 8300, manufactured by PerkinElmer Co., Ltd.), and the metal cation content was calculated from the total amount.

[0064] [Measurement of Anion Content and Anion Species] The anion content and anion species in the organic solvent dispersion or the metal element-doped metal oxide dispersion were measured by ion chromatography using an anion analyzer (manufactured by Thermo SCIENTIFIC, trade name: Dionex ICS-2100). The detected peaks were analyzed using a standard solution, for example, F － , Cl － , NO ２－ ,Br － , NO ３－ , S.O. ４ ２－ , P.O. ３ ４－ , COO －The anion species were identified, and the amount of each anion species was quantified, and the total value was taken as the anion content.

[0065] [Confirmation of Doped Element] The doped element was confirmed by measurement using X-ray photoelectron spectroscopy (XPS). Specifically, the organic solvent dispersion or the metal element-doped metal oxide dispersion was placed in a petri dish, dried at 120°C, and then pulverized in a mortar to prepare a powder. The powder was measured using a scanning X-ray photoelectron spectrometer (manufactured by ULVAC-PHI, Inc., product name: PHI 5000 VersaProbe II) under the following conditions: measurement range: 0 to 1200 eV, X-ray source: AlKa 1486.6 eV (25 W, 15 kV), and analysis area diameter: 1000 μm.

[0066] [Confirmation of Chemical State of Doped Element] The chemical state of the doped element was confirmed by measurement using a thermal analyzer (manufactured by Rigaku Corporation, trade name Thermo plus EVO). Specifically, the organic solvent dispersion or metal element-doped metal oxide dispersion was placed in a petri dish, dried at 120°C, and then pulverized in a mortar to prepare a powder, which was measured using the thermal analyzer under measurement conditions of a heating rate of 10°C / min, a measurement temperature range of 40°C to 1000°C, and an air atmosphere. For example, in Example 1, Mg(OH) was identified from the DTA curve in the measurement temperature range of 200°C to 400°C. ２ It was confirmed whether an endothermic peak due to the

[0067] [Measurement of Doping Element Content] A measurement sample was prepared by adding ultrapure water to a mixed solution of 0.1 g of an organic solvent dispersion or a metal element-doped metal oxide dispersion, 1.0 mL of 63% nitric acid, and 0.5 mL of concentrated sulfuric acid until the total amount reached 10 g. The amounts of elements (Cs, Ti, Sn, Zn) and metal doping elements (Mg, Li, Ca, and In) in the metal oxide particles were measured using an ICP-OES (trade name Optima 8300, manufactured by PerkinElmer Co., Ltd.), and the doping element contents were calculated from these amounts. For example, in Example 1, the doping element content was calculated as (mass of Mg as a metal doping element / atomic weight of Mg) / (mass of Zn as a metal oxide particle element / atomic weight of Zn)×100 (converted into a percentage).

[0068] [Measurement of solid content] 1 g of the organic solvent dispersion or metal element-doped metal oxide dispersion was placed in a crucible, dried at 100° C., and then fired at 200° C. for 30 minutes, and the firing residue was weighed and calculated. This solid content mainly contains ZnO and MgO in Example 1 described below, for example.

[0069] [Average Primary Particle Diameter] The average primary particle diameter of the particles was measured using a transmission electron microscope (trade name: JEM-F200, manufactured by JEOL Ltd.). Specifically, the particles were photographed, and the particle size distribution of 500 randomly selected particles photographed was determined, and the average value of the primary particle diameters equivalent to a circle was calculated as the average primary particle diameter.

[0070] [Ligand Molecular Length] The ligand molecular length was calculated using simulation software. Specifically, a chemical structure file of the ligand was created using chemical structure drawing software Chemdraw (manufactured by PerkinElmer), and the molecular length was calculated from the file using simulation software Winmostar (manufactured by Molsys Co., Ltd.).

[0071] [Measurement of PL Intensity of QDs Laminated with Charge-Transporting Ink Composition] The PL intensity evaluation element was evaluated for fluorescence intensity using a spectrofluorometer (trade name F-7000, manufactured by Hitachi High-Tech Corporation). The measurement conditions for the spectrofluorometer were an excitation wavelength of 360 nm, a measurement wavelength range of 380 to 700 nm, and a photomultiplier voltage of 400 V. The peak-top fluorescence intensity and wavelength for each example were measured, with the peak-top fluorescence intensity measured for the PL characteristic evaluation element with only the quantum dot layer set to 100. The PL intensity evaluation element and the PL intensity evaluation element with only the quantum dot layer were prepared by the method described below. A quantum dot dispersion (QNA Corporation, trade name PureBlue.dots in Toluene_v2, toluene dispersion, concentration 3% by mass) was applied to a glass substrate using a spin coater and then baked at 100°C for 10 minutes to form a quantum dot thin film with a thickness of 40 nm on the substrate. An electron transport ink composition was applied to the glass substrate on which the resulting quantum dot thin film layer was formed, and then baked at 140°C for 15 minutes to form an electron transport film with a thickness of 40 nm on the substrate. The glass substrate was then placed between sealing substrates, and the sealing substrates were bonded together with an adhesive (MORESCO Corporation, trade name MORESCO Moisture Cut WB90US(P)). The bonded sealing substrates were irradiated with UV light (wavelength: 365 nm, irradiation dose: 6,000 mJ / cm2) to obtain a device for PL intensity evaluation. All of the work up to this point was carried out in a nitrogen atmosphere with an oxygen concentration of 2 ppm or less and a dew point of -76°C or less to prevent deterioration of characteristics due to the effects of oxygen, water, etc. in the air. As a reference sample, a PL intensity evaluation element was fabricated that contained only a quantum dot layer in the same manner as the fabrication of the PL intensity evaluation element, except that no electron transport film was formed.

[0072] [Measurement of Absolute Quantum Yield] 150 μl of a measurement sample prepared by diluting the solids content to 0.5% by mass with a dispersion solvent of the charge transport ink composition, for example, 2-(2-isobutoxyethoxy)ethanol in Example 1 described below, was placed in a quartz cell, and the absolute quantum yield was measured from the peak derived from the emission spectrum whose peak top was in the wavelength range of 500 nm to 600 nm using an absolute PL quantum yield measurement device (trade name Quantaurus-QY C9920-02G, manufactured by Hamamatsu Photonics). The measurement conditions for the absolute PL quantum yield measurement device were room temperature and an excitation wavelength of 365 nm, and a blank sample was prepared by placing 150 μl of the dispersion solvent of the charge transport ink composition, for example, 2-(2-isobutoxyethoxy)ethanol in Example 1 described below, in a quartz cell. The absolute quantum yield was calculated using the following formula (2): Absolute quantum yield = luminescence amount / absorption amount = (integral value of the emission spectrum of the measurement sample) / {(integral value of the excitation light spectrum of the blank sample) - (integral value of the excitation light spectrum of the measurement sample)} formula (2) (For example, in Example 1, the integral range of the excitation light spectrum was 355 nm to 375 nm, and the integral range of the emission spectrum was 400 nm to 740 nm.)

[0073] [Measurement of Current Density] The charge transporting ink composition was applied to a film of O ２ The solution was applied to an ITO substrate (Foresight Corporation, product name ITO (50 nm) Zebra Substrate_ver. 2.0, a 25 mm x 25 mm x 0.7 mm glass substrate with a 50 nm thick ITO film patterned on the surface) from which impurities had been removed using a plasma cleaning device (150 W, 30 seconds), and then pre-baked at 100°C for 30 seconds in an air atmosphere. This was then followed by main baking at 140°C for 15 minutes to form a 40 nm thin film on the ITO substrate. The surface of the obtained thin film was then coated with a vapor deposition device at a vacuum level of 1.0 x 10 －５An 80 nm thick aluminum thin film was formed at a pressure of 0.2 Pa and 0.2 nm / sec. Thereafter, to prevent deterioration of characteristics due to the influence of oxygen, water, etc. in the air, the ITO substrate and a desiccant (manufactured by Dynic Co., Ltd., product name HD-071010W-40) were placed between sealing substrates (manufactured by Premium Glass Co., Ltd., cell size 19 mm x 21 mm x 0.7 mm, excavation depth 0.4 mm or more) in a nitrogen atmosphere with an oxygen concentration of 2 ppm or less and a dew point of -76°C or less, and the sealing substrates were bonded together using an adhesive (manufactured by MORESCO Co., Ltd., product name MORESCO Moisture Cut WB90US(P)). 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 to obtain an electron-only device (EOD). A voltage of 1.0 V was applied to the device at room temperature and pressure for 0.01 seconds to measure the current density.

[0074] [Evaluation of QDEL Device Characteristics] First, an ITO substrate (Foresight Corporation, product name ITO (50 nm) Zebra Substrate_ver. 2.0, 25 mm × 25 mm × 0.7 mm glass substrate with a 50 nm thick ITO film patterned on its surface) was prepared by removing impurities from the substrate surface using an O2 plasma cleaning device at 150 W for 30 seconds. A PEDOT:PSS aqueous dispersion (Heraeus, product name Clevios™) was applied to the substrate as a hole injection layer (HIL) using a spin coater, and the substrate was pre-baked at 80°C for 1 minute in an air atmosphere. This was then baked at 150°C for 30 minutes to form a 30 nm HIL thin film on the ITO substrate. Next, PVK (polyvinylcarbazole, product number 368350, average molecular weight 25,000 to 50,000, manufactured by Aldrich) dissolved in chlorobenzene (manufactured by Junsei Chemical Co., Ltd.) at 0.5% by mass was applied onto the HIL thin film as a hole transport layer (HTL) using a spin coater, followed by post-baking at 200°C for 30 minutes in a nitrogen atmosphere to form a 20 nm HTL thin film on the HIL thin film. Next, a quantum dot dispersion (QNA, product name PureBlue.dots in Toluene_v2, toluene dispersion, concentration 3% by mass) was applied onto the HTL thin film as an emission layer (EmL) using a spin coater, followed by post-baking at 100°C for 10 minutes in a nitrogen atmosphere to form a 40 nm EmL thin film on the HTL thin film. Next, a charge transporting ink composition of an example or comparative example described below was applied as an electron transport layer (ETL) onto the EmL thin film using a spin coater, and then pre-baked at 100°C for 30 seconds in a nitrogen atmosphere. Then, the composition was baked at 140°C for 15 minutes to form a 40 nm ETL thin film on the EmL thin film. A vacuum evaporation apparatus was used to apply a 40 nm ETL thin film onto the surface of the obtained ETL thin film. －５An 80 nm thick aluminum thin film was formed at a pressure of 0.2 Pa and 0.2 nm / sec. Thereafter, in order to prevent deterioration of characteristics due to the influence of oxygen, water, etc. in the air, the ITO substrate on which the aluminum thin film had been formed and a desiccant (manufactured by Dynic Co., Ltd., product name HD-071010W-40) were placed between sealing substrates (manufactured by Premium Glass Co., Ltd., cell size 19 mm x 21 mm x 0.7 mm, excavation depth 0.4 mm or more) in a nitrogen atmosphere with an oxygen concentration of 2 ppm or less and a dew point of -76°C or less, and the sealing substrates were bonded together using an adhesive (manufactured by MORESCO Co., Ltd., product name MORESCO Moisture Cut WB90US(P)). The bonded sealing substrates were irradiated with UV light (wavelength: 365 nm, irradiation dose: 6,000 mJ / cm). ２ ), and then annealed at 80°C for 1 hour to cure the adhesive, yielding a QDEL device that emits blue light. This QDEL device was subjected to voltages of 0 to 12 V at 0.25 V intervals for 0.01 seconds at 25°C and atmospheric pressure, and the current density and luminescence intensity were measured. From the obtained measurement data, the voltage, current efficiency, external quantum efficiency, and LT90 at which 10 cd of luminescence was observed were calculated. The external quantum efficiency was calculated using the following formula (3): External quantum efficiency = 8.06 × 10 ５ × P × λ / I ... Equation (3) (P is the luminous intensity [W / m ２ ], λ is wavelength [m], and I is current [A]. LT90 was calculated by measuring the time it took for the initial luminance to decrease to 90%, assuming that the initial luminance was 100%, and normalizing the time in Example 1 to 100.

[0075] [Example 1] A 1-L recovery flask was charged with 197.40 g of methanol (Kanto Chemical Co., Inc., purity >99.5%) as an organic solvent and 12.43 g of zinc acetate dihydrate (Kanto Chemical Co., Inc., purity >99.0%) as a zinc salt. The mixture was stirred for 10 minutes with a magnetic stirrer to completely dissolve the zinc acetate dihydrate, producing a zinc acetate methanol solution. Next, a separate recovery flask was charged with 197.90 g of methanol as an organic solvent and 1.14 g of magnesium acetate tetrahydrate (as the salt of the metal element to be doped, such that the magnesium element ratio was 10 mol% relative to the zinc element content in the 12.43 g of zinc acetate dihydrate). The mixture was stirred to produce a solution in which the magnesium acetate tetrahydrate was completely dissolved. The entire amount of this solution was poured into the zinc acetate methanol solution, yielding a mixed solution of zinc acetate, magnesium acetate, and methanol. Next, 22.83 g of 48% potassium hydroxide aqueous solution as an alkaline solution and 195.40 g of methanol as an organic solvent were mixed and stirred, and the resulting solution was poured entirely into the zinc acetate, magnesium acetate, and methanol mixed solution and heated with stirring at 60°C for 2 hours to obtain a reaction solution. The resulting reaction solution was placed in a centrifuge tube and centrifuged at 9000 rpm for 3 minutes, after which the supernatant was removed to obtain a precipitate. Methanol was added to the resulting precipitate, and the mixture was shaken, followed by centrifugation again to remove the supernatant to obtain a precipitate. Methanol was added to the resulting precipitate and re-dispersed to obtain an organic solvent dispersion (A) containing magnesium-doped zinc oxide particles.

[0076] Next, as a washing step for removing metal cations, 50 g of the obtained organic solvent dispersion (A) and 100 g of methanol were placed in an ultrafilter, and the step of concentrating the dispersion until the particle solid content became 3 mass % was repeated five times, thereby obtaining an organic solvent dispersion (B) of magnesium-doped zinc oxide particles having a reduced amount of metal cations.

[0077] The solid content of the obtained dispersion (B) was 3.0% by mass, the metal cation content was 10 ppm or less (below the lower limit of quantification), and the anion species was COO － The anion content was 1407 ppm, and the doped element was detected as Mg element from the XPS spectrum. The chemical state of the doped element was Mg(OH). ２No endothermic peak due to the above was confirmed, and the average primary particle diameter of the magnesium-doped zinc oxide particles observed by TEM was 5 nm.

[0078] [Production Example 2] In Production Example 2, an organic solvent dispersion containing core-shell particles formed by coating the magnesium-doped zinc oxide particles contained in Dispersion (B) of Production Example 1 with a metal oxide layer (shell) was investigated. First, a mixture of 0.42 g of tin chloride pentahydrate and 1.68 g of methanol was added to 63.98 g of Organic Solvent Dispersion (B) containing magnesium-doped zinc oxide particles obtained by the same process as in Production Example 1, and the mixture was heated at 60°C for 3 hours with stirring to obtain a reaction solution. The resulting reaction solution was placed in a centrifuge tube and centrifuged, after which the supernatant was removed to obtain a precipitate.

[0079] Next, as a washing step for removing metal cations, the obtained precipitate was added with methanol to a solid content of 3% by mass, followed by shaking, and then centrifuging again to remove the supernatant. This step was repeated five times to obtain a precipitate. Furthermore, the obtained precipitate was redispersed in methanol to a solid content of 3% by mass, thereby obtaining an organic solvent dispersion (C) containing tin oxide-coated, magnesium-doped zinc oxide particles. That is, the particles are magnesium-doped zinc oxide particles coated with a tin oxide layer.

[0080] The solid content of the obtained dispersion was 2.3% by mass, the metal cation content was 10 ppm or less (below the lower limit of quantification), and the anion species was COO － The anion content was 1407 ppm, and the doped element was detected as Mg element from the XPS spectrum. The chemical state of the doped element was Mg(OH). ２ No endothermic peak due to the above was confirmed, and the average primary particle size of the tin oxide-coated magnesium-doped zinc oxide particles observed by TEM was 5 nm.

[0081] Comparative Production Example 1 An organic solvent dispersion (A) containing magnesium-doped zinc oxide particles was obtained by the same process as in Production Example 1. However, the second centrifugal washing and the washing process using an ultrafilter in Production Example 1 were not performed. The solids concentration of the obtained dispersion (A) was 2.8 mass %, the metal cation content was 2840 ppm, and the anion species was COO － The anion content was 1407 ppm, and the doped element was detected as Mg element from the XPS spectrum. The chemical state of the doped element was Mg(OH). ２ No endothermic peak due to the above was confirmed, and the average primary particle diameter of the magnesium-doped zinc oxide particles observed by TEM was 5 nm.

[0082] Example 1: 5.00 g of the dispersion (B) of magnesium-doped zinc oxide particles prepared in Example 1 and 2.85 g of 2-(2-isobutoxyethoxy)ethanol were placed in a 50 mL recovery flask, the pressure reduced to 100 Torr using an evaporator, and the mixture was heated at 80°C for 10 minutes. The pressure was then reduced to 50 Torr and the mixture was heated at 80°C for 2 hours to remove the methanol, yielding a dispersion of magnesium-doped zinc oxide particles in a high-boiling-point solvent. 0.0375 g (25% by mass, based on the solids content of the dispersion) of propionic acid (manufactured by Kanto Chemical Co., Inc., purity >98.0%) was added as a ligand, and the mixture was stirred at room temperature for 10 minutes and then heated at 52°C for 90 minutes, yielding a dispersion of magnesium-doped zinc oxide particles in a high-boiling-point solvent (metal element-doped metal oxide dispersion). The 50% volume average diameter of the resulting dispersion was 32 nm, and the 90% volume average diameter was 74 nm. Next, 0.67 parts by mass (2.000 g) of 2-(2-isobutoxyethoxy)ethanol was added to 100 parts by mass (0.150 g as solids) of the high-boiling point solvent dispersion, and the mixture was stirred. The mixture was then filtered through a PP syringe filter (Puradisc syringe filter, manufactured by Cytiva (Whatman)) with a pore size of 0.2 μm to prepare a charge-transporting ink composition. The absolute quantum yield of the resulting charge-transporting ink composition was 0.8%, the PL intensity of the QDs coated with the charge-transporting ink composition was 122% (peak top wavelength: 456 nm), and the current density was 201 mA / cm. ２The QDEL device obtained in the above section [Evaluation of QDEL Device Characteristics] had a voltage of 10.9 V at 10 cd, a current efficiency of 0.3 cd / A, an external quantum efficiency of 0.27%, and an LT90 of 100%.

[0083] Example 2: 5.00 g of the dispersion (C) of tin oxide-coated magnesium-doped zinc oxide particles prepared in Example 2 and 2.85 g of 2-(2-isobutoxyethoxy)ethanol were placed in a 50 mL recovery flask, the flask was evaporated to 100 Torr, heated at 80°C for 10 minutes, and then evaporated to 50 Torr and heated at 80°C for 2 hours to remove the methanol, yielding a dispersion of magnesium-doped zinc oxide particles in a high-boiling point solvent. 0.0375 g (25% by mass, based on the solids content of the dispersion) of propionic acid (Kanto Chemical Co., Inc., purity >98.0%) was added as a ligand, stirred at room temperature for 10 minutes, and then heated at 52°C for 10 minutes to yield a dispersion of magnesium-doped zinc oxide particles in a high-boiling point solvent (metal element-doped metal oxide dispersion). The resulting dispersion had a 50% volume average diameter of 17 nm and a 90% volume average diameter of 39 nm. Next, 0.67 parts by mass (2.000 g) of 2-(2-isobutoxyethoxy)ethanol was added to 100 parts by mass (0.150 g as solids) of the high-boiling point solvent dispersion, and the mixture was stirred. The mixture was then filtered through a PP syringe filter with a pore size of 0.2 μm (Puradisc syringe filter, manufactured by Cytiva (Whatman) Co., Ltd.) to prepare a charge-transporting ink composition. The resulting charge-transporting ink composition had an absolute quantum yield of 1.8%, PL characteristics of 70% (peak top wavelength: 456 nm), and a current density of 222 mA / cm. ２ The QDEL device obtained in the above section [Evaluation of QDEL Device Characteristics] had a voltage of 10.6 V at 10 cd, a current efficiency of 0.3 cd / A, an external quantum efficiency of 0.25%, and an LT90 of 114%.

[0084] Comparative Example 1: 5.00 g of the dispersion (A) of magnesium-doped zinc oxide particles prepared in Comparative Production Example 1 and 2.69 g of 2-(2-isobutoxyethoxy)ethanol were placed in a 50 mL recovery flask, the pressure reduced to 100 Torr using an evaporator, and the mixture was heated at 80°C for 10 minutes. The pressure was then reduced to 50 Torr and the mixture was heated at 80°C for 2 hours to remove the methanol, yielding a dispersion of magnesium-doped zinc oxide particles in a high-boiling-point solvent. 0.0354 g (25% by mass, based on the solids content of the dispersion) of propionic acid (manufactured by Kanto Chemical Co., Inc., purity >98.0%) was added as a ligand, and the mixture was stirred at room temperature for 10 minutes and then heated at 52°C for 90 minutes, yielding a dispersion of magnesium-doped zinc oxide particles in a high-boiling-point solvent (metal element-doped metal oxide dispersion). The 50% volume average diameter of the resulting dispersion was 70 nm, and the 90% volume average diameter was 393 nm.

[0085]

[0086] As shown in Table 1, Production Examples 1 and 2 differ in that a washing step for removing metal cations is carried out, whereas Comparative Production Example 1 does not. Also, Production Example 1 and Comparative Production Example 1 do not coat the particles contained in the dispersion, whereas Production Example 2 differs in that the particles contained in the dispersion are coated and have a core-shell structure.

[0087]

[0088] As shown in the evaluation results in Table 2, the dispersions of Examples 1 and 2 were found to have excellent dispersibility of metal element-doped metal oxide particles, unlike the dispersion of Comparative Example 1. Furthermore, as shown in the coating film evaluation in the evaluation results in Table 2, the coating films of the charge transport ink compositions prepared using the dispersions of Examples 1 and 2 were found to fully satisfy the properties required for an electron transport layer (defect levels, PL intensity of the quantum dots when laminated as an ETL on a quantum dot layer, and charge transport properties).

[0089] Furthermore, as shown by the evaluation results of the absolute quantum yield, the dispersions of Examples 1 and 2 had absolute quantum yields of 0.8 to 1.8%, and it was found that almost no luminescence was observed even when irradiated with excitation light of 365 nm. When defect levels due to oxygen vacancies exist in the metal element-doped metal oxide particles, yellow luminescence occurs around 570 nm, and the absolute quantum yield value becomes high. These results indicate that the particles contained in the dispersions of Examples 1 and 2 have few oxygen vacancies.

[0090] Furthermore, evaluation of PL intensity evaluation elements showed that PL characteristics of PL intensity evaluation elements laminated with the charge transport ink compositions of Examples 1 and 2 were 70 to 122%, demonstrating that PL intensity, which indicates the degree of light emission from QDs that passed through the electron transport layer, could be maintained. When the metal-element-doped metal oxide particles contained in the charge transport layer have many defects, excitons generated within the QDs are trapped in the defect levels of the charge transport layer, resulting in a decrease in PL intensity. Therefore, the particles of Examples 1 and 2 have few defects, and it was shown that laminating the charge transport ink composition on QDs does not result in a decrease in PL intensity.

[0091] Furthermore, as shown by the evaluation results of the EOD device, when the charge transporting ink compositions of Examples 1 and 2 were formed into coating films, the current density was 201 to 222 mA / cm ２ It was found that the QDEL device exhibited sufficient charge transport properties. Furthermore, as shown in the evaluation results of the QDEL device, blue light emission was observed from the QDs used as the emitting layer EmL, demonstrating that the charge transport ink composition of the present invention can be used as an electron transport layer ETL. Furthermore, the LT90 results showed that the charge transport ink composition of Example 1 provided a sufficient device operating life, but Example 2 also provided a higher LT90 of 114%, demonstrating a longer device operating life. This is because the magnesium-doped zinc oxide particles were coated with tin oxide, thereby improving their stability as an electron transport layer ETL.

[0092] The dispersion of the present invention has excellent dispersibility of metal element-doped metal oxide particles, and by using this dispersion, the properties required for an electron transport layer (for example, flatness, defect amount, PL intensity of the quantum dots when laminated as an ETL on a quantum dot layer, and charge transportability) are satisfied. Therefore, it is possible to provide a dispersion, a charge transport ink composition, a charge transport thin film, and an electronic device such as an organic EL device or a quantum dot EL device, which have excellent properties.

Claims

1. A metal element-doped metal oxide dispersion liquid comprising metal element-doped metal oxide particles and a solvent as a dispersion medium, wherein the metal cation content calculated from the Li, Na, K, and Ca contained in the solvent is 1 to 2700 ppm, wherein the metal oxide particles are particles whose main component is zinc oxide, and the metal element doped into the zinc oxide-based particles comprises one or more elements selected from Al, Mg, Li, Ca, Ga, and In, and the doped metal element is contained in a ratio of 2 to 20 mol % relative to the zinc element.

2. The metal element-doped metal oxide dispersion according to claim 1, wherein the metal element-doped metal oxide particles have an average primary particle size of 2 to 50 nm.

3. The metal element-doped metal oxide dispersion liquid according to claim 1, wherein the powder obtained by drying the metal element-doped metal oxide dispersion liquid at 120°C is subjected to thermal analysis by heating the powder in an air atmosphere at a temperature increase rate of 10°C / min, and the DTA curve obtained at measurement temperatures of 200°C to 400°C shows no endothermic peak.

4. The surface of the metal element-doped metal oxide particles is coated with a metal oxide layer and / or a metal sulfide layer as a coating layer, the metal oxide particles are particles containing zinc oxide as a main component, and the coating layer is Al ２ O ３ , MgO, SiO ２ , SnO ２ 2. The metal element-doped metal oxide dispersion according to claim 1, comprising one or more metal oxides and / or metal sulfides selected from the group consisting of ZnS and ZnS.

5. The metal element-doped metal oxide dispersion according to claim 1, wherein the 50% volume average diameter, as measured by dynamic light scattering, is 2 to 50 nm, the 90% volume average diameter is 2 to 100 nm, and the value obtained by subtracting the 10% volume average diameter from the 90% volume average diameter is 50 nm or less.

6. The metal element-doped metal oxide dispersion according to claim 4, wherein the metal element-doped metal oxide dispersion having a solids content of 0.5 mass % has an absolute quantum yield of 0 to 10%, calculated from the peak top in the wavelength range of 500 nm to 600 nm in the emission spectrum when irradiated with ultraviolet light having a wavelength of 365 nm.

7. The metal element-doped metal oxide dispersion liquid according to claim 1, wherein the solvent comprises one or more organic solvents selected from the group consisting of alcohols, ketones, esters, ethers, amides, hydrocarbons, cyano group-containing solvents, halogen-containing solvents, sulfonyl group-containing solvents, and carboxyl group-containing solvents.

8. The compound further contains a ligand having an amine group, a carboxylic acid group, or a thiol group, and is expressed by the following formula (1): χ = Vm / kT × (δs - δm)^2 + 0.34 ... formula (1) (Vm is the molecular volume of the solvent [m ３ ], k is the Boltzmann constant [J / K], T is the temperature in the system of the metal element-doped metal oxide dispersion [K], and δs is the Hansen solubility parameter of the solvent [Pa １／２ ], and δm is the Hansen solubility parameter of the ligand [Pa １／２ 2. The metal element-doped metal oxide dispersion according to claim 1, wherein the χ parameter calculated from the above formula is 0.34 to 0.

50.

9. The metal element-doped metal oxide dispersion according to claim 8, wherein the amount of the ligand is 1 to 200 mass % based on the metal element-doped metal oxide particles.

10. A charge transporting ink composition comprising the metal element-doped metal oxide dispersion liquid according to claim 1 and a solvent.

11. A charge transporting thin film obtained from the charge transporting ink composition according to claim 10.

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

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

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

15. A method for producing a metal element-doped metal oxide dispersion liquid according to claim 1, comprising the following steps (a) and (b): step (a): adding an alkaline solution to a solution obtained by mixing an organic solvent, a zinc salt, and a salt of the metal element to be doped as raw materials, to produce an organic solvent dispersion liquid containing metal element-doped metal oxide particles; and step (b): washing the organic solvent dispersion liquid to remove metal cations.

16. The method for producing a metal element-doped metal oxide dispersion according to claim 15, further comprising the following steps (c) and (d), in this order or in reverse order: step (c): adding a ligand to the organic solvent dispersion from which the metal cations have been removed, and heating at 20°C to 150°C for 0.1 to 20 hours; and step (d): adding a high-boiling organic solvent to the organic solvent dispersion from which the metal cations have been removed, and removing the organic solvent derived from the raw material.

Images