Method for in-situ NH 4i-assisted preparation of cspbi 3 colloidal nanoplateles

Abstract

Disclosed in the present invention is a method for in-situ NH4I-assisted preparation of CsPbI3 colloidal nanoplateles, comprising the following steps: S1. respectively preparing a lead iodide precursor solution, an ammonium iodide precursor solution, and a cesium oleate precursor solution; and S2. mixing the lead iodide precursor solution with the ammonium iodide precursor solution under stirring, adding the cesium oleate precursor solution for reaction to obtain a nanoplatele stock solution, and purifying and separating the nanoplatele stock solution to obtain CsPbI3 nanoplateles. In the present invention, in the method for the in-situ NH4I-assisted preparation of CsPbI3 colloidal nanoplateles, NH4I is used for in-situ replication synthesis of the CsPbI3 nanoplateles, the regulation of the growth kinetics of a system is achieved, the reaction process is more controllable, and the synthesized nanoplateles have a narrower peak width at half height, and a more uniform phase distribution, meeting requirements of light emitting in a red light range.

Description

A method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and in particular relates to a method for in-situ assisted preparation of CsPbI3 colloidal nanosheets using NH4I, and also relates to a method for in-situ assisted preparation of CsPbI3 colloidal nanosheets using NH4I. Background Art

[0002] Colloidal metal halide perovskite nanosheets offer advantages over their bulk counterparts, such as higher exciton binding energy, narrow emission peaks, large absorption cross-sections, and high photoluminescence quantum yields, making them ideal materials for the development of high-efficiency perovskite light-emitting diodes (LEDs). Compared to perovskite quantum dots, a popular research area, perovskite nanosheets have larger lateral dimensions, greater maneuverability in material size and morphology control, and exhibit anisotropic luminescence, which is beneficial for improving light extraction efficiency in LED devices. Currently, there are two main approaches to preparing colloidal perovskite nanocrystals in the laboratory. One is the hot injection method, which increases the supersaturation of the precursor in the system, causing explosive nucleation at high temperatures (>110°C), precipitating nanocrystals, and rapidly cooling to terminate the reaction. This reaction requires vacuum conditions and an inert atmosphere, making the operation cumbersome. Furthermore, due to the low activation energy required for the formation of perovskite nanocrystals, the growth kinetics of perovskite nanosheets prepared using traditional hot injection methods are difficult to control. The second method is the ligand-assisted reprecipitation method, which first uses a surfactant to assist in the dissolution of each precursor, then mixes the precursors at low temperature (<80°C) and rapidly stirs them, and finally adds an anti-solvent to stop the reaction. This scheme usually uses polar solvents (such as DMF to dissolve the precursors), which may cause a certain degree of damage to the material structure (i.e., polarity-induced material phase transition or ligand shedding to produce defects). Therefore, the preparation of high-quality perovskite nanosheets with uniform phase distribution remains a major challenge.

[0003] Existing technologies for improving the uniformity of perovskite nanosheet phase distribution mostly rely on ligand-assisted self-assembly (LAS) via hot injection. The specific process of LAS is as follows: Short-chain organic amine ligands, such as octylamine (C8), are used. These ligands have the ability to coordinate with halide ions on the nanosheet surface, filling the A-site cation vacancies. They are more active than the commonly used oleylamine (OLA), resulting in more frequent dynamic binding to the nanocrystal surface. This allows for more effective guidance of lateral nanocrystal growth and inhibition of longitudinal growth within the reaction system, enabling the nanocrystals to self-assemble into more uniform nanosheets. However, the inherently high energy of the hot injection method makes it very easy for nanosheets to cross energy barriers (particularly for I-based nanocrystals), resulting in a phase with uneven layer numbers. The difficulty in producing high-quality thin films with well-stacking properties significantly limits the application of nanosheets in LED devices, particularly for iodine (I)-based perovskite nanosheets. Therefore, finding suitable nanosheet preparation methods to address these challenges is key to achieving high-quality perovskite nanosheet LED devices.

[0004] The Bi Wengang team of Hebei University of Technology reported a method to use metal ions to assist in slowing down the growth rate of CsPbBr3 nanosheets. + ions and PbBr6 4- The octahedral coordination effect and Cs + Form a certain degree of competitive binding to achieve slow release of PbBr6 4- The effect of the wavelength conversion factor (V) effectively reduces the growth rate of CsPbBr3 nanosheets, resulting in high-quality nanosheets with uniform phase distribution (FWHM ≈ 15nm). The conversion relationship between energy (eV) and wavelength (nm) is: 1240 / wavelength = energy. The emission peak of CsPbBr3 nanosheets is located in the blue light range (430-500nm). Due to differences in band structure, their half-width at half maximum is narrower (FWHM typically less than 20nm) compared to CsPbI3 nanosheets, which emit in the red light range (580-660nm) (FWHM typically greater than 35nm).

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a method for in-situ assisted preparation of CsPbI3 colloidal nanosheets using NH4I, so as to solve the problem that the CsPbI3 colloidal nanosheets prepared in the prior art with a red luminescence range have poor phase distribution uniformity.

[0007] A method for in-situ preparation of CsPbI3 colloidal nanosheets assisted by NH4I comprises the following steps:

[0008] S1. preparing a lead iodide precursor solution, an ammonium iodide precursor solution, and a cesium oleate precursor solution respectively;

[0009] S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

[0010] The present invention's in-situ NH₄I-assisted method for preparing CsPbI₃ colloidal nanosheets improves upon the currently common method for preparing all-inorganic red-emitting perovskite nanocrystals (CsPbI₃). NH₄I is introduced into the ligand-assisted reprecipitation process to regulate growth kinetics. NH₄+ binds to surface I⁻ ions, exhibiting higher activity and a faster dynamic binding frequency than organic amine ions. This effectively inhibits the longitudinal growth of the nanosheets, kinetically reducing their growth rate. Compared to thermodynamically controlled synthesis processes, the reaction is more controllable, resulting in CsPbI₃ nanosheets with a more uniform phase distribution.

[0011] In the present invention, the reaction temperature in S2 is 28-55° C., and the reaction time is 30-90 min.

[0012] In the present invention, the volume ratio of the lead iodide precursor solution, the ammonium iodide precursor solution and the cesium oleate precursor solution is 2-6:1:0.1-0.2.

[0013] In the present invention, the lead iodide precursor solution, the ammonium iodide precursor solution, and the cesium oleate precursor solution are used to form a non-polar solvent reaction system, and mesitylene is used as the reaction solvent. The use of mesitylene as a non-polar solvent avoids the performance loss caused by the polar environment during the growth of nanocrystals.

[0014] In the present invention, the ammonium iodide precursor solution comprises ammonium iodide, mesitylene and a surfactant; the mass volume ratio of the ammonium iodide to mesitylene is 1.4-2.2 mg / mL, and the volume ratio of the surfactant to mesitylene is 0.01-0.02:1.

[0015] Furthermore, the ammonium iodide precursor solution is prepared by adding a certain amount of ammonium iodide and a surfactant to mesitylene and stirring to obtain a saturated NH4I solution.

[0016] Furthermore, the surfactant is oleic acid and octylamine.

[0017] In the present invention, the lead iodide precursor solution includes lead iodide, zinc iodide, mesitylene and a surfactant; the molar volume ratio of the lead iodide to mesitylene is 0.007-0.014 mmol:1 mL, the volume ratio of the surfactant to mesitylene is 0.01-0.02:1; and the molar ratio of the lead iodide to zinc iodide is 10-50:1.

[0018] Furthermore, the lead iodide precursor solution is prepared by mixing lead iodide and zinc iodide in a certain proportion, adding a certain amount of mesitylene and a surfactant, and stirring to obtain a PbI2 precursor solution. The addition of a trace amount of zinc iodide can, on the one hand, dope zinc ions, which, by virtue of their smaller ionic radius than lead ions, cause lattice contraction and improve structural stability. On the other hand, it can supplement the iodine source to a certain extent and passivate defects. (Note: If the amount of zinc iodide is too large, more surfactants will need to be introduced to assist dissolution, and the microscopic process will be more uncontrollable, so the alloying structure will not be discussed.)

[0019] Furthermore, the surfactant is oleic acid and octylamine.

[0020] Furthermore, the stirring temperature is 60-100°C.

[0021] In the present invention, the cesium oleate precursor solution comprises cesium acetate and oleic acid, and the molar volume ratio of the cesium acetate to the oleic acid is 0.08-0.12 mmol:1 mL.

[0022] In the present invention, the nanosheet stock solution is purified and separated in S2, and the specific process is as follows: methyl acetate is used as an anti-solvent to purify the nanosheet stock solution, centrifuged, retaining the precipitate, and then redispersed with hexane, centrifuged, and the supernatant is collected to obtain CsPbI3 nanosheets.

[0023] Furthermore, the volume ratio of the methyl acetate to the nanosheet stock solution is 1.5-3:1, and the volume ratio of the hexane to the nanosheet stock solution is 1-3:5.

[0024] Furthermore, oleic acid is added to the methyl acetate. A trace amount of oleic acid can supplement the surface ligands, prevent the increase of surface defects caused by the ligand shedding during the cleaning process, and has a certain protective effect on the material.

[0025] A CsPbI3 colloidal nanosheet is prepared by the above method.

[0026] The present invention has the following beneficial effects:

[0027] (1) The NH4I in-situ assisted preparation method of CsPbI3 colloidal nanosheets of the present invention adopts NH4I to replicate the synthesis of CsPbI3 nanosheets in situ, which realizes the regulation of the growth dynamics of the system, makes the reaction process more controllable, and the synthesized nanosheets have a narrower half-peak width and a more uniform phase distribution of the nanosheets, which can meet the requirements of luminescence in the red light range.

[0028] (2) The method of the present invention can be carried out at a lower reaction temperature. Compared with the hot injection method for synthesizing CsPbI3 nanosheets, the nanosheet material has better quality and larger size, mild reaction conditions, and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0030] FIG1 is a flow chart of the synthesis of CsPbI3 colloidal nanosheets by in-situ assisted growth of NH4I according to the present invention;

[0031] FIG2 is a schematic diagram of the operation of NH4I in-situ assisted growth of CsPbI3 colloidal nanosheets;

[0032] FIG3 is a schematic diagram of the synthesis operation of CsPbI3 colloidal nanosheets by hot injection method;

[0033] FIG4 is the absorption spectra of CsPbI3 colloidal nanosheets synthesized by hot injection and in situ assisted growth of CsPbI3 colloidal nanosheets by NH4I;

[0034] FIG5 is a fluorescence spectrum of CsPbI3 colloidal nanosheets synthesized by hot injection method and CsPbI3 colloidal nanosheets grown by NH4I in situ;

[0035] Figure 6 shows the effect of adding ZnI2 on the fluorescence spectrum of CsPbI3 colloidal nanosheets;

[0036] Figure 7 shows the effect of different NH4I addition amounts on the fluorescence spectra of CsPbI3 colloidal nanosheets;

[0037] Figure 8 shows the effect of different reaction temperatures on the fluorescence spectra of CsPbI3 colloidal nanosheets;

[0038] FIG9 is a TRPL decay curve of CsPbI3 colloidal nanosheets synthesized by hot injection method and CsPbI3 colloidal nanosheets grown by NH4I in situ;

[0039] FIG10 is a TEM image of nanosheets synthesized by hot injection method in Comparative Example 1;

[0040] FIG11 is a TEM image of nanosheets prepared by in-situ assisted growth of NH4I in Example 1. DETAILED DESCRIPTION

[0041] The present invention provides a method for preparing CsPbI3 colloidal nanosheets with the aid of NH4I in situ. The method regulates the growth kinetics of CsPbI3 colloidal nanosheets by in-situ addition of ammonium iodide (NH4I) ligands. The in-situ addition of NH3I ligands significantly slows down the growth process of CsPbI3 nanosheets, significantly improves the phase distribution of the nanosheets, obtains pure-phase CsPbI3 nanosheets, and enhances their application potential in LED devices.

[0042] Example 1

[0043] As shown in Figures 1 and 2, the method for preparing CsPbI3 colloidal nanosheets using NH4I in situ as an auxiliary method includes the following steps:

[0044] S1. Prepare lead iodide precursor solution, ammonium iodide precursor solution, and cesium oleate precursor solution respectively.

[0045] The specific process is as follows:

[0046] PbI2 precursor: Weigh 0.08 mmol of PbI2 and 0.002 mmol of ZnI2, add them to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 80°C overnight to obtain a PbI2 precursor solution.

[0047] NH4I precursor: Weigh 15 mg of NH4I powder and add it to 10 ml of mesitylene (120 μl of oleic acid and 60 μl of octylamine as solubilizing ligands). Stir at 80°C for one day and then at room temperature for one day to obtain a saturated solution of NH4I.

[0048] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0049] S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

[0050] The specific process is as follows:

[0051] Step 1: In a nitrogen glove box, add 2 ml of PbI2 precursor and 500 μl of NH4I precursor to a 5 ml reagent bottle, set the magnetic stirrer speed to 1000 rpm, and stir at 40°C and 1000 rpm for 5 minutes.

[0052] Step 2: Quickly inject 65 μl of Cs-OA into the reagent bottle and continue to stir vigorously for 30 to 60 minutes to obtain the nanosheet stock solution.

[0053] Step 3: Take 500ul of nanosheet stock solution, mix it with 1ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 100ul of hexane, continue centrifuging at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0054] Example 2

[0055] A method for in-situ preparation of CsPbI3 colloidal nanosheets assisted by NH4I comprises the following steps:

[0056] S1. Prepare lead iodide precursor solution, ammonium iodide precursor solution, and cesium oleate precursor solution respectively.

[0057] The specific process is as follows:

[0058] PbI2 precursor: Weigh 0.1 mmol of PbI2 and 0.002 mmol of ZnI2, add to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 100°C overnight to obtain a PbI2 precursor solution.

[0059] NH4I precursor: Weigh 17 mg of NH4I powder and add it to 10 ml of mesitylene (120 μl of oleic acid and 60 μl of octylamine as solubilizing ligands). Stir at 80°C for one day and then at room temperature for one day to obtain a saturated solution of NH4I.

[0060] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0061] S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

[0062] The specific process is as follows:

[0063] Step 1: In a nitrogen glove box, add 2 ml of PbI2 precursor and 500 μl of NH4I precursor to a 5 ml reagent bottle, set the magnetic stirrer speed to 1000 rpm, and stir at 40 ° C and 1000 rpm for 5 minutes.

[0064] Step 2: Quickly inject 60 μl of Cs-OA into the reagent bottle and continue to stir vigorously for 30 to 60 minutes to obtain the nanosheet stock solution.

[0065] Step 3: Take 500ul of nanosheet stock solution, mix it with 1.5ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 100ul of hexane, continue centrifugation at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0066] Example 3

[0067] A method for in-situ preparation of CsPbI3 colloidal nanosheets assisted by NH4I comprises the following steps:

[0068] S1. Prepare lead iodide precursor solution, ammonium iodide precursor solution, and cesium oleate precursor solution respectively.

[0069] The specific process is as follows:

[0070] PbI2 precursor: Weigh 0.08 mmol of PbI2 and 0.002 mmol of ZnI2, add them to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 80°C overnight to obtain a PbI2 precursor solution.

[0071] NH4I precursor: Weigh 14 mg of NH4I powder, add it to 10 ml of mesitylene (120 μl of oleic acid and 60 μl of octylamine as solubilizing ligands), and stir at 80°C for two days to obtain a saturated solution of NH4I.

[0072] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0073] S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

[0074] The specific process is as follows:

[0075] Step 1: In a nitrogen glove box, add 2 ml of PbI2 precursor and 500 μl of NH4I precursor to a 5 ml reagent bottle, set the magnetic stirrer speed to 1000 rpm, and stir at 50°C and 1000 rpm for 5 minutes.

[0076] Step 2: Quickly inject 65 μl of Cs-OA into the reagent bottle and continue to stir vigorously for 30 to 60 minutes to obtain the nanosheet stock solution.

[0077] Step 3: Take 500ul of nanosheet stock solution, mix it with 1ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 100ul of hexane, continue centrifuging at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0078] Comparative Example 1

[0079] As shown in FIG3 , a method for preparing CsPbI3 colloidal nanosheets includes the following steps:

[0080] Steps:

[0081] (1) Preparation of CsPbI3 colloidal nanosheet precursor solution

[0082] PbI2 precursor: Weigh 0.08 mmol of PbI2 and 0.002 mmol of ZnI2, add them to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 80°C overnight to obtain a PbI2 precursor solution.

[0083] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0084] (2) Preparation of CsPbI3 colloidal nanosheets

[0085] The specific process is as follows:

[0086] Step 1: Add 2 ml of PbI2 precursor to a 5 ml reagent bottle in a nitrogen glove box, set the magnetic stirrer speed to 1000 r / min, and stir at 40°C and 1000 r / min for 5 minutes.

[0087] Step 2: Quickly inject 80ul of Cs-OA into the reagent bottle and continue to stir vigorously for 10min to obtain the nanosheet stock solution.

[0088] Step 3: Take 500ul of nanosheet stock solution, mix it with 1ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 100ul of hexane, continue centrifuging at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0089] Comparative Example 2

[0090] A method for preparing CsPbI3 colloidal nanosheets comprises the following steps:

[0091] (1) Preparation of CsPbI3 colloidal nanosheet precursor solution

[0092] PbI2 precursor: Weigh 0.08 mmol of PbI2, add it to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 80°C overnight to obtain a PbI2 precursor solution.

[0093] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0094] (2) Preparation of CsPbI3 colloidal nanosheets

[0095] The specific process is as follows:

[0096] Step 1: Add 2 ml of PbI2 precursor to a 5 ml reagent bottle in a nitrogen glove box, set the magnetic stirrer speed to 1000 r / min, and stir at 40°C and 1000 r / min for 5 minutes.

[0097] Step 2: Quickly inject 80ul Cs-OA into the reagent bottle and continue to stir vigorously for 5 minutes.

[0098] min to obtain the nanosheet stock solution.

[0099] Step 3: Take 500ul of nanosheet stock solution, mix it with 1ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 100ul of hexane, continue centrifuging at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0100] Comparative Example 3

[0101] A method for preparing CsPbI3 colloidal nanosheets comprises the following steps:

[0102] S1. Preparation of CsPbI3 colloidal nanosheet precursor solution

[0103] PbI2 precursor: Weigh 0.08 mmol of PbI2 and 0.002 mmol of ZnI2, add them to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 80°C overnight to obtain a PbI2 precursor solution.

[0104] NH4I precursor: Weigh 14 mg of NH4I powder, add it to 10 ml of mesitylene (120 μl of oleic acid and 60 μl of octylamine as solubilizing ligands), and stir at 80°C for two days to obtain a saturated solution of NH4I.

[0105] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0106] S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

[0107] The specific process is as follows:

[0108] Step 1: In a nitrogen glove box, add 2 ml of PbI2 precursor and 400 μl of NH4I precursor to a 5 ml reagent bottle, set the magnetic stirrer speed to 1000 rpm, and stir at 40°C and 1000 rpm for 5 minutes.

[0109] Step 2: Quickly inject 65 μl of Cs-OA into the reagent bottle and continue to stir vigorously for 30 minutes to obtain the nanosheet stock solution.

[0110] Step 3: Take 500ul of nanosheet stock solution, mix it with 1ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 80ul of hexane, continue centrifuging at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0111] Comparative Example 4

[0112] A method for preparing CsPbI3 colloidal nanosheets comprises the following steps:

[0113] S 1. Preparation of CsPbI3 colloidal nanosheet precursor solution

[0114] PbI2 precursor: Weigh 0.08 mmol of PbI2 and 0.002 mmol of ZnI2, add them to 10 ml of mesitylene (100 ul of oleic acid and 50 ul of octylamine as solubilizing ligands), and stir at 80°C overnight to obtain a PbI2 precursor solution.

[0115] NH4I precursor: Weigh 14 mg of NH4I powder, add it to 10 ml of mesitylene (120 μl of oleic acid and 60 μl of octylamine as solubilizing ligands), and stir at 80°C for two days to obtain a saturated solution of NH4I.

[0116] Cs-OA precursor: Weigh 0.1 mmol of CsAc, add 1 ml of deoxygenated oleic acid, and sonicate until the solution is clear to obtain a Cs-OA precursor solution.

[0117] S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

[0118] The specific process is as follows:

[0119] Step 1: In a nitrogen glove box, add 2 ml of PbI2 precursor and 500 μl of NH4I precursor to a 5 ml reagent bottle, set the magnetic stirrer speed to 1000 rpm, and stir at 60 ° C and 1000 rpm for 5 minutes.

[0120] Step 2: Quickly inject 65 μl of Cs-OA into the reagent bottle and continue to stir vigorously for 30 minutes to obtain the nanosheet stock solution.

[0121] Step 3: Take 500ul of the nanosheet stock solution, mix it with 1ml of methyl acetate (containing 5ul of OA), and centrifuge it at 6000r / min for 3min. Discard the supernatant, then disperse the precipitate with 80ul of hexane, continue centrifuging at 6000r / min for 1min, collect the supernatant, and obtain CsPbI3 nanosheets.

[0122] The prepared CsPbI3 colloidal nanosheets and NH4I in situ assisted growth CsPbI3 colloidal nanosheets were tested and characterized respectively.

[0123] (1) Ultraviolet-visible absorption characterization (UV-vis)

[0124] The CsPbI3 colloidal nanosheets prepared in Comparative Example 1 and Example 1N were respectively H4 The UV-visible absorption (UV-vis) characterization of the CsPbI3 colloidal nanosheets prepared by in situ assisted growth was performed as follows: the UV-visible spectrophotometer was turned on and the instrument self-calibrated; a cuvette filled with hexane was placed in the sample holder, the scan range was set to 400 to 800 nm, and background subtraction was performed; the hexane was removed, the diluted nanosheets were placed in, and the measurement was started. The results are shown in Figure 4.

[0125] The results show that the CsPbI3 colloidal nanosheets prepared in comparative example 1 have two absorption peaks, while the CsPbI3 colloidal nanosheets grown with the in situ assistance of NH4I have only one exciton absorption peak, indicating that the phase distribution in the CsPbI3 system grown with the in situ assistance of NH4I is purer than that of the CsPbI3 colloidal nanosheets.

[0126] (2) Fluorescence spectroscopy characterization (PL)

[0127] Fluorescence spectroscopy (PL) was performed on the CsPbI3 colloidal nanosheets prepared in comparative examples 1-4 and the CsPbI3 colloidal nanosheets prepared by in-situ assisted growth of NH4I in Example 1, respectively. The operation was as follows: a light source with an excitation wavelength of 405 nm was selected, and the hexane containing the cuvette was placed on the sample stage. The sample stage was raised into the integrating sphere, the test software was opened, the integrating sphere shading plate was closed, the spectrum was darkened, the shading plate was opened, an initial background measurement was performed, the diluted nanosheets were replaced, and fluorescence spectroscopy was performed. The results are shown in Table 1 and Figures 5-8.

[0128] Table 1 Specific performance parameters of CsPbI3 colloidal nanosheets prepared in different groups

[0129] The results in Table 1 and Figure 5 show that the half-value width of the CsPbI3 colloidal nanosheets grown with the in-situ NH4I-assisted growth method is 29.9 nm, and the photoluminescence quantum yield (PLQY) is 95%. The surface NH4I-assisted growth not only achieves a more pure phase distribution but also effectively passivates surface defects. Compared with CsPbI3 colloidal nanosheets synthesized by the hot injection method, the in-situ NH4I-assisted growth method exhibits a narrower half-value width and achieves a more pure phase distribution.

[0130] In Figure 6, the CsPbI3 colloidal nanosheets prepared without the addition of ZnI2 have two emission peaks with similar intensities (i.e., two types of nanosheets with different layers, n=3 and n=4 in the figure). After the addition of ZnI2, the lattice shrinks, which improves the stability of the prepared CsPbI3 colloidal nanosheets (especially the nanosheets with n=3), increases the emission peak intensity around 600nm, and suppresses the emission peak intensity around 625nm. After the addition of ZnI2, the phase distribution is purer.

[0131] In Figure 7, when different contents of NH4I are added, the emission peak intensity of the nanosheets added with 500ul ammonium iodide is higher than that of the nanosheets added with 400ul ammonium iodide, indicating that more ammonium iodide is effectively combined with the surface of the nanosheets, suppressing surface defects and improving the photoluminescence intensity.

[0132] In Figure 8, under different reaction temperatures, the peak position of the sample synthesized at 60°C is red-shifted and the peak shape is broadened compared to the sample synthesized at 40°C, indicating that the increase in temperature provides more energy, which accelerates the crystallization rate of the nanosheets, resulting in larger sample sizes and more uneven size distribution. The reaction temperature has a great influence on the performance of CsPbI3 colloidal nanosheets.

[0133] (3) Time-resolved photoluminescence characterization (TRPL)

[0134] Time-resolved photoluminescence (TRPL) characterization was performed on the CsPbI3 colloidal nanosheets prepared in Comparative Example 1 and the CsPbI3 colloidal nanosheets prepared by NH4I in-situ assisted growth in Example 1, respectively. The operation was as follows: a 360 nm laser light source was used, the test peak position was set to 600 nm, the test was started, and the results were fitted with a double exponential fitting. The results are shown in Figure 9.

[0135] The results show that the carrier lifetime of CsPbI3 colloidal nanosheets grown by in situ assisted NH4I is 24.57ns, which is 8 times that of CsPbI3 colloidal nanosheets, indicating that the NH4I in situ assisted growth method can effectively reduce the surface defect density of nanosheets and inhibit non-radiative recombination.

[0136] (4) TEM image characterization

[0137] The CsPbI3 colloidal nanosheets prepared in Comparative Example 1 and Example 1N were respectivelyH4 I The CsPbI3 colloidal nanosheets prepared by in situ assisted growth were characterized by TEM images, see Figures 10 and 11.

[0138] Figure 10 shows a TEM image of nanosheets prepared by the hot injection method. Compared to the nanosheets prepared by this method, the phase distribution is more complex, with several different-sized crystal morphologies observed even at a 20 nm scale. The nanosheets prepared by the method of the present invention are all rectangular, as shown in Figure 11, and exhibit greater stability under electron beam irradiation. The nanosheets produced by the in-situ NH₄I-assisted growth method of the present invention exhibit higher quality and larger size, demonstrating that this method effectively controls the growth kinetics.

[0139] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for in-situ preparation of CsPbI3 colloidal nanosheets assisted by NH4I, characterized in that: The following steps are involved: S1. preparing a lead iodide precursor solution, an ammonium iodide precursor solution, and a cesium oleate precursor solution respectively; S2. Mixing the lead iodide precursor solution and the ammonium iodide precursor solution, stirring, adding the cesium oleate precursor solution to react, obtaining a nanosheet stock solution, and purifying and separating the nanosheet stock solution to obtain CsPbI3 nanosheets.

2. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 1, characterized in that: In S2, the reaction temperature is 28-55° C., and the reaction time is 30-90 min.

3. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 1, characterized in that: The volume ratio of the lead iodide precursor solution, the ammonium iodide precursor solution and the cesium oleate precursor solution is 2-6:1:0.1-0.

2.

4. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 1, characterized in that: The lead iodide precursor solution, the ammonium iodide precursor solution and the cesium oleate precursor solution are used to construct a non-polar solvent reaction system, and mesitylene is used as a reaction solvent.

5. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 4, characterized in that: The ammonium iodide precursor solution includes ammonium iodide, mesitylene and a surfactant; the mass volume ratio of the ammonium iodide to mesitylene is 1.4-2.2 mg / mL, and the volume ratio of the surfactant to mesitylene is 0.01-0.02:

1.

6. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 4 or 5, characterized in that: The lead iodide precursor solution includes lead iodide, zinc iodide, mesitylene and a surfactant; the molar volume ratio of the lead iodide to mesitylene is 0.007-0.014 mmol:1 mL, the volume ratio of the surfactant to mesitylene is 0.01-0.02:1; and the molar ratio of the lead iodide to zinc iodide is 10-50:

1.

7. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 4 or 5, characterized in that: The cesium oleate precursor solution includes cesium acetate and oleic acid, and the molar volume ratio of the cesium acetate to the oleic acid is 0.08-0.12 mmol:1 mL.

8. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 1, characterized in that: In S2, the nanosheet stock solution is purified and separated. The specific process is as follows: methyl acetate is used as an anti-solvent to purify the nanosheet stock solution, centrifuged, and the precipitate is retained. It is then redispersed with hexane, centrifuged, and the supernatant is collected to obtain CsPbI3 nanosheets.

9. The method for in-situ preparation of CsPbI3 colloidal nanosheets using NH4I as an auxiliary method according to claim 8, characterized in that: The volume ratio of the methyl acetate to the nanosheet stock solution is 1.5-3:1, and the volume ratio of the hexane to the nanosheet stock solution is 1-3:

5.

10. A CsPbI3 colloidal nanosheet, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

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