Perovskite quantum dot composite material, ink, and method for producing perovskite quantum dot composite material

Abstract

Provided are a perovskite quantum dot composite material manufacturing method that conveniently forms core-shell particles in a single-stage synthesis step, a perovskite quantum dot composite material that, by forming an ionic crystal layer comprising a halogen compound in a shell layer, suppresses surface flaws in perovskite quantum dots and has an extremely high PLQY, and an ink that includes said perovskite quantum dot composite material. The perovskite quantum dot composite material comprises core particles and a shell layer that is present so as to cover the peripheries of the core particles, wherein the core particles comprise a halogenated metal perovskite, the shell layer comprises an organic halogen compound that has an ionic crystal structure with the same halogen composition as the core particles, the PLQY is 75% or greater, and the quantity of variation in light emission wavelength at room temperature during a period until 10,000 minutes have elapsed is 5 nm or less.

Description

[Technical Field]

[0001] The present invention relates to a method for producing perovskite quantum dots with high photoluminescence quantum yield, as well as to said perovskite quantum dots and inks. [Background technology]

[0002] Perovskite quantum dots are particles (dots) with a perovskite crystal structure that exhibit unique optical properties according to quantum mechanics, with diameters ranging from 1 nm to several tens of nm. They have attracted attention in recent years because the emission wavelength they emit when excited can be continuously controlled by their chemical composition and particle size, and they exhibit luminescence properties with very little variation in the emission wavelength distribution. Their practical application in a wide range of fields, including electronics, medicine, and agriculture, is being considered, including as wavelength conversion materials when excited by light and as self-luminous materials when excited by electricity (Patent Document 1).

[0003] Due to their large specific surface area, perovskite quantum dots are susceptible to surface defects. Therefore, their surfaces are generally protected by capping with organic ligands such as organic amines or organic acids. However, it is difficult to completely protect the defects that form on the particle surface. These surface defects act as deactivated areas and are the main cause of reduced photoluminescence quantum yield (PLQY). Perovskite quantum dots are particularly susceptible to halogen defects on the particle surface.

[0004] Examples of surface protection of perovskite quantum dots include CsPb(Cl a Br 1-a-b I bPatent Document 2 describes a quantum dot composite comprising all-inorganic perovskite quantum dots having the chemical formula: 3 (where 0≦a≦1, 0≦b≦1) and a mutagenic protective film on the surface of the all-inorganic perovskite quantum dots. In the quantum dot composite, the mutagenic protective film is made of mesoporous particles, inorganic shell layer encapsulants, ligand exchangers, microcapsules, polymer encapsulants, silicon-containing material encapsulants, oxide or nitride dielectric encapsulants, or combinations thereof.

[0005] A method for producing the AMX3 structure, which is an organometallic halide, has also been described (Patent Document 3), and in one embodiment, the AMX3 structure is described as a crystalline wafer, a nanostructure (e.g., nanowire), a qubit, or an alloy of any of the above, as a layer in, on, or around a particle (e.g., a layer in a shell-core particle and part of a quantum dot).

[0006] Incidentally, inorganic oxide coatings such as silica (SiO2) coatings and titanic acid coatings are known to be less likely to cause surface defects after coating layer formation, and to exhibit very little change in emission wavelength over time because they do not undergo Ostwald ripening or aggregation and fusion. Non-Patent Document 1 reports a technique for coating the surface of pre-synthesized perovskite quantum dots CsPbBr3 with silica through multiple synthesis steps.

[0007] However, coating the surface of perovskite quantum dots with SiO2 does not compensate for surface defects in the already formed perovskite quantum dots, so while durability increases, PLQY does not. Furthermore, the process requires a two-step reaction: the production of perovskite quantum dots and the formation of the coating layer, making it inefficient. Furthermore, the SiO2 coating layer is an insulating layer, so it does not conduct electricity to the core perovskite quantum dots, making it unusable for applications requiring electron exchange, such as electrically excited light-emitting devices and solar cells. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6783296 [Patent Document 2] Patent No. 6631973 [Patent Document 3] Special Publication No. 2018-512364 [Non-patent literature]

[0009] [Non-Patent Document 1] Peiyuan Cao, et al, “High stability of silica-wrapped CsPbBr3 perovskite quantum dots for light emitting application”, CERAM. INT. 2020, 46(3), 3882-3888 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a method for producing a perovskite quantum dot composite material that easily forms core-shell particles in a single synthesis step, and to provide a perovskite quantum dot composite material and an ink containing the same, in which surface defects of the perovskite quantum dots are suppressed by forming an ionic crystal layer made of an organic halide in the shell layer, thereby achieving a very high PLQY. [Means for solving the problem]

[0011] The present invention comprises the following items. [1] A perovskite quantum dot composite material comprising a core particle and a shell layer surrounding the core particle, wherein the core particle is made of a metal halide perovskite, and the shell layer is made of an organic halogen compound having an ionic crystal structure with the same halogen composition as the core, the PLQY being 75% or more, and the change in emission wavelength over 10,000 minutes at room temperature being 5 nm or less. [2] A perovskite quantum dot composite material comprising a core particle and a shell layer surrounding the core particle, wherein the core particle material is an inorganic perovskite nanocrystal composed of elements from Groups 1, 14, and 17 of the Periodic Table, and the shell layer material is an ionic crystal composed of an organic cation and an element from Group 17, and wherein the PLQY is 75% or more. [3] The perovskite quantum dot composite material according to [1] or [2], wherein the solubility of the shell layer material in an aprotic polar solvent is at least twice the solubility of the core particle material in an aprotic polar solvent. [4] The perovskite quantum dot composite material according to any one of [1] to [3], wherein the perovskite quantum dot composite material has an average particle size of 1 to 30 nm.

[0012] [5] An ink comprising the perovskite quantum dot composite material according to any one of [1] to [4], a polar solvent having a liquid dielectric constant of 20 or more, and a non-polar solvent that is miscible with the polar solvent and has a liquid dielectric constant of 10 or less.

[0013] [6] A method for producing a perovskite quantum dot composite material, comprising: Step 1: preparing a precursor solution by mixing a polar solvent having a liquid dielectric constant of 20 or more, an alkali metal halide, a metal halide, and an organic halogen compound; and Step 2: injecting the precursor solution into a nonpolar solvent having a liquid dielectric constant of 10 or less. [7] The method for producing a perovskite quantum dot composite material according to [6], wherein step 1 is a step of preparing a precursor solution by mixing a core particle material consisting of an alkali metal halide and a metal halide with a shell layer material consisting of an organic halogen compound, and the ratio of the molar amount of the shell layer material added (amount added / amount required) to the molar amount of the minimum amount of shell layer material required to cover the surface of the core particle is 1.00 to 2.40. [8] The method for producing a perovskite quantum dot composite material according to [6] or [7], wherein in step 2, the temperatures of the precursor solution and the nonpolar solvent are set to 40°C or less. [9] The method for producing a perovskite quantum dot composite material according to any one of [6] to [8], wherein in step 2, the non-polar solvent further contains at least one selected from the group consisting of organic acids and organic amine compounds. [Effects of the Invention]

[0014] The present invention provides a method for producing a perovskite quantum dot composite material that allows for the simple formation of core-shell particles in a single synthesis step. In this production method, an ionic crystal layer is formed on the surface of the core particle during shell layer formation. This suppresses surface defects in the perovskite quantum dots, and the resulting perovskite quantum dot composite material has a very high PLQY. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 shows a process for forming a perovskite quantum dot composite material by injecting a precursor solution containing a core particle material and a shell layer material into a solution containing a non-polar solvent with a liquid dielectric constant of 10 or less, an organic acid, and an organic amine compound. [Figure 2] Figure 2 is a graph showing the relationship between x and y in a perovskite quantum dot composite material, where the average particle size (nm) of the core particles, which are the light emitters, is taken as the x-axis (horizontal axis) and the molar amount of shell layer material actually added to coat the surface of the core particles is taken as the y-axis (vertical axis). [Figure 3] FIG. 3 is a graph plotting the PLQY of the perovskite quantum dot composite materials of Examples 1 to 6 and Comparative Examples 1 to 7, with the ratio of the molar amount of shell layer material actually added to the molar amount of shell layer material required to coat the surface of the core particle on the horizontal axis and the PLQY of the perovskite quantum dot composite materials on the vertical axis. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below with reference to the drawings. [Perovskite quantum dot composite materials] The perovskite quantum dot composite material of the present invention comprises a core particle and a shell layer surrounding the core particle, wherein the core particle is made of a metal halide perovskite and the shell layer is made of an organic halogen compound having an ionic crystal structure with the same halogen composition as the core particle, and wherein the change in emission wavelength is 5 nm or less and the change in PLQY is 5% or less over 10,000 minutes at room temperature.

[0017] The core particle material is an inorganic material with a perovskite-type crystal structure represented by the general formula AMX3, and specifically, is an inorganic perovskite nanocrystal composed of elements from groups 1, 14, and 17 of the periodic table. A represents an alkali metal such as cesium, rubidium, potassium, sodium, or lithium. Of these, cesium is preferred. By using an alkali metal as an inorganic cation, it is possible to prepare a perovskite quantum dot composite material that has low solubility in nonpolar solvents, unlike common organic cations. M represents lead, germanium, tin, silicon, etc. Among these, lead and tin are preferred. Furthermore, antimony, bismuth, copper, nickel, cobalt, iron, manganese, chromium, cadmium, europium, ytterbium, and silver may be contained within the range of 5% or less of the element ratio of M. X represents a halogen such as chlorine, bromine, and iodine. Specific examples of AMX3 include CsPb(Cl a Br 1-a-b I b )3(0≦a≦1, 0≦b≦1, a+b≦1), CsSn(Cl a Br 1-a-b I b )3(0≦a≦1, 0≦b≦1, a+b≦1), CsGe(Cl a Br 1-a-b I b )3(0≦a≦1, 0≦b≦1, a+b≦1), CsSn y Pb (1-y) (Cl a Br 1-a-b I b )3(0≦a≦1, 0≦b≦1, a+b≦1, 0 <y<1)、CsGe z Pb(1-z) (Cl a Br 1-a-b I b )3(0 ≤ a ≤ 1, 0 ≤ b ≤ 1, a + b ≤ 1, 0 < z < 1), CsGe z Sn (1-z) (Cl a Br 1-a-b I b )3(0 ≤ a ≤ 1, 0 ≤ b ≤ 1, a + b ≤ 1, 0 < z < 1), and CsPb (1-y-z) Sn y Ge z (Cl a Br 1-a-b I b )3(0 ≤ a ≤ 1, 0 ≤ b ≤ 1, a + b ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1), etc.

[0018] The shell layer material forming the shell layer is represented by the general formula BX, and specifically, it is an organic halogen compound composed of an organic cation and a Group 17 element. In the general formula BX, X represents a halogen, and B represents an organic acid that forms a halide with X. BX includes, for example, formamidinium hydrohalide (FAX), methylamine hydrohalide (MAX), guanidinium hydrohalide (GAX), and ethylamine hydrohalide (EAX), etc. These usually exist as salts. For example, formamidinium hydrohalide (FAX) exists as formamidinium hydrobromide, formamidinium hydrochloride, and formamidinium hydroiodide, methylamine hydrohalide (MAX) exists as methylamine hydrobromide, methylamine hydrochloride, and methylamine hydroiodide, guanidinium hydrohalide (GAX) exists as guanidinium hydrobromide, guanidinium hydrochloride, and guanidinium hydroiodide, and ethylamine hydrohalide (EAX) exists as ethylamine hydrobromide, ethylamine hydrochloride, and ethylamine hydroiodide. BX serving as the shell layer material needs to have the same halogen composition as the core particles AMX3. If the halogen composition is different, halogen exchange may occur between BX and AMX3, and the color tone may change reversibly. It is also preferable that BX is an ammonium halide salt instead of an amine hydrohalide salt, since BX is in a solid state at room temperature.

[0019] The shell layer material is soluble in polar solvents and sparingly soluble in non-polar solvents. The solubility of the shell layer material in a polar solvent is preferably at least twice that of the core particle material in a polar solvent. By selecting the structures of the shell layer material and core particle material so as to achieve such a solubility, the core particles are precipitated first during synthesis, resulting in a core-shell structure without forming a mixed crystal, which is a crystalline structure in which the shell layer material and the core particle material are mixed to a certain degree of uniformity.

[0020] In this specification, a polar solvent is an aprotic solvent that has a liquid dielectric constant of 20 or more and is miscible with a nonpolar solvent described below. Examples of the polar solvent include, but are not limited to, N-methylpyrrolidone (NMP; liquid dielectric constant 32.2), N,N-dimethylformamide (DMF; liquid dielectric constant 36.7), and acetonitrile (liquid dielectric constant 35.9). On the other hand, a non-polar solvent is a solvent with a liquid dielectric constant of 10 or less. Examples of the non-polar solvent include, but are not limited to, toluene (liquid dielectric constant 2.4), hexane (liquid dielectric constant 1.9), octadecene, ethyl acetate (liquid dielectric constant 6.4), chlorobenzene (liquid dielectric constant 5.6), and chloroform (liquid dielectric constant 4.8).

[0021] The perovskite quantum dot composite material of the present invention has a core particle that is an inorganic perovskite nanocrystal made of a metal halide, and a shell layer that is made of an organic halide compound that forms an ionic crystal structure with the same halogen composition as the core particle. The perovskite quantum dot composite material can remain stable for a long period of time, and the change in emission wavelength over 10,000 minutes at room temperature is 5 nm or less.

[0022] The average particle size of the perovskite quantum dot composite material is usually 1 to 30 nm, preferably 2 to 20 nm, and more preferably 4 to 16 nm. By setting the average particle size of the perovskite quantum dot composite material within this range, it is possible to prepare an ink containing the perovskite quantum dot composite material that has high solvent dispersibility.

[0023] As described above, the perovskite quantum dot composite material comprises a core particle and a shell layer that surrounds the core particle. In order for the shell layer to function, it must be formed on the surface of the core particle with a certain thickness. In the perovskite quantum dot composite material of the present invention, the molar amount of shell layer material required to coat the surface of the core particle is y, and the average particle size of the core particle is x, then y=15x -1 The relationship between the x and y values ​​holds. 15 is a value calculated from experimental values. Figure 2 is a graph showing the relationship between x and y in perovskite quantum dot composite materials, where the average particle size (nm) of the core particles, which are the light emitters, is on the x axis and the molar amount of shell layer material actually added to coat the surface of the core particles is on the y axis.

[0024] The amount of shell layer material required depends on the total surface area of ​​the core particles. Even if the molar amount of core particles is the same, if the particle size of the core particles is large, the total surface area will be smaller and the amount of shell layer material required will be less. On the other hand, if the particle size of the core particles is small, the surface area per particle will be smaller, but as the number of core particles increases, the total surface area will also increase and the amount of shell layer material required will increase. In other words, the molar amount of shell layer material required can be determined from the molar amount and particle size of the core particles.

[0025] The molar ratio of the added shell layer material (amount added / amount required) to the minimum molar amount of shell layer material required to cover the surface of the core particle is typically 1.00 to 2.40, preferably 1.05 to 2.00, and more preferably 1.05 to 1.60. The shell layer material coats the surface of the core particle, significantly improving the PLQY. Figure 3 is a graph plotting the PLQY of the perovskite quantum dot composite materials of Examples 1 to 6 and Comparative Examples 1 to 5, with the horizontal axis representing the ratio of the molar amount of shell layer material actually added to the molar amount of shell layer material required to coat the surface of the core particle, and the vertical axis representing the PLQY of the perovskite quantum dot composite materials.

[0026] The average particle size of the core particles in the perovskite quantum dot composite material, which serves as the light emitter, is typically 1 to 25 nm, preferably 1 to 18 nm, and more preferably 3 to 15 nm. If the core particles are too small, the emission wavelength will vary significantly due to the quantum confinement effect, and the crystal structure will not be able to be maintained properly, resulting in a large variation in the emission wavelength. If the core particles are too large, the stability of excitons during excitation will decrease, resulting in a decrease in PLQY. From the perspective of emission characteristics, the average particle size of the core particles is preferably within a specified range. On the other hand, the thickness of the shell layer is generally 0.5 to 5 nm, although this depends on the size of the core particles. If the shell layer is too thin, halogen deficiency, Ostwald ripening, aggregation, and fusion will occur in areas where the coating is insufficient, resulting in a decrease in PLQY.

[0027] The average particle size of the perovskite quantum dot composite material of the present invention can be determined using a dynamic light scattering photometer (DLS), a transmission electron microscope (TEM), etc. For example, it can be determined from the average diameter in the major axis direction measured by observing 50 to 100 perovskite quantum dot composite materials with a TEM. The average particle size of the core particles is determined by the maximum wavelength (λ) of photoluminescence (PL) measured by a fluorescence spectrophotometer. PL The energy band gap of the core particle, which is the light emitter, changes depending on the particle size, and the maximum wavelength (λ PLFor example, in the case of perovskite quantum dots CsPbBr3, the average particle size of the core particles is 2.6 nm, and the maximum wavelength (λ PL ) is 450 nm, the average particle size is 6.2 nm, and the maximum wavelength (λ PL ) is 500 nm, the average particle size is 15 nm, and the maximum wavelength (λ PL ) is 523 nm. The thickness of the shell layer can be determined by dividing the difference between the average particle size of the perovskite quantum dot composite and the average particle size of the core particles by two.

[0028] The perovskite quantum dot composite material of the present invention can emit light in the visible to near-infrared wavelength region. It is preferable that it emits light upon excitation, and more preferably emits light upon excitation by excitation light or electrical excitation. The wavelength of the excitation light may be, for example, 200 nm to 800 nm, 250 nm to 750 nm, or 300 nm to 600 nm.

[0029] [ink] The ink of the present invention contains the perovskite quantum dot composite material, a polar solvent having a liquid dielectric constant of 20 or more, and a non-polar solvent that is miscible with the polar solvent and has a liquid dielectric constant of 10 or less. By using this composition, the ink has a stable structure in which the surfaces of the perovskite quantum dots are coated with a shell layer of the general formula BX. When the core-shell state of the perovskite quantum dot composite material in the ink is observed using a transmission electron microscope (TEM) or electron diffraction (ED), it is found that the surfaces of the core particles are coated with the shell layer material. When the ink is irradiated with excitation light, for example, ultraviolet light with a wavelength of 370 nm, it emits blue to red fluorescence (wavelength of 450 to 800 nm).

[0030] The volume ratio of the non-polar solvent to the polar solvent is usually at least 7 times, preferably at least 10 times, and more preferably at least 15 times. From the viewpoints of suppressing re-dissolution of the precipitated perovskite quantum dot composite material and increasing the reaction yield, it is desirable to use a smaller amount of polar solvent than non-polar solvent. The polar solvent may be partially removed after synthesis of the perovskite quantum dot composite material, or a non-polar solvent may be added after synthesis.

[0031] [Method for manufacturing perovskite quantum dot composite materials] The method for producing a perovskite quantum dot composite material of the present invention includes step 1 of preparing a precursor solution by mixing a polar solvent having a liquid dielectric constant of 20 or more, an alkali metal halide, a metal halide, and an organic halogen compound, and step 2 of injecting the precursor solution into a non-polar solvent having a liquid dielectric constant of 10 or less.

[0032] In step 1, a precursor solution is prepared by mixing a polar solvent having a liquid dielectric constant of 20 or more, an alkali metal halide, a metal halide, and an organic halogen compound. Examples of alkali metal halides that can be used include cesium bromide (CsBr), cesium iodide (CsI), cesium chloride (CsCl), rubidium bromide (RbBr), rubidium iodide (RbI), rubidium chloride (RbCl), potassium bromide (KBr), potassium iodide (KI), potassium chloride (KCl), sodium bromide (NaBr), sodium iodide (NaI), and sodium chloride (NaCl). These compounds can be used alone or in combination of two or more in any ratio. Examples of metal halides that can be used 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 of two or more in any ratio.

[0033] Examples of organic halogen compounds include methylamine hydrobromide (CHN·HBr), methylamine hydroiodide (CHN·HI), methylamine hydrochloride (CHN·HCl), formamidine hydrobromide (CHN·HBr), formamidine hydroiodide (CHN·HI), formamidine hydrochloride (CHN·HCl), guanidinium hydrobromide (CHN·HBr), guanidinium hydroiodide (CHN·HI), guanidinium hydrochloride (CHN·HCl), ethylamine hydrobromide (C2H7N·HBr), ethylamine hydrochloride (C2H7N·HCl), and ethylamine hydroiodide (C2H7N·HI). These compounds can be used alone or in combination in any ratio. The mixing ratio of the alkali metal halide to the metal halide is usually a molar ratio of 1:10 to 10:1, preferably 1:3 to 3:1, and more preferably 1:1.5 to 1.5:1. As the difference in the mixing ratio increases, the metal elements at the M site of the core particle take on perovskite crystal structures with different valences, and the PLQY tends to decrease. The mixing ratio of either the alkali metal halide or the metal halide having a smaller molar amount, which is the core particle material, to the organic halogen compound is usually 1:0.6 to 1:10, preferably 1:0.8 to 1:7, and more preferably 1:1 to 1:5. The concentration of the alkali metal halide or metal halide in the precursor solution is 0.01 to 0.30 mol / l, preferably 0.02 to 0.10 mol / l, and the concentration of the organic halogen compound is 0.01 to 1.0 mol / l, preferably 0.02 to 0.60 mol / l.

[0034] In step 2, the precursor solution prepared in step 1 is poured into a non-polar solvent having a liquid dielectric constant of 10 or less, as shown in FIG. Here, a feature of the present invention is that a precursor solution containing both the core particle material and the shell layer material is injected into a nonpolar solvent with a liquid dielectric constant of 10 or less, i.e., the core particle material and the shell layer material are injected simultaneously into the nonpolar solvent. By using this method, many core particles are precipitated at the reaction interface between the precursor solution and the nonpolar solvent, forming a highly concentrated suspended particle field. The shell layer is precipitated later in this suspended particle field. If the surface area of ​​the core particles at the reaction interface is sufficiently large, crystal growth by the shell layer material becomes energetically advantageous, making it easier to coat the surface of the core particles with the shell layer material.

[0035] On the other hand, if a precursor solution containing only the core particle material is first injected into a nonpolar solvent with a liquid dielectric constant of 10 or less, and then the shell layer material is injected, the core particles precipitate and disperse in the nonpolar solvent before the shell layer material is injected. Because the core particles are completely dispersed at a relatively low density in the nonpolar solvent, when the shell layer material is injected into the nonpolar solvent, the number of core particles present at the reaction interface is small, making it difficult for the shell layer material to coat the surfaces of the core particles, resulting in the majority of the shell layer material being precipitated alone. As a result, the surface coating of the core particles is insufficient and uneven, resulting in core particles containing surface defects, and the PLQY of the resulting perovskite quantum dot composite material is not sufficiently improved.

[0036] In step 2, the non-polar solvent having a liquid dielectric constant of 10 or less preferably further contains at least one selected from the group consisting of organic acids and organic amine compounds. When organic acids and organic amine compounds are added, the shell layer or core particles are partially modified with alkyl chains. The presence of such modified sites adjusts the crystal growth of the core particles during the synthesis of perovskite quantum dot composites, allowing for control of the particle size of the core particles. As a result, the maximum emission wavelength can be shifted to a predetermined wavelength and the variation in the emission wavelength distribution can be reduced.

[0037] It is preferable to add at least one of an organic acid and an organic amine compound. Examples of organic acids include carboxylic acids such as oleic acid, stearic acid, palmitic acid, glutaric acid, sebacic acid, and benzoic acid; phosphorus oxoacid compounds such as octylphosphonic acid, tetradecylphosphonic acid, and di-tert-octylphosphinic acid; and sulfinic acids such as benzenesulfinic acid. The organic amine compound may be any of aliphatic amine compounds, aromatic amine compounds, and quaternary ammonium salts. Examples include aliphatic amine compounds having 3 to 16 carbon atoms, such as oleylamine, propylamine, butylamine, pentylamine, octylamine, hexadecylamin, and octadecylamine; aromatic amine compounds having 6 to 34 carbon atoms, such as aniline, benzylamine, phenethylamine, 3-phenyl-2-propen-1-amine, phenylmethylamine, 2,2'-iminodibenzoic acid, 3-phenylpropylamine, 4-phenylbutylamine, naphthylamine, 4-aminobiphenyl, and 3,4,5-tris(prop-2-en-1-yloxy)benzylamine; and aliphatic quaternary ammonium salt compounds, such as didecyldimethylammonium salt, benzyltrimethylammonium bromide, 3-(N,N-dimethyloctadecylammonio)propanesulfonate salt, and stearyltrimethylammonium salt. The compound may also be a compound having an acid and an amino group in one compound, such as γ-aminobutyric acid and 3-[(3-methacrylamidopropyl)dimethylammonio]propane-1-sulfonic acid.

[0038] The concentration of the organic acid and organic amine compound added may be equal to or less than the concentration at which they dissolve in the precursor solution and nonpolar solvent in step 2. In general, it is preferable that the concentration is 1 mass % or more relative to the total weight of the alkali metal halide and metal halide added. The organic acid and organic amine compound may be removed after synthesis of the perovskite quantum dot composite material. Alternatively, to impart higher dispersion stability to the perovskite quantum dot composite material, another organic acid and another organic amine compound may be added after removal. Alternatively, another organic acid and another organic amine compound may be added without removing the organic acid and the organic amine compound.

[0039] In step 2, for ease of processing and stability of the shell layer material, it is preferable to keep the temperature of the precursor solution and nonpolar solvent at 40°C or less. For example, some of the organohalogen compounds dissociate and evaporate in the polar solvent due to chemical equilibrium. If the temperature is increased, the amount of shell layer material in the precursor solution decreases, resulting in insufficient coating.

[0040] As described above, the perovskite quantum dot composite material of the present invention has a very high PLQY, specifically, a PLQY of 75% or more, preferably 80% or more, and more preferably 90% or more. Furthermore, the shell layer contains an ionic crystal layer of an organic halogen compound, resulting in a stable structure with reduced surface defects. Therefore, even after 10,000 minutes at room temperature, the change in emission wavelength is 5 nm or less, and the PLQY can be stably maintained. This is believed to be because the shell layer material forms BMX3 ionic crystals with the crystal edges on the core particle surface, and the strong halogen retention by the crystal layer improves the PLQY.

[0041] The perovskite quantum dot composite material of the present invention can be used as a wavelength converting material in the form of a composition containing the perovskite quantum dot composite material and a curable material, which may be any of a thermoplastic resin, a thermosetting resin, glass, and ceramics. Furthermore, the perovskite quantum dot composite material of the present invention can be used as a material that emits light when electrically excited by applying an ink containing the dispersed perovskite quantum dot composite material to a substrate, such as a glass plate, a resin plate, or a semiconductor plate. [Example]

[0042] 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. [Example 1] A precursor solution was prepared so that the molar amount (mol / mol) of shell layer material actually added to the core particle surface was 1.05 compared to the molar amount (mol / mol) of shell layer material required to coat the surface of the core particle (hereafter referred to as "added amount / required amount"). Specifically, 1.41 mg of cesium bromide (CsBr), 2.42 mg of lead(II) bromide (PbBr2), and 3.34 mg of methylamine hydrobromic acid (CH5N·HBr) were dissolved in 0.2 ml of N,N-dimethylformamide (DMF). A non-polar solvent was prepared by placing 4.5 ml of ethyl acetate, 16.7 μl of oleic acid, and 13.3 μl of oleylamine in a 9 ml screw tube, into which the precursor solution was poured at room temperature under atmospheric pressure with stirring. The resulting mixture was centrifuged at 16,500 rpm in a tabletop centrifuge (AS165W, manufactured by AS ONE Corporation) for 2 minutes, after which a portion of the supernatant was removed and the precipitate was re-dispersed in toluene. The mixture was then centrifuged at 16,500 rpm for 3 minutes, after which the supernatant was recovered to obtain an ink containing a dispersed perovskite quantum dot composite material.

[0043] The PLQY was measured using an integrating sphere attached to a fluorescence spectrophotometer FP-8600 (JASCO Corporation; excitation wavelength 350 nm). The PLQY was 95%, and the maximum wavelength of photoluminescence (PL) (λ PL ) was 461 nm. λ PL The particle size of the core of the light-emitting perovskite quantum dot composite material was calculated from the above data, and was found to be 3.5 nm.

[0044] Table 1 shows the method of adding the shell layer material, the molar amount of shell layer material required to coat the surface of the core particle (hereinafter referred to as the "required amount"), the molar amount of shell layer material actually added (hereinafter referred to as the "added amount"), the added amount / required amount, and the maximum wavelength (λ) of photoluminescence (PL) of the perovskite quantum dot composite material. PL ) and particle size, and PLQY.

[0045] The ink containing dispersed perovskite quantum dot composite material was placed in a screw tube, the lid was closed, and the tube was left standing in the atmosphere at room temperature for 10,000 minutes. PL ) and PLQY, the maximum wavelength (λ PL ) was changed by 2 nm, and the rate of change in PLQY was -3%.

[0046] [Example 2] A precursor solution was prepared so that the ratio of added amount to required amount was 1.26. That is, an ink of a perovskite quantum dot composite material was prepared in the same manner as in Example 1, except that the amount of methylamine hydrobromide (CHN HBr) was changed from 3.34 mg to 4.00 mg.

[0047] As in Example 1, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL The PLQY was 97%, and the maximum wavelength of photoluminescence (PL) (λ PL ) was 461 nm and the core particle size was 3.5 nm. The results are shown in Table 1 and Figure 2.

[0048] [Example 3] A precursor solution was prepared with a ratio of added amount to required amount of 1.60 by dissolving 4.26 mg of cesium bromide (CsBr), 7.34 mg of lead(II) bromide (PbBr), and 4.48 mg of methylamine hydrobromic acid (CHN HBr) in 0.6 ml of N,N-dimethylformamide (DMF). A non-polar solvent was prepared by placing 4.5 ml of ethyl acetate, 120 μl of oleic acid, and 6.0 μl of oleylamine in a 9 ml screw tube, into which the precursor solution was poured with stirring at room temperature under atmospheric pressure. The resulting mixture was centrifuged at 16,500 rpm in a tabletop centrifuge (AS165W, manufactured by AS ONE Corporation) for 3 minutes, after which a portion of the supernatant was removed and the precipitate was re-dispersed in toluene. The mixture was then centrifuged again at 16,500 rpm for 3 minutes, after which the supernatant was recovered to obtain an ink containing a dispersed perovskite quantum dot composite material.

[0049] PLQY was measured using an integrating sphere attached to a fluorescence spectrophotometer FP-8600 (JASCO Corporation; excitation wavelength 400 nm). PLQY was measured using the maximum wavelength (λ PL The PLQY was 96%, and the maximum wavelength of photoluminescence (PL) (λ PL ) was 515 nm and the core particle size was 12 nm. The results are shown in Table 1 and Figure 2.

[0050] [Example 4] A precursor solution was prepared so that the ratio of added amount to required amount was 2.40. That is, an ink of a perovskite quantum dot composite material was prepared in the same manner as in Example 3, except that the amount of methylamine hydrobromic acid (CHN HBr) was changed from 4.48 mg to 6.72 mg.

[0051] As in Example 3, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL The PLQY was 95%, and the maximum wavelength of photoluminescence (PL) (λ PL ) was 516 nm and the core particle size was 12 nm. The results are shown in Table 1 and Figure 2.

[0052] [Example 5] A precursor solution was prepared with a ratio of added amount to required amount of 1.26 by dissolving 169.2 mg of cesium bromide (CsBr), 290.4 mg of lead(II) bromide (PbBr), and 480 mg of methylamine hydrobromic acid (CHN HBr) in 24.0 ml of N,N-dimethylformamide (DMF). A non-polar solvent was prepared by mixing 600 ml of ethyl acetate, 2220 μl of oleic acid, and 1780 μl of oleylamine. Using a forced thin-film microreactor ULREA SS-11-75 (M Technique Co., Ltd.), the precursor solution was injected into the reactor at 4 ml / min and the nonpolar solvent at 90 ml / min while stirring at a disk rotation speed of 4000 rpm under atmospheric conditions at room temperature. Three minutes after the start of injection, the mixed solution discharged from the reactor was collected for one minute. The resulting mixture was used in the same manner as in Example 1 to recover an ink of the perovskite quantum dot composite material.

[0053] As in Example 1, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL The PLQY was 99%, and the maximum wavelength of photoluminescence (PL) (λ PL ) was 460 nm and the core particle size was 3.5 nm. The results are shown in Table 1 and Figure 2.

[0054] [Example 6] A precursor solution was prepared with a ratio of added amount to required amount of 1.00 by dissolving 4.26 mg of cesium bromide (CsBr), 7.34 mg of lead(II) bromide (PbBr), and 3.76 mg of formamidine hydrobromide (CHN HBr) in 0.6 ml of N,N-dimethylformamide (DMF). A non-polar solvent was prepared by placing 4.5 ml of ethyl acetate, 60.0 μl of oleic acid, and 3.0 μl of oleylamine in a 9 ml screw tube, into which the precursor solution was poured with stirring at room temperature under atmospheric pressure. The resulting mixture was used in the same manner as in Example 3 to recover an ink of the perovskite quantum dot composite material.

[0055] As in Example 3, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL The PLQY was 91%, and the maximum wavelength of photoluminescence (PL) (λPL ) was 512 nm and the core particle size was 10 nm. The results are shown in Table 1 and Figure 2.

[0056] As shown in FIG. 2, in Examples 1 to 6 where the added amount / required amount was 1.00 to 2.40, surface defects of the perovskite quantum dots were suppressed, and the PLQY was extremely high at 91 to 99%.

[0057] [Comparative Example 1] A precursor solution was prepared by dissolving 1.41 mg of cesium bromide (CsBr) and 2.42 mg of lead (II) bromide (PbBr2) in 0.2 ml of N,N-dimethylformamide (DMF). 4.5 ml of ethyl acetate, 16.7 μl of oleic acid, and 13.3 μl of oleylamine were placed in a 9 ml screw tube, and the precursor solution was poured into the tube at room temperature under atmospheric pressure while stirring. The resulting mixture was used in the same manner as in Example 1 to recover an ink of the perovskite quantum dot composite material.

[0058] As in Example 1, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL ) and the particle size of the core of the perovskite quantum dot composite material. PL ) was 507 nm, and the core particle size was 7.0 nm. The perovskite quantum dot composite material of Comparative Example 1, which had no shell layer, had a low PLQY of 15%. The results are shown in Table 1 and Figure 2.

[0059] The ink containing dispersed perovskite quantum dot composite material was placed in a screw tube and left for 30 minutes in room temperature with the lid closed. PL ) and PLQY, the maximum wavelength (λ PL The change in PLQY was 16 nm and the change in PLQY was -52%. After standing for 10,000 minutes, the compound was deactivated and no longer emitted light.

[0060] Comparative Example 2 A precursor solution was prepared with a ratio of added amount to required amount of 0.63 by dissolving 1.41 mg of cesium bromide (CsBr), 2.42 mg of lead(II) bromide (PbBr), and 2.00 mg of methylamine hydrobromic acid (CHN HBr) in 0.2 ml of N,N-dimethylformamide (DMF). 4.5 ml of ethyl acetate, 16.7 μl of oleic acid, and 13.3 μl of oleylamine were placed in a 9 ml screw tube, and the precursor solution was poured into the tube at room temperature under atmospheric pressure while stirring. The resulting mixture was used in the same manner as in Example 1 to recover an ink of the perovskite quantum dot composite material.

[0061] As in Example 1, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL ) and the particle size of the core of the perovskite quantum dot composite material. PL The particle diameter of the perovskite quantum dots was 461 nm and the core particle size was 3.5 nm. Because the amount of doping / required was small, the surface protection of the perovskite quantum dots was insufficient, and the PLQY was 13%. The results are shown in Table 1 and Figure 2.

[0062] Comparative Example 3 A precursor solution was prepared so that the ratio of added amount to required amount was 0.84. That is, a perovskite quantum dot composite material was produced in the same manner as in Comparative Example 2, except that the amount of methylamine hydrobromic acid (CHN HBr) was changed from 2.00 mg to 2.67 mg in Comparative Example 2.

[0063] As in Example 1, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL ) and the particle size of the core of the perovskite quantum dot composite material. PL ) was 461 nm, and the core particle size was 3.5 nm. PLQY was 28%. Although the ratio of added amount / required amount was larger than in Comparative Example 2, the PLQY was insufficient because it was only 0.84. The results are shown in Table 1 and Figure 2.

[0064] Comparative Example 4 A precursor solution was prepared by dissolving 4.26 mg of cesium bromide (CsBr) and 7.34 mg of lead (II) bromide (PbBr2) in 0.6 ml of N,N-dimethylformamide (DMF). 4.5 ml of ethyl acetate, 120 μl of oleic acid, and 6.0 μl of oleylamine were placed in a 9 ml screw tube, and the precursor solution was poured into the tube at room temperature under atmospheric pressure while stirring. The resulting mixture was used in the same manner as in Example 3 to recover an ink of the perovskite quantum dot composite material.

[0065] As in Example 3, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL ) and the particle size of the core of the perovskite quantum dot composite material. PL The particle diameter of the core was 12 nm and the PLQY was 50%. As in Comparative Example 1, Comparative Example 4 did not have a shell layer, and therefore the PLQY was insufficient. However, the particle size of the core particles, which are the light emitters, was large, and therefore the PLQY was higher than that of Comparative Example 1. The results are shown in Table 1 and Figure 2.

[0066] Comparative Example 5 A precursor solution was prepared with a ratio of added amount to required amount of 0.80 by dissolving 4.26 mg of cesium bromide (CsBr), 7.34 mg of lead(II) bromide (PbBr), and 2.24 mg of methylamine hydrobromic acid (CHN HBr) in 0.6 ml of N,N-dimethylformamide (DMF). 4.5 ml of ethyl acetate, 120 μl of oleic acid, and 6.0 μl of oleylamine were placed in a 9 ml screw tube, and the precursor solution was poured into the tube at room temperature under atmospheric pressure while stirring. The resulting mixture was used in the same manner as in Example 3 to recover an ink of the perovskite quantum dot composite material.

[0067] As in Example 3, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL) and the particle size of the core of the perovskite quantum dot composite material. PL The particle diameter of the core was 12 nm and the PLQY was 22%. The results are shown in Table 1 and Figure 2.

[0068] Comparative Example 6 A precursor solution was prepared by dissolving 1.41 mg of cesium bromide (CsBr) and 2.42 mg of lead (II) bromide (PbBr2) in 0.2 ml of N,N-dimethylformamide (DMF). 4.5 ml of ethyl acetate, 16.7 μl of oleic acid, and 13.3 μl of oleylamine were placed in a 9 ml screw tube. The precursor solution was poured into the tube at room temperature under atmospheric pressure while stirring. Perovskite quantum dots precipitated and became completely dispersed. Furthermore, a solution of 3.71 mg of methylamine hydrobromic acid (CH5N·HBr) dissolved in 18.5 μL of DMF was added to the dispersion. The ratio of the amount of shell layer material added to the amount of core particle material / required amount was 1.17. The resulting mixture was used in the same manner as in Example 1 to recover an ink of the perovskite quantum dot composite material.

[0069] As in Example 1, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL ) and the particle size of the core of the perovskite quantum dot composite material. PL The particle diameter of the core was 3.5 nm and the PLQY was 68%. Although the ratio of added amount to required amount was 1.17, which was greater than 1, the perovskite quantum dots contained surface defects and had insufficient PLQY due to the later addition of the shell layer material. The results are shown in Table 1 and Figure 2.

[0070] Comparative Example 7 A precursor solution was prepared by dissolving 4.26 mg of cesium bromide (CsBr) and 7.34 mg of lead (II) bromide (PbBr2) in 0.6 ml of N,N-dimethylformamide (DMF). 4.5 ml of ethyl acetate, 120 μl of oleic acid, and 6.0 μl of oleylamine were placed in a 9 ml screw tube. The precursor solution was poured into the tube at room temperature under atmospheric pressure while stirring. Perovskite quantum dots precipitated and became completely dispersed. Furthermore, a solution of 4.48 mg of methylamine hydrobromic acid (CH5N·HBr) dissolved in 22.3 μL of DMF was added to the dispersion. The ratio of the amount of shell layer material added to the amount of core particle material / required amount was 1.60. The resulting mixture was used in the same manner as in Example 3 to recover an ink of the perovskite quantum dot composite material.

[0071] As in Example 3, the PLQY and the maximum wavelength of photoluminescence (PL) (λ PL ) and the particle size of the core of the perovskite quantum dot composite material. PL The particle diameter of the core was 12 nm and the PLQY was 70%. In Comparative Example 7, in which the shell layer material was added later and the ratio of added amount / required amount was 1.60, the PLQY was higher than that of Comparative Example 4, in which no shell layer material was added at all, but was still insufficient. The results are shown in Table 1 and Figure 2.

[0072] [Table 1]

[0073] It can be seen that in Examples 1 to 6, in which a predetermined amount or more of coating layer material was simultaneously added, a very high PLQY was achieved. Although a slight improvement in PLQY was observed with post-addition, the coating layer was not uniform, so simultaneous addition was found to be superior. As described above, the perovskite quantum dot composite material of the present invention has excellent stability of the emission wavelength and a high PLQY.

[0074] It is expected that wavelength conversion materials and self-luminous materials with excellent luminescence properties and stability can be produced by using the perovskite quantum dot composite material of the present invention.

Claims

1. The core particle is composed of a core particle and a single shell layer surrounding the core particle, A perovskite quantum dot composite material, wherein the core particle is made of a metal halide perovskite, and the shell layer is made of an organic halogen compound having an ionic crystal structure with the same halogen composition as the core particle, The metal halide perovskite has the general formula AMX ３ (A is cesium, M is lead, and X is bromine), the organic halogen compound is formamidine hydrobromide or methylamine hydrobromide, The perovskite quantum dot composite material has an average core particle size of 3.5 to 12 nm, an emission wavelength of 461 nm or more and 516 nm or less, a PLQY of 91% or more, and a change in emission wavelength of 2 nm or less over 10,000 minutes at room temperature.

2. 10. An ink comprising the perovskite quantum dot composite material of claim 1, an aprotic polar solvent having a liquid dielectric constant of 20 or more, and a non-polar solvent having a liquid dielectric constant of 10 or less and miscible with the polar solvent.

3. A method for producing the perovskite quantum dot composite material according to claim 1, The molar amount Y of the shell layer material required to cover the surface of the core particle is calculated by subtracting the average particle diameter X (nm) of the intended core particle from the molar amount Y of the shell layer material required to cover the surface of the core particle by Y=15X －１ and a step 1 of preparing a precursor solution by mixing an aprotic polar solvent having a liquid dielectric constant of 20 or more, a core particle material comprising an alkali metal halide and a metal halide, wherein the alkali metal halide is cesium bromide and the metal halide is lead bromide, and a shell layer material comprising formamidine hydrobromide or methylamine hydrobromide, so that the ratio of the molar amount of the shell layer material to the molar amount Y of the shell layer material covering the surfaces of the core particles determined in the step (molar amount to be added / molar amount Y determined in the step) is 1.00 to 2.40; Step 2: injecting the precursor solution into a solution comprising a non-polar solvent having a liquid dielectric constant of 10 or less and at least one selected from the group consisting of an organic acid and an organic amine compound at a temperature of 40°C or less to prepare a perovskite quantum dot composite material having a single shell layer; and A method for producing a perovskite quantum dot composite material, characterized in that the core particles of the perovskite quantum dot composite material have an average particle size of 3.5 to 12 nm, an emission wavelength of 461 nm or more and 516 nm or less, a PLQY of 91% or more, and a change in emission wavelength of 2 nm or less over 10,000 minutes at room temperature.

4. 4. The method for producing a perovskite quantum dot composite material according to claim 3, wherein the solubility of the shell layer material in an aprotic polar solvent is at least twice as high as the solubility of the core particle material in an aprotic polar solvent.

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