Normal-temperature preparation method of ultra-small perovskite quantum dots

Abstract

The invention relates to a normal-temperature preparation method of ultra-small perovskite quantum dots. The method comprises the following steps: in normal-temperature air, mixing environment-friendly low-toxicity terpene with a high-polarity solvent (such as N, N-dimethylformamide and the like), and respectively mixing with CsBr and PbBr2 powder to prepare a terpene ligand; the method comprises the following steps: mixing a terpene ligand, oleic acid and oleylamine to prepare a terpene reaction precursor; and adding the terpene reaction precursor into an anti-solvent to form a precipitate so as to prepare the CsPbBr3 perovskite quantum dot capable of emitting ultra-small-size dark blue light. According to the method, the quantum dots with the ultra-small particle size smaller than 3 nm can be prepared, and by changing the volume ratio of terpene in the ligand solution or the variety of terpene, the light-emitting wave band of the prepared quantum dots can cover a deep blue light area of 440-460 nm and can be expanded to a purple light area of 415 nm.

Description

Technical Field

[0001] The invention belongs to the field of nanocrystal luminescent materials, and specifically relates to a method for preparing ultra-small perovskite quantum dots at room temperature. Background Art

[0002] CsPbBr3 perovskite quantum dots have shown great application prospects in the field of ultra-high-definition display due to their excellent luminescence performance and room-temperature preparation characteristics. For the demand for deep blue light (below 460nm) in display applications, ultra-small-sized CsPbBr3 perovskite quantum dots (particle size below 3nm) have important application value. However, at room temperature, CsPbBr3 perovskite quantum dots have extremely fast nucleation and growth rates, allowing them to grow into perovskite crystals of about 10nm in tens of seconds, making it difficult to achieve ultra-small-sized controlled synthesis.

[0003] At present, small-sized CsPbBr3 perovskite quantum dots can be prepared by suppressing the crystal growth rate through low-temperature liquid nitrogen (Adv.Optical Mater.2021,2100300); this method is not very controllable, and it is difficult to prepare perovskite quantum dots with a particle size of less than 3nm and an emission peak of less than 460nm. For room temperature preparation, Chinese patent CN112125332A discloses a recrystallization-based all-bromine perovskite blue light quantum dot and its preparation method; it uses cesium bromide and lead bromide as reactants, oleic acid and oleylamine as ligands, and N,N-dimethylformamide as solvent, and prepares CsPbBr3 perovskite quantum dots below 3nm based on recrystallization; but its emission peak wavelength is between 460-480nm, which is difficult to meet the deep blue light emission requirements. Chinese patent CN114507519B discloses a room-temperature green synthesis method for deep blue light perovskite quantum dots. By using a low-toxic solvent to prepare a Cs precursor, deep blue light CsPbBr3 perovskite quantum dots with an emission peak at 454nm are prepared; however, the particle size is difficult to reach below 3nm, and the hydrochloric acid, hydrobromic acid, etc. involved in the preparation process increase the complexity of the process.

[0004] For achieving ultra-small particle size of CsPbBr3 perovskite quantum dots below 3nm and deep blue light emission peak below 460nm at room temperature, Chinese patent CN116925743A discloses a method for preparing deep blue light efficient narrow-band perovskite quantum dots. It uses alkyl trimethylammonium bromide and N,N-dimethylformamide to prepare soft template precursor solution, cesium halide, lead halide, amine hydrobromide and N,N-dimethylformamide to prepare precursor solution, and combines anti-solvent mixing to prepare deep blue light emitting CsPbBr3 perovskite quantum dots below 3nm with emission peak at 440-446nm through precipitation reaction; however, the alkyl trimethylammonium bromide used is highly toxic, and it is difficult to achieve large-scale regulation of the spectrum in the deep blue light region (440-460nm).

[0005] Therefore, achieving the room-temperature, low-toxic synthesis of ultra-small perovskite quantum dots and their deep blue light regulation remains a challenge for the industry. Summary of the invention

[0006] The purpose of the present invention is to provide a room temperature preparation method for ultra-small perovskite quantum dots in view of the shortcomings in the current technology. The method induces the synthesis of quantum dots by using low-toxic terpene ligands, avoids the use of highly toxic halide ammonium salts, and realizes the spectrum regulation of the deep blue light of CsPbBr3 perovskite quantum dots in the whole area. The preparation method comprises the following steps: mixing environmentally friendly low-toxic terpenes with high polarity solvents (such as N,N-dimethylformamide, etc.) under normal temperature air, and then mixing with CsBr and PbBr2 powders respectively to prepare terpene ligands; mixing terpene ligands, oleic acid and oleylamine to prepare terpene reaction precursors; adding the terpene reaction precursors to anti-solvents to form precipitation to prepare ultra-small-sized deep blue light emitting CsPbBr3 perovskite quantum dots. The present invention can prepare ultra-small quantum dots with a particle size of less than 3nm, and by changing the volume ratio of terpenes in the ligand solution or the type of terpenes, the luminescence band of the prepared quantum dots can cover the deep blue light region of 440-460nm and expand to the purple light region of 415nm.

[0007] The technical solution of the present invention is:

[0008] A method for preparing ultra-small perovskite quantum dots at room temperature, the method comprising the following steps:

[0009] 1) The first step is to prepare the "terpene ligand" solution

[0010] At room temperature and in air, solvent A and solvent B are mixed and stirred for 0.1-5 hours to obtain solvent C; wherein the volume of solvent A:B=1:(1-30), and the stirring speed is 100-600 revolutions per minute; CsBr and PbBr2 powders are weighed and poured into containers respectively, and solvent C is added respectively, and stirred for 0.1-12 hours, and the stirring speed is 100-800 revolutions per minute to obtain solution D and solution E, i.e., "terpene ligand" solution;

[0011] Wherein, solvent A is N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone or N-methylpyrazoline, and solvent B is terpene; wherein the concentration of solution D and solution E is 0.01 to 5M;

[0012] The terpene is specifically terpinene, pinolene, phellandrene, dipentene, sabinene or limonene.

[0013] 2) The second step is to prepare the terpene precursor solution

[0014] At room temperature and in air, solution D and solution E are mixed and stirred for 0.1-2 hours to obtain solution F; wherein the volume of solution D:E=1:(0.1-10), and the stirring speed is 300-600 revolutions per minute; oleic acid and oleylamine are respectively added to solution F, and stirring is continued to prepare terpene precursor solution G;

[0015] Wherein, the volume ratio of solution D to solution F is (0.1-0.9):1;

[0016] The volume ratio of oleic acid to solution F is (0.01-1):1; the volume ratio of oleylamine to solution F is (0.005-1):1;

[0017] 3) The third step is to prepare ultra-small CsPbBr3 perovskite quantum dots

[0018] At room temperature and in an air atmosphere, solution G is added dropwise to toluene or xylene under stirring; wherein the volume ratio of solution G to toluene or xylene is (0.1-1):1, the stirring speed is 100-600 revolutions per minute, and the stirring time is 0.2-4 hours, to obtain quantum dot solution H; solution H is taken and solvent I and solvent J are added, mixed evenly, and centrifuged to obtain a precipitate, which is the purified ultra-small size CsPbBr3 quantum dots;

[0019] Wherein, solvent I is n-hexane, n-octane or n-pentane, solvent J is ethyl acetate, methyl acetate, methyl formate or ethyl formate; the volume ratios of solvent I and solvent J to solution H are (0.1-1):1 and (0.2-2):1 respectively.

[0020] The average particle size of the perovskite quantum dots is 2.3nm-2.9nm.

[0021] When the volume ratio of terpene added to the terpene ligand solution increases from 85% to 66%, the emission peak of the obtained quantum dots can cover 438nm-460nm.

[0022] When the terpene types transition from pinolene to phellandrene, dipentene, and limonene in sequence, under the same process, the quantum dot emission peaks can be achieved at 438nm, 460nm, 457nm, and 415nm, covering the 440nm-460nm deep blue light band, and can be expanded to the purple light region of 415nm.

[0023] The beneficial effects of the present invention are:

[0024] In the present invention, the prepared "terpene ligand" can slow down the rate at which Cs ions participate in the formation of quantum dots during the growth of CsPbBr3 perovskite quantum dots (i.e., compared with the case where this ligand is not used, the number of Cs ions participating in the formation of quantum dots at the same time is reduced), thereby reducing the reaction rate of quantum dots, and thus facilitating the generation of ultra-small-sized deep blue light CsPbBr3 perovskite quantum dots. Therefore, the preparation method of the present invention has made a breakthrough in using low-toxic and environmentally friendly terpene-induced slow-release cation ligands, and can reduce the growth rate by slowing down the supply of raw materials for crystal growth, and can prepare ultra-small particle size quantum dots below 3nm (the average particle size can be as small as about 2.3nm); by regulating the concentration and type of terpene, the emission peak of quantum dots can be widely regulated in the entire deep blue light region of 440-460nm, and can be expanded to the purple light region of 415nm; in addition, this method effectively avoids the use of highly toxic organic halide ammonium salts, making the process low-toxic, simpler and safer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The morphology and particle size distribution of the material prepared in Example 1; wherein, Figure 1 (a) is the transmission electron microscope morphology of the prepared quantum dots. Figure 1 (b) is the statistical distribution diagram of the particle size of the prepared quantum dots;

[0026] Figure 2 is the morphology and particle size distribution diagram of the comparison sample; among them, Figure 2 (a) is the transmission electron microscope morphology of the comparative quantum dots. Figure 2 (b) is the particle size statistical distribution diagram of the comparative sample quantum dots;

[0027] Figure 3 The photoluminescence spectra of the material prepared in Example 1 and its comparative sample;

[0028] Figure 4 Infrared spectra of surface organic groups of the material prepared in Example 1 and its comparative sample;

[0029] Figure 5 The element contents of the material prepared in Example 1 and its comparative sample; wherein, Figure 5 (a) is the elemental energy spectrum and ratio of quantum dots generated by the reaction of 0.5 h under the induction of terpinene ligand. Figure 5 (b) is the elemental energy spectrum and ratio of quantum dots generated by the control sample (without terpinene) after 0.5 h of reaction. Figure 5 (c) The elemental energy spectrum and ratio of quantum dots generated by the reaction of terpinene ligand for 1 h;

[0030] Figure 6The spectrum and emission peak position of the material prepared in Example 2-4 in the deep blue light band are regulated;

[0031] Figure 7 The morphology and particle size distribution diagram of the material prepared in Example 5; wherein, Figure 7 (a) is the transmission electron microscope morphology of the prepared quantum dots. Figure 7 (b) is the statistical distribution diagram of the particle size of the prepared quantum dots;

[0032] Figure 8 This is the photoluminescence spectrum of the material prepared in Example 5;

[0033] Fig. 9 This is the photoluminescence spectrum of the material prepared in Example 6;

[0034] Fig.10 This is the photoluminescence spectrum of the material prepared in Example 7. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0036] The quantum dot preparation materials involved in the present invention are all known materials and can be commercially available or prepared.

[0037] Example 1: Preparation of CsPbBr3 deep blue light quantum dots induced by “terpinene ligand”

[0038] The first step is the preparation of "terpinene ligand"

[0039] At room temperature and in air, N,N-dimethylformamide and terpinene were mixed and stirred for 0.5 hours to obtain a mixed solvent A; wherein the volume ratio of N,N-dimethylformamide to terpinene was 1:5, and the stirring speed was 300 revolutions per minute; 0.1 mmol of CsBr and PbBr2 powders were weighed and poured into two glass bottles respectively, and 10 ml of solvent A was added respectively, and stirred for 1 hour at a stirring speed of 500 revolutions per minute; "terpinene ligand" solutions B and C were obtained;

[0040] Step 2: Prepare terpinene precursor solution

[0041] At room temperature and in air, 10 ml of solution B and 10 ml of solution C were mixed and stirred for 0.2 hours at a stirring speed of 500 revolutions per minute to obtain solution D; 0.25 ml of oleic acid and 0.15 ml of oleylamine were added to solution D respectively, and the speed was kept constant while continuing to stir to prepare terpinene precursor solution E;

[0042] The third step is to prepare ultra-small size CsPbBr3 deep blue light quantum dots

[0043] At room temperature and in an air atmosphere, solution E was added dropwise into xylene under stirring; wherein the volume ratio of solution E to xylene was 1:10, the stirring speed was 400 revolutions per minute, and the stirring time was 0.5 hour to obtain a quantum dot solution; 2 ml of the quantum dot solution was added with 1 ml of n-hexane and 2 ml of ethyl acetate, mixed evenly, and centrifuged to obtain a precipitate, which was the purified ultra-small CsPbBr3 quantum dots.

[0044] Comparative Example 1

[0045] The other steps are the same as those in Example 1, except that in the first step, "mixing N,N-dimethylformamide and terpinene" is changed to single N,N-dimethylformamide, that is, the mixed solvent A is N,N-dimethylformamide;

[0046] Example 1 The material obtained by the method of the present invention is shown in the following figure by transmission electron microscopy (Talos F200X, FEI). Figure 1 As shown in the figure, the average particle size distribution is about 2.3nm, which is an ultra-small size CsPbBr3 quantum dot synthesized at room temperature; the comparison sample is the CsPbBr3 quantum dot synthesized without adding terpinene and other reaction conditions are the same, and its average particle size distribution is about 9nm, as shown in the figure. Figure 2 The photoluminescence spectrum of the obtained material was characterized by a spectrometer (USB2000+, Ocean Optics) as shown in Figure 3 As shown in the figure, its emission peak is around 440nm, which belongs to the deep blue light emission region; while the emission peak of the control sample is around 520nm, which does not belong to the blue light emission region. The surface organic ligands of the prepared materials were characterized by infrared spectrometer (Nicolet iS50, ThermoFisher), as shown in the figure. Figure 4 As shown, the prepared quantum dots have the wavelengths of 3015, 1473, and 780 cm -1 The characteristic peaks of CH, CH2 and CC (cyclic) groups are shown at the positions, corresponding to the peaks of the characteristic groups of terpinene, while the control sample does not contain the above characteristic peaks, thus proving the inducing effect of the "cationic-terpinene" ligand in the synthesis process of CsPbBr3 deep blue light quantum dots.

[0047] like Figure 5 As shown, the energy spectra and element ratios of the quantum dots obtained by reacting with the terpinene ligand for 0.5 h and 1 h, and the quantum dots of the control sample (reacting without the terpinene ligand for 0.5 h) were characterized by energy dispersive X-ray spectrometry. Figure 5(a) It can be seen that during the growth of CsPbBr3 perovskite quantum dots induced by terpinene, the Cs atomic percentage was 8.46% after 0.5 h of reaction; in contrast, without terpinene, the Cs atomic percentage was 21.42% after 0.5 h of reaction. Figure 5 (b). It can be seen that the use of terpinene ligands can reduce the number of Cs atoms involved in the formation of quantum dots under the same time, that is, slow down the rate at which Cs ions participate in the reaction. In addition, under the induction of terpinene ligands, after the reaction was carried out for 1 hour, the percentage of Cs atoms in the generated quantum dots increased to 16.29%, as shown in Figure 2. Figure 5 (c), but still lower than the 21.42% of the aforementioned control sample. This further illustrates that the terpinene ligand can slow down the rate at which Cs ions participate in the quantum dot reaction, thereby reducing the growth rate of the quantum dots, which is beneficial to prolonging the time that the quantum dots maintain their ultra-small size, and is beneficial to the generation of ultra-small size deep blue perovskite quantum dots.

[0048] Example 2-4: Deep blue light regulation of CsPbBr3 quantum dots induced by “terpinene ligand”

[0049] The other steps are the same as those in Example 1, except that the volume ratio of N,N-dimethylformamide to terpinene is changed from 1:5 to 1:4, 1:3, and 1:2, respectively;

[0050] The emission spectra of the quantum dots obtained at different terpinene volume ratios are shown in Figure 2. Figure 6 As shown, when the volume ratio of terpene added to the terpene ligand solution increases from 83% to 66%, corresponding to volume ratios of 83%, 80%, 75%, and 66%, the emission peaks of the prepared quantum dots are 438nm, 444nm, 451nm, and 460nm, respectively, achieving full coverage regulation in the deep blue light region.

[0051] Example 5: Preparation of CsPbBr3 Deep Blue Light Quantum Dots Induced by “Pheretene Ligand”

[0052] The first step is the preparation of "phellandrene ligand"

[0053] At room temperature and in air, N-methylpyrrolidone and phellandrene were mixed and stirred for 1 hour to obtain a mixed solvent A; wherein the volume ratio of N-methylpyrrolidone to phellandrene was 1:3, and the stirring speed was 400 revolutions per minute; 0.1 mmol of CsBr and PbBr2 powders were weighed and poured into glass bottles respectively, and 10 ml of solvent A was added respectively, and stirred for 1.5 hours, and the stirring speed was 400 revolutions per minute; "phellandrene ligand" solutions B and C were obtained;

[0054] Except that in the third step, xylene is adjusted to toluene, n-hexane is adjusted to n-octane, and ethyl acetate is adjusted to methyl acetate, the other steps are the same as those in Example 1.

[0055] Example 5 The morphology and particle size distribution of the material obtained by the method of the present invention are as follows Figure 7 As shown in Figure 2, the average particle size is about 2.9 nm, which is an ultra-small size quantum dot; its photoluminescence spectrum is shown in Figure 2. Figure 8 As shown, the emission peak is at 460nm, which belongs to the deep blue light region.

[0056] Example 6: Preparation of CsPbBr3 Deep Blue Light Quantum Dots Induced by “Dipentene Ligand”

[0057] Except for the first step, terpinene is adjusted to dipentene; in the third step, n-hexane is adjusted to n-pentane, and ethyl acetate is adjusted to methyl formate, the other steps are the same as in Example 1.

[0058] Example 6 The photoluminescence spectrum of the material obtained by the method of the present invention is as follows Fig. 9 As shown, the emission peak is at 457nm, which belongs to the deep blue light region.

[0059] Example 7: Preparation of CsPbBr3 purple light quantum dots induced by “limonene ligand”

[0060] Except for the first step, terpinene is adjusted to limonene; in the third step, ethyl acetate is adjusted to ethyl formate, and the other steps are the same as those in Example 2.

[0061] Example 7 The photoluminescence spectrum of the material obtained by the method of the present invention is as follows Fig.10 As shown, the emission peak is at 415nm, which is beyond the deep blue light region and belongs to the purple light region.

[0062] From the above embodiments, it can be seen that quantum dots prepared from different terpene types can obtain different emission peaks. For example, terpinene can achieve quantum dot emission peaks at 438nm, 444nm, 451nm, and 460nm, covering the deep blue light region; phellandrene and dipentene can achieve quantum dot emission peaks at 460nm and 457nm, respectively; limonene can even achieve quantum dot emission peaks beyond the deep blue light region, emitting in the purple light region at 415nm.

[0063] The above embodiments show that the inventive method has the introduction and induction process of "terpene ligand", and the preparation is carried out in a room temperature air atmosphere, which effectively simplifies the synthesis process of ultra-small size deep blue light CsPbBr3 quantum dots and reduces the cost; it realizes the room temperature controllable synthesis of quantum dots with a particle size of less than 3nm, and the luminescent band can cover the 440-460nm deep blue light region, and can be expanded to the purple light region of 415nm.

[0064] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing ultra-small perovskite quantum dots at room temperature, characterized in that the method comprises the following steps: The first step is to prepare the "terpene ligand" solution At room temperature and in air, solvent A and solvent B are mixed and stirred for 0.1-5 hours to obtain solvent C; CsBr and PbBr are weighed. 2 The powders are poured into containers respectively, and solvent C is added respectively, and stirred for 0.1-12 hours to obtain solution D and solution E, i.e., "terpene ligand" solution; in, Solvent A is N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone or N-methylpyrazoline, and solvent B is terpene; the volume ratio is solvent A: solvent B = 1: (1-30); the concentration of CsBr in solution D is 0.01-5M, and the concentration of PbBr in solution E is 0.01-5M. 2 The concentration is 0.01~5M; Step 2: Preparation of terpene precursor solution At room temperature and in air, solution D and solution E are mixed and stirred for 0.1-2 hours to obtain solution F; oleic acid and oleylamine are added to solution F respectively, and stirring is continued to prepare terpene precursor solution G; Wherein, the volume ratio of solution D to solution F is (0.1-0.9):1; The volume ratio of oleic acid to solution F is (0.01-1):1; the volume ratio of oleylamine to solution F is (0.005-1):1; the volume ratio, solution D: solution E = 1:(0.1-10); Step 3: Preparation of ultra-small size CsPbBr 3 Perovskite quantum dots At room temperature and in air, solution G is added dropwise to toluene or xylene under stirring for 0.2-4 hours to obtain quantum dot solution H; solution H is added with solvent I and solvent J, mixed evenly, and centrifuged to obtain a precipitate, which is the purified ultra-small size CsPbBr 3 quantum dots; Among them, solvent I is n-hexane, n-octane or n-pentane, solvent J is ethyl acetate, methyl acetate, methyl formate or ethyl formate; the volume ratio of solution G to toluene or xylene is (0.1-1):1; the volume ratios of solvent I and solvent J to solution H are (0.1-1):1 and (0.2-2):1 respectively.

2. The method for preparing ultra-small perovskite quantum dots at room temperature as claimed in claim 1, characterized in that the terpene is specifically terpinene, terpinene, phellandrene, dipentene, sabinene or limonene.

3. The room temperature preparation method of ultra-small perovskite quantum dots as described in claim 1 is characterized in that in the first step, the stirring speed of solvent C is 100-600 revolutions per minute; the stirring speed of solution D and solution E is 100-800 revolutions per minute; the stirring speed of the second step is 300-600 revolutions per minute; and the stirring speed in the third step is 100-600 revolutions per minute.

4. The room temperature preparation method of ultra-small size perovskite quantum dots as described in claim 1, characterized in that the average particle size of the perovskite quantum dots is 2.3nm-2.9nm.

5. The room temperature preparation method of ultra-small perovskite quantum dots as described in claim 1 is characterized in that when the volume ratio of terpene added to the terpene ligand solution is in the trend of 85%-66%, the emission peak of the obtained quantum dots can cover 438nm-460nm.

6. The room temperature preparation method of ultra-small perovskite quantum dots as described in claim 1 is characterized in that when the terpene types transition from terpinene to phellandrene, dipentene, and limonene in sequence, under the same process, the quantum dot emission peaks can be achieved at 438nm, 460nm, 457nm, and 415nm, covering the 440nm-460nm deep blue light band, and can be expanded to the purple light region belonging to 415nm.

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