Method for producing nanocrystal particles

Abstract

The present invention controls a process temperature T (°C) and a process time t (second) with which preparation of a solution is carried out by dissolving lead bromide, an organic acid, and an amine in a solvent.

Description

Method for manufacturing nanocrystalline particles

[0001] This invention relates to a method for producing nanocrystalline particles.

[0002] Nanocrystalline particles having a perovskite crystal structure are superior to non-perovskite nanocrystalline particles that do not have a perovskite crystal structure, such as InP and CdSe, in terms of high optical density, high quantum efficiency, and high color purity corresponding to a narrow full width at half maximum (FWHM). On the other hand, perovskite nanocrystalline particles have the challenge of being difficult to control in terms of stability compared to non-perovskite nanocrystalline particles. Nanocrystalline particles having a perovskite crystal structure are sometimes referred to as perovskite nanocrystalline particles.

[0003] Perovskite-type photoresponsive nanocrystalline particles are being investigated as materials for photoelectric conversion layers in solar power generation, color filters, and backlight sources utilizing trichromatic white light. Furthermore, perovskite-type nanocrystalline particles are known to be used as materials for green and red light emitters excited by blue light-emitting diodes.

[0004] Several synthesis methods are being investigated for perovskite-type nanocrystalline particles, including hot injection, ligand-assisted reprecipitation, and flow synthesis. Among these, flow synthesis is expected to offer greater productivity compared to the batch-type hot injection method, as it allows for continuous synthesis by simply supplying the raw material solution.

[0005] Nanoscale 2019, 11 p18790 describes using a reaction solution prepared by heating at 120°C to produce CsPbBr ３The document discloses a flow synthesis method for synthesizing perovskite luminescent particles. The flow synthesis method of Patent Document 1 further discloses that perovskite luminescent particles with emission peak wavelengths ranging from 462 nm to 520 nm are synthesized in an inline process by controlling the reaction temperature range up to 120°C and the reaction time. The wavelength range of such perovskite luminescent particles corresponds to the emission colors from blue to green in the color gamut defined by BT2020. In the color gamut defined by BT2020, the wavelengths to which each chromaticity point of RGB lies on the spectral locus are 630 nm for red, 532 nm for green, and 467 nm for blue.

[0006] On the other hand, J. Am. Chem. Soc. 2016, 138 p14202 states that CsPbBr has an emission peak wavelength of 530-535 nm. ３－ｘ I ｘ In perovskite luminescent particles, the emission quantum efficiency is said to be less than 50%, and FAPbBr ３ Perovskite luminescent particles are being investigated. FAPbBr has a photoluminescence quantum yield (PLQY) of 85% at an emission peak wavelength of 530 nm and a full width at half maximum (FWHM) of 22 nm. ３ It is synthesized by a hot injection method using a reaction solution prepared by heating at 120°C.

[0007] Nanoscale 2019, 11 p18790J. Am. Chem. Soc. 2016,138 p14202

[0008] However, further improvements were needed in terms of the emission color and manufacturing method of nanocrystalline particles containing a perovskite crystal structure composed of formamidine, lead, and bromine. The green emission peak wavelength of nanocrystalline particles containing a perovskite crystal structure may be below 535 nm, which has low visual sensitivity, and it is hoped that a longer wavelength band (536 nm to 545 nm) than 535 nm, which has high visual sensitivity, will be achieved. In addition, the full width at half maximum (FWHM) of the green emission peak of nanocrystalline particles containing a perovskite crystal structure may be broadened, or the PLQY may be less than 85%, and improvements in color purity and high PLQY are expected, respectively.

[0009] This invention has been made in view of the above background art, and aims to provide a method for producing nanocrystalline particles containing a perovskite-type crystal structure composed of formamidine, lead, and bromine, which have green luminescence sensitivity and high quantum efficiency and are capable of flow synthesis.

[0010] To achieve this objective, a method for producing nanocrystalline particles according to an embodiment of the present invention comprises: a dissolution preparation step of preparing a dissolution by dissolving lead bromide, an organic acid, and an amine in a solvent; and a synthesis step of synthesizing nanocrystalline particles containing a perovskite-type crystal structure composed of formamidine, lead, and bromine, wherein the dissolution preparation step is carried out under conditions that satisfy general formulas (1) to (4), when the process temperature T (°C) and process time t (seconds) for preparing the dissolution. General formula (1): 134 ≤ T ≤ 154 General formula (2): t ≥ 600 General formula (3): t ≥ -66.667 × T + 10133 General formula (4): t ≤ -60 × T + 10740

[0011] According to the present invention, it is possible to provide a method for producing nanocrystalline particles containing a perovskite-type crystal structure composed of formamidine, lead, and bromine, which have green luminescence sensitivity and high quantum efficiency and can be synthesized by flow synthesis.

[0012] This figure shows a schematic diagram of the dissolution preparation step, in which lead bromide, an organic acid, and an amine according to the first embodiment are dissolved in a solvent to prepare a dissolution. This figure shows the process window of the dissolution preparation step for preparing the dissolution according to the first embodiment. This figure illustrates the schematic configuration of a flow synthesis apparatus that continuously performs the dissolution preparation step and the synthesis step according to the first embodiment. This figure illustrates the schematic configuration of an oil bath for checking the liquid delivery temperature in the synthesis step according to the first embodiment. This figure illustrates the schematic configuration of an oil bath for checking the liquid delivery temperature in the synthesis step according to the first embodiment. This figure illustrates the schematic configuration of an oil bath for checking the liquid delivery temperature in the synthesis step according to the first embodiment.

[0013] A preferred embodiment of the present invention will be described in detail below with reference to Figures 3 and 4A to 4C.

[0014] A method for producing nanocrystalline particles containing a perovskite-type crystal structure according to an embodiment of the present invention comprises a solution preparation step of preparing a solution by dissolving lead bromide, an organic acid, and an amine in a solvent. Furthermore, a method for producing nanocrystalline particles containing a perovskite-type crystal structure according to this embodiment comprises a synthesis step of mixing the solution with a formamidine salt solution to synthesize nanocrystalline particles containing a perovskite-type crystal structure composed of formamidine, lead, and bromine. Moreover, when the process temperature T (°C) and process time t (seconds) for preparing the solution are set, the solution preparation step is carried out under conditions that satisfy the following general formulas (1) to (4): General formula (1) 134 ≤ T ≤ 154 General formula (2) t ≥ 600 General formula (3) t ≥ -66.667 × T + 10133 General formula (4) t ≤ -60 × T + 10740

[0015] The following describes each embodiment in more detail.

[0016] <First Embodiment> Figure 1 shows a schematic of the dissolution preparation step, in which lead bromide, an organic acid, and an amine according to the first embodiment are dissolved in a solvent to prepare a dissolution. Figure 2 shows the process window of the synthesis step for synthesizing nanocrystalline particles containing a perovskite-type crystal structure according to the first embodiment. Table 1 shows the experimental results that form the basis for the process window of the dissolution preparation step shown in Figure 2.

[0017]

[0018] In the experimental results shown in Table 1, processes exhibiting precipitation of lead compounds (dp), low absolute quantum luminescence yield LP (PLQY < 0.85), short-wavelength shift of emission center wavelength (LW), and by-products such as amide compound 4 or oxide 5 (MC) are indicated with a corresponding symbol. Furthermore, processes corresponding to suitable lead solution preparation steps, where no events unsuitable for such flow synthesis or unsuitable luminescence properties were observed, are marked with a circle (○).

[0019] The process conditions suitable for flow synthesis, as read from Table 1, are shown in Figure 2. The process window can be considered to be the area enclosed by boundary lines [1] to [5]. Corresponding to boundary lines [1], [2], [3], [4], and [5], the following general formulas (1) to (4) are derived for the dissolution process temperature T (°C) and dissolution process time t (seconds). Boundary lines [1], [2] 134 ≤ T ≤ 154 General formula (1) Boundary line [3] t ≥ 600 General formula (2) Boundary line [4] t ≥ -66.667 × T + 10133 General formula (3) Boundary line [5] t ≤ -60 × T + 10740 General formula (4)

[0020] This embodiment includes a solvent preparation step in which lead bromide, an organic acid, and an amine are dissolved in a solvent to prepare a solvent. The organic acid and amine act as dispersion ligands for the perovskite luminescent particles.

[0021] In this embodiment, either saturated or unsaturated fatty acids can be used as organic acids. Examples of saturated fatty acids include lauric acid, caprylic acid, palmitic acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, palmitoleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, and vaccenic acid. These unsaturated fatty acids are suitable organic acids for use in flow synthesis because they are liquid in a temperature range of 5°C to 35°C. Aromatic carboxylic acids such as salicylic acid can also be used. Furthermore, the above organic acids may be used individually or in combination.

[0022] The organic acids applied in this embodiment include fatty acids, and the amines applied in this embodiment include aliphatic amines.

[0023] In this embodiment, either saturated or unsaturated amines can be used as the amine. Primary to tertiary amines can also be used.

[0024] Examples of primary saturated amines include octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine, nonadecylamine, eicosylamine, henicosylamine, docosylamine, and tricosylamine.

[0025] Examples of primary unsaturated amines include oleylamine, octenamine, nonenamine, decenamine, undecenamine, dodecenamine, tridecenamine, tetradecenamine, pentadecenamine, and hexadeceneamine.

[0026] Examples of secondary amines include dimethyloctylamine, dimethyldecylamine, dimethyldodecylamine, dimethyltetradecylamine, dimethylhexadecylamine, and dimethyloctadecylamine.

[0027] Examples of tertiary amines include trimethyloctylamine, trimethyldecylamine, trimethyldodecylamine, trimethyltetradecylamine, trimethylhexadecylamine, and trimethyloctadecylamine. These amines may be used individually or in combination.

[0028] In this embodiment, it is preferable to use a solvent with a high boiling point, specifically one with a boiling point of 180°C or higher. Using a high boiling point solvent avoids pulsating currents and boiling in the mixer and supply channel during flow synthesis, enabling stable flow synthesis.

[0029] As solvents used in this embodiment, 1-octadecene, hexadecene, tetradecane, pentadecane, heptadecane, octadecane, tridecene, tridecane, tetradecene, pentadecene, tridecene, dodecene, etc. can be used.

[0030] The process of preparing the solution obtained by dissolving lead bromide, an organic acid, and an amine in a solvent in this embodiment will be explained with reference to Figures 1 and 2 and Table 1.

[0031] Lead bromide reacts reversibly with organic acids and amines, as shown in Figure 1. Lead bromide is dissolved by using organic acids and amines in stoichiometric excesses. One of the two bromine atoms in lead bromide is eliminated, forming a monosubstituted salt (1) with the organic acid. The bromine atom eliminated during this process is Br － and H from organic acids ＋ This forms an amine HBr salt (3). Next, bromine is eliminated from the monosubstituted salt (1) and forms a disubstituted salt (2) with the organic acid, thereby preparing the solution. The nanocrystalline particles composed of formamidine, lead, and bromine in this embodiment are synthesized by mixing the disubstituted salt (2), the amine HBr salt (3), and the formamidine salt solution. Heating is required to form the disubstituted salt (2), but an amide compound (4) is easily produced as a by-product from the organic acid and amine. The amine itself is also oxidized, and an oxide (5) is easily produced as a by-product. These by-products represent an irreversible reaction in the preparation of the solution in this embodiment. Therefore, the concentration of organic acid and amine in the reaction system decreases during preparation. In particular, when the amine concentration in the reaction system decreases, it becomes difficult to maintain the form of the amine HBr salt (3), and it reversibly becomes an amine, Br － It then recombines with Pb.

[0032] In this embodiment, the solution obtained by dissolving lead bromide, an organic acid, and an amine in a solvent refers to a solution in which a disubstituted salt (2) and an amine HBr salt (3) are formed from lead bromide. In this embodiment, the solution is considered to be a solution obtained by dissolving lead bromide, an organic acid, and an amine in a solvent if the amount of undissolved lead bromide is 3% or less relative to the number of moles of lead bromide before dissolution began.

[0033] The nanocrystalline particles containing a perovskite crystal structure synthesized from a di-substituted salt (2), an amine HBr salt (3), and a formamidine salt solution are likely to dissolve in the presence of an amine at high temperatures. Therefore, when preparing a solution in which lead bromide, an organic acid, and an amine are dissolved in a solvent, the molar number of the amine used is preferably 6 times or more and 9 times or less, more preferably 7 times or more and 8.5 times or less, relative to the molar number of lead bromide. When the molar number of the amine is less than 6 times that of lead bromide, it becomes difficult for lead bromide to dissolve. On the other hand, when it exceeds 9 times, the nanocrystalline particles containing the perovskite crystal structure to be synthesized are likely to dissolve during synthesis. The molar number of the organic acid is preferably 15 times or more and 18 times or less, more preferably 16 times or more and 17 times or less, relative to the molar number of lead bromide. When the molar number of the organic acid is less than 15 times that of lead bromide, it becomes difficult for lead bromide to dissolve. On the other hand, when it exceeds 18 times, the nanocrystalline particles composed of formamidine, lead, and bromine to be synthesized tend to become coarse particles during synthesis. Furthermore, a large number of nanoplatelets showing an emission peak at about 510 nm are likely to be by-produced. The molar number of the organic acid is preferably 0.4 times or more and 1.7 times or less, more preferably 0.45 times or more and 0.6 times or less, relative to the molar number of the amine. When it is less than 0.45 times, it becomes difficult for lead bromide to dissolve, and when it exceeds 1.7 times, the nanocrystalline particles composed of formamidine, lead, and bromine are likely to dissolve during synthesis.

[0034] In the present embodiment, when the process temperature is T (°C) and the process time is t (seconds), the solution preparation process is performed under the conditions that satisfy the following general formula (1).

[0035] Note that the process temperature in the present embodiment refers to the temperature of the actual solution. For example, when the solution is placed in a flask and the flask is heated in an oil bath, the temperature of the solution in the flask rather than the temperature of the oil in the oil bath is referred to as the process temperature. The process time refers to the time during which the process temperature acts on the solution. When the temperature difference between the oil temperature of the oil bath and the temperature of the solution in the flask is controlled to be below a predetermined temperature difference, the oil temperature of the oil bath may be used as the positive temperature for substitution. General formula (1) 134 ≤ T ≤ 154 General formula (2) t ≥ 600 General formula (3) t ≥ -66.667 × T + 10133 General formula (4) t ≤ -60 × T + 10740

[0036] In the synthesis of the nanocrystalline particles composed of formamidine, lead, and bromine in this embodiment, dissolution by the amine coexisting with the precipitation of the nanocrystalline particles occurs competitively. As a result of the intensive study by the present inventor, by preparing the dissolution solution under the conditions satisfying the general formulas (1) to (4), the disubstituted salt (2) and the amine HBr salt (3) are sufficiently generated, and it has been found that the by-production of the amide compound (4) and the oxide (5) is suppressed. Further, it has been found that by suppressing the by-production of the amide compound (4) and the oxide (5), the surface of the particles precipitated by the presence of the amine during synthesis is dissolved, and the particle diameter is controlled to a particle diameter with an emission peak wavelength of 535 nm or more. Furthermore, even if nanoplates are by-produced due to the presence of an appropriate amount of amine, there is also an effect of dissolving them. Also, although the dissolution solution in which lead bromide, an organic acid, and an amine are dissolved in a solvent is prepared by heating, it has also been found that precipitation of lead bromide hardly occurs even when cooled to room temperature after preparation.

[0037] To form the disubstituted salt (2), heating is required as described above, and thereby the amide compound (4) and the oxide (5) are also by-produced, but these by-productions can be suppressed by adopting the process temperature T satisfying the general formula (1). When the process temperature T is lower than 134°C, the disubstituted salt (2) is not sufficiently generated, and the perovskite luminescent particles tend to exhibit an emission peak wavelength shorter than 535 nm. When the process temperature T is higher than 154°C, lead bromide tends to precipitate from the dissolution solution due to the by-production of the amide compound (4) and the oxide (5), and particularly when the dissolution solution is cooled to room temperature after preparation, precipitation is likely to occur significantly.

[0038] In this embodiment, the process time t (seconds) is performed under the condition that also satisfies the following general formula (2). General formula (2) t≧600

[0039] When t is smaller than 600, the disubstituted salt (2) is not sufficiently generated, and the perovskite luminescent particles tend to exhibit an emission peak wavelength shorter than 535 nm. This is presumably because when the generation of the disubstituted salt (2) is insufficient, the particle diameter becomes smaller due to dissolution by the amine.

[0040] In this embodiment, the process temperature T (°C) and process time t (seconds) are performed under conditions that satisfy the following general formulas (3) and (4). General formula (3): t ≥ -66.667 × T + 10133 General formula (4): t ≤ -60 × T + 10740

[0041] Here, by satisfying the conditions of general formulas (3) and (4), the precipitation of lead compounds and the like is suppressed even when the solution is cooled to room temperature after preparation, and it becomes possible to synthesize nanocrystalline particles by flow synthesis using a pump that can deliver liquids at room temperature.

[0042] In this embodiment, the formamidine salt solution is a fatty acid salt solution of formamidine, and is prepared by replacing the fatty acid portion of the fatty acid salt of formamidine with a different fatty acid. When the fatty acid salt of formamidine is difficult to dissolve, a different fatty acid is added to replace the fatty acid portion and make the fatty acid salt of formamidine soluble. As the formamidine salt to be used, it is preferable to use formamidine acetate due to its availability, but since it is difficult to dissolve in the aforementioned solvent, the acetate is replaced with a different fatty acid salt to improve solubility.

[0043] Since fatty acids also act as dispersion ligands for perovskite luminescent particles, they can function as ligands if they are replaced with the desired fatty acids beforehand. In this embodiment, either saturated or unsaturated fatty acids can be used. Examples of saturated fatty acids include lauric acid, caprylic acid, palmitic acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, palmitoleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, and vaccenic acid.

[0044] In this embodiment, in the synthesis step for synthesizing nanocrystalline particles containing a perovskite-type crystal structure, the molar ratio of formamidine to lead (FA / Pb) is preferably 2.5 or higher.

[0045] When the FA / Pb ratio is less than 2.5, nanocrystalline particles containing a perovskite-type crystal structure do not precipitate, or the particle size is small, making it easier to obtain materials that exhibit emission peak wavelengths shorter than 535 nm.

[0046] In this embodiment, nanocrystalline particles containing a perovskite crystal structure are manufactured by flow synthesis. Nanocrystalline particles containing a perovskite crystal structure composed of formamidine, lead, and bromine exhibit different particle sizes and emission peak wavelengths depending on the synthesis temperature. By synthesizing nanocrystalline particles containing a perovskite crystal structure by flow synthesis, nanocrystalline particles can be continuously manufactured at a constant synthesis temperature.

[0047] The flow synthesis method for nanocrystalline particles according to this embodiment includes a synthesis step of adjusting a solution containing lead bromide, acid, and amine and a formamidine salt solution to a predetermined temperature in separate liquid delivery pipes. The flow synthesis method for nanocrystalline particles according to this embodiment also includes a synthesis step of continuously supplying a heated solution to a mixer at a liquid delivery temperature of x°C, and mixing the solution containing lead bromide, acid, and amine and the formamidine salt solution with the mixer at a liquid mixing temperature of y°C.

[0048] In the synthesis process, the liquid delivery temperature x and liquid mixing temperature y are set to satisfy general formulas (5) to (7). By performing the synthesis process in this manner, perovskite luminescent particles with a narrow FWHM and a PLQY of 85% or more can be produced, even if the emission peak wavelength is 535 nm or higher. General formula (5): 130 ≤ x ≤ 360 General formula (6): 130 ≤ y ≤ 160 General formula (7): y - x ≤ 3

[0049] When x and y exceed 160°C, excessive dissolution of the precipitated particle surface by amine occurs, and the emission peak wavelength tends to become smaller than 535 nm. On the other hand, when x and y are lower than 130°C, the formation of nanoplates as a by-product becomes significant. Furthermore, the difference between the liquid mixing temperature y (°C) and the liquid delivery temperature x (°C) is preferably 3°C or less, and preferably 1°C or less.

[0050] The nanocrystalline particles containing the perovskite crystal structure in this embodiment are produced by flow synthesis from a solution of lead bromide, acid, and amine, and a formamidine salt solution. Flow synthesis in this embodiment refers to the continuous synthesis of compounds while the reaction solution flows through a channel or the space of a mixer. As shown in Figure 3, multiple reaction solutions are continuously supplied to the mixer 2 by the pump 1, and nanocrystalline particles containing the perovskite crystal structure are continuously produced. The supply pipe that delivers the liquid between the pump 1 and the mixer 2 is designated as the forward channel 3, and the supply pipe that discharges the liquid from the mixer is designated as the backward channel 4. The mixer 2 and a portion of the backward channel 4 are heated to a high temperature of y°C by the heating means 5. Perovskite luminescent particles are recovered from the heating means 5 through an ice bath 6 to the recovery unit 7. The solution of lead bromide, acid, and amine, and the formamidine salt solution are supplied from the reaction tank 8 to the pump 1, respectively. When multiple reaction solutions are supplied and heated to x°C in the forward channel 3, and then continuously supplied to the mixer 2, the multiple reaction solutions are mixed while their temperature rises from x°C to y°C. The mixer 2 that can be used in this embodiment is not particularly limited and commercially available microreactors can be used. For example, T-shaped reactors from YMC Corporation, three-way joints from From, DH-type mixers and α-type mixers from Nakamura Superhard Co., Ltd., K2-24-M and K1-24M from Noritake Corporation, and SMCR from Kobe Steel, Ltd. can be used. The liquid supply pipes used in the forward channel 3 and the backward channel 4 are not particularly limited and can be made of synthetic resin, ceramic, glass, metal, etc., but stainless steel and nickel alloys are preferred from the viewpoint of heat resistance and corrosion resistance. Examples of such stainless steels include austenitic stainless steels such as SUS304 and SUS316, and nickel alloys such as Hastelloy (registered trademark). The heating means 5 is not particularly limited, but can include an oil bath, Peltier element, ribbon heater, rubber heater, hot plate, etc. Among these, an oil bath allows the mixer and the liquid delivery pipe to be heated in the same tank, and also makes it easier to bring the temperature of the reaction solution and the mixing temperature closer together. Furthermore, by using a single tank for the heating means 5, the heated reaction solution can be delivered to the mixer without lowering its temperature.If the heating means 5 between the mixer 2 and the forward flow path 3 is separated (using separate heating means), the temperature of the heated reaction solution may decrease between the heating means. Examples of the pump 1 that can be used in this embodiment include a diaphragm pump, a turbine pump, a piston pump, a screw pump, a plunger pump, a gear pump, a centrifugal pump, a propeller pump, and the like. Among these, the plunger pump suppresses pulsating flow, and by using a multi-plunger configuration, the effect of suppressing pulsating flow is enhanced. When intense pulsating flow occurs, variations in the mixing ratio of the reaction solutions are likely to occur.

[0051] In this embodiment, when the process temperature T (°C) and the process time t (seconds) for preparing the dissolution solution are considered, 150 ≤ T ≤ 154 and 1200 ≤ t ≤ 1500 are satisfied. Also, when the liquid feeding temperature for continuously feeding liquid to the mixer is x °C and the liquid mixing temperature for mixing the solutions in the mixer is y °C, the liquid feeding temperature x (°C) and the liquid mixing temperature y (°C) are set to satisfy 155 °C or higher and 160 °C or lower.

[0052] The present inventors have found that under the above conditions, nanocrystalline particles containing a perovskite crystal structure composed of formamidine, lead, and bromine with a luminescence peak wavelength of 540 nm or more and a PLQY exceeding 90% are synthesized. This is considered to be a suitable condition where the disubstituted salt (2) and the amine HBr salt (3) are sufficiently generated, the by-production of the amide compound (4) and the oxide (5) is suppressed, and the dissolution amount of the surface of the precipitated particles during synthesis depends on the synthesis temperature in the presence of an appropriate amount of amine.

[0053] The perovskite crystal structure composed of formamidine, lead, and bromine in this embodiment is not particularly limited, and may be a compound having any of a three-dimensional structure, a two-dimensional structure, and a pseudo-two-dimensional structure. In the case of a three-dimensional structure, the perovskite compound is represented by ABX ３ and in the case of a two-dimensional structure, it is represented by A ２ BX ４ The three-dimensional perovskite compound represented by ABX ３ becomes FAPbBr ３ A ２ BX ４ The two-dimensional perovskite compound represented by is FA ２PbBr ４ This is the result. In addition, perovskite compounds doped with Eu, Gd, Yb, Mn, Ce, Bi, Sm, Ho, and Tb may also be used.

[0054] In this embodiment, a specific example of a method for producing perovskite luminescent particles according to the embodiment will be described using the embodiment.

[0055] A solution of lead bromide, acid, and amine was prepared with the following composition.

[0056] Lead bromide and 1-octadecene were placed in a flask with a stirring bar and immersed in an oil bath heated to 160°C. Next, oleic acid was added and the stirring bar was rotated with a magnetic stirrer to disperse the lead bromide. After 25 minutes, the liquid temperature in the flask stabilized at 154°C (process temperature T). Oleylamine heated to 154°C was then added, and the dissolution of lead bromide was started while degassing with a diaphragm pump. After 20 minutes (process time t: 1200 seconds), the flask was removed from the oil bath and cooled in a water bath, but no lead bromide precipitated, and a solution of lead bromide, acid, and amine dissolved was prepared. Lead bromide 1.242 (g) (3.375 mmol as lead) Oleic acid 18 (ml) Oleylamine 9 (ml) 1-Octadecene 63 (ml)

[0057] The formamidine salt solution was prepared with the following composition.

[0058] Formamidine acetate, oleic acid, and 1-octadecene were placed in a flask, and a stirring bar was added. The flask was then immersed in an oil bath heated to 120°C. While degassing with a diaphragm pump, the stirring bar was rotated with a magnetic stirrer to replace the formamidine acetate with oleate. After 30 minutes, the flask was removed from the oil bath and cooled in a water bath. No precipitation of formamidine acetate or oleate occurred, and a formamidine salt solution was prepared. Formamidine acetate 1.054 (g) (10.125 mmol as FA) Oleic acid 27.2 (ml) 1-Octadecene 62.8 (ml)

[0059] An oil bath heated to 160°C was used as the heating means 5. A GL Sciences PU-916 plunger pump was used as pump 1, and a Noritake K2-24-M mixer was used as mixer 2. A SUS314 tube with an outer diameter of 1 / 8 inch and an inner diameter of 2.17 mm was used for the forward flow path 3 connecting pump 1 and mixer 2. The same SUS314 tube was also used for the rear flow path 4 at the discharge section from the mixer. The rear flow path 4, from the connection point with mixer 2 for a length of 0.18 m, was immersed in the oil bath together with mixer 2, and the rest was connected to the recovery unit 7 via the atmosphere and an ice water bath 6.

[0060] As shown in Figure 3, a solution of lead bromide, acid, and amine dissolved at room temperature was pumped at a rate of 20 ml / min into the forward channel 3, which was immersed in an oil bath of a heating means 5 heated to 160°C. Next, the temperature of the reaction solution B discharged from the end point 10 of the forward channel 3 was measured using a thermocouple 9 placed at the end point 10 of the forward channel 3. As shown in Figures 4A to 4C, the length of the forward channel immersed in the oil bath was increased, and it was confirmed that the temperature rose to 158.8°C when it was immersed for 1.2 m. When the formamidine salt solution at room temperature was pumped at a rate of 20 ml / min, the forward channel reached 158.8°C when it was immersed for 1.2 m, similar to the solution of lead bromide, acid, and amine. Both the forward channel 3 of the lead bromide, acid, and amine solution and the formamidine salt solution were immersed in the same oil bath as the mixer 2 for a length of 1.2 m and connected to the mixer 2. As a result, the reaction solutions, heated to 184.8°C and 185°C, are continuously supplied to mixer 2. By supplying a solution of lead bromide, acid, and amine at a rate of 20 ml / min, and a formamidine salt solution at a rate of 20 ml / min, the molar ratio of formamidine to lead is FA / Pb = 3.0, and these are supplied to mixer 2. Since mixer 2 is immersed in an oil bath heated to 160°C, the reaction solutions are mixed in the mixer at 160°C, resulting in perovskite luminescent particles (FAPbBr). ３ The following was synthesized: The synthesis solution containing perovskite luminescent particles was cooled in an ice bath 6 and discharged into a recovery unit 7 at a rate of 40 ml / min.

[0061] When the emission was evaluated using blue light-emitting diode light with a maximum peak wavelength of 445 nm, the PLQY was 90.3%, the emission peak wavelength was 540 nm, and the full width at half maximum of the emission peak was 22 nm.

[0062] In this example, the solvent used in Example 1 was changed from 1-octadecene to dodecane, and the formamidine salt solution was prepared with the following composition, so that the molar ratio of formamidine to lead was FA / Pb = 3.4, and the solution was delivered to mixer 2 in the same manner as in Example 1. Formamidine acetate 1.1981 (g) (10.125 mmol as FA) Oleic acid 30.9 (ml) Dodecane 59.1 (ml)

[0063] Emission evaluation revealed a PLQY of 88.1%, an emission peak wavelength of 542 nm, and a full width at half maximum of 21 nm.

[0064] In this example, the process was carried out in the same manner as in Example 1, except that the process temperature T was set to 134°C and the process time t was set to 2400 seconds. When the emission evaluation was performed, the PLQY was 91%, the emission peak wavelength was 536 nm, and the full width at half maximum of the emission peak was 22 nm.

[0065] In this example, the process was carried out in the same manner as in Example 3, except that the process temperature T was set to 134°C and the process time t was set to 1200 seconds. When the emission evaluation was performed, the PLQY was 91%, the emission peak wavelength was 537 nm, and the full width at half maximum of the emission peak was 22.5 nm.

[0066] In this example, the procedure was carried out in the same manner as in Example 1, except that the process time t was set to 1500 seconds. When the emission evaluation was performed, the PLQY was 88%, the emission peak wavelength was 538 nm, and the full width at half maximum of the emission peak was 22 nm.

[0067] In this example, the solvent used in Example 1 was changed from 1-octadecene to dodecane, and the formamidine salt solution was prepared with the following composition, so that the molar ratio of formamidine to lead was FA / Pb = 4, and the solution was delivered to mixer 2 in the same manner as in Example 1. Formamidine acetate 1.409 (g) (11.912 mmol as FA) Oleic acid 26.3 (ml) Dodecane 63.7 (ml)

[0068] Emission evaluation revealed a PLQY of 88%, an emission peak wavelength of 540 nm, and a full width at half maximum of 21 nm.

[0069] In this example, the solvent used in Example 1 was changed from 1-octadecene to dodecane, and the formamidine salt solution was prepared with the following composition, so that the molar ratio of formamidine to lead was FA / Pb = 2.5, and the solution was delivered to mixer 2. The procedure was the same as in Example 1. Formamidine acetate 0.8806 (g) (7.445 mmol as FA) Oleic acid 17.1 (ml) Dodecane 72.9 (ml)

[0070] Emission evaluation revealed a PLQY of 87%, an emission peak wavelength of 536 nm, and a full width at half maximum of 23 nm.

[0071] In this example, the procedure was the same as in Example 2, except that the following composition was used to prepare the mixture, resulting in a molar ratio of formamidine to lead of FA / Pb = 3.5, which was then supplied to the mixer 2, and the mixture was mixed at 130°C in the mixer using a heating means 5 that was temperature-controlled to 130°C. Formamidine acetate 1.398 (g) (11.813 mmol as FA) Oleic acid 35.7 (ml) Dodecane 54.3 (ml)

[0072] Emission evaluation revealed a PLQY of 90%, an emission peak wavelength of 536 nm, and a full width at half maximum of 22 nm.

[0073] In this example, the procedure was the same as in Example 1, except that the formamidine salt solution prepared in Example 1 with the following composition was used and the perovskite luminescent particles were synthesized by the hot injection method. Formamidine acetate 1.054 (g) (10.125 mmol as FA) Oleic acid 27.2 (ml) 1-Octadecene 22.8 (ml)

[0074] Lead bromide and 1-octadecene were placed in a flask, a stirring bar was added, and the flask was immersed in an oil bath heated to 160°C. Next, oleic acid was added, and the stirring bar was rotated with a magnetic stirrer to disperse the lead bromide. After 25 minutes, the liquid temperature in the flask stabilized at 154°C (process temperature T). Oleylamine heated to 154°C was then added, and the dissolution of lead bromide was started while degassing with a diaphragm pump. After 20 minutes (process time t: 1200 seconds), degassing was stopped, and a formamidine salt solution heated to 154°C was added to the flask. After 5 seconds, the flask was removed from the oil bath and cooled in an ice bath. Luminescence evaluation showed a PLQY of 88.3%, an emission peak wavelength of 538 nm, and a full width at half maximum of 22 nm.

[0075] [Comparative Example 1] In this comparative example, a solution was prepared by dissolving lead bromide, acid, and amine with the same composition as in Example 1. Unlike Example 1, the process temperature T was set to 163°C. When the process time t reached 600 seconds, precipitation of the initially dissolved lead bromide was observed. When the flask was removed from the oil bath and cooled in a water bath at a process time t of 1200 seconds, the precipitation of lead bromide increased further, making it difficult to pump the solution with pump 1.

[0076] [Comparative Example 2] This example was carried out in the same manner as in Example 1, except that a formamidine salt solution prepared with the following composition was used: Formamidine acetate 0.705 (g) (5.956 mmol as FA) Oleic acid 13.2 (ml) Dodecane 76.8 (ml)

[0077] When the emission evaluation was performed, the PLQY was 68%, the emission peak wavelength was 531 nm, and the full width at half maximum of the emission peak was 34 nm, indicating a decrease in emission characteristics compared to Example 1.

[0078] [Comparative Example 3] In this comparative example, the procedure was the same as in Example 5, except that the process time t was set to 3600 seconds. When the solution of lead bromide, acid, and amine was cooled in a water bath, a small precipitate of lead bromide was observed at the bottom of the flask. After removing the precipitated lead bromide, the solution of lead bromide, acid, and amine was used. When the emission was evaluated, the PLQY was 79%, the emission peak wavelength was 538 nm, and the full width at half maximum of the emission peak was 21 nm, resulting in a lower PLQY than in Example 5.

[0079] [Comparative Example 4] In this comparative example, the procedure was the same as in Example 5, except that the process temperature T was set to 124°C. When the emission evaluation was performed, the PLQY was 89%, the emission peak wavelength was 534 nm, and the full width at half maximum of the emission peak was 23 nm, so the emission peak wavelength fell slightly short of 535 nm.

[0080] [Comparative Example 5] In this comparative example, the procedure was the same as in Example 1, except that a heating means 5, which was temperature-controlled to 130°C, was used and the mixture was mixed in a mixer at 130°C. When the emission evaluation was performed, the main emission peak wavelength was 532 nm with a PLQY of 85%, and the full width at half maximum of the emission peak was 24 nm, but an emission peak originating from the nanoplate was also confirmed at 508 nm.

[0081] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0082] This application claims priority based on Japanese Patent Application No. 2024-167061, filed on 26 September 2024, and all of its contents are incorporated herein by reference.

[0083] 1. Pump 2. Mixer 3. Forward channel 4. Backward channel 5. Heating means 6. Ice bath 7. Recovery unit 8. Reaction tank 9. Thermocouple 10. End of forward channel

Claims

1. A method for producing nanocrystalline particles, comprising: a dissolution preparation step of preparing a dissolution by dissolving lead bromide, an organic acid, and an amine in a solvent; and a synthesis step of mixing the dissolution with a formamidine salt solution to synthesize nanocrystalline particles containing a perovskite-type crystalline structure composed of formamidine, lead, and bromine, wherein the dissolution preparation step is performed under conditions that satisfy general formulas (1) to (4), when the process temperature T (°C) and process time t (seconds) for preparing the dissolution. General formula (1) 134 ≤ T ≤ 154 General formula (2) t ≥ 600 General formula (3) t ≥ -66.667 × T + 10133 General formula (4) t ≤ -60 × T + 10740 2. The synthesis step comprises: adjusting a first solution containing the lead bromide, the acid, and the amine, and a second solution containing a formamidine salt to a predetermined liquid temperature in separate liquid delivery pipes; delivering the first solution and the second solution, whose liquid temperatures have been adjusted, to a mixer at a delivery temperature x°C; and mixing the first solution and the second solution with the mixer at a liquid mixing temperature y°C, wherein the delivery temperature x (°C) and the liquid mixing temperature y (°C) satisfy general formulas (5) to (7). The method for producing nanocrystalline particles according to claim 1. General formula (5): 130 ≤ x ≤ 360 General formula (6): 130 ≤ y ≤ 160 General formula (7): y - x ≤ 3 3. The perovskite-type crystal structure is FAPbBr ３ A method for producing nanocrystalline particles according to claim 1 or 2, characterized in that it is the same as described above.

4. The method for producing nanocrystalline particles according to claim 1 or 2, characterized in that the acid is a fatty acid and the amine is an aliphatic amine.

5. The method for producing nanocrystalline particles according to claim 1 or 2, characterized in that the molar ratio of formamidine to lead in the synthesis step for synthesizing nanocrystalline particles containing the perovskite-type crystal structure is 2.5 or more.

6. The method for producing nanocrystalline particles according to claim 1 or 2, characterized in that the formamidine salt solution is a fatty acid salt solution of formamidine, and is prepared by replacing the fatty acid portion of the fatty acid salt of formamidine with a different fatty acid.

7. When the process temperature T (°C) and process time t (seconds) for preparing the dissolving solution are given, the process temperature T and process time t (seconds) satisfy general formulas (8) and (9), and in the synthesis step, when the liquid is continuously supplied to the mixer at a supply temperature x°C and the first solution and the second solution are mixed by the mixer at a liquid mixing temperature y°C, the synthesis step satisfies general formulas (10) to (12), as described in claim 1 or 2. General formula (8) 150 ≤ T ≤ 154 General formula (9) 1200 ≤ t ≤ 1500 General formula (10) 150 ≤ x ≤ 360 General formula (11) 150 ≤ y ≤ 160 General formula (12) y - x ≤ 3

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