A method for preparing perovskite nanosheets based on ligand-assisted reprecipitation

Abstract

This invention discloses a method for preparing perovskite nanosheets based on ligand-assisted reprecipitation. The method is as follows: 1. Obtain a cesium precursor solution. 2. Obtain a lead halide precursor solution. 3. Mix the cesium precursor solution with a mixed solution of one or more lead halide precursors obtained in step 2 and stir vigorously; then, add acetone to promote nanosheet formation. 4. Purify the product obtained in step 3 by centrifugation; the resulting solid product is halide perovskite nanosheets. This invention uses a ligand-assisted reprecipitation method to synthesize perovskite nanosheets; the reaction can be carried out at room temperature, and the operation is simple. This invention achieves the adjustment of nanosheet thickness by adjusting the ratio of cesium ions in the cesium precursor solution to lead ions in the mixed solution of lead halide precursors. In this invention, the direct synthesis of mixed halide perovskite nanosheets can be conveniently achieved by simultaneously adding a mixed solution of multiple lead halide precursors.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot technology and relates to the field of preparation technology of mixed halogen perovskite nanosheets. Specifically, it relates to a method for preparing perovskite nanosheets based on ligand-assisted reprecipitation. Background Technology

[0002] Hybrid halide perovskites can be synthesized as colloidal nanosheets (NPls), exhibiting monolayer (ML) level thickness control and strong quantum confinement effects. This allows for tunable emission across the entire visible light wavelength range by controlling the thickness of bromide or iodide-based perovskite nanoparticles. Furthermore, compared to their bulk counterparts, NPls exhibit narrow emission peaks, high exciton binding energies, and a higher proportion of radiative recombination, making them ideal candidates for light-emitting diode (LED) applications.

[0003] The inherent ionic crystal properties and high vacancy concentration of perovskite materials lead to unstable crystal structures, particularly evident in nanosheets, which are only a few atomic layers thick. While this instability poses challenges to perovskite nanosheets in electroluminescence or quantum information applications, it also opens up new avenues for their use. Nanosheets irradiated with intense continuous laser light gradually coalesce and eventually transform into a bulk phase, resulting in a change in emission wavelength. This suggests that perovskite nanosheets have the potential to become excellent photographic inks for displays, optical information recording and storage, anti-counterfeiting, and encryption.

[0004] Currently, the mainstream synthesis method for perovskite nanosheets is the hot injection method, which is only applicable to monohalogen perovskite nanosheets and the thickness of the nanosheets is difficult to adjust. In addition, there are no reports on the direct synthesis of mixed halogen perovskite nanosheets. Summary of the Invention

[0005] To address the current problem of the inability to directly synthesize mixed halide perovskite nanosheets, the main objective of this invention is to provide a direct preparation method for mixed halide perovskite nanosheets. In this method, a ligand-assisted reprecipitation method is used to prepare mixed halide perovskite nanosheets, which can achieve the direct preparation of mixed halide perovskite nanosheets with controllable nanosheet thickness and simple operation.

[0006] This invention provides a method for preparing perovskite nanosheets based on ligand-assisted reprecipitation, comprising the following steps:

[0007] Step 1: Add Cs2CO3 powder to oleic acid and stir to dissolve, thus obtaining a cesium precursor solution.

[0008] Step 2: Prepare a mixed solution of one or more lead halide precursors; The preparation process of the mixed solution of lead halide precursors is as follows: Add oleylamine, oleic acid, and the corresponding type of lead halide to toluene, stir and dissolve to obtain a lead halide precursor solution.

[0009] Step 3: Mix the cesium precursor solution with the mixed solution of one or more lead halide precursors obtained in Step 2 and stir vigorously at 900-1200 r / min for 4-10 s; then, add acetone to promote the formation of nanosheets and continue stirring for 1-3 min. The volume ratio of acetone to the mixed solution after vigorous stirring is (0.5-3):1.

[0010] Step 4: The product obtained in Step 3 is purified by centrifugation. The resulting solid product is halide perovskite nanosheets.

[0011] The prepared halide perovskite nanosheets have the chemical formula CsPbX3, where X is one or more halogens (Cl, Br, and I). When X is multiple halogens, the sum of the number of atoms of each halogen is 3. For example, when the halogens are Br and I, the chemical formula of the above CsPbX3 is CsPbI. x Br 3-x .

[0012] Preferably, in step three, the molar ratio of cesium ions in the cesium precursor solution to lead ions in the mixed solution of all lead halide precursors is (1-5):10.

[0013] Preferably, the reaction temperature in step three is 20℃~38℃.

[0014] Preferably, the thickness of the g halide perovskite nanosheets obtained in step four is 2.8 nm to 9.6 nm; the molar ratio Y of cesium ions in the cesium precursor solution and lead ions in the mixed solution of all lead halide precursors is adjusted according to the target thickness X of the perovskite nanosheets; the larger the target thickness X, the larger the molar ratio Y.

[0015] Preferably, the duration of vigorous stirring in step four is 5 to 20 seconds.

[0016] Preferably, the concentration of cesium ions in the cesium precursor solution obtained in step one is 18.1 mmol / L to 21 mmol / L. The concentration of lead ions in the lead halide precursor mixed solution obtained in step two is 9.05 mmol / L to 10.5 mmol / L.

[0017] Preferably, the stirring and dissolving process in steps one and two is as follows: stirring continuously at 900 r / min to 1200 r / min for 60 min to 90 min at 90℃ to 120℃.

[0018] Preferably, in step two, the volume ratio of oleylamine to oleic acid is 1:(0.9-1.05); the volume ratio of oleylamine to toluene is 1:(90-100).

[0019] Preferably, in step two, a mixed solution of two lead halide precursors is prepared, with the two lead halides being Br and I, respectively.

[0020] Preferably, in step four, the centrifugation speed is 3000 r / min to 6000 r / min, and the duration is 2 min to 5 min.

[0021] Preferably, in step four, the solid product obtained by centrifugation is dispersed in anhydrous n-hexane.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention uses a ligand-assisted reprecipitation method to synthesize perovskite nanosheets. The reaction can be carried out at room temperature and is simple to operate.

[0024] 2. This invention achieves the adjustment of nanosheet thickness by adjusting the ratio of cesium ions in the cesium precursor solution to lead ions in the mixed solution of lead halide precursor.

[0025] 3. In this invention, the direct synthesis of mixed halide perovskite nanosheets can be conveniently achieved by simultaneously adding a mixed solution of multiple lead halide precursors. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the reaction apparatus used in Embodiment 1 of the present invention.

[0027] Figure 2 The fluorescence and absorption spectra of the mixed halide perovskite nanosheets prepared in Example 1 of this invention are shown.

[0028] Figure 3 This is a transmission electron microscope image of the mixed halide perovskite nanosheets prepared in Example 1 of the present invention.

[0029] Figure 4 The image shows the EDS spectrum of the mixed halide perovskite nanosheets prepared in Example 1 of this invention.

[0030] Figure 5 The fluorescence and absorption spectra of the mixed halide perovskite nanosheets prepared in Example 2 of this invention are shown.

[0031] Figure 6 This is a transmission electron microscope image of the mixed halide perovskite nanosheets prepared in Example 2 of the present invention.

[0032] Figure 7The image shows the EDS spectrum of the mixed halide perovskite nanosheets prepared in Example 2 of this invention.

[0033] Figure 8 The fluorescence and absorption spectra of the mixed halide perovskite nanosheets prepared in Example 3 of this invention are shown.

[0034] Figure 9 This is a transmission electron microscope image of the mixed halide perovskite nanosheets prepared in Example 3 of the present invention.

[0035] Figure 10 The image shows the EDS spectrum of the mixed halide perovskite nanosheets prepared in Example 3 of this invention.

[0036] Figure labels: 1. Pipette; 2. Sampling bottle; 3. Rotor; 4. Magnetic stirrer. Detailed Implementation

[0037] To facilitate understanding of the technical means, creative features, objectives, and effects of this invention, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the scope of protection of this invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0038] As analyzed in the background section of this invention, existing preparation methods mostly employ the hot-injection method to synthesize CsPbX3 perovskite nanosheets. However, this method is cumbersome, cannot easily control the thickness of the nanosheets, and cannot synthesize perovskite nanosheets containing mixed halogens. Therefore, this invention employs a ligand-assisted reprecipitation method to synthesize perovskite nanosheets. In this invention, the chemical formula of the all-inorganic perovskite quantum dots is CsPbX3, where X is one or more halogens (Cl, Br, and I). When X is multiple halogens, the sum of the number of atoms of each halogen is 3. For example, when the halogens are Br and I, the chemical formula of the above CsPbX3 is CsPbI. x Br 3-x .

[0039] To further understand the present invention, the following embodiments illustrate the method for preparing perovskite nanosheets based on ligand-assisted reprecipitation provided by the present invention. The scope of protection of the present invention is not limited by the following embodiments.

[0040] Example 1

[0041] A method for preparing perovskite nanosheets based on ligand-assisted reprecipitation includes the following steps:

[0042] (1) Preparation of cesium precursor: 0.0326 g of Cs2CO3 powder was added to 10 mL of oleic acid and stirred continuously at 100 °C until dissolved to obtain cesium precursor solution.

[0043] (2) Preparation of lead bromide precursor: 0.0368 g of PbBr2, 100 μL of oleylamine and 100 μL of oleic acid were added to 10 mL of toluene and stirred continuously at 100 °C until dissolved to obtain a mixed solution of PbBr2 precursor.

[0044] (3) Preparation of lead iodide precursor: 0.0462 g of PbI2, 100 μL of oleylamine and 100 μL of oleic acid were added to 10 mL of toluene and stirred continuously at 100 °C until dissolved to obtain a mixed solution of PbI2 precursor.

[0045] (4) Constructing the reaction apparatus; such as Figure 1 As shown, the reaction apparatus includes a pipette 1, a sampling bottle 2, a rotor 3, and a magnetic stirrer 4. The rotor 3 is placed in the sampling bottle 2, and the magnetic stirrer 4 drives the rotor 3 to rotate, achieving magnetic stirring. At room temperature, the rotor is first placed in the sampling bottle, and 3 mL of a PbBr2 precursor mixture and 3 mL of a PbI2 precursor mixture are added to the sampling bottle using a pipette; then, 300 μL of a cesium precursor solution is added to the sampling bottle using a pipette; after vigorous stirring with the magnetic stirrer for 5 seconds, 4 mL of acetone is added to the sampling bottle to promote nanosheet formation, and magnetic stirring continues for 1 minute; the acetone acts as a poor solvent, rapidly reducing the solubility of the nanocrystals in the solution, promoting their rapid precipitation and nanosheet formation.

[0046] (5) Centrifuge the reaction product at 4000 rpm / min for 3 minutes, and disperse the obtained solid product in 4 mL of anhydrous n-hexane to obtain perovskite nanosheets.

[0047] The fluorescence and absorption spectra of the mixed halide perovskite nanosheets prepared in this embodiment are shown in [reference needed]. Figure 2 The transmission electron microscope image of the mixed halide perovskite nanosheets prepared in this embodiment is shown in [reference]. Figure 3 The EDS spectrum of the mixed halide perovskite nanosheets prepared in this embodiment is shown in [reference]. Figure 4 . Figure 2 The results show that, in terms of optical properties, the four-layer CsPbBr2.7I0.3 nanosheets exhibit a distinct exciton absorption peak at 475 nm, with a clear characteristic, and a fluorescence emission peak at 495 nm, indicating a good quantum confinement effect and exciton binding energy. This property has potential application value in optoelectronic devices such as solar cells and photodetectors. Figure 3The nanosheets were shown to have a regular rectangular shape and consistent size, with a thickness of approximately 2.8 nm, indicating a highly controlled synthesis process. Figure 4 Energy-dispersive X-ray spectroscopy (EDS) analysis further confirmed the elemental composition of the nanosheets, showing that the ratio of bromine to iodine was close to 1:9, thus confirming that we synthesized CsPbBr2.7I0.3 nanosheets with mixed halogens.

[0048] Example 2

[0049] A method for preparing perovskite nanosheets based on ligand-assisted reprecipitation. The difference between this embodiment and Example 1 is that in step (4) of this embodiment, the injection volume of PbBr2 precursor mixed solution and PbI2 precursor mixed solution is 1.2 mL, and the rest of the preparation process and parameters are consistent with those of Example 1.

[0050] The fluorescence and absorption spectra of the perovskite quantum dots prepared in this embodiment are shown in [reference]. Figure 5 The transmission electron microscope image of the perovskite quantum dots prepared in this embodiment is shown in the figure. Figure 6 The EDS spectrum of the mixed halide perovskite nanosheets prepared in this embodiment is shown in [reference]. Figure 7 . Figure 5 The results show that, in terms of optical properties, the 8-layer CsPbBr2.7I0.3 nanosheets exhibit a distinct exciton absorption peak with a clear feature at 487 nm, and a fluorescence emission peak at 516 nm, indicating a good quantum confinement effect and exciton binding energy. Figure 6 TEM images of 8-layer CsPbBr2.7I0.3 nanosheets are shown, indicating that the nanosheets have a regular rectangular shape and uniform size, with a thickness of approximately 4.8 nm. Figure 7 We found that the ratio of bromine to iodine remained stable even with increased thickness, which demonstrates the reproducibility and reliability of the synthesis method in terms of elemental composition control.

[0051] Example 3

[0052] A method for preparing perovskite nanosheets based on ligand-assisted reprecipitation. The difference between this embodiment and Example 1 is that in step (4) of this embodiment, the injection volume of the PbBr2 precursor mixed solution and the PbI2 precursor mixed solution is 1 mL, the injection volume of the cesium precursor solution is 500 μl, and the injection volume of acetone is 5 mL. The rest of the preparation process and parameters are the same as those in Example 1.

[0053] The fluorescence and absorption spectra of the perovskite quantum dots prepared in this embodiment are shown in [reference]. Figure 8 The transmission electron microscope image of the perovskite quantum dots prepared in this embodiment is shown in the figure. Figure 9The EDS spectrum of the mixed halide perovskite nanosheets prepared in this embodiment is shown in [reference]. Figure 10 .Depend on Figure 8 It can be seen that the fluorescence peaks and absorption band edges of these thicker nanosheets are located at 558 nm and 539 nm, respectively. Figure 9 The synthesized CsPbBr2.7I0.3 nanosheets have an average size of 9.6 nm, and TEM images show their geometric features and crystal quality. Figure 10 EDS analysis validated the elemental composition, further confirming the high purity and compositional consistency of the synthesized nanosheets.

[0054] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects:

[0055] The quantum dots synthesized by the method of this invention have similar characteristics to perovskite nanosheets synthesized by the existing thermal injection method.

[0056] This invention employs a ligand-assisted reprecipitation method to achieve the synthesis of mixed halide perovskite nanosheets at room temperature; the thickness of the nanosheets is controlled by adjusting the ratio of cesium ions to lead ions.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing perovskite nanosheets based on ligand-assisted re-precipitation, characterized by: Includes the following steps: Step 1: Add Cs2CO3 powder to oleic acid and stir to dissolve, thus obtaining a cesium precursor solution; Step 2: Prepare a mixed solution of two lead halide precursors; The preparation process of the mixed solution of lead halide precursors is as follows: Add oleylamine, oleic acid, and the corresponding type of lead halide to toluene, stir and dissolve to obtain a lead halide precursor solution; The two lead halides corresponding to the mixed solution of the two lead halide precursors are Br and I, respectively; Step 3: Mix the cesium precursor solution with the mixed solution of the two lead halide precursors obtained in Step 2 and stir vigorously at 900-1200 r / min for 4-10 seconds; then add acetone and continue stirring for 1-3 minutes; the volume ratio of acetone to the mixed solution after vigorous stirring is (0.5-3):1; the molar ratio of cesium ions in the cesium precursor solution to lead ions in all the mixed lead halide precursor solutions is (1-5):10; adjust the molar ratio Y of cesium ions in the cesium precursor solution to lead ions in all the mixed lead halide precursor solutions according to the target thickness X of the perovskite nanosheets between 2.8 nm and 9.6 nm; the larger the target thickness X, the larger the molar ratio Y. Step 4: Centrifuge the product obtained in Step 3 to obtain a solid product of perovskite nanosheets.

2. The method according to claim 1, wherein the method is characterized by: The reaction temperature in step three is 20 ℃~38 ℃.

3. The method according to claim 1, wherein the method is characterized by: The concentration of cesium ions in the cesium precursor solution obtained in step one is 18.1 mmol / L to 21 mmol / L; the concentration of lead ions in the lead halide precursor mixed solution obtained in step two is 9.05 mmol / L to 10.5 mmol / L.

4. The method for preparing perovskite nanosheets based on ligand-assisted reprecipitation according to claim 1, characterized in that: The stirring and dissolving process in steps one and two is as follows: stirring continuously at 90 ℃~120 ℃ and a speed of 900 r / min~1200 r / min for 60 min~90 min.

5. The method for preparing perovskite nanosheets based on ligand-assisted reprecipitation according to claim 1, characterized in that: In step two, the volume ratio of oleylamine to oleic acid is 1:(0.9~1.05); the volume ratio of oleylamine to toluene is 1:(90~100).

6. The method for preparing perovskite nanosheets based on ligand-assisted reprecipitation according to claim 1, characterized in that: In step four, the centrifugation speed is 3000 r / min to 6000 r / min, and the time is 2 min to 5 min; the solid product obtained by centrifugation is dispersed in anhydrous n-hexane.

Images