Chalcogenide perovskite

Abstract

This chalcogenide perovskite has an average particle size of less than 40 nm, and the actual band gap value matches the range of a semiconductor-specific band gap (Eg, bulk) calculated according to formula (A) on the basis of the calculated value (E g, calc(HSE06)) of the band gap determined by a density functional method that uses a hybrid functional (HSE 06).

Description

Chalcogenide Perovskites

[0001] The present invention relates to chalcogenide perovskites.

[0002] In recent years, semiconductor light-emitting materials have been widely used as light-emitting materials in lighting and display devices, wavelength conversion (color conversion, down-conversion) elements, and also as photoelectric conversion materials in photoelectric conversion elements. In these fields, high durability (e.g., stability against water, oxygen, heat, etc.) and high light absorption properties are required for the materials. As a means to solve the above problems, BaZrS ３ Chalcogenide perovskites such as the above have been investigated (see, for example, Non-Patent Documents 1 and 2). Chalcogenide perovskites have both very good durability and a higher optical absorption coefficient than conventional materials.

[0003] VKRavi et al., “Colloidal BaZrS3 chalcogenide perovskite nanocrystals for thin film device fabrication”, The Royal Society of Chemistry, Nanoscale, 2021, Vol.13, p.1616-1623R. Yang et al., “Low-Temperature, Solution-Based Synthesis of Luminescent Chalcogenide Perovskite BaZrS3 Nanoparticles”, J. Am. Chem. Soc. 2022, 144, 35, 15928-15931

[0004] When semiconductor materials are used as light-emitting materials, there are two types of light emission: one that utilizes the band gap inherent to the semiconductor material and one that utilizes the quantum size effect. Quantum dots (semiconductor nanocrystalline particles) such as CdSe, InP, and halide perovskites are used as materials that utilize the quantum size effect. Quantum dots require strict size control to control the absorption and emission wavelengths, which results in high manufacturing costs. Furthermore, quantum dots have more discrete electronic levels than bulk materials, resulting in a lower absorption coefficient, making them unsuitable not only for light-emitting materials but also for photoelectric conversion elements. On the other hand, when using light-emitting materials that utilize the band gap inherent to the semiconductor material, the particle size is larger than that of quantum dots, resulting in lower dispersion stability and causing defects during manufacturing, such as aggregation and nozzle clogging.

[0005] An object of the present invention is to provide a chalcogenide perovskite that emits light in a band gap specific to the semiconductor material and has a small grain size.

[0006] According to the present invention, the following chalcogenide perovskite and the like are provided: 1. The average particle size is less than 40 nm, and the measured value of the band gap is smaller than the calculated value (E) of the band gap obtained by the density functional method using the hybrid functional (HSE06). ｇ，ｃａｌｃ（ＨＳＥ０６） ) based on the band gap (E ｇ，ｂｕｌｋ ) range, consistent with that of chalcogenide perovskites. 2. The chalcogenide perovskite according to 1, wherein the measured value of the band gap is greater than 0 eV and less than 2.09 eV. 3. The chalcogenide perovskite according to 1 or 2, wherein the measured value of the band gap is 1.0 eV or more and 2.0 eV or less. 4. The chalcogenide perovskite according to any one of 1 to 3, wherein the measured value of the band gap is 1.8 eV or more and 2.0 eV or less. 5. The chalcogenide perovskite according to any one of 1 to 4, wherein the average particle size is 4 nm or more and less than 40 nm. 6. The chalcogenide perovskite according to 5, wherein the average particle size is 5 nm or more. 7. The chalcogenide perovskite according to 6, wherein the average particle size is 6 nm or more. 8. The chalcogenide perovskite according to any one of 5 to 7, wherein the average particle size is less than 35 nm. 9. 10. The chalcogenide perovskite according to claim 9, wherein the average particle size is less than 30 nm. 11. The chalcogenide perovskite according to any one of claims 1 to 10, wherein the chalcogenide perovskite has a composition represented by the following formula (101) or (102): ABCh ３ ...(101) A' ２ A ｎ－１ B ｎ Ch ３ｎ＋１ ...(102) (In formulas (101) and (102), A and A' are Ca, Mg, Sr, Ba, or a combination thereof, B is Ti, Zr, Hf, or a combination thereof, and Ch is S, Se, Te, or a combination thereof. In formula (102), n is an integer of 1 or more and 10 or less. In formula (102), A and A' may be the same as or different from each other. The chalcogenide perovskite may be a solid solution in which part or all of A, A', B, and Ch in the composition represented by formula (101) or (102) are substituted with other elements.) 12. The chalcogenide perovskite according to 11, wherein n is 1 or more and 3 or less. 13. The chalcogenide perovskite has a composition of BaZrS ３The chalcogenide perovskite according to 11 or 12, wherein: 14. A powder comprising the chalcogenide perovskite according to any one of 1 to 13. 15. A solution comprising the chalcogenide perovskite according to any one of 1 to 13. 16. A thin film comprising the chalcogenide perovskite according to any one of 1 to 13. 17. A sheet comprising the chalcogenide perovskite according to any one of 1 to 13. 18. A device comprising the chalcogenide perovskite according to any one of 1 to 13. 19. The device according to 18, wherein the device is a photoelectric conversion element.

[0007] According to the present invention, it is possible to provide a chalcogenide perovskite that emits light at a band gap specific to the semiconductor material and has a small particle size.

[0008] 1 shows the measured and calculated band gap values ​​of chalcogenide perovskite. 2 shows a regression line created based on the measured and calculated band gap values ​​of chalcogenide perovskite. 3 shows an X-ray diffraction spectrum of the synthesized product obtained in Example 1. 4 shows an STEM image (200,000 magnification) of the synthesized product obtained in Example 1. 5 shows an STEM image (400,000 magnification) of the synthesized product obtained in Example 1. 6 shows a fluorescence spectrum of the synthesized product obtained in Example 1.

[0009] The following describes embodiments of the invention. In this specification, "x to y" represents a numerical range of "greater than or equal to x and less than or equal to y." The upper and lower limits of the numerical ranges can be combined in any manner. Furthermore, among the individual embodiments of the aspects of the present invention described below, two or more embodiments that are not mutually contradictory can be combined, and an embodiment combining two or more embodiments is also an embodiment of the aspects of the present invention.

[0010] A chalcogenide perovskite according to one embodiment of the present invention emits light at a band gap specific to the semiconductor and has an average particle size of less than 40 nm. Here, the band gap specific to the semiconductor will be described. The band gap specific to the semiconductor can be calculated relatively accurately by a density functional method using the hybrid functional Heyd-Scuseria-Ernzerhof (HSE06). However, it has been reported that the band gap calculated by DFT calculation of chalcogenide perovskites is smaller than the actually measured value (see References 1 to 3 below). 1. Y. Nishigaki et al., "Extraordinary Strong Band-Edge Absorption in Distorted Chalcogenide Perovskites", Sol. RPL. 2020, 1900555 2. S. Sharma et al., “Bandgap Tuning in BaZrS3 Perovskite Thin Films”, ACS Appl. Electron. Mater. 2021, 3, 8, 3306-3312 3. K. Hanazawa et al., “Material Design of Green-Light-Emitting Semiconductors: Perovskite-Type Sulfide SrHfS3”, J. Am. Chem. Soc. 2022, 141, 13, 5343-5349

[0011] The calculated and measured band gap values ​​for each chalcogenide perovskite reported to date are shown in Figure 1. Figure 2 shows a regression line created by plotting the calculated and measured band gap values ​​for each chalcogenide perovskite in Figure 1, with the measured values ​​on the vertical axis and the calculated values ​​on the horizontal axis. Note that [1] in Figure 1 indicates the value from Reference 1, [2] indicates the value from Reference 2, and [3] indicates the value from Reference 3. The units are eV.

[0012] In FIG. ３ and SrHfS ３There are two measured and calculated values ​​for each of these, and it can be seen that there is a discrepancy of about 5% between the two values. The causes of this discrepancy include differences in samples between the literature, differences in fitting when calculating the band gap from the diffuse reflectance spectrum, and differences in DFT calculation conditions. From this, it can be seen that the calculated band gap (E ｇ，ｃａｌｃ（ＨＳＥ０６） ) may cause an error between the value calculated from the regression line and the actual measured value. Therefore, the range is set by adding a measurement error of ±5% to the value calculated using the regression line, that is, E calculated by the following formula (A). ｇ，ｂｕｌｋ is the inherent band gap of the semiconductor. (In the formula, E ｇ，ｃａｌｃ（ＨＳＥ０６） is the calculated band gap value obtained by the density functional method using the hybrid functional (HSE06).

[0013] The fact that the measured band gap value falls within the range of values ​​calculated from the above formula (A) means that the luminescence of the chalcogenide perovskite is not due to a quantum size effect, but rather is luminescence due to the band gap inherent to the semiconductor material. In the present application, the measured band gap value can be measured based on a fluorescence spectrum or a diffuse reflectance spectrum. In the case of measurement based on a fluorescence spectrum, the fluorescence spectrum is measured, and the measured emission peak energy corresponds to the measured band gap value. Note that measurement based on a fluorescence spectrum is preferable because measurement of the band gap based on a diffuse reflectance spectrum may result in errors due to fitting.

[0014] In one embodiment, the measured band gap is greater than 0 eV and less than 2.09 eV, greater than or equal to 1.0 eV, greater than or equal to 1.5 eV, greater than or equal to 1.7 eV, or greater than or equal to 1.8 eV, or less than or equal to 2.05 eV, less than or equal to 2.0 eV, or less than or equal to 1.98 eV.

[0015] The chalcogenide perovskite of this embodiment has an average particle size of less than 40 nm. This allows the particles to emit light at the band gap specific to the semiconductor material, while maintaining good dispersion stability and suppressing defects during production, such as aggregation and nozzle clogging. In one embodiment, the average particle size is 4 nm or more, 5 nm or more, or 6 nm or more. This makes it easier for light emission to occur at the band gap specific to the semiconductor material rather than at the quantum size effect, eliminating particle size dependence of the emission wavelength. Furthermore, the average particle size is less than 35 nm, less than 32 nm, or less than 30 nm. This can be adjusted appropriately depending on the use form of the chalcogenide perovskite particles. In this application, the average particle size is measured by microscopy of the dispersion. Details are described in the Examples. The carrier confinement effect can be enhanced by coating the chalcogenide perovskite of this embodiment with a material having a larger band gap than the chalcogenide perovskite (core-shell structure). In the case of a core-shell structure, the absorption edge may shift due to absorption by the shell material, so it is preferable to measure the band gap based on the fluorescence spectrum rather than the diffuse reflectance spectrum.

[0016] A chalcogenide perovskite according to one embodiment is a compound having a perovskite-type crystal structure and containing chalcogen (a Group 16 element other than oxygen (S, Se, or Te)), and in addition to the chalcogen, contains two or more metal elements, such as a transition metal element and an alkaline earth metal element, as components of the perovskite-type crystal structure.

[0017] In one embodiment, the chalcogenide perovskite has a composition represented by, for example, the following formula (101) or (102): ABCh ３ ...(101) A' ２ A ｎ－１ B ｎ Ch ３ｎ＋１ ... (102)

[0018] In formulas (101) and (102), A and A' are Mg, Ca, Sr, Ba, or a combination of these in any ratio; B is Ti, Zr, Hf, or a combination of these in any ratio; and Ch is S, Se, Te, or a combination of these in any ratio. In formula (102), n is an integer of 1 or more and 10 or less. n is preferably 1 or more and 3 or less. In formula (102), A and A' may be the same or different.

[0019] In one embodiment, the chalcogenide perovskite may be a solid solution in which part or all of A, A', B, and Ch in the composition represented by formula (101) or (102) are substituted with other elements.

[0020] Chalcogenide perovskite (ABCh) represented by formula (101) ３ ) represents, for example, a cubic perovskite, a tetragonal perovskite, an orthorhombic perovskite, or a double perovskite crystal structure. ２ A ｎ－１ B ｎ Ch ３ｎ＋１ ) represents, for example, the crystal structure of a Ruddlesden-Popper type layered perovskite. In one embodiment, the composition of the chalcogenide perovskite is BaZrS ３ It is preferable that:

[0021] In one embodiment, the chalcogenide perovskite is surface-modified with a ligand. The chalcogenide perovskite of this embodiment, surface-modified with a ligand, can be easily dispersed in a dispersion medium such as a solvent or a polymer compound.

[0022] There are no limitations on the type of ligand used to modify the surface of the chalcogenide perovskite, and any ligand generally used for dispersing nanoparticles may be used, including, for example, oleylamine, oleic acid, dodecanethiol, and trioctylphosphine.

[0023] The dispersion medium may be liquid or solid. The liquid dispersion medium may be, for example, a solvent selected from the group consisting of water and non-aqueous solvents such as toluene and hexane, or a solution in which components other than the chalcogenide perovskite are dispersed in these solvents. The solid dispersion medium may be, for example, a polymer compound such as polyethylene.

[0024] For example, in order to disperse a chalcogenide perovskite synthesized by a solid-phase synthesis method in the above-mentioned dispersion medium, it is necessary to perform surface modification by modifying the surface of the chalcogenide perovskite with a ligand to improve dispersibility in various dispersion media. In contrast, when synthesizing a chalcogenide perovskite by a liquid-phase synthesis method, the synthesis reaction is carried out in a state in which the ligand is previously present in the liquid phase that serves as the reaction liquid for the liquid-phase synthesis, and thereby the chalcogenide perovskite can be obtained as particles surface-modified with the ligand.

[0025] A composition according to one embodiment comprises the chalcogenide perovskite according to the present embodiment, which has been surface-modified with a ligand, dispersed in a dispersion medium. As described above, particles of chalcogenide perovskite surface-modified with a ligand can be easily dispersed in a dispersion medium such as a solvent or a polymer compound. Therefore, the composition according to this embodiment has the chalcogenide perovskite uniformly dispersed in the dispersion medium, and exhibits favorable properties as a composition.

[0026] The chalcogenide perovskite according to this aspect can be synthesized, for example, by the synthesis method according to one embodiment of the present invention, i.e., by reacting a complex having a first metal atom and a complex having a second metal atom, both of which have ligands that do not contain oxygen atoms (O) or halogen atoms as coordinating atoms, in a liquid phase, setting the temperature of the liquid phase to 120°C to 450°C, and setting the reaction time to 0 seconds or more. Note that 0 seconds refers to the start of the reaction between the complex having the first metal atom and the complex having the second metal atom; for example, in the hot injection method, this refers to the time when the complex having the first metal atom, the complex having the second metal atom, and the complex having the first metal atom are all present in the liquid phase, and in the heat-up method, this refers to the time when the liquid phase reaches a predetermined temperature. The present inventors have found that when synthesizing chalcogenide perovskite in the liquid phase, the presence of components containing halogen atoms, such as halides, or components containing oxygen atoms (O), such as acetates, during liquid-phase synthesis can inhibit the reaction and affect the purity and crystal structure of the target chalcogenide perovskite. Examples of halogen atoms include fluorine atoms (F), chlorine atoms (Cl), bromine atoms (Br), and iodine atoms (I).

[0027] In this embodiment, a complex having a first metal atom and a complex having a second metal atom, both of which have ligands that do not contain oxygen atoms or halogen atoms as coordinating atoms, are reacted in the liquid phase. This allows the liquid-phase synthesis reaction to proceed without the presence of components containing oxygen atoms, such as metal acetates, or components containing halogen atoms, such as metal halides, in the liquid phase. This prevents reactions between the constituent elements of the chalcogenide perovskite and oxygen atoms and halogen atoms in the liquid phase. As a result, a crystal structure similar to that obtained by solid-phase synthesis can be obtained.

[0028] In this embodiment, the band gap of the resulting chalcogenide perovskite can be adjusted by controlling the composition of the chalcogenide perovskite, for example, by adjusting the constituent elements and the amounts of the raw materials used. ３Then, the measured band gap is 1.96 eV (see Example 1). The average particle size of the resulting chalcogenide perovskite can be controlled, for example, by adjusting the concentration of each complex in the liquid phase and the reaction time. Hereinafter, the methods for synthesizing the complex having a first metal atom and the complex having a second metal atom, which are starting materials, and the chalcogenide perovskite will be described.

[0029] [Complex Having a First Metal Atom and Complex Having a Second Metal Atom] The ligands of the complex having a first metal atom and the complex having a second metal atom used in this embodiment are not particularly limited, as long as they do not contain an oxygen atom or a halogen atom as a coordinating atom. Examples include ligands coordinated with an atom selected from the group consisting of a nitrogen atom (N), a sulfur atom (S), a selenium atom (Se), a tellurium atom (Te), a carbon atom (C), and a phosphorus atom (P).

[0030] The ligands that coordinate with nitrogen atoms include alkylamines (NR amines) such as amine, dimethylamine, diethylamine, and methylethylamine. ２ arylamines (NHAr) such as phenylamine; trialkylsilylamines (N(SiR) such as silylamine and trimethylsilylamine) ３ ) ２ ), nitrogen-containing aromatic rings such as pyrazole, etc.

[0031] The ligands that coordinate with sulfur atoms include dithiocarbamate (S ２ CNR ２ ), xanthate (S ２ COR), trithiocarbamate (S ２ CSR), dithioester (S ２ Examples of the ligand that coordinates with a selenium atom or a tellurium atom include compounds in which some or all of the sulfur atoms of the above-mentioned ligand that coordinates with a sulfur atom are substituted with selenium atoms or tellurium atoms.

[0032] The complex having the first metal atom and the complex having the second metal atom may be a single compound (multinuclear complex). Preferably, the first metal atom and the second metal atom may be bonded via a ligand coordinated by a sulfur atom, a selenium atom, or a tellurium atom. Examples of multinuclear complexes in which the ligand is coordinated by a sulfur atom include heterobimetallic thiolates and heterobimetallic sulfides. Examples of multinuclear complexes in which the ligand is coordinated by a selenium atom or a tellurium atom include those in which some or all of the sulfur atoms in a multinuclear complex in which the ligand is coordinated by a sulfur atom are replaced with selenium atoms or tellurium atoms.

[0033] Examples of the ligand coordinated at a carbon atom include alkanes such as methyl and ethyl; unsaturated hydrocarbon rings such as cyclopentadiene, cyclooctadiene, and indene, or benzyl groups and other groups derived from the above-mentioned unsaturated hydrocarbon rings; and cyanide (CN).

[0034] Examples of the ligands that coordinate with phosphorus atoms include trialkylphosphines (PRs) such as trioctylphosphine and tricyclohexylphosphine. ３ triarylphosphines (PAr) such as triphenylphosphine and tri(o-tolyl)phosphine; ３ ); diphosphine (R ２ P-(CH ２ ) ｍ -PR ２ ) etc.

[0035] The ligand may be a derivative of the above-mentioned ligand.

[0036] In each of the general formulas above, R is a hydrogen atom, a saturated hydrocarbon group having 1 to 20 carbon atoms, or an unsaturated hydrocarbon. When one ligand contains two or more R, the R may be the same or different from each other. Ar is an aryl group having 6 to 20 carbon atoms, such as a phenyl group, a naphthyl group, or an anthracenyl group, which may have a substituent. Examples of the substituent include alkyl groups having 1 to 10 carbon atoms. When one ligand contains two or more Ar, the Ar may be the same or different from each other. m is an integer from 1 to 10.

[0037] Among the above-mentioned ligands, ligands coordinated by nitrogen atoms or ligands coordinated by sulfur atoms are preferred. Also preferred are ligands having a structure selected from the group consisting of the following formulas (1) to (7): S ２ CNR ａ ２ (1) S ２ COR (2) S ２ CSR ａ (3) S ２ CR ａ (4) SR ａ (5) NR ａ ２ (6) N(SiR ａ ３ ) ２ (7) (wherein, R ａ is a hydrogen atom, a saturated hydrocarbon group having 1 to 20 carbon atoms, or an unsaturated hydrocarbon group having 1 to 20 carbon atoms. ａ When the ａ may be the same or different.)

[0038] Examples of the saturated hydrocarbon group and unsaturated hydrocarbon include an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, a cycloalkenyl group having 3 to 20 carbon atoms, a cycloalkynyl group having 3 to 20 carbon atoms, a cycloalkadienyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms. The saturated hydrocarbon group and the unsaturated hydrocarbon may have a substituent. An example of the substituent is an alkyl group having 1 to 10 carbon atoms.

[0039] In one embodiment, the ligand is preferably a compound represented by the above formula (1). ａ is preferably an alkyl group having 1 to 10 carbon atoms, and more preferably an alkyl group having 2 to 6 carbon atoms.

[0040] The ligand used in this embodiment can be synthesized by a conventional method, or a commercially available compound may be used.

[0041] In one embodiment, the metal atom of the complex having the first metal atom is a metal atom selected from alkaline earth metal elements, and the metal atom of the complex having the second metal atom is a metal atom selected from transition metal elements. In one embodiment, the metal atom of the complex having the first metal atom is at least one of Mg, Ca, Sr, and Ba, and the metal atom of the complex having the second metal atom is at least one of Ti, Zr, and Hf.

[0042] The complex having the first metal atom and the complex having the second metal atom can be synthesized by selecting raw material components according to the type of metal atom and ligand possessed by each of them and by a known method. Alternatively, a commercially available metal complex may be used. Hereinafter, as an example of a method for synthesizing a complex having the first metal atom and a complex having the second metal atom, a method for synthesizing a complex having a ligand (S ２ CNR ２ Metal complexes (M(S ２ CNR ２ ) Ｘ ) synthesis will be described.

[0043] First, at least one metal source (M) serving as a source of metal atoms for the metal complex, such as at least one selected from Ba, Sr, Ca, Mg, Ti, Zr, and Hf, or a salt thereof, is dissolved in a solvent such as water. The solvent is not particularly limited as long as it is capable of dissolving the metal source (M), and may be, for example, an organic solvent. Next, ammonia or an amine compound is added to the solution containing the dissolved metal source as a source of nitrogen (N) contained in the complex ligand to be synthesized, and the mixture is stirred. As the amine compound, primary amines or secondary amines can be used without any particular limitation, and the type of substituted hydrocarbon group, etc., in these amine compounds is also not particularly limited.

[0044] Next, a source of sulfur (S) contained in the complex ligand to be synthesized is added to the solution containing the nitrogen (N) source and stirred. ２However, other compounds can be used depending on the composition of the complex ligand to be synthesized. When Se or Te is contained instead of sulfur (S), CSe ２ , CTe ２ Next, the solid produced by stirring or the precipitate deposited in the solution can be isolated by a known method to obtain the target metal complex.

[0045] [Method for synthesizing chalcogenide perovskite] In this embodiment, the chalcogenide perovskite is synthesized by reacting the above-described complex having the first metal atom and complex having the second metal atom in a solvent. The solvent is selected based on the solubility of the complex having the first metal atom and complex having the second metal atom, and the H ２ The solvent can be appropriately selected from the viewpoint of S generation efficiency, etc. Examples of the solvent include saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, aromatic hydrocarbons, nitrogen-containing heterocyclic compounds, alcohols, aldehydes, carboxylic acids, primary amines, secondary amines, tertiary amines, phosphine compounds, and thiols. Taking into consideration that the liquid phase may be heated to a high temperature of, for example, 300°C or higher in the liquid-phase synthesis stage described below, it is preferable to use a solvent with a higher boiling point. For example, alkenes having 10 to 30 carbon atoms, such as octadecene, have a high boiling point and can be suitably used as the solvent.

[0046] In one embodiment, in addition to the complex having a first metal atom and the complex having a second metal atom, a chalcogen compound can be added to the liquid phase. For example, when neither the ligands of the complex having a first metal atom nor the complex having a second metal atom contain a chalcogen element such as sulfur (S), or when the chalcogen elements contained in the ligands are insufficient, the composition of the target chalcogenide perovskite can be adjusted by adding a chalcogen compound to the liquid phase. As the chalcogen compound, one that does not contain oxygen atoms (O) and halogen atoms is preferably used. For example, sulfur or carbon disulfide (CS) ２ ), hydrogen sulfide (H ２S), sulfides such as selenium or selenides, tellurium or tellurides, hexanethiol, octanethiol, decanethiol, dodecanethiol (n-dodecanethiol, t-dodecanethiol), hexadecanethiol, mercaptopropylsilane, thiourea compounds (S═C(NR ２ ) ２ ), sulfur-trioctylphosphine (trioctylphosphine sulfide; S-TOP), sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA), bis(trimethylsilyl) sulfide, ammonium sulfide, sodium sulfide, selenium-trioctylphosphine (Se-TOP), selenium-tributylphosphine (Se-TBP), and selenium-triphenylphosphine. Among these, thiourea compounds (S═C(NR ２ ) is, for example, carbon disulfide (CS ２ ) and therefore can be suitably used as a chalcogen compound.

[0047] In one embodiment, in addition to the above-described complex having a first metal atom and complex having a second metal atom, an amine compound can be further added to the liquid phase. The amine compound functions as a reaction initiator. The amine compound may also be used as the above-described solvent. The amine compound is preferably one that does not contain oxygen atoms (O) or halogen atoms. Examples include alkylamines having one alkyl group, such as oleylamine, hexadecylamine, and octadecylamine, dialkylamines having two alkyl groups having 1 to 30 carbon atoms, and trialkylamines (e.g., trioctylamine) having three alkyl groups having 1 to 30 carbon atoms. From the viewpoint of fully exhibiting its function as a reaction initiator between the ligand and the metal component, the amine compound is preferably added in an amount equal to or greater than the total amount of the ligands contained in the complex having a first metal atom and the complex having a second metal atom added to the liquid phase. Furthermore, from the viewpoint of exhibiting the function as a surfactant that adheres to the surfaces of the chalcogenide perovskite particles that are finally obtained, the amine compound may be added to the liquid phase in an amount in excess of the aforementioned amount (equivalent to the total number of ligands).

[0048] The synthesis method of this embodiment involves reacting the above-described complex having a first metal atom and complex having a second metal atom with, as needed, a chalcogen compound and an amine compound in a liquid phase, and the procedure is not particularly limited. The synthesis of this embodiment can be carried out by known methods such as a hot injection method, a heat-up method, or a flow synthesis method. The compounding ratio of the complex having a first metal atom and the complex having a second metal atom can be adjusted according to the composition of the target chalcogenide perovskite.

[0049] In one embodiment of the synthesis method, when raw material components include a complex having at least a first metal atom, a complex having a second metal atom, and a solvent, a first raw material containing at least the solvent and a second raw material containing at least the remaining raw material components not included in the first raw material are prepared. The second raw material is then added to the first raw material, causing a reaction. In this embodiment, it is preferable to preheat at least one of the first raw material and the second raw material, and then add the second raw material to the first raw material. Alternatively, the second raw material may be added to the first raw material and then heated to cause a reaction.

[0050] The synthesis method of this embodiment will be described below using the hot injection method as an example. First, the first raw material is preheated. The temperature rise rate is not particularly limited, but is, for example, 1 to 30°C / min, typically 1 to 10°C / min. The temperature of the first raw material after heating is not particularly limited, but may be, for example, room temperature to 450°C, or 120 to 360°C.

[0051] Next, the second raw material is added to the first raw material to cause a reaction between the complex having the first metal atom and the complex having the second metal atom. The second raw material may also be preheated, as with the first raw material. The addition rate of the second raw material is not particularly limited, but is preferably adjusted taking into account the decrease in liquid phase temperature due to the addition of the second raw material. The liquid phase temperature after mixing is 120 to 450°C, preferably 120 to 400°C, and more preferably 220 to 360°C.

[0052] For example, either the complex having the first metal atom or the complex having the second metal atom may contain a ligand represented by the above formula (1) (dithiocarbamate (S ２ CNR ２)), if the liquid phase temperature is 120°C or higher, the metal complex having the ligand can initiate a reaction with an amine compound, and the reaction between the complex having the first metal atom and the complex having the second metal atom proceeds smoothly. Note that the reaction can also be initiated without using an amine compound, but in this case, it is preferable to set the liquid phase temperature higher than 120°C. Furthermore, by setting the liquid phase temperature to 360°C or lower, evaporation of a commonly used solvent is suppressed, allowing for stable liquid phase synthesis.

[0053] In this embodiment, by adding the second raw material to the first raw material in a preheated state, once all of the components contributing to the synthesis of the chalcogenide perovskite (the solvent, the complex having the first metal atom, and the complex having the second metal atom) are in a liquid phase, all of these components are suddenly brought to a high temperature state, so that the reaction of the complex having the first metal atom and the reaction of the complex having the second metal atom can start at approximately the same time. As a result, the reaction of the complex having the first metal atom and the reaction of the complex having the second metal atom proceed in a well-balanced manner, allowing the synthesis of a high-purity chalcogenide perovskite.

[0054] When the above-mentioned amine-based compound is added to the liquid phase as a reaction initiator, the raw material components include a solvent, a complex having a first metal atom, a complex having a second metal atom, and an amine-based compound. The combination of the first raw material component and the second raw material component is not particularly limited. For example, the first raw material may be a solvent alone, and the second raw material may be a mixture of a complex having a first metal atom, a complex having a second metal atom, and an amine-based compound. Alternatively, the first raw material may be a mixture of a solvent and an amine-based compound, and the second raw material may be a mixture of a complex having a first metal atom and a complex having a second metal atom. Alternatively, the first raw material may be a mixture of either a complex having a first metal atom or a complex having a second metal atom and a solvent, and the second raw material may be a mixture of the other of a complex having a first metal atom or a complex having a second metal atom and an amine-based compound.

[0055] Furthermore, when the chalcogen compound is added to the liquid phase, the raw material components include a solvent, a complex having a first metal atom, a complex having a second metal atom, and a chalcogen compound. In this case, the combination of the first raw material component and the second raw material component is not particularly limited. For example, the first raw material may be a solvent alone, and the second raw material may be a mixture of a complex having a first metal atom, a complex having a second metal atom, and a chalcogen compound. Alternatively, the first raw material may be a mixture of a solvent and a chalcogen compound, and the second raw material may be a mixture of a complex having a first metal atom and a complex having a second metal atom. Alternatively, the first raw material may be a mixture of either a complex having a first metal atom or a complex having a second metal atom and a solvent, and the second raw material may be a mixture of the other of a complex having a first metal atom or a complex having a second metal atom and a chalcogen compound.

[0056] The liquid phase obtained by adding the second raw material to the first raw material is heated and stirred for 0 seconds or longer, preferably 10 hours or longer and 24 hours or shorter, while maintaining the temperature at 120 to 450° C., preferably 120 to 400° C., and more preferably 220 to 360° C. After stirring is completed, the precipitate deposited in the liquid phase is isolated by a known method, thereby obtaining the target chalcogenide perovskite particles.

[0057] The above-mentioned series of liquid phase syntheses are preferably carried out in a state where components such as water and oxygen are removed as much as possible so that they are not present in the synthesis atmosphere. For example, the above-mentioned series of liquid phase syntheses are preferably carried out in an inert atmosphere filled with nitrogen or argon.

[0058] The synthesis of this embodiment may be performed, for example, by a flow synthesis method described below. First, a complex having a first metal atom, a complex having a second metal atom, and at least one of a chalcogen compound and an amine compound are each dissolved in a solvent and circulated separately as three or four raw material flows. Next, the raw material flows are merged simultaneously or stepwise to initiate the reaction. At this time, it is preferable to preheat at least one of the raw material flows before merging. The raw material flow to be preheated is preferably the flow with the highest flow rate. Furthermore, since the reaction field in flow synthesis is small, the temperature can be instantly raised even if the raw material flows are heated immediately after merging, and the reaction of the complex having the first metal atom and the reaction of the complex having the second metal atom can start approximately simultaneously. The heating rate during heating and the temperature of the components after heating are the same as in the hot injection method. The following steps are the same as in the hot injection method.

[0059] According to flow synthesis, the components contributing to the synthesis of chalcogenide perovskite can be heated in a short time after joining, allowing the reaction of the complex containing the first metal atom and the complex containing the second metal atom to start at approximately the same time. Furthermore, because the reaction field is small in flow synthesis, the collision probability between the raw materials, i.e., reaction efficiency, is high. Therefore, the reaction of the complex containing the first metal atom and the reaction of the complex containing the second metal atom proceed in a well-balanced manner, allowing the synthesis of chalcogenide perovskite with high purity. Furthermore, the yield of chalcogenide perovskite is increased, reducing energy costs. Furthermore, the amount of waste impurities contained in the final synthesis product can be reduced, thereby reducing environmental impact. Furthermore, accidents such as explosions on the production line caused by impurities can be prevented, thereby improving production safety.

[0060] The synthesis method of this embodiment described above allows chalcogenide perovskite particles to be obtained without a calcination step. Generally, when a calcination step is performed, nano-sized primary particles aggregate to form secondary particles. However, by not performing a calcination step, the formation of such secondary particles is suppressed. Therefore, fine chalcogenide perovskite nanoparticles can be obtained.

[0061] Furthermore, since the synthesis method of this embodiment is a liquid-phase synthesis method, impurities are less likely to be mixed into the particles during the synthesis process compared to solid-phase synthesis methods. Liquid-phase synthesis methods are characterized by uniform nucleation and particle growth from the liquid phase, and by preventing aggregation of the nuclei generated in the liquid phase, it is possible to obtain fine nanoparticles with a narrow particle size distribution (see, for example, "Kanie, S. et al., 'Liquid-Phase Synthesis of Size- and Shape-Controlled Functional Inorganic Nanoparticles and Their Application to Hybrid Materials by Precise Surface Organic Modification,' Journal of the Japanese Society for Crystal Growth, 2017, Vol. 44, No. 2, pp. 66-73"). Therefore, according to the synthesis method of this embodiment, the particles are less likely to be mixed with impurities, and chalcogenide perovskite nanoparticles with a narrow and uniform particle size distribution can be obtained.

[0062] Chalcogenide perovskite nanoparticles can be used in various product forms, such as powder, solution, ink, resin, thin film, and sheet. Potential applications include light-emitting devices, photoelectric conversion elements, and other devices.

[0063] (Powder) The powder is a state in which chalcogenide perovskite nanoparticles are aggregated. Hereinafter, chalcogenide perovskite nanoparticles are sometimes referred to as primary particles, and chalcogenide perovskite nanoparticles in an aggregated state are sometimes referred to as secondary particles. Ligands may be attached to the surfaces of the primary particles and secondary particles. In order to improve the luminescence properties and properties such as the dispersibility and film-forming properties of the chalcogenide perovskite nanoparticles, other materials may be added as additives to the powder of chalcogenide perovskite nanoparticles.

[0064] The use of the powder of chalcogenide perovskite nanoparticles is not particularly limited. For example, the powder may be dispersed in a solvent to prepare a solution, dispersed in a resin or solid medium to prepare a composite, sintered to be used as a sputtering target, or used as a powder directly as a source for evaporation or the like.

[0065] (Solution) A solution is a state in which chalcogenide perovskite nanoparticles are dispersed in a solvent. "Dispersed" refers to a state in which the chalcogenide perovskite nanoparticles are floating or suspended in the solvent, and some may be precipitated. Furthermore, ligands may be attached to the surfaces of the primary particles and secondary particles.

[0066] The solution may contain one or more solvents, including, but not limited to, the following: Water; esters such as methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, and pentyl acetate; ketones such as γ-butyrolactone, acetone, dimethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; ethers such as diethyl ether, methyl tert-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, and phenetole; ethers such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol, methoxypropanol, diacetone alcohol, cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, and 2,2,2-trifluoroethanol. alcohols such as ethanol and 2,2,3,3-tetrafluoro-1-propanol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate and triethylene glycol dimethyl ether; organic solvents having an amide group such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetamide and N,N-dimethylacetamide; organic solvents having a nitrile group such as acetonitrile, isobutyronitrile, propionitrile and methoxyacetonitrile; organic solvents having a carbonate group such as ethylene carbonate and propylene carbonate; organic solvents having a halogenated hydrocarbon group such as methylene chloride and chloroform; organic solvents having a hydrocarbon group such as n-pentane, cyclohexane, n-hexane, benzene, toluene and xylene; dimethyl sulfoxide, etc.

[0067] Furthermore, in order to improve the luminescence characteristics, dispersibility of the chalcogenide perovskite nanoparticles, film-forming properties, and other properties, an additive such as an acid, a base, or a binder material may be added to the solution. The use of the solution is not particularly limited. For example, the solution may be used for film formation by a coating method, a spray method, a doctor blade method (or other solution film-forming method), for preparing a composite by combining with a solid dispersion medium, or for preparing a device using these.

[0068] (Thin Film) A thin film is a planar aggregate of chalcogenide perovskite nanoparticles. Ligands may be attached to the surfaces of the primary particles and secondary particles. To improve properties such as luminescence characteristics and dispersibility of the chalcogenide perovskite nanoparticles, other materials may be added to the thin film as additives.

[0069] The method for producing the thin film is not particularly limited. Examples include coating, spraying, doctor blade, inkjet, and other solution film-forming methods; and methods using vacuum processes such as sputtering and vacuum deposition. Furthermore, chalcogenide perovskite nanoparticles may be coated or otherwise formed into a film, and then calcined or otherwise treated to lose their particle shape.

[0070] (Sheet) A sheet is a planar dispersion medium in which chalcogenide perovskite nanoparticles are dispersed. Ligands may be attached to the surfaces of the primary particles and secondary particles.

[0071] The material used as the dispersion medium for the sheet can be any polymer known to those skilled in the art for this purpose. In a suitable embodiment, this type of polymer is substantially translucent or substantially transparent. For example, polymers suitable for the dispersion medium for the sheet include, but are not limited to, polyvinyl butyral, polyvinyl acetate, silicone, and silicone derivatives. Silicone derivatives include, but are not limited to, polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane, fluorinated silicones, vinyl- and hydride-substituted silicones, ionomers, polyethylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polypropylene, polyester, polycarbonate, polystyrene, polyacrylonitrile, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-methacrylic acid copolymer film, nylon, and the like.

[0072] To improve properties such as luminescence characteristics and dispersibility of the chalcogenide perovskite nanoparticles, the sheet may contain additives such as silica fine particles or the solvent described above for the solution. The method for producing the sheet is not particularly limited. For example, the sheet may be produced by kneading and stretching a powder and a dispersion medium, or by mixing and applying an ink containing chalcogenide perovskite nanoparticles with a dispersion medium or a precursor thereof.

[0073] (Devices) The chalcogenide perovskite nanoparticles, and the above-mentioned powders, solutions, films, and sheets are expected to be used in various devices for down-conversion of ultraviolet light, blue light, etc., or as light-receiving materials. Examples of the types of devices include light-emitting devices such as LEDs and organic ELs, display devices including such light-emitting devices, lighting devices including such light-emitting devices, image sensors, photoelectric conversion devices, and bioluminescent tags.

[0074] Synthesis Example 1 (Synthesis of Ba diisobutyldithiocarbamate) Barium hydroxide (5140 mg) was weighed into a 100 ml three-neck flask, 50 ml of purified water was added, and the flask was sealed and stirred. Next, diisobutylamine (10.39 ml) was added to the three-neck flask, and after stirring for another 10 minutes, carbon disulfide (3.63 ml) was added and stirred for 3 hours. Gradual precipitation of a white solid was observed upon stirring. The precipitated solid was collected by filtration, washed with hexane, and then vacuum dried to obtain a compound containing Ba diisobutyldithiocarbamate. The yield was approximately 70%.

[0075] Synthesis Example 2 (Synthesis of Zr diisobutyldithiocarbamate) Zirconium chloride (2913 mg) was weighed into a 200 ml three-neck flask, 75 ml of THF was added, and the container was sealed and stirred for approximately 15 minutes. Next, diisobutylamine (29.2 ml) was added to the three-neck flask and stirred for 10 minutes. After that, carbon disulfide (10.2 ml) was added and stirred for an additional 3 hours. After stirring was completed, the precipitated solid was filtered, and the filtrate was recovered and transferred to another container. The solvent was then removed from the recovered filtrate using a known method, and the resulting residue was dispersed in hexane to obtain a white suspension. The white suspension was filtered, and the resulting solid was washed with hexane and then vacuum-dried to obtain a synthetic product containing Zr diisobutyldithiocarbamate. The yield was approximately 80%.

[0076] Example 1 Ba diisobutyldithiocarbamate (527.94 mg) obtained in Synthesis Example 1 and Zr diisobutyldithiocarbamate (908.76 mg) obtained in Synthesis Example 2 were weighed into a 50 ml three-necked flask, and 1-octadecene (5 ml) was added and stirred. Then, the three-necked flask was heated to a temperature of 1000° C., and the internal atmosphere was changed to N 2 ２While still in the ambient atmosphere, the flask was moved into a draft chamber and heated to 310°C at a rate of 5°C / min. Then, room-temperature oleylamine (3,200 mg) was injected using a Luer-Lock syringe. The solution in the three-neck flask was then stirred for 18 hours while maintained at 310°C, and then cooled to room temperature. The solution in the flask was divided into two. One solution was precipitated by adding butanol, which was then recovered by centrifugation to obtain a powder of the synthesized product. The other solution was precipitated by adding toluene and ethanol, which was then centrifuged. The supernatant was then discarded, and the residue was dispersed in toluene to obtain a dispersion of the synthesized product.

[0077] The X-ray diffraction spectrum of the synthesized product obtained in Example 1 was measured under the following conditions. The results are shown in Figure 3. [X-ray diffraction analysis] X-ray wavelength: 1.5418 Å (CuKα radiation) Measurement range: 5 to 60 (deg) Measurement method: 2θ-θ method Measurement sample: A sample powder of the synthesized product was filled into a glass sample holder with a depression, and the surface was smoothed using a glass plate, and then the measurement was performed. The synthesized product obtained in Example 1 was determined to be BaZrS synthesized by solid-phase synthesis, based on the JCPDS card (No. 00-015-0327) in which the peak positions showing the top five peak intensities in the X-ray diffraction analysis spectrum were 1.5418 Å (CuKα radiation) Measurement range: 5 to 60 (deg) Measurement method: 2θ-θ method Measurement sample: A sample powder of the synthesized product was filled into a glass sample holder with a depression, and the surface was smoothed using a glass plate, and then the measurement was performed. ３ (GdFeO ３ It was confirmed that the composition of the compound obtained in Example 1 was almost identical to that of BaZrS ３ It can be seen that...

[0078] The average particle size of the dispersion of the synthesized product obtained in Example 1 was measured by microscopy. Microscopy refers to a method of directly measuring the size and number of particles on an image obtained by an optical microscope or an electron microscope. Diameters used as indicators for evaluating particle size include Feret diameter, Heywood diameter, Martin diameter, and Krumbein diameter. However, from the perspective of ease of calculation by image analysis, the diameter evaluated using the Heywood diameter as an indicator was adopted as the particle size. The dispersion of the synthesized product obtained in Example 1 was observed using a scanning transmission electron microscope (STEM) (manufactured by JEOL Ltd., "JSM-7610F") at an acceleration voltage of 5 kV and a magnification of 200,000 or 400,000. The STEM images obtained by the observation are shown in Figure 4 (magnification: 200,000) and Figure 5 (magnification: 400,000). The average Heywood diameter determined by microscopy from Figures 4 and 5 was 13.5 nm.

[0079] The fluorescence spectrum of the dispersion of the synthesized product obtained in Example 1 was measured under the following conditions. The results are shown in Figure 6. The measured value of the emission peak energy, i.e., the band gap, was 1.96 eV. This measured value of the band gap was calculated by the formula (A) of BaZrS ３ The semiconductor intrinsic band gap (E ｇ，ｂｕｌｋ ) is 1.9485 ± 0.0974 eV ((E ｇ，ｃａｌｃ（ＨＳＥ０６） ) = 1.77 eV) [Fluorescence spectrum measurement] Measurement device: PL lifetime measurement device (Hamamatsu Photonics, C12132) Excitation light wavelength: 532 nm Measurement range: 580 to 1200 nm Measurement sample: The dispersion was filled into a quartz cell, which was then placed in a sample holder in the device and subjected to measurement.

[0080] The chalcogenide perovskite of the present invention, and powders, solutions, films, and sheets containing the chalcogenide perovskite, can be used, for example, as light-emitting materials in light-emitting devices such as displays, wavelength conversion elements, and photoelectric conversion elements such as solar cells and sensors.

[0081] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. The average particle diameter is less than 40 nm. The measured band gap is the same as the calculated band gap (E) obtained using the density functional method with the hybrid functional (HSE06). ｇ，ｃａｌｃ（ＨＳＥ０６） Based on this, the semiconductor-specific band gap (E) is calculated using the following formula (A). ｇ，ｂｕｌｋ A chalcogenide perovskite that matches the range of ). [Math 3]

2. The chalcogenide perovskite according to claim 1, wherein the measured value of the band gap is greater than 0 eV and less than 2.09 eV.

3. The chalcogenide perovskite according to claim 1, wherein the measured value of the band gap is 1.0 eV or more and 2.0 eV or less.

4. The chalcogenide perovskite according to claim 1, wherein the measured value of the band gap is 1.8 eV or more and 2.0 eV or less.

5. The chalcogenide perovskite according to claim 1, wherein the average particle diameter is 4 nm or more and less than 40 nm.

6. The chalcogenide perovskite according to claim 5, wherein the average particle diameter is 5 nm or more.

7. The chalcogenide perovskite according to claim 6, wherein the average particle diameter is 6 nm or more.

8. The chalcogenide perovskite according to claim 5, wherein the average particle size is less than 35 nm.

9. The chalcogenide perovskite according to claim 8, wherein the average particle diameter is less than 32 nm.

10. The chalcogenide perovskite according to claim 9, wherein the average particle size is less than 30 nm.

11. The chalcogenide perovskite according to claim 1, wherein the chalcogenide perovskite has a composition represented by the following formula (101) or (102). ABC( ３ ・・・(101) A’ ２ A ｎ－１ B ｎ Ch ３ｎ＋１ ・・・(102) (In formulas (101) and (102), A and A' are Ca, Mg, Sr, Ba, or a combination thereof, respectively; B is Ti, Zr, Hf, or a combination thereof; and Ch is S, Se, Te, or a combination thereof. In formula (102), n is an integer between 1 and 10. In formula (102), A and A' may be the same or different. The chalcogenide perovskite may be a solid solution in which some or all of A, A', B, and Ch in the composition represented by formula (101) or (102) are substituted with other elements.)

12. The chalcogenide perovskite according to claim 11, wherein n is 1 or more and 3 or less.

13. The composition of the aforementioned chalcogenide perovskite is BaZrS ３ The chalcogenide perovskite according to claim 11.

14. A powder comprising the chalcogenide perovskite according to any one of claims 1 to 13.

15. A solution comprising the chalcogenide perovskite according to any one of claims 1 to 13.

16. A thin film comprising the chalcogenide perovskite described in any one of claims 1 to 13.

17. A sheet comprising the chalcogenide perovskite according to any one of claims 1 to 13.

18. A device comprising the chalcogenide perovskite according to any one of claims 1 to 13.

19. The device according to claim 18, wherein the device is a photoelectric conversion element.

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