Colloidal solution, method for producing same, and display device

Abstract

The present disclosure achieves a quantum dot (QD) ink having good lightfastness and coating performance. A colloidal solution (1) comprises: a dispersion medium (100); and semiconductor nanoparticles and composite particles (10) dispersed in the dispersion medium (100) as dispersoids. The composite particles (10) comprise: semiconductor nanoparticles (11); and a matrix component (12) constituting a particulate phase that is immiscible with the dispersion medium (100). The content of the composite particles (10) is 50 mass% or less of the total amount of dispersoids.

Description

Colloidal solution, its manufacturing method and display device

[0001] The present disclosure relates to a colloidal solution, a method for producing the same, and a display device.

[0002] Various display devices equipped with light-emitting elements have been developed. Known examples of such light-emitting elements include OLEDs (organic light-emitting diodes) and QLEDs (quantum dot light-emitting diodes). The use of quantum dot technology in the manufacture of such light-emitting elements is also being considered. One example of quantum dot (QD) technology for manufacturing such display devices is a known QD ink, which is used to manufacture a QD film containing a blue-absorbing material and contains the blue-absorbing material and 0.1 to 30% by mass of a scattering material (see, for example, Patent Document 1).

[0003] International Publication No. 2020 / 068379

[0004] Generally, QD inks can be degraded by light absorption. Degradation caused by high-energy-density light is particularly pronounced. When the QD ink contains particles significantly larger than QDs, such as the scattering materials described above, the light is scattered, effectively suppressing degradation caused by irradiated light. However, the inclusion of particles larger than QDs in the QD ink can degrade the application properties of the QD ink, resulting in a film that does not perform the desired function.

[0005] One aspect of the present disclosure aims to provide a technology that can realize a QD ink that has good light resistance and coating performance.

[0006] In order to solve the above problems, a colloidal solution according to one embodiment of the present disclosure is a colloidal solution containing a dispersion medium, and semiconductor nanoparticles and composite particles containing semiconductor nanoparticles dispersed in the dispersion medium as dispersoids, wherein the composite particles have a matrix component that constitutes a particulate phase that is incompatible with the dispersion medium, and the content of the composite particles is 50 mass% or less of the total dispersoids.

[0007] In addition, in order to solve the above-mentioned problems, a method for producing a colloidal solution according to one embodiment of the present disclosure suspends semiconductor nanoparticles, a dispersion medium, and a matrix component that is incompatible with the dispersion medium, and produces composite particles containing semiconductor nanoparticles, in an amount of 50% by mass or less of the total dispersed matter, in which the particulate phase that is incompatible with the dispersion medium and that is constituted by the matrix component contains semiconductor nanoparticles.

[0008] Furthermore, a display device according to an aspect of the present disclosure includes a semiconductor functional layer formed by applying the above-described colloidal solution and composed of the semiconductor nanoparticles.

[0009] According to one aspect of the present disclosure, a QD ink having good lightfastness and coating performance can be realized, and a device having an excellent film made of such a QD ink can be provided.

[0010] FIG. 1 is a diagram schematically showing the effect of light on a colloidal solution according to the present disclosure; FIG. 2 is a diagram schematically showing the effect of light on a colloidal solution of conventional semiconductor nanoparticles; FIG. 3 is a diagram schematically showing a first aspect of a composite particle in a colloidal solution according to the present disclosure; FIG. 4 is a diagram schematically showing a second aspect of a composite particle in a colloidal solution according to the present disclosure; FIG. 5 is a diagram schematically showing a display device according to an embodiment of the present disclosure; FIG. 6 is a diagram schematically showing the layer structure of a light-emitting element according to an embodiment of the present disclosure.

[0011] In embodiments of the present disclosure, colloidal solutions containing semiconductor nanoparticles such as QDs are further imparted with light scattering properties, thereby reducing the amount of light and light density impinging on the colloidal solution and improving the light resistance of the colloidal solution.

[0012] Colloidal Solution A colloidal solution according to an embodiment of the present disclosure contains a dispersion medium, semiconductor nanoparticles, and composite particles.

[0013] [Dispersion Medium] The dispersion medium may be any liquid that can be used in a dispersion liquid of semiconductor nanoparticles. The dispersion medium may be, for example, a liquid component used as a dispersion medium for QD ink. For example, the dispersion medium may be a polar solvent, examples of which include water, N,N-dimethylformamide, dimethyl sulfoxide, ethanol, isopropyl alcohol, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. Alternatively, the dispersion medium may be a nonpolar solvent, examples of which include hexane, octane, decane, dodecane, tetradecane, and toluene.

[0014] [Semiconductor Nanoparticles] Semiconductor nanoparticles are a type of dispersoid in a colloidal solution and are dispersed as dispersoid in a dispersion medium. Semiconductor nanoparticles are inorganic or organic particles that exhibit semiconductor properties and are nano-sized particles. Examples of semiconductor nanoparticles include nano-sized particles of Si, PbS, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, ZnSeTe, AIGS, ZnO, MgZnO, AlZnO, LiZnO, and NiO. Semiconductor nanoparticles may be particles with a core-shell structure. For example, semiconductor nanoparticles may have the above-mentioned particle as a core particle and a shell layer covering it, and may be particles that exhibit semiconductor properties as a whole. Note that the shell layer is composed of a different component from the core particle.

[0015] The particle size of the semiconductor nanoparticles is, for example, an average particle size, and can be measured, for example, by observation with a transmission electron microscope. The smaller the particle size of the semiconductor nanoparticles, the more preferable it is. For example, the average particle size may be 30 nm or less, 20 nm or less, or 15 nm or less. The lower limit of the particle size of the semiconductor nanoparticles is not limited, but may be, for example, 10 nm or more.

[0016] The structure of the semiconductor nanoparticles is not limited, and they may have a ligand. For example, the semiconductor nanoparticles may be core-shell particles having a shell layer composed of zinc halide containing 10 mol % or more of zinc. Semiconductor nanoparticles with such a structure can form clusters with a portion of other ligands such as xanthic acids to enhance light scattering, while filling the zinc vacancies in the shell with the other ligands, thereby maintaining good optical properties of the semiconductor nanoparticles.

[0017] [Composite Particles] The composite particles contain the semiconductor nanoparticles and a matrix component. The matrix component is a component that constitutes a particulate phase that is incompatible with the dispersion medium. The matrix component will be described later.

[0018] In the colloidal solution according to the present disclosure, the content of the composite particles is 50% by mass or less of the total dispersed phase. The content of the composite component may be an amount that can scatter light irradiated onto the colloidal solution so as to sufficiently suppress the light degradation described below, and may be appropriately determined depending on the light irradiated or the light resistance of the semiconductor nanoparticles. From this perspective, the content of the composite component may be 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less.

[0019] <Matrix Component> The matrix component is appropriately selected from components capable of forming a particulate phase that is incompatible with the dispersion medium in the colloidal solution, depending on the type of dispersion medium. For example, when the dispersion medium is a polar solvent, the matrix component may be an alkoxysilane. When the matrix component is an alkoxysilane, the semiconductor nanoparticles preferably have a silane-based ligand that has affinity for the alkoxysilane.

[0020] Furthermore, when the dispersion medium is a nonpolar solvent, the matrix component may contain a polar solvent in an amount of less than 10% by mass relative to the dispersion medium. In this case, the content of the polar solvent may be 5% by mass or less, or 3% by mass or less relative to the dispersion medium, as long as a particulate liquid phase can be formed in the dispersoid. In this case, it is preferable that the matrix component further contains a ligand of the semiconductor nanoparticles or a component having affinity therefor.

[0021] The matrix component may be another component used in place of or in combination with the above-mentioned component. For example, the matrix component may further contain a xanthogenic acid. The matrix component further contains a xanthogenic acid, which is preferable from the viewpoint of enhancing the stability of the semiconductor nanoparticles in the colloidal solution by multidentate coordination with the semiconductor nanoparticles. The xanthogenic acid may be one or more types, and examples of xanthogenic acids include zinc methylxanthogenate, zinc ethylxanthogenate, zinc isopropylxanthogenate, and zinc butylxanthogenate.

[0022] The content of xanthogenic acids in the colloidal solution can be appropriately determined within a range that achieves the above-mentioned effects. For example, the mass-based content of xanthogenic acids relative to the content of semiconductor nanoparticles is preferably more than half the mass of the semiconductor nanoparticles. Furthermore, the content of xanthogenic acids in the colloidal solution is preferably 1 mass% or more.

[0023] The upper limit of the xanthogenic acid content can be determined appropriately within the range in which the above-mentioned effects are obtained, and may be, for example, 200 mass % or less of the semiconductor nanoparticle content, or 100 mg / ml or less in the colloidal solution.

[0024] The matrix component may further contain a zinc halide. Similar to the case where the matrix component further contains a xanthogenic acid, the case where the matrix component further contains a zinc halide is also preferable from the viewpoint of enhancing the stability of the semiconductor nanoparticles. One or more types of zinc halide may be used, and examples of zinc halides include zinc fluoride, zinc chloride, zinc iodide, and zinc bromide.

[0025] The content of zinc halide in the colloidal solution can be appropriately determined within the range in which the above-mentioned effects can be obtained.For example, it is preferable that the mass-based content of zinc halide is more than half the mass of the semiconductor nanoparticles.In addition, in terms of the content in the colloidal solution, the content of zinc halide is preferably 1 mass% or more.

[0026] The upper limit of the zinc halide content can be determined appropriately within the range in which the above-mentioned effects are obtained, and may be, for example, 50 mass % or less of the semiconductor nanoparticle content, or 25 mg / ml or less in the colloidal solution.

[0027] [Other Components] The colloidal solution of the present disclosure may further contain other components in addition to the components described above, as long as the effects of the present disclosure are obtained. Examples of such other components include conventional scattering materials. Conventional scattering materials are, for example, metal oxide particles with a diameter of 100 nm or more, examples of which include titanium oxide particles, zirconium oxide particles, aluminum oxide particles, and zinc oxide particles. When the scattering material is further contained, the colloidal solution may be used after removing the scattering material by filtration. In the present disclosure, the colloidal solution may further contain a rigid medium such as the scattering material.

[0028] The content of the scattering material can be appropriately determined within a range in which scattered light can be obtained, for example, 50 mass % or less of the total medium in the colloidal solution. Even in such a form, photodegradation of the colloidal solution can be suppressed by light scattering, and the stability of the colloidal solution can be improved.

[0029] However, in the present disclosure, the composite particles can suppress photodegradation of the colloidal solution by scattering light, and therefore the colloidal solution of the present disclosure does not need to substantially contain a rigid medium such as a scattering material.

[0030] [Light Scattering Properties] Colloidal particles have light scattering properties due to the composite particles. The composite particles can be prepared depending on the light to be scattered. For example, the composite particles have light scattering properties for light of a wavelength absorbed by semiconductor nanoparticles. The wavelength of light absorbed by semiconductor nanoparticles can be determined by measuring the absorption characteristics of a colloidal solution containing only semiconductor nanoparticles as a dispersoid. It is preferable for the composite particles to have such light scattering properties in order to fully exhibit the light resistance of the colloidal solution.

[0031] The wavelength of light absorbed by the semiconductor nanoparticles may be 300 nm or more, which is effective from the viewpoint of preventing photodegradation of the semiconductor nanoparticles in the colloidal solution due to light abundant in nature.

[0032] The composite particles only need to have a particle size substantially larger than the wavelength of light absorbed by the semiconductor nanoparticles. The particle size of the composite particles can be measured, for example, by dynamic light scattering. The particle size of the composite particles can be adjusted by the type or amount of matrix components. For example, the volume-based median kinetic diameter of the colloidal solution may be equal to or greater than the wavelength of the light. The kinetic diameter of the colloidal solution refers to the particle size of the composite particles. Having the volume-based median kinetic diameter equal to or greater than the wavelength of the light is preferable from the viewpoint of enhancing the scattering of light absorbed by the semiconductor nanoparticles.

[0033] Furthermore, when a film having an average thickness of 50 nm is produced by spin-coating the colloidal solution, the arithmetic mean roughness Ra of the film may be 50 nm or less. Having an Ra of 50 nm or less is preferable from the viewpoint of suppressing photodegradation of the colloidal solution due to light scattering and enhancing the photostability of the colloidal solution. The smaller the Ra, the more preferable it is within a range in which the effects of the present disclosure can be obtained. From this viewpoint, the Ra may be 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less.

[0034] In the colloidal solution of the present disclosure, the proportion of primary particles larger than twice the average diameter of the semiconductor nanoparticles may be less than 5% by volume relative to the semiconductor nanoparticles. The average diameter here refers to the median diameter based on volume. Furthermore, the term "primary particles" refers to the particle diameter of the semiconductor nanoparticles. Such a colloidal solution is advantageous from the viewpoint of achieving the above-mentioned Ra.

[0035] Furthermore, the haze of the colloidal solution of the present disclosure at an optical path length of 1 cm may be 5% or more. Colloidal solutions typically have a cloudy appearance because the composite particles exhibit light scattering properties. The haze can be appropriately determined within a range in which the light scattering effect of the composite particles is fully exhibited, and from this perspective, it may be 10% or more, or 20% or more. The haze should be sufficiently high from the perspective of exhibiting light scattering properties, and the upper limit of the haze may be appropriately set, as necessary, to a value greater than 5% within a range in which the effects of the present disclosure can be obtained.

[0036] FIG. 1 is a schematic diagram illustrating the effect of light on a colloidal solution according to the present disclosure. The colloidal solution CS according to the present disclosure contains composite particles, as described above. The composite particles are composed of semiconductor nanoparticles and matrix components that form liquid-phase particles that are incompatible with the dispersoid, and therefore have a particle size that is sufficiently larger than that of semiconductor nanoparticles. Therefore, even when the colloidal solution CS is irradiated with irradiation light Li, the irradiation light Li is scattered by the composite particles and becomes scattered light Ls, and does not substantially reach the depths of the colloidal solution CS. Therefore, the region Aa where photodegradation of the semiconductor nanoparticles occurs due to irradiation with irradiation light Li does not occur or is sufficiently limited.

[0037] FIG. 2 is a diagram schematically illustrating the effect of light on a conventional colloidal solution of semiconductor nanoparticles. Assume that this colloidal solution CS does not contain any scattering material. When the colloidal solution CS is irradiated with irradiation light Li, the irradiation light Li passes through the colloidal solution CS. This is because the particle size of the semiconductor nanoparticles is sufficiently small compared to the wavelength of the irradiation light Li. Therefore, photodegradation of the semiconductor nanoparticles occurs in the vicinity of the irradiation light Li irradiating the colloidal solution CS, and the region Aa where this photodegradation occurs is widespread within the colloidal solution CS.

[0038] [Method for Producing Colloidal Solution] The colloidal solution of the present disclosure can be produced by gently agglomerating some of the semiconductor nanoparticles in a dispersion of semiconductor nanoparticles. That is, the colloidal solution of the present disclosure can be produced by suspending semiconductor nanoparticles, a dispersion medium, and a matrix component that is incompatible with the dispersion medium, and producing composite particles containing semiconductor nanoparticles, in which the particulate phase constituted by the matrix component and incompatible with the dispersion medium contains semiconductor nanoparticles, in an amount of 50 mass% or less of the total dispersed matter.

[0039] From the viewpoint of introducing desired ligands into the semiconductor nanoparticles, the production method may further include a step of adding one or more components selected from the group consisting of zinc halide, mercaptosilane, and xanthogenic acids to the semiconductor nanoparticles or a dispersion thereof to obtain a slurry. The dispersoid in the slurry is used for the semiconductor nanoparticles to be suspended in a dispersion medium. By introducing these ligands into the semiconductor nanoparticles, the colloidal solution can be maintained in a stable state, enabling the production of products using the colloidal solution with a high yield.

[0040] The introduction of the ligand may be a replacement of the above-mentioned ligand or an addition. That is, when the semiconductor nanoparticles originally have a ligand, the original ligand may be removed and then the above-mentioned ligand may be added. Alternatively, the above-mentioned ligand may be added to the semiconductor nanoparticles in a state where the semiconductor nanoparticles originally have a ligand, so that a portion of the above-mentioned ligand is introduced into the semiconductor nanoparticles.

[0041] The production method may further include a step of filtering the produced colloidal solution, which is preferable from the viewpoint of enabling high-yield production of products using the colloidal solution.

[0042] (First Aspect) Fig. 3 is a diagram schematically illustrating a first aspect of composite particles in a colloidal solution according to the present disclosure. The colloidal solution 1 includes a dispersion medium 100 and composite particles 10 formed therein. The composite particles 10 include semiconductor nanoparticles 11 and a matrix component 12. Note that in Fig. 3, the semiconductor nanoparticles 11 that do not constitute the composite particles 10 in the dispersion medium 100 are omitted.

[0043] In the first embodiment, the dispersion medium 100 is a polar solvent such as water, ethanol, or DMF. The semiconductor nanoparticles 11 are QDs having, for example, mercaptosilane (e.g., (3-mercaptopropyl)triethoxysilane) as a ligand. The matrix component 12 is, for example, an alkyl silicate (CxHyOzSiw, e.g., tetramethylorthosilicate).

[0044] The semiconductor nanoparticles 11 and the matrix component 12 are loosely spaced close to each other and behave as a group, forming a composite particle 10. The composite particle 10 forms a refractive index boundary on the μm scale, causing light scattering, but is flexible and therefore does not interfere with coating and film formation.

[0045] In this way, the formation of large micelles (composite particles 10) in colloidal solution 1 increases the intensity of light scattering, further improving the light resistance of the colloidal solution. For example, colloidal solution 1 exhibits light scattering properties with a haze of about 20% in a solution with an optical path length of 1 cm, and can achieve a median volume ratio of the dynamic diameter that is equal to or greater than the wavelength of light absorbed by semiconductor nanoparticles 11. In this way, colloidal solution 1 exhibits strong light scattering, further improving its light resistance.

[0046] (Second Aspect) Fig. 4 is a diagram schematically illustrating a second aspect of composite particles in a colloidal solution according to the present disclosure. The colloidal solution 2 includes a dispersion medium 200 and a composite particle 20 formed therein. The composite particle 20 includes a semiconductor nanoparticle 11 and matrix components 22A and 22B. Note that the semiconductor nanoparticles 11 in the dispersion medium 200 are omitted from Fig. 4.

[0047] In the second embodiment, the dispersion medium 200 is a non-polar solvent, such as toluene. The semiconductor nanoparticles 11 are QDs having, for example, mercaptosilane (e.g., (3-mercaptopropyl)triethoxysilane) as a ligand. The matrix component 22A is a polar solvent, such as water. The matrix component 22B is, for example, mercaptosilane or its reaction product with water. The mercaptosilane is the same as the ligand of the semiconductor nanoparticles 11.

[0048] The semiconductor nanoparticles 11 and the matrix components 22A and 22B are loosely spaced close to each other and behave as a group, forming a composite particle 20. As in the first embodiment, the composite particle 20 forms a refractive index boundary surface on the μm scale, causing light scattering, but is flexible and therefore does not interfere with coating and film formation.

[0049] Similar to the colloidal solution, the colloidal solution 2 exhibits light scattering properties with a haze of about 20% in a solution with an optical path length of 1 cm, and can achieve a median volume ratio of the dynamic diameter that is equal to or greater than the wavelength of light absorbed by the semiconductor nanoparticles 11. Therefore, the colloidal solution 2 also exhibits strong light scattering, further improving its light resistance.

[0050] Furthermore, the composite particles 20 of the colloidal solution 2 contain water as a matrix component, which makes it easier to form large (flexible) micelles, which is advantageous from the viewpoint of increasing the light scattering intensity and improving light resistance.

[0051] The display device of the present disclosure has a semiconductor functional layer formed by coating the colloidal solution and composed of semiconductor nanoparticles. The semiconductor functional layer may contain the matrix component, a reaction product of the matrix component in the colloidal solution, or a residue thereof.

[0052] The content of the organic component in the semiconductor functional layer is preferably low from the viewpoint of fully exhibiting the desired function of the semiconductor functional layer. The organic component refers to the ligand of the organic component possessed by the semiconductor nanoparticles, its free form, or their residues. From the above viewpoint, the content of the organic component in the semiconductor functional layer may be 10 vol% or less, 5 vol% or less, or 3 vol% or less. Furthermore, with regard to the composition of the semiconductor functional layer, for example, 90 vol% or more of the semiconductor functional layer is composed of a reaction product of the semiconductor nanoparticles and the matrix component, and the reaction product of the matrix component may be silicon oxide or zinc sulfide. In such a semiconductor functional layer, deterioration of the semiconductor functional layer due to current or light is further suppressed, which is preferable from the viewpoint of extending the life of the display device.

[0053] The thickness of the semiconductor functional layer is thinner than the wavelength of visible light, and may be, for example, 100 nm or less, or 50 nm or less. Furthermore, from the viewpoint of the light-emitting characteristics of the display device, the arithmetic mean roughness Ra of the semiconductor functional layer is preferably less than the thickness of the semiconductor functional layer, more preferably equal to or less than half the thickness of the semiconductor functional layer, and even more preferably equal to or less than one-tenth the thickness of the semiconductor functional layer.

[0054] The display device of the present disclosure is a full-color display device having light-emitting elements that emit light of each color, for example, RGB, and at least one of the light-emitting elements of each color is fabricated using the colloidal solution of the present disclosure. The display device of the present disclosure can be configured in the same manner as known display devices that include light-emitting elements, except that it includes the light-emitting elements.

[0055] [Specific Embodiments] The display device and the light-emitting element included therein according to the present disclosure will be further described below with reference to the drawings. In the following description, when a symbol R, G, or B representing each emitted color is added to a symbol, it means a configuration of a specific emitted color, and when a symbol representing each emitted color is not added, it means a configuration common to all colors regardless of the emitted color.

[0056] 5 is a diagram schematically illustrating a display device according to an embodiment of the present disclosure. As shown in FIG. 5 , the display device 50 includes a frame region NDA and a display region DA. The display region DA of the display device 50 includes a plurality of pixels PIX, each of which includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. The red subpixel RSP includes a red light-emitting element, the green subpixel GSP includes a green light-emitting element, and the blue subpixel BSP includes a blue light-emitting element. In the stacking direction, the display device 50 has a configuration in which, for example, a substrate, a barrier layer, a thin-film transistor, a bank and light-emitting element, a sealing layer, and a functional film are stacked in this order.

[0057] FIG. 6 is a diagram schematically illustrating the layer configuration of a light-emitting element in this embodiment. As shown in FIG. 6 , a light-emitting element 60 is disposed on a barrier layer 62 disposed on a substrate 61. The barrier layer 62 is formed of, for example, an insulator. Banks 63 that separate the subpixels SP in the planar direction are formed on the barrier layer 62. The light-emitting element 60 is configured by stacking a first electrode 64, a hole injection layer 65, a hole transport layer 66, a light-emitting layer 67, an electron transport layer 68, and a second electrode 69 in this order. Examples of the light-emitting element 60 include an OLED and a QLED.

[0058] The first electrode 64 is also referred to as an anode. The first electrode 64 is conductive and has optical properties, for example, of reflecting part of visible light and transmitting the rest. The first electrode 64 includes both an electrode material that reflects visible light and an electrode material that transmits visible light.

[0059] Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, and Ag, alloys of these metal materials, and stacks (e.g., ITO / Ag / ITO) of these metal materials or their alloys with transparent metal oxides (e.g., indium tin oxide (ITO), indium zinc oxide, indium gallium zinc oxide, etc.). Examples of electrode materials that transmit visible light include thin films made of transparent metal oxides, metal materials such as Al and Ag, and nanowires made of these metal materials.

[0060] The first electrode 64 can be formed by a known method for forming an electrode layer in a light-emitting device. For example, the first electrode 64 can be formed by a physical vapor deposition (PVD) method or a chemical vapor deposition (CVD) method. Examples of physical vapor deposition methods include vacuum deposition, sputtering, electron beam (EB) deposition, and ion plating. Examples of methods for patterning the first electrode 64 include photolithography and inkjet printing.

[0061] The hole injection layer 65 is composed of a hole injection material capable of stabilizing the injection of holes into the light emitting layer 67. The hole injection material may be one or more types. Examples of hole injection materials include the encapsulated nickel oxide nanoparticles of the present disclosure, as well as poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS), Ni(OH) ２ , and CuSCN.

[0062] The hole transport layer 66 is composed of a hole transport material that can stabilize the transport of holes into the light-emitting layer 67. The hole transport material may be one or more types. Examples of hole transport materials include the encapsulated nickel oxide nanoparticles of the present disclosure, as well as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), Ni(OH) ２ and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (poly-TPD).

[0063] In the present disclosure, the encapsulated nickel oxide nanoparticles of the present disclosure may be contained in only one of the hole injection layer 65 and the hole transport layer 66, or may be contained in both.

[0064] The hole injection layer 65 or hole transport layer 66 containing the encapsulated nickel oxide nanoparticles of the present disclosure can be prepared by coating an ink containing the encapsulated nickel oxide nanoparticles. The hole injection layer 65 or hole transport layer 66 can be prepared by any known method for preparing a layer of a light-emitting element by coating an ink, except that an ink containing the encapsulated nickel oxide nanoparticles is used. For example, the hole injection layer 65 or hole transport layer 66 can be prepared using a slit coater or inkjet printing.

[0065] The encapsulated nickel oxide nanoparticles of the present disclosure are small, uniform nanoparticles that are encapsulated by a host. Therefore, they are uniformly dispersed in the ink solvent. A solvent with appropriate wettability for the application area is selected as the ink solvent. By applying ink containing uniformly dispersed encapsulated nickel oxide nanoparticles, the encapsulated nickel oxide nanoparticles are uniformly applied to the application area, forming a flat layer. Therefore, in the present disclosure, a flat hole injection layer 65 or hole transport layer 66 can be formed using the encapsulated nickel oxide nanoparticles.

[0066] The light-emitting layer 67 may be composed of quantum dots (QDs). QDs refer to dots with a maximum width of 100 nm or less. The shape of the QDs may be spherical (circular cross-sectional shape), or may be, for example, a polygonal cross-sectional shape, a rod-like shape, a branch-like shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0067] The QDs may have a core structure, a core / shell structure, a core / shell / shell structure, or a core / shell structure with a continuously varying core / shell ratio. The QDs may have a ligand, and if the QD has a core structure, the ligand may be provided on the surface of the core structure, or if the QD has a shell structure, the ligand may be provided on the surface of the shell structure.

[0068] Materials that make up the core structure of QDs include, if they are unicomponent, Si and C. If they are binary, they include CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, and ZnTe. If they are ternary, they include CdSeTe, GaInP, and ZnSeTe. If they are quaternary, they include AIGS.

[0069] Binary materials that make up the shell structure of QDs include CdS, CdTe, CdSe, ZnS, ZnSe, and ZnTe, and ternary materials include CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AIP.

[0070] The electron transport layer 68 is made of an electron transporting material that can stabilize the transport of electrons into the light-emitting layer 67. Examples of the electron transporting material include fine particles containing one or more elements selected from the group consisting of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf.

[0071] The second electrode 69 is also referred to as a cathode. The second electrode 69 is conductive, for example, conductive and transparent to visible light. Examples of electrode materials constituting the second electrode 69 include the above-mentioned electrode materials that are transparent to visible light, such as ITO and Ag nanowires (NW). The second electrode 69 can be fabricated by the method described above for the first electrode 64, depending on the electrode material. From the viewpoint of simplifying the manufacturing process, the second electrode 69 is integrally formed on both the electron transport layer 68 and the bank 63. The second electrode 69 may be formed on the electron transport layer 68, but not on the bank 63.

[0072] [Summary] When a semiconductor functional layer is fabricated using the colloidal solution of the present disclosure, the composite particles form a phase incompatible with the dispersion medium, i.e., a particulate aggregate formed by gentle aggregation. Therefore, when a force for forming a film is applied to the colloidal solution, the composite particles collapse, and the semiconductor nanoparticles and matrix components in the composite particles diffuse into the film. As a result, a semiconductor functional layer essentially composed of semiconductor nanoparticles is formed. The colloidal solution of the present disclosure, which realizes this film formation mechanism, is advantageous for forming nanometer-order thin films for electroluminescence (EL) applications.

[0073] Furthermore, the colloidal solution of the present disclosure does not require filtration to remove light-scattering particles, as compared with conventional colloidal solutions containing scattering materials. Furthermore, since the composite particles are a flexible particulate aggregate, the composite particles can pass through a filter that can filter out particles of the same size as the composite particles even when the colloidal solution is subjected to filtration.

[0074] Furthermore, in the colloidal solution of the present disclosure, the matrix component may be a ligand of the semiconductor nanoparticles, which can further enhance the functionality of the semiconductor nanoparticles in the semiconductor functional layer.

[0075] According to the present disclosure, it is possible to realize a colloidal solution of semiconductor nanoparticles that has good light resistance and coating performance, and to increase the yield of products having a semiconductor functional layer made of the semiconductor nanoparticles. The present disclosure, which has such effects, is expected to contribute to the achievement of, for example, Goal 12 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Responsible Consumption and Production."

[0076] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0077] The colloidal solution of the present disclosure is useful as a coating material for producing a semiconductor functional layer substantially composed of semiconductor nanoparticles. The colloidal solution of the present disclosure is also useful as a technique for increasing the light scattering properties of a colloidal solution without adding a light scattering material.

[0078] 1, 2, CS colloidal solution 10, 20 composite particles 11 semiconductor nanoparticles 12, 22A, 22B matrix components 100, 200 dispersion medium 50 display device 61 substrate 62 barrier layer 63 bank 64 first electrode 65 hole injection layer 66 hole transport layer 67 light-emitting layer 68 electron transport layer 69 second electrode DA display area NDA frame area PIX pixel Aa area where photodegradation occurs Li irradiated light Ls scattered light

Claims

1. A colloidal solution containing a dispersion medium, and semiconductor nanoparticles and composite particles containing semiconductor nanoparticles dispersed in the dispersion medium as dispersoids, wherein the composite particles have a matrix component that constitutes a particulate phase that is incompatible with the dispersion medium, and the content of the composite particles is 50 mass% or less of the total dispersoids.

2. The colloidal solution according to claim 1, wherein the composite particles have light scattering properties for light having a wavelength that is absorbed by the semiconductor nanoparticles.

3. The colloidal solution according to claim 2, wherein the wavelength of the light is 300 nm or more.

4. The colloidal solution according to claim 2 or 3, wherein the volume-based median kinetic diameter of the colloidal solution is equal to or greater than the wavelength of light.

5. The colloidal solution according to claim 1, wherein when a film having an average thickness of 50 nm is produced by spin casting of said colloidal solution, the arithmetic mean roughness Ra of said film is 50 nm or less.

6. The colloidal solution according to claim 1, wherein the semiconductor nanoparticles are core-shell particles having a shell layer composed of zinc halide containing 10 mol % or more of zinc, and further containing zinc halide.

7. The colloidal solution according to claim 1, further comprising a xanthogenic acid.

8. The colloidal solution according to claim 7, wherein the content by mass of said xanthogenic acids is more than half the content by mass of said semiconductor nanoparticles.

9. The colloidal solution according to claim 7 or 8, wherein the content of said xanthogenic acids is 1% by mass or more.

10. The colloidal solution according to any one of claims 1 to 9, wherein the dispersion medium is a polar solvent, and the matrix component comprises an alkoxysilane.

11. The colloidal solution according to claim 10, wherein the content of the alkoxysilane on a mass basis is more than half the content of the semiconductor nanoparticles.

12. The colloidal solution according to claim 10 or 11, wherein the content of the alkoxysilane is 1 mass % or more.

13. A colloidal solution according to any one of claims 1 to 9, wherein the dispersion medium is a non-polar solvent, and the matrix component contains less than 10% by mass of a polar solvent relative to the dispersion medium.

14. The colloidal solution of claim 13, wherein the matrix component further comprises a mercaptosilane.

15. The colloidal solution according to claim 14, wherein the content of said mercaptosilane on a mass basis is more than half the content of said semiconductor nanoparticles.

16. The colloidal solution according to claim 14 or 15, wherein the content of the mercaptosilane is 1% by mass or more.

17. A method for producing a colloidal solution, comprising suspending semiconductor nanoparticles, a dispersion medium, and a matrix component that is incompatible with the dispersion medium, and producing composite particles containing semiconductor nanoparticles, the composite particles comprising the matrix component and a particulate phase that is incompatible with the dispersion medium and contains semiconductor nanoparticles, in an amount of 50 mass% or less of the total dispersed matter.

18. The method for producing a colloidal solution according to claim 17, further comprising the step of adding one or more components selected from the group consisting of zinc halide, mercaptosilane and xanthogenic acids to semiconductor nanoparticles or a dispersion thereof to obtain a slurry, and using the dispersoid in the slurry to suspend the semiconductor nanoparticles in the dispersion medium.

19. The method for producing a colloidal solution according to claim 17 or 18, further comprising a step of filtering the produced colloidal solution.

20. A display device having a semiconductor functional layer composed of the semiconductor nanoparticles formed by coating the colloidal solution according to any one of claims 1 to 16.

21. The display device according to claim 20, wherein the content of the organic component in the semiconductor functional layer is 10 volume % or less.

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