Production method of perovskite quantum dot and perovskite quantum dot

Abstract

To provide a production method of perovskite quantum dots maintaining high PLQY by adding a boron hydride compound and a sodium compound in a production process of the perovskite quantum dots to control an emission wavelength in a wavelength region shorter than 550 nm.SOLUTION: A production method of perovskite quantum dots represented by general formula (1) ApBqXr (in the formula, A is a monovalent cation, B is a divalent cation of a group 14 element, X is a halide ion, p is an integer of 1 to 4, q is 1 or 2, and r is an integer of 3 to 9) has a step 1 to recover crude nanoparticles by mixing a precursor solution formed by dissolving a perovskite precursor in a good solvent and a solution formed by dissolving an organic base compound and an organic acid compound in a poor solvent at 40°C or lower to prepare a suspension followed by sedimentation, and a step 2 to obtain a nanoparticle mixed dispersion liquid by dispersing the crude nanoparticles again with addition of a non-polar organic solvent and subsequently removing coarse powders with classification while a boron hydride compound and a sodium compound are added collectively or added with division in two steps between the step 1 and the step 2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing perovskite quantum dots without compromising their high photoluminescence quantum yield. [Background technology]

[0002] Perovskite quantum dots have high absorbance and a high photoluminescence quantum yield (PLQY). By changing their composition and layer structure, it is possible to control the emission wavelength and narrow the half-width, achieving high color purity. Therefore, they are expected to be applied to highly functional materials such as light-emitting diodes (LEDs), optical amplifiers, single-photon sources, and solar cells.

[0003] Perovskite quantum dots can control the emission wavelength by changing the halogen composition ratio, but it is known that defects are easily formed inside the crystal or on the surface, resulting in a significant decrease in PLQY. In particular, when controlling emission wavelengths shorter than green light, the PLQY decreases significantly because defect-induced trap levels exist in the energy band gap. In particular, in the halogen exchange from Br to Cl, defects increase significantly as the exchange rate increases and the emission wavelength shifts shorter.

[0004] The reduction in PLQY due to defect formation in perovskite quantum dots can also be caused by moisture in the raw materials, solvent, or atmosphere. Although dehydration of solvents and drying of raw materials are typically performed prior to the synthesis of halogenated perovskite nanocrystals, it is difficult to completely remove water. Among the raw materials, formamidine hydrobromide (FABr) and cesium bromide (CsBr) are prone to hygroscopicity and are easily absorbed into good solvents. Therefore, the precursor solution in the perovskite quantum dot synthesis process is prone to moisture. To solve this problem, prior art has already been reported that suppresses defects within the crystals by sodium doping through the addition of sodium bromide (NaBr) (e.g., Patent Document 1). Patent Document 1 describes a composite light-emitting material that includes a perovskite nanomaterial and a matrix, the perovskite nanomaterial having a core-shell structure in which the core is γ-CsPbI3 and the shell is MPbX3 or M4PbX6 (M is Li, Na, K, or Rb, and X is a halogen), and that in order to control the band gap of the γ-CsPbI3 quantum dots, alkali halides (LiX, NaX, KX, or RbX; X is Cl, Br, or I) or alkali carbonates (Li2CO3, Na2CO3, K2CO3, or Rb2CO3) are added to the raw materials as coating agents.

[0005] According to Patent Document 2, the method includes the steps of synthesizing a first inorganic halide perovskite nanoparticle (ABX3; A is Cs or CH3NH, B is Pb or Sn, and X is a halogen anion), and synthesizing a halogen salt (CX'; C is Cs + , Na + , K. + , NH4 + or Bu4N +In a method for synthesizing inorganic halide perovskite nanoparticles, the method includes the steps of preparing a solution by mixing a first inorganic halide perovskite nanoparticle (ABX'3; A is Cs or CH3NH, B is Pb or Sn, and X' is a halogen anion) with a polar solvent, and adding the first inorganic halide perovskite nanoparticles to the solution to synthesize second inorganic halide perovskite nanoparticles (ABX'3; A is Cs or CH3NH, B is Pb or Sn, and X' is a halogen anion). Through two anion exchanges, the first inorganic halide perovskite nanoparticle synthesis step and the second inorganic halide perovskite nanoparticle synthesis step, can synthesize second inorganic halide perovskite nanoparticles having an AB-X'3 bond stronger than the C-X' bond of the halogen salt. When cesium lead tribromide (CsPbBr3) is used as the first inorganic halide perovskite nanoparticles, sodium iodide (NaI) or ammonium chloride (NH4Cl) is used as the halogen salt. According to Patent Document 2, the cations of the halide salts exhibit a cationic effect on the defects of the first inorganic halide perovskite and are suitable for anion exchange. + Anion exchange does not occur with cations with large molecular size, such as NaI and NH4Cl, because they cannot passivate the defects.

[0006] Additionally, Patent Document 3 describes that in the process of manufacturing an LED by the hot injection method, a highly efficient and long-life perovskite quantum dot LED can be obtained by bringing a perovskite quantum dot dispersion liquid containing perovskite quantum dots and a low-dielectric-constant solvent into contact with an arylammonium halide salt in a solid or liquid state to exchange halogen anions.

[0007] Thus, there is a demand for a method for synthesizing perovskite nanocrystals that suppresses the formation of defects inside or on the surface of the crystal that cause a decrease in PLQY, and that exhibits luminescence properties such as high luminescence efficiency (PLQY of 80% or more), high color purity (full width at half maximum (FWHM) < 25 nm), and a wide color gamut (emission wavelength 450 to 730 nm). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2022-542724 [Patent Document 2] Japanese Patent Publication No. 2023-36021 [Patent Document 3] Japanese Patent Application Publication No. 2019-140309 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method for producing perovskite quantum dots that can control the emission wavelength mainly in the wavelength region shorter than 550 nm by adding a boron hydride compound and a sodium compound in the production process of perovskite quantum dots, thereby enabling the production of perovskite quantum dots that maintain a high photoluminescence quantum yield (PLQY). [Means for solving the problem]

[0010] The present invention comprises the following items. [1] A method for producing a nanoparticle-mixed dispersion liquid, comprising: a step 1 of mixing a precursor solution obtained by dissolving a perovskite precursor in a good solvent with a solution obtained by dissolving an organic base compound and an organic acid compound in a poor solvent at 40°C or less to prepare a suspension, and recovering coarse nanoparticles by sedimentation; and a step 2 of adding a non-polar organic solvent to the coarse nanoparticles to re-disperse them, and then removing coarse particles by classification to obtain a nanoparticle-mixed dispersion liquid, wherein a boron hydride compound and a sodium compound are added all at once or in two stages between the steps 1 and 2, p B q X r (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, and X is a halide ion; p is an integer of 1 or more and 4 or less; q is 1 or 2; and r is an integer of 3 or more and 9 or less).

[0011] [2] A method for producing a nanoparticle-containing dispersion liquid, comprising: a step 1 of preparing a suspension by mixing a precursor solution obtained by dissolving a perovskite precursor in a good solvent with a solution obtained by dissolving an organic base compound and an organic acid compound in a poor solvent at 40°C or less, and recovering coarse nanoparticles by sedimentation; a step 2 of adding a non-polar organic solvent to the coarse nanoparticles to redisperse them, and then removing coarse particles by classification to obtain a nanoparticle-containing dispersion liquid; and a step 3 of substituting a part of the halogens by adding a halide containing one or more halogens to the nanoparticle-containing dispersion liquid, wherein a boron hydride compound and a sodium compound are added all at once or in two stages between the steps 1 and 2, p B q X' r (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

[0012] [3] The method for producing perovskite quantum dots according to [1] or [2], wherein the boron hydride compound and the sodium compound are added all at once in step 1 rather than being added in two separate steps, and in step 1, the perovskite precursor, the boron hydride compound, and the sodium compound are dissolved in a good solvent to prepare a precursor solution.

[0013] [4] The method for producing perovskite quantum dots according to [1] or [2], wherein the boron hydride compound and the sodium compound are not added all at once but are added in two separate steps, in steps 1 and 2, in which in step 1 a precursor solution is prepared by dissolving the perovskite precursor, the boron hydride compound, and the sodium compound in a good solvent, and in step 2 a non-polar organic solvent, the boron hydride compound, and the sodium compound are added to the crude nanoparticles to redisperse them.

[0014] [5] The amount of the sodium compound added is p B q X r(wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, and X is a halide ion; p is an integer of 1 or more and 4 or less; q is 1 or 2; and r is an integer of 3 or more and 9 or less), or the amount of substance (mol) of A in the general formula (2)A p B q X' r (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less), the amount of substance (mol) of X is 0.03 to 0.50 times the amount of substance (mol) of A in the formula (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

[0015] [6] The method for producing perovskite quantum dots according to [1] or [2], wherein the molar ratio (mol) of the sodium compound to the molar ratio (mol) of the boron hydride compound is 0.3 to 3.0 times.

[0016] [7] The method for producing perovskite quantum dots according to [1] or [2], wherein the compound consisting of a boron hydride compound and a sodium compound is sodium borohydride.

[0017] [8] A compound of general formula (2): A, characterized in that the photoluminescence quantum yield (PLQY) is 82% or more in the wavelength range of 463 to 500 nm. p B q X' r (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

[0018] [9] The perovskite quantum dots according to [8], characterized in that the particle size of the perovskite quantum dots is 4 to 30 nm. [Effects of the Invention]

[0019] According to the present invention, in the manufacturing process of halogenated perovskite quantum dots, a boron hydride compound and a sodium compound are added to convert the very small amount of water contained therein into boron hydride ions (BH4 - ) is reduced and generates hydrogen, effectively suppressing defect formation, while sodium ions (Na + ) substitution increases the lattice energy of the A and X sites, stabilizing the crystal structure of the perovskite quantum dots and making them closer to perfect crystals. By adding boron hydride compounds and sodium compounds in the manufacturing process of perovskite quantum dots by halogen exchange, it is possible to control the emission wavelength in the short wavelength region, mainly in the region shorter than 550 nm, and obtain perovskite quantum dots that maintain a high photoluminescence quantum yield (PLQY). [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a graph showing PLQY (%) versus emission wavelength peak top (nm) when various amounts of FAPbCl were added in step 4 to the perovskite quantum dot dispersions obtained in Example 1, Comparative Example 1, and Reference Example 1. [Figure 2] FIG. 2 shows (a) a transmission electron microscope image of the perovskite quantum dots obtained in step 2 of Comparative Example 1, (b) a transmission electron microscope image of the perovskite quantum dots obtained in step 2 of Example 1, (c) the particle size distribution of the perovskite quantum dots obtained in step 2 of Comparative Example 1, and (d) the particle size distribution of the perovskite quantum dots obtained in step 2 of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0021] The method for producing perovskite quantum dots (PeQDs) of the present invention is a method using the ligand-assisted reprecipitation (LARP) method. Hereinafter, a first embodiment and a second embodiment will be described in this order. First Embodiment The method for producing perovskite quantum dots of the present invention includes the following steps: Step 1: mixing a precursor solution in which a perovskite precursor is dissolved in a good solvent with a solution in which an organic base compound and an organic acid compound are dissolved in a poor solvent at 40°C or below to prepare a suspension, and recovering coarse nanoparticles by sedimentation; and Step 2: adding a nonpolar organic solvent to the coarse nanoparticles to redisperse them, and then removing coarse particles by classification to obtain a nanoparticle-mixed dispersion. Between Steps 1 and 2, a boron hydride compound and a sodium compound are added all at once or in two stages.

[0022] The perovskite quantum dots have the general formula (1): A p B q X r (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, and X is a halide ion; p is an integer of 1 or more and 4 or less; q is 1 or 2; and r is an integer of 3 or more and 9 or less).

[0023] Perovskite quantum dots are colloidal crystals with sizes ranging from several nanometers to several tens of nanometers. Colloidal quantum dots are luminescent semiconductor nanoparticles. Among luminescent nanoparticles whose light absorption and luminescence regions can be controlled by changing the size of the crystal grains, perovskite-type luminescent nanoparticles are particularly excellent in this property and are suitable in that they can be easily synthesized by a solution process.

[0024] General formula (1):A p B q X r Specifically, A represents an organic and / or inorganic monovalent cation occupying the A site, B represents a divalent metal cation of Group 14 occupying the B site, and X represents a halide ion occupying the X site. The B is surrounded by the X in an octahedral shape, and the octahedra share the X at their vertices, forming a perovskite structure.

[0025] The monovalent organic cations that occupy the A site are primary, secondary, and quaternary ammonium ions, formamidinium ions (CH(NH2)2 +;FA), guanidinium ion ((H2N)2C=NH2 + ;GA), imidazolium ion, 1-methylimidazolium ion, pyridinium ion, 1-methylpyridinium ion, pyrrolidinium ion, and thiouronium ion.

[0026] Specific examples of primary to quaternary ammonium ions include ammonium ion (NH4 + ), methylammonium ion (CH3NH3 + ;MA), dimethylammonium ion, ethylammonium ion (CH3CH2NH3 + ;EA), diethylammonium ion, propylammonium ion, isopropylammonium ion, butylammonium ion, isobutylammonium ion, t-butylammonium ion, benzylammonium ion and phenethylammonium ion. Of these, methylammonium ion is preferred.

[0027] Monovalent inorganic cations are alkali metal ions, such as cesium, rubidium, potassium, sodium, and lithium.

[0028] Among these, from the viewpoint of the tolerance factor (TF) of the crystal structure, A p B q X r It is preferred that 60 mol % or more, preferably 70 mol % or more, and more preferably 80 mol % or more of the A-site cations in the cations are at least one type selected from the group consisting of cesium ions, rubidium ions, MA, EA, FA, and GA. A may be of only one type, or may be of two or more types.

[0029] The divalent metal cations of Group 14 occupying the B site are lead ions, germanium ions, or tin ions. Of these, lead ions and tin ions are preferred. Furthermore, antimony ions, bismuth ions, copper ions, nickel ions, cobalt ions, iron ions, manganese ions, chromium ions, cadmium ions, europium ions, ytterbium ions, and silver ions may be included, with the element ratio of lead ions, germanium ions, or tin ions being 5% or less. B may be of only one type, or may be of two or more types.

[0030] Halide ions that occupy the X site are chloride, bromide, and iodide. p B q X r X may be of only one type or of two or more types, and may also contain monovalent pseudohalogen ions such as cyanide, isothiocyanate, oxocyanate, thiocyanate, selenocyanate, sulfide, fulminate ion, azide ion, borohydride ion, and hexafluorophosphate ion, provided that the elemental ratio of halide ions is 20% or less.

[0031] A p B q X r In the formula, p represents an integer of 1 or more and 4 or less, q represents 1 or 2, and r represents an integer of 3 or more and 9 or less. Preferably, p:q:r represents positive numbers in the ratios of 1:1:3, 4:1:6, and 2:1:4.

[0032] A, B, and X can be appropriately selected taking into consideration the energy band gap of the perovskite quantum dots and the sizes of A, B, and X. p B q X r A specific example of this is Cs a1 MA a2 EA a3 FA a4 GA a5 K a6 Rb (p-a1-a2-a3-a4-a5-a6) Pb b1 Sn b2 Ge(q-b1-b2) (Cl (1-y-z) Br y I z ) r (0≦a1≦p, 0≦a2≦p, 0≦a3≦p, 0≦a4≦p, 0≦a5≦p, 0≦a6≦p, a1+a2+a3+a4+a5+a6≦p, 0≦b1≦q, 0≦b2≦q, b1+b2≦q, 0≦y≦1, 0≦z≦1, y+z≦1), etc. However, the present invention is not limited to these specific examples.

[0033] For the crystalline structure of ABX3, which is a typical perovskite structure, to be stable, TF must be in the range of 0.70 to 1.10. p B q X r Suitable examples of are metal halide perovskites such as CsPbBr3 (TF=0.86), FAPbBr3 (TF=1.01), CsPbI3 (TF=0.85) and CsSnI3 (TF=0.92).

[0034] The particle size of the metal halide perovskite is not particularly limited as long as it is within a range that allows it to function as a luminescent material, but the particle size is generally 1.0 to 30 nm in terms of the average primary particle size, preferably 4 to 30 nm or 2.0 to 20 nm, and more preferably 4.0 to 16 nm. Here, the primary particle size is the Heywood diameter (diameter equivalent to the projected circle area). When the average particle size is within the above range, a quantum confinement effect is exerted, resulting in a high PLQY, while at the same time, the sedimentation rate in the dispersion is sufficiently slow, allowing the metal halide perovskite to be dispersed and stabilized.

[0035] The shape of the metal halide perovskite is not particularly limited. Examples include spherical, cubic, cylindrical, polyhedral, and scale shapes. Among these, from the viewpoints of dispersion stability and crystal lattice distortion within the particles, either spherical or cubic shapes, or both, are preferred.

[0036] In step 1, a precursor solution in which a perovskite precursor is dissolved in a good solvent is mixed with a solution in which an organic base compound and an organic acid compound are dissolved in a poor solvent at 40°C or below to prepare a suspension, and crude nanoparticles are recovered by sedimentation. The perovskite precursor has the general formula (1): A p B q X r The compound comprises a compound containing an organic and / or inorganic monovalent cation (hereinafter simply referred to as "monovalent cation") occupying the A site in the formula (I), a compound containing a divalent metal cation occupying the B site, and a compound containing a halide ion occupying the X site.

[0037] An example of a compound containing a monovalent cation that forms the A site is a compound consisting of the monovalent cation and X. When the monovalent cation is an inorganic cation, specifically an alkali metal ion, the compound containing the monovalent cation is an alkali halide.

[0038] When the monovalent cation is an organic cation, specific examples of compounds containing the monovalent cation include ammonium halide salts such as methylammonium bromide and methylammonium iodide, and formamidine hydrohalide salts such as formamidine hydrobromide (CH(NH)Br) and formamidine hydroiodide (CH(NH)I).

[0039] Compounds containing divalent metal cations that form the B site include halides of germanium ions, tin ions, lead ions, antimony ions, or bismuth ions. Specific examples include lead(II) bromide (PbBr2), lead(II) iodide (PbI2), lead(II) chloride (PbCl2), tin(II) bromide (SnBr2), tin(II) iodide (SnI2), tin(II) chloride (SnCl2), germanium(II) bromide (GeBr2), germanium(II) iodide (GeI2), and germanium(II) chloride (GeCl2). These compounds can be used alone or in combination in any ratio. Furthermore, antimony, bismuth, copper, nickel, cobalt, iron, manganese, chromium, cadmium, europium, ytterbium, and silver may be contained within a range of 5% or less of the B site element ratio.

[0040] Compounds containing a halide ion occupying the X site include compounds comprising the halide ion and the aforementioned monovalent cation occupying the A site or a divalent Group 14 metal cation occupying the B site, as well as hydrogen chloride, hydrogen bromide, and hydrogen iodide. Furthermore, monovalent pseudohalogen ions such as dicyanide ions, oxocyanide ions, thiocyanide ions, selenocyanide ions, fulminate ions, borohydride ions, and hexafluorophosphate ions may be contained within the range of 10% or less of the element ratio at the X site.

[0041] The organic base compound may be any of aliphatic amines, aromatic amines, and quaternary ammonium salts, and specific examples thereof include aliphatic amines having 3 to 24 carbon atoms, such as oleylamine, propylamine, butylamine, pentylamine, octylamine, hexadecylamine, octadecylamine, 2-hexyldecane-1-amine, 2-decyltetradecane-1-amine, stearylamine, and cyclohexylamine; aniline, benzylamine, phenethylamine, 3-phenyl-2-propene-1-amine, phenylmethyl ... aromatic amines having 6 to 34 carbon atoms, such as naphthylamine, 2,2'-iminodibenzoic acid, 3-phenylpropylamine, 4-phenylbutylamine, naphthylamine, 4-aminobiphenyl, and 3,4,5-tris(prop-2-en-1-yloxy)benzylamine; and quaternary ammonium salts, such as didecyldimethylammonium salt, benzyltrimethylammonium bromide salt, 3-(N,N-dimethyloctadecylammonio)propanesulfonate salt, and stearyltrimethylammonium salt. These compounds can be used alone or in combination of two or more in any ratio.

[0042] Organic acid compounds include organic carboxylic acids, organic sulfonic acids, organic sulfinic acids, and phosphorus oxoacid compounds (organic phosphonic acids, organic phosphonates, and organic phosphinic acids). Examples include organic carboxylic acids such as oleic acid, stearic acid, palmitic acid, glutaric acid, sebacic acid, benzoic acid, and 3,4,5-tri(2-propenoxy)benzoic acid; organic sulfinic acids such as benzenesulfinic acid; organic phosphonic acids such as octylphosphonic acid, tetradecylphosphonic acid, and tri-n-octylphosphine oxide; and organic phosphinic acids such as di-t-octylphosphinic acid and diisooxylphosphinic acid. These compounds can be used alone or in combination in any ratio.

[0043] The organic base compound is mainly represented by the general formula (1): A p B q X r The compound that forms a coordinate bond with X in (B) and the organic acid compound that forms a coordinate bond with B act to both uniformize particle size and fill surface defects when producing perovskite-type luminescent nanoparticles. Adding both an organic base compound and an organic acid compound improves both the yield and PLQY of the nanoparticle dispersion. Furthermore, when the nanoparticle surface is modified with the long chains of the organic base compound or organic acid compound, this site acts to regulate particle growth and uniform particle size.

[0044] The good solvent used in step 1 may be any solvent that has high solubility for the perovskite precursor, organic base compound, and organic acid compound, and is preferably an aprotic polar solvent that is miscible with the poor solvent and nonpolar organic solvent described below.Specific examples include N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and acetonitrile.

[0045] The poor solvent used in step 1 is preferably an organic solvent with low polarity. Specifically, examples of the poor solvent include pentane, cyclopentane, hexane, cyclohexane, heptane, cycloheptane, 1-hexene, cis-2-hexene, trans-2-hexene, cis-3-hexene, trans-3-hexene, 3,3-dimethyl-1-butene, cyclohexene, cycloheptene, octane, nonane, decane, cyclopropane, cyclobutane, cyclooctane, decalin, norbornane, methylcyclohexane, methylcyclohexene, 1,1-dimethylcyclohexane, cis-1,2-dimethylcyclohexane, cis-1,3-dimethylcyclohexane, and trans-1,3-dimethylcyclohexane. Examples of suitable solvents include cyclohexane, cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane, 1,2,4,5-tetramethylcyclohexane, 1,1,3,3,5-pentamethylcyclohexane, (cyclopentylmethyl)cyclohexane, dicyclohexylmethane, 1-ethyl-2-propylcyclohexane, amylcyclohexane, 1,1'-ethylenebiscyclohexane, isobutylcyclohexane, o-xylene, m-xylene, p-xylene, chloroform, triethylamine, carbon tetrachloride, propylene glycol monomethyl ether acetate (PGM-Ac), and diethyl ether. These may be used alone or in combination in any desired ratio.

[0046] The solution of the organic base compound and the organic acid compound dissolved in the poor solvent acts as a nonpolar solvent for the perovskite precursor solution. In step 1, when the perovskite precursor solution is added to the nonpolar solvent, solid particles in the perovskite precursor solution that are insoluble in the nonpolar solvent are emulsified or dispersed to form a suspension. After liquid-phase synthesis of a crude nanoparticle solution (suspension) from perovskite precursors, organic base compounds, and organic acid compounds, the organic solvent is removed from the crude nanoparticle solution by sedimentation to obtain crude nanoparticles. Sedimentation is usually performed by centrifugation. In step 1, there is loss of unreacted perovskite precursors and products that do not settle during sedimentation, but the yield is still over 80%.

[0047] In step 2, the coarse nanoparticles are redispersed in a nonpolar organic solvent, and then the coarse particles are removed by classification to obtain a nanoparticle-mixed dispersion. There are no particular restrictions on the classification method as long as it can remove coarse particles to leave only particles with a predetermined diameter or less, and can improve particle flowability by aligning the particle size distribution. However, centrifugation using a centrifugal classifier is preferred because it allows for efficient classification.

[0048] The nanoparticle concentration in the nanoparticle mixed dispersion obtained in step 2 is usually 0.01 to 100 mg / mL, preferably 0.1 to 50 mg / mL, and more preferably 0.5 to 20 mg / mL. The concentration is calculated by attaching an integrating sphere to a fluorescence spectrophotometer FP-8600 (manufactured by JASCO Corporation; excitation wavelength 370 nm) and determining the dilution ratio at which the absorbance of the nanoparticle mixed dispersion becomes 0.5. Examples of nonpolar organic solvents that can be used include alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and decalin, and aromatic hydrocarbons such as toluene.

[0049] During steps 1 and 2, the borohydride compound and the sodium compound are added all at once or in two separate steps.

[0050] The borohydride compound is an ionic compound containing a borohydride complex ion. Specific examples include sodium borohydride, lithium borohydride, potassium borohydride, rubidium borohydride, cesium borohydride, methylammonium borohydride, formamidine borohydride, lithium triethylborohydride, sodium triacetoxyborohydride, sodium cyanoborohydride, tetrabutylammonium borohydride, tetraethylammonium borohydride, benzyltriethylammonium borohydride, tetrabutylammonium borohydride, and tetramethylammonium triacetoxyborohydride.

[0051] Sodium compounds contain sodium ions (Na +) are ionic compounds containing sodium bromide, sodium iodide, sodium chloride, sodium borohydride, sodium tetraborate, sodium hydroxide, sodium oxalate, sodium cyanate, sodium thiocyanate, sodium hexafluorophosphate, sodium formate, sodium acetate, and other inorganic sodium compounds, alkyl sodium compounds, and aromatic sodium compounds.

[0052] The molar ratio of the molar mass of the sodium compound to the molar mass of the boron hydride compound is usually 0.3 to 3.0, preferably 0.5 to 2.0, and more preferably 0.9 to 1.1. For example, the molar ratio of the boron hydride compound and the sodium compound is 1.0.

[0053] The borohydride compound and the sodium compound may be separate compounds, or may be a mixture of borohydride ions (BH4), such as sodium borohydride (NaBH4). - ) and sodium ions in sodium compounds (Na + ) may be used. In the present invention, sodium borohydride (NaBH4) is preferably used. When lithium borohydride or potassium borohydride is used as the boron hydride compound, it is necessary to use these compounds in combination with a sodium compound. The reason is that sodium ions (Na + ), the ionic radius of the lithium ion (Li + ) cannot fully compensate for the deficiency of the cation sites, while potassium ions (K + ) sodium ions (Na + ) and therefore cannot compensate for the deficiency of the cation sites.

[0054] The boron hydride compound and the sodium compound may be added all at once in step 1. In this case, a precursor solution is prepared by dissolving the perovskite precursor, the boron hydride compound, and the sodium compound in a good solvent.

[0055] The boron hydride compound and the sodium compound may be added in two separate stages between Step 1 and Step 2.

[0056] However, it is preferable to add the borohydride compound and the sodium compound all at once in step 1, since they are easily dissolved in the good solvent used in step 1.

[0057] It is known that the photoluminescence quantum yield (PLQY) of perovskite quantum dots decreases when defects are formed inside or on the surface of the crystal. Defect formation occurs when traces of moisture contained in the raw materials, solvents, or air react with the general formula (1): A p B q X r If this small amount of water is not removed sufficiently, sodium will not easily enter the perovskite structure, and the defect complementing effect will be reduced.

[0058] However, in the present invention, by adding a boron hydride compound and a sodium compound, such as sodium borohydride, in step 1, it is possible to capture moisture in the solvent and raw materials. The reaction in this case is hydrolysis as shown below. This hydrolysis is highly reactive and proceeds easily at room temperature.

[0059] NaBH4+ 2H2O → 4H2+ NaBO2 The resulting NaBO2 is involved in the synthesis of perovskite quantum dots, and the following reaction occurs: We will explain this using the reaction of formamidine hydrobromide (FABr) with lead(II) bromide (PbBr2) as an example.

[0060] FABr + PbBr2+ xNaBO2→ FA (1-x) Na x PbBr3+ xFABO2

[0061] The amount of the sodium compound added is p B q Xr The amount of A in the compound is usually 0.03 to 0.50 times, preferably 0.04 to 0.30 times, and more preferably 0.05 to 0.20 times the amount of A in the compound.

[0062] The amount of the boron hydride compound added is p B q X r The amount of A in the compound is usually 0.03 to 0.50 times, preferably 0.04 to 0.30 times, and more preferably 0.05 to 0.20 times the amount of A in the compound. The molar ratio (mol) of the sodium compound to the molar ratio (mol) of the boron hydride compound is preferably 0.3 to 3.0 times, more preferably 0.5 to 2.0 times.

[0063] Second Embodiment The method for producing perovskite quantum dots of the present invention includes the following steps: Step 1: mixing a precursor solution in which a perovskite precursor is dissolved in a good solvent with a solution in which an organic base compound and an organic acid compound are dissolved in a poor solvent at 40°C or below to prepare a suspension, and recovering coarse nanoparticles by sedimentation; Step 2: adding a nonpolar organic solvent to the coarse nanoparticles to redisperse them, and then removing coarse particles by classification to obtain a nanoparticle-mixed dispersion; and Step 3: adding a halide containing one or more halogens to the nanoparticle dispersion to replace some of the halogens. Between Steps 1 and 2, a boron hydride compound and a sodium compound are added all at once or in two stages.

[0064] The perovskite quantum dots are represented by the general formula (2)A p B q X' r (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, and X' is two or more types of halide ions; p is an integer of 1 or more and 4 or less; q is 1 or 2; and r is an integer of 3 or more and 9 or less).

[0065] The second embodiment is the same as the first embodiment up to step 1 and step 2, but differs from the first embodiment in that it further includes step 3. In step 3, a halide containing one or more halogens is added to the nanoparticle dispersion obtained in step 2 to replace some of the halogens. Here, the perovskite crystals emit light with a peak (λ PL ), and its optical and electrical properties depend on the band gap. Halogen exchange is a simple method to change the band gap and tune the emission wavelength. Step 3 involves changing the type and composition of halide ions in the perovskite nanocrystals to tune the emission wavelength of the perovskite quantum dots.

[0066] The halide used in step 3 is, for example, a perovskite precursor (CH4N2·PbCl3) made of formamidine hydrochloride (CH(NH2)2Cl) and lead(II) chloride (PbCl2). The halide can be synthesized by using an ammonium halide salt such as methylammonium chloride or a formamidinium halide salt such as formamidinium chloride as the compound containing a monovalent cation that forms the A site in the general formula ABX3; lead(II) chloride (PbCl), lead(II) iodide (PbI), lead(II) chloride (PbCl), tin(II) chloride (SnCl), tin(II) iodide (SnI), germanium(II) chloride (GeCl), germanium(II) iodide (GeI), or germanium(II) chloride (GeCl); and a compound containing a divalent metal cation as the compound containing a halide ion that forms the X site in the general formula ABX3.

[0067] In step 3, when the halide is added to the nanoparticle dispersion obtained in step 2, halogen exchange occurs through the following reaction: The slight change in crystal structure caused by halogen exchange changes the luminescence characteristics upon light irradiation.

[0068] When a boron hydride compound and a sodium compound are added between steps 1 and 2, sodium is inserted into the center of the perovskite structure. Therefore, the composition of the nanoparticles in the nanoparticle dispersion becomes CH4N2·H (1-x) Na x This results in PbBr3. When a halide is added to this, the following halogen exchange reaction occurs. This is explained using the example of adding lead(II) chloride (PbCl2) to a nanoparticle mixed dispersion consisting of formamidine hydrobromide (FABr) and lead(II) bromide (PbBr2). FA (1-x) Na x PbBr3+ yFAPbCl3→ FA (1-x+y) Na x Pb (1+y) (Cl y Br)3

[0069] Disordered structures (defects) caused by halogen exchange cause a decrease in PLQY, and it is known that, particularly in the case of halogen exchange from Br to Cl, defects increase significantly as the exchange rate increases and the emission wavelength shifts to shorter wavelengths. However, in the present invention, the addition of a boron hydride compound and a sodium compound between steps 1 and 2 effectively suppresses crystal defects in the perovskite. In this way, by adjusting the halogen exchange and suppressing structural changes in the perovskite nanocrystals, the emission wavelength can be adjusted and the photostability of the resulting perovskite quantum dots can be improved.

[0070] The amount of halide added to the nanoparticle dispersion obtained in step 2 is usually 0.03 to 0.50 times the amount (mol), preferably 0.04 to 0.30 times the amount (mol), and more preferably 0.05 to 0.20 times the amount (mol).

[0071] The perovskite quantum dots obtained in the second embodiment are represented by the general formula (2): A p B q X' r(wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

[0072] A, B, p, q, and r in general formula (2) are the same as A, B, p, q, and r in general formula (1). However, in the second embodiment, since halogen exchange is performed in step 3, X' is two or more types of halide ions.

[0073] In perovskite quantum dots, if the X site in the ABX3 structure is chlorine, the color will be blue to purple, if it is bromine, it will be green, and if it is iodine, it will be red. By appropriately changing the composition of the X site, the desired emission color can be obtained. When the X site is bromine, the lattice energy is smallest and the perovskite structure is most stable. Therefore, it is desirable to first synthesize nanoparticles with bromine at the X site, and then adjust the color by halogen exchange. These two or more types of halide ions are Br - and other halogens (F - , Cl - or I - The other halogen atoms are preferably one or more of the following: The X site in the perovskite quantum dots typically contains 5 to 90 mol %, preferably 10 to 85 mol %, and more preferably 40 to 80 mol % of other halogen atoms in terms of molar ratio.

[0074] General formula (2):A p B q X' r The perovskite quantum dots represented by the formula (1) have a high photoluminescence quantum yield (PLQY) of 82% or more in the wavelength region of 463 to 500 nm. These perovskite quantum dots exhibit no deterioration even when left in the atmosphere for 7 days, demonstrating excellent atmospheric stability and luminous efficiency. The particle size of such perovskite quantum dots is usually 1 to 30 nm, preferably 2.0 to 20 nm, and more preferably 4.0 to 16 nm.

[0075] The photoluminescence quantum yield (PLQY) and emission wavelength peak (λ ) were measured by fluorometry for the nanoparticle mixed dispersion obtained in step 2 and the perovskite quantum dot dispersion obtained by halogen exchange in step 3. PL ) measurement, the PLQY retention rate (%) is as high as 94.0 to 101.7%. In addition, the emission wavelength peak (λ PL ) shifts, and the desired emission color can be obtained. For example, when some of the bromine-containing nanoparticles are exchanged with chlorine, the emission wavelength shifts to the shorter wavelength side, and the color of the dispersion changes from green to blue. The PLQY maintenance rate (%) is calculated by dividing the PLQY (%) of the nanoparticle-mixed dispersion obtained in step 2 by the PLQY (%) of the halogen-mixed perovskite quantum dot dispersion exchanged in step 3, and multiplying the result by 100. [Example]

[0076] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. The synthesis and evaluation methods for the perovskite quantum dots (PeQDs) of Examples 1 to 9 and Comparative Examples 1 to 4 are described below.

[0077] [Example 1] Preparation of PeQD dispersions (i) Step 1 (crude nanoparticles) A precursor solution was prepared by dissolving 75 mg (0.6 mmol) of formamidine hydrobromide (CH4N2·HBr), 220 mg (0.6 mmol) of lead(II) bromide (PbBr2), and 1.13 mg (0.03 mmol) of sodium borohydride in 1 mL of N,N-dimethylformamide (DMF). As a non-polar solvent, 737 μL (2.3 mmol) of oleic acid and 70 μL (0.21 mmol) of oleylamine were dissolved in 10 mL of propylene glycol monomethyl ether acetate (PGM-Ac). The nonpolar solvent was placed in a screw tube, and 0.6 mL of the precursor solution was added to it while stirring at room temperature. After 3 minutes of stirring, a crude PeQD dispersion was obtained. 1.35 mL of the crude PeQD dispersion was placed in a centrifuge tube and centrifuged at 16,500 rpm for 3 minutes using a tabletop centrifuge, AS165W (manufactured by AS ONE Corporation). The supernatant was then removed to obtain crude nanoparticles.

[0078] (ii) Step 2 (Nanoparticle mixed dispersion) The crude nanoparticles were redispersed by adding 1 mL of toluene as a dispersion medium, and then centrifuged at 16,500 rpm for 2 minutes in a tabletop centrifuge AS165W (manufactured by AS ONE Corporation) to recover the supernatant. Images of the nanoparticles obtained from the supernatant taken with a transmission electron microscope (TEM) and the results of particle size distribution measurements are shown in Figure 2(b) and (d). Average particle size d avg was 5.80 nm (Fig. 2(d)). An integrating sphere was attached to a fluorescence spectrophotometer FP-8600 (JASCO Corporation; excitation wavelength 370 nm), and the solution was diluted with toluene to a sample absorption of 0.5, yielding a PeQD dispersion. The optical properties were measured, revealing a photoluminescence quantum yield (PLQY) of 101.7% and a peak emission wavelength (λ PL ) was 524 nm. Table 1 shows the optical properties of the nanoparticle mixed dispersion.

[0079] (iii) Step 3 (wavelength tuning crystal) A screw cap tube was charged with 100 mL of toluene, and a solution of 241.6 mg (3 mmol) of formamidine hydrochloride (CH4N2·HCl) and 834.3 mg (3 mmol) of lead(II) chloride (PbCl2) dissolved in 7 mL of N,N-dimethylformamide (DMF) was added and stirred for 3 minutes. The resulting slurry was discarded, and 90 mL of toluene was added and stirred for 3 minutes. After centrifugation at 16,500 rpm for 3 minutes in a tabletop centrifuge, the supernatant was removed and the resulting crystals were dried in a vacuum oven at 40°C and 4 kPa for 10 hours to obtain FAPbCl3 powder.

[0080] (iv) Step 4 (wavelength-converted PeQD dispersion) FAPbCl3 powder, 1 mL of toluene, and 2 μL of oleylamine were placed in a screw tube, and 2 mL of the PeQD dispersion prepared in step 2 was then poured into the tube. Ultrasonic waves were applied to the outside of the screw tube for 5 minutes using a tabletop ultrasonic cleaner. After visually confirming that the color of the dispersion had changed to blue, the tube was centrifuged at 16,500 rpm for 1 minute in a tabletop centrifuge, and the supernatant was collected to obtain the wavelength-converted PeQD dispersion. The optical properties of the resulting wavelength-converted PeQD dispersion were measured under the same conditions as in step 2. The PLQY was 97.1%, λ PL The PLQY maintenance rate was calculated using the following formula from the PLQY before and after wavelength conversion.

[0081]

number

[0082] [Example 2] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that the amount of sodium borohydride added in step 1 was changed from 1.13 mg (0.03 mmol) to 2.26 mg (0.06 mmol). The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 97.6%, and the λ PL is 523 nm, the PLQY of the wavelength-converted PeQD dispersion is 90.7%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 93%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0083] [Example 3] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that the amount of sodium borohydride added in step 1 was changed from 1.13 mg (0.03 mmol) to 4.54 mg (0.12 mmol). The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 95.2%, and the λ PL is 524 nm, the PLQY of the wavelength-converted PeQD dispersion is 97.3%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 102%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0084] [Example 4] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that sodium borohydride was not added in step 1 and 1.13 mg (0.03 mmol) of sodium borohydride was added to the dispersion medium in step 2. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 95.5%, and the λ PL is 523 nm, the PLQY of the wavelength-converted PeQD dispersion is 79.0%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 83%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0085] [Example 5] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that 1.13 mg (0.03 mmol) of sodium borohydride was added to the dispersion medium in step 2 in addition to step 1. The total amount of sodium borohydride added in steps 1 and 2 was 1.13 mg (0.03 mmol). The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 94.0%, and the λPL is 523 nm, the PLQY of the wavelength-converted PeQD dispersion is 80.3%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 85%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0086] [Example 6] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that 3.09 mg (0.03 mmol) of sodium bromide and 1.62 mg (0.03 mmol) of potassium borohydride were added in place of 1.13 mg (0.03 mmol) of sodium borohydride added in step 1 so that the molar ratio of sodium to borohydride ions was 1.0. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 91.4%, and the λ PL is 523 nm, the PLQY of the wavelength-converted PeQD dispersion is 86.2%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 94%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0087] [Example 7] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that 6.17 mg (0.06 mmol) of sodium bromide and 1.62 mg (0.03 mmol) of potassium borohydride were added in place of 1.13 mg (0.03 mmol) of sodium borohydride added in step 1 so that the molar ratio of sodium to borohydride ions was 2.0. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 95.0%, and the λ PL is 521 nm, the PLQY of the wavelength-converted PeQD dispersion is 92.7%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 98%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0088] [Example 8] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that 3.09 mg (0.03 mmol) of sodium bromide and 3.24 mg (0.06 mmol) of potassium borohydride were added in place of 1.13 mg (0.03 mmol) of sodium borohydride added in step 1 so that the molar ratio of sodium to borohydride ions was 0.5. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 93.8%, and the λ PL is 520 nm, the PLQY of the wavelength-converted PeQD dispersion is 85.0%, λ PL The PLQY retention rate before and after wavelength conversion was calculated to be 91%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0089] [Example 9] (i) Process 1 A precursor solution was prepared by dissolving 67.2 mg (0.6 mmol) of methylamine hydrobromide (CH3N2·HBr), 220 mg (0.6 mmol) of lead(II) bromide (PbBr2), and 1.13 mg (0.03 mmol) of sodium borohydride in 1 mL of N,N-dimethylformamide (DMF). As a non-polar solvent, 737 μL (2.3 mmol) of oleic acid and 70 μL (0.21 mmol) of oleylamine were dissolved in 10 mL of propylene glycol monomethyl ether acetate (PGM-Ac). The nonpolar solvent was placed in a screw tube, and 0.6 mL of the precursor solution was added to it while stirring at room temperature. After 3 minutes of stirring, a crude PeQD dispersion was obtained. 1.35 mL of the crude PeQD dispersion was placed in a centrifuge tube and centrifuged at 16,500 rpm for 3 minutes using a tabletop centrifuge, AS165W (manufactured by AS ONE Corporation). The supernatant was then removed to obtain crude nanoparticles. (ii) Step 2, Step 3, Step 4 The same procedure was carried out as in Example 1. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 92.4%, and the λ PL was 516nm. The optical properties of the PeQD dispersions are shown in Table 1.

[0090] [Comparative Example 1] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that sodium borohydride was not added in steps 1 to 3. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 97.9%, and the λ PL is 526 nm, the PLQY of the wavelength-converted PeQD dispersion is 33.7%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 34%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0091] Comparative Example 2 A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that the 1.13 mg (0.03 mmol) of sodium borohydride added in step 1 was changed to 1.62 mg (0.03 mmol) of potassium borohydride. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 96.7%, and the λ PL is 526 nm, the PLQY of the wavelength-converted PeQD dispersion is 32.6%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 34%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion. The TEM image and particle size distribution of the nanoparticles obtained from the supernatant in step 2 are shown in Figure 2(a) and (c). avg was 6.75 nm.

[0092] Uniform cubic crystals were confirmed in the appearance of the PeQD particles in both Example 1 and Comparative Example 1. This confirms that borohydride ions and sodium ions have almost no effect on the crystal size or shape.

[0093] Comparative Example 3 A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that the 1.13 mg (0.03 mmol) of sodium borohydride added in step 1 was changed to 0.65 mg (0.03 mmol) of lithium borohydride. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 83.7%, and the λ PL is 522 nm, the PLQY of the wavelength-converted PeQD dispersion is 17.4%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 21%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0094] Comparative Example 4 A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 9, except that sodium borohydride was not added in step 1. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 69.3%, and the λ PL was 519nm. The optical properties of the PeQD dispersions are shown in Table 1.

[0095] [Reference example 1] A PeQD dispersion and a wavelength-converted PeQD dispersion were obtained under the same conditions as in Example 1, except that the 1.13 mg (0.03 mmol) of sodium borohydride added in step 1 was changed to 3.09 mg (0.03 mmol) of sodium bromide. The optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion were measured under the same conditions as in Example 1. The PLQY of the PeQD dispersion was 97.5%, and the λPL is 522 nm, the PLQY of the wavelength-converted PeQD dispersion is 59.4%, λ PL The PLQY maintenance rate before and after wavelength conversion was calculated to be 61%. Table 1 shows the optical properties of the PeQD dispersion and the wavelength-converted PeQD dispersion.

[0096] [Table 1]

[0097] It is known that the PLQY of a PeQD dispersion decreases with increasing defects. The PLQY of the PeQD dispersion in Example 9 was higher than that of Comparative Example 4. Furthermore, in both Comparative Example 4 and Example 9, the amount of defects in the crystal increased due to halogen exchange of the synthesized PeQD. Therefore, the PLQY retention rate was significantly reduced in chemical compositions that are prone to defect formation. The PLQY retention rate of Example 1 was higher than that of Comparative Examples 1 to 3. The sodium compound and boron hydride compound were effective in compensating for defects in PeQD during synthesis and suppressing defect formation.

[0098] In Examples 1 to 9 and Comparative Examples 2 and 3, hydrogen gas was confirmed to be generated after the addition of the boron hydride compound, indicating the occurrence of a dehydration reaction. By removing the trace amounts of moisture that inhibit the doping of sodium ions into PeQDs, sodium ions can be appropriately doped into the A site.

[0099] Figure 1 shows the changes in emission wavelength and PLQY when halogen exchange was performed on the perovskite quantum dots produced in Example 1, Comparative Example 1, and Reference Example 1 by varying the amount of FAPbCl3 powder added in step 3 from 0 to 4.85 times the amount of FAPbBr3 produced in step 2. As the amount of FAPbCl3 powder added increases, the proportion of other halogens at the X site of the perovskite quantum dots increases, the emission wavelength shifts to shorter wavelengths, and a tendency for PLQY to decrease due to an increase in defects is observed. Compared to Comparative Example 1, Example 1 and Reference Example 1 suppressed the decrease in PLQY due to the short wavelength shift, demonstrating the effect of sodium ions in compensating for defects in PeQDs and suppressing defect formation. In particular, Example 1, which added boron hydride ions in addition to sodium ions, suppressed the decrease in PLQY compared to Reference Example 1, and achieved a higher PLQY at all wavelengths compared to Comparative Example 1 and Reference Example 1. We believe that the removal of moisture by boron hydride ions, a confounding factor in the effect of sodium ions in compensating for defects and suppressing defect formation, improved the PLQY maintenance rate and achieved a PLQY of 82% or more over a wide wavelength range (Figure 1).

Claims

1. a step 1 of preparing a suspension by mixing a precursor solution obtained by dissolving a perovskite precursor in a good solvent with a solution obtained by dissolving an organic base compound and an organic acid compound in a poor solvent at 40°C or less, and recovering crude nanoparticles by sedimentation; and step 2 of adding a non-polar organic solvent to the coarse nanoparticles to re-disperse them, and then removing coarse particles by classification to obtain a nanoparticle mixed dispersion. a boron hydride compound and a sodium compound are added at once or in two separate steps between the step 1 and the step 2; General formula (1)A ｐ B ｑ X ｒ (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X is a halide ion, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

2. a step 1 of preparing a suspension by mixing a precursor solution obtained by dissolving a perovskite precursor in a good solvent with a solution obtained by dissolving an organic base compound and an organic acid compound in a poor solvent at 40°C or less, and recovering crude nanoparticles by sedimentation; Step 2: adding a non-polar organic solvent to the coarse nanoparticles to re-disperse them, and then removing coarse particles by classification to obtain a nanoparticle mixed dispersion; a step 3 of adding a halide containing one or more halogens to the nanoparticle mixed dispersion to replace a part of the halogens; a boron hydride compound and a sodium compound are added at once or in two separate steps between the step 1 and the step 2; General formula (2)A ｐ B ｑ X' ｒ (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

3. The borohydride compound and the sodium compound are added together in step 1 rather than being added in two separate steps, 3. The method for producing perovskite quantum dots according to claim 1, wherein in step 1, a precursor solution is prepared by dissolving a perovskite precursor, a boron hydride compound, and a sodium compound in a good solvent.

4. The borohydride compound and the sodium compound are not added all at once, but are added in two separate steps in Step 1 and Step 2, In step 1, a precursor solution is prepared by dissolving a perovskite precursor, a boron hydride compound, and a sodium compound in a good solvent; 3. The method for producing perovskite quantum dots according to claim 1 or 2, wherein in step 2, a non-polar organic solvent, a boron hydride compound, and a sodium compound are added to the crude nanoparticles to redisperse them.

5. The amount of the sodium compound added is determined by the formula (1): A ｐ B ｑ X ｒ or the amount of A in the general formula (2): A ｐ B ｑ X' ｒ The method for producing perovskite quantum dots according to claim 1 or 2, wherein the amount of substance (mol) of A in the compound (A) is 0.03 to 0.50 times the amount of substance (mol) of A in the compound (A).

6. 3. The method for producing perovskite quantum dots according to claim 1, wherein the molar ratio (mol) of the sodium compound to the molar ratio (mol) of the boron hydride compound is 0.3 to 3.0 times.

7. 3. The method for producing perovskite quantum dots according to claim 1, wherein the compound consisting of a boron hydride compound and a sodium compound is sodium borohydride.

8. A compound represented by the general formula (2) A, characterized in that the photoluminescence quantum yield (PLQY) is 82% or more in the wavelength range of 463 to 500 nm. ｐ B ｑ X' ｒ (wherein A is a monovalent cation, B is a divalent cation of a Group 14 element, X' is two or more types of halide ions, p is an integer of 1 or more and 4 or less, q is 1 or 2, and r is an integer of 3 or more and 9 or less).

9. The perovskite quantum dots according to claim 8, wherein the particle size of the perovskite quantum dots is 4 to 30 nm.

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