An orderly oriented perovskite nanosheet film, a preparation method thereof and a solar cell device

Abstract

This invention discloses an ordered perovskite nanosheet thin film, its preparation method, and a solar cell device. The method includes: first, adding cesium carbonate and oleic acid to a three-necked flask, evacuating the gas, and heating to obtain a cesium oleate precursor solution; then, purging with nitrogen and maintaining the temperature; next, adding lead iodide and octadecene sequentially to the three-necked flask, evacuating the gas, heating, purging with nitrogen, injecting oleic acid and oleylamine, reacting to form a lead iodide precursor solution, injecting it into the lead iodide precursor solution, reacting, quenching, and obtaining a crude perovskite nanosheet solution; purifying and dispersing the crude solution in a nonpolar solvent to obtain a perovskite nanosheet dispersion; dropping the dispersion onto the surface of deionized water, where it self-assembles into a thin film at the gas-liquid interface; then, immersing a substrate perpendicular to the liquid surface into deionized water and pulling it up to transfer the film to the substrate surface, obtaining an ordered perovskite nanosheet thin film. This invention effectively reduces carrier transport resistance and nonradiative recombination, improving the photoelectric performance of the perovskite nanosheet thin film.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic materials technology, specifically an ordered oriented perovskite nanosheet thin film, its preparation method, and a solar cell device. Background Technology

[0002] Halide perovskites possess core optoelectronic advantages such as high defect tolerance, long carrier diffusion length, and high light absorption coefficient. They also have the advantages of low preparation cost and good solution processability, showing great application potential in optoelectronic devices such as solar cells, light-emitting diodes, and photodetectors.

[0003] As a typical representative of low-dimensional perovskite materials, halide perovskite nanosheets inherit the excellent intrinsic optoelectronic properties of halide perovskites. Their unique two-dimensional layered structure endows the material with many outstanding characteristics. The two-dimensional confined structure gives it a larger exciton binding energy and high oscillator strength, which greatly enhances the material's light absorption capacity and optical gain. Compared with traditional three-dimensional perovskite materials or perovskite quantum dots, it has a larger absorption cross section and significant optical nonlinearity. At the same time, halide perovskite nanosheets perform excellently in breaking the exciton migration limit. The long-distance charge carrier transport behavior provides favorable conditions for efficient charge transport, providing new possibilities for breaking through the performance bottleneck of perovskite optoelectronic devices.

[0004] Existing methods for preparing halide perovskite nanosheet films mainly include spin coating and blade coating. Although these traditional solution processing methods are simple to operate and suitable for industrial preparation needs, the random dispersion of perovskite nanosheets in the dispersion makes it difficult to precisely control the stacking and orientation behavior of nanosheets during film formation. This results in the common problem of disordered nanosheet orientation in the prepared halide perovskite nanosheet films, which makes it difficult to fully utilize the strong anisotropy advantages conferred by the two-dimensional confined structure of halide perovskite nanosheets. This leads to the obstruction of carrier transport and the aggravation of nonradiative recombination in the device, which seriously restricts the practical application of perovskite nanosheet films in high-performance optoelectronic devices. Summary of the Invention

[0005] The purpose of this invention is to provide an ordered perovskite nanosheet thin film, its preparation method, and a solar cell device, which can precisely control the ordered arrangement and orientation structure of the perovskite nanosheets, thereby effectively reducing carrier transport resistance and non-radiative recombination, and improving the photoelectric performance of the perovskite nanosheet thin film.

[0006] This invention is achieved through the following technical solution: A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.31~0.46 mmol of cesium carbonate and 12.8~15.84 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 80~120℃, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm; Step 2: Add 1.5-3 mmol lead iodide and 84.6-125 mmol octadecene sequentially to a three-necked flask. First, evacuate the gas, then stir and heat to 100-120°C and react for 1 h. Next, purge the three-necked flask with nitrogen gas, then inject 4-8 mL oleic acid and 4-6 mL oleylamine. React for 20 min to form a transparent lead iodide precursor solution. Cool to 70-90°C and maintain the temperature. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 2-3 min, transfer to an ice-water bath for quenching, and cool to 25-30℃ to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution to obtain pure perovskite nanosheets, and disperse them in a non-polar solvent to obtain a perovskite nanosheet dispersion with a concentration of 10~50 mg / mL. Step 5: Pour deionized water into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand to allow the non-polar solvent to evaporate and the perovskite nanosheets to float in the atmosphere. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 3-5 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 50-200 nm.

[0007] Furthermore, the specific process of step 4 is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 8000~10000 rpm for 5 min to separate the precipitate. Disperse the precipitate in toluene, then add ethyl acetate at twice the volume of toluene, centrifuge at 7000~9000 rpm for 5 min to separate the precipitate, and disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 2000-4000 rpm for 5 min, collect the supernatant and store it at 4℃ for 24 h, then centrifuge it at 2000-4000 rpm for 5 min, collect the supernatant and filter it with a polytetrafluoroethylene filter, and then vacuum dry it to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in a non-polar solvent to obtain a perovskite nanosheet dispersion with a concentration of 10~50 mg / mL. Furthermore, the nonpolar solvent is n-hexane, toluene, or n-octane.

[0008] Furthermore, the temperature of the deionized water in step 5 is 4~20℃.

[0009] Furthermore, the settling time in step 5 is 10~60 s.

[0010] An ordered perovskite nanosheet thin film with a polarization degree of 0.06~0.41 and an orientation degree of 74%~94%.

[0011] A solar cell device comprising an ordered-oriented perovskite nanosheet thin film as described in claim 6.

[0012] A solar cell device is prepared by the following method: Step 1: Deposit a SnO2 layer onto the FTO conductive glass substrate as an electron transport layer; Step 2: Pour deionized water into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand. The perovskite nanosheets will then... The liquid interface self-assembles into a thin film. The FTO conductive glass substrate is immersed vertically into deionized water, and then pulled out of the FTO conductive glass substrate. The thin film is transferred to the substrate surface. The immersion and pulling are repeated several times to deposit an ordered oriented perovskite nanosheet thin film of the required thickness on the surface of the FTO conductive glass substrate. Step 3: Deposit carbon electrodes on the surface of perovskite nanosheet films to finally obtain solar cell devices.

[0013] Further, the specific process of step 1 is as follows: a SnO2 aqueous solution with a mass fraction of 2%~2.5% is dropped onto the surface of an FTO conductive glass substrate, and a film is formed by spin coating at a speed of 3000~4000 rpm. The film is then annealed at 150°C to form a SnO2 layer.

[0014] The present invention has the following beneficial technical effects: 1) This invention adopts the Langmuir-Schaefer gas-liquid interface self-assembly strategy, which induces the long-range ordered and highly vertical self-assembly of perovskite nanosheets at the gas-liquid interface through solvent evaporation, thereby effectively reducing carrier transport resistance and non-radiative recombination, and improving the photoelectric properties of perovskite nanosheet films. In this process, the ordered arrangement and orientation structure of perovskite nanosheets can be precisely controlled by selecting non-polar solvents with different evaporation rates, thereby improving the applicability of the film.

[0015] 2) This invention enables efficient transfer of thin films from the liquid surface to the substrate, and obtains perovskite nanosheet thin films with nanosheets perpendicular to the substrate, arranged in a long-range ordered manner, uniform, dense and highly polarized, which can significantly improve charge transport efficiency and has broad application prospects in the field of optoelectronic devices.

[0016] 3) The photoelectric conversion efficiency of the carbon-based perovskite nanosheet solar cell device prepared by the present invention based on ordered orientation perovskite nanosheet thin film can reach 5.39%. Attached Figure Description

[0017] Figure 1 This is a transmission electron microscope (TEM) image of the perovskite nanosheet thin film prepared in Example 1 of the present invention; Figure 2 The ultraviolet-visible absorption spectrum and photoluminescence fluorescence spectrum of the perovskite nanosheet film prepared in Example 1 of this invention; Figure 3 These are physical images of perovskite nanosheet films spread on different nonpolar solvent surfaces in Examples 1 to 3 of the present invention. Figure 4 These are transmission electron microscope (TEM) images of the perovskite nanosheet films prepared in Examples 1 to 3 of this invention. Figure 5 This is a bar chart showing the orientation degree of the perovskite nanosheets with their edges facing upwards in the perovskite nanosheet films prepared in Examples 1 to 3 of this invention; Figure 6 This is a schematic diagram of the self-assembly mechanism of the perovskite nanosheet thin film of the present invention; Figure 7 This is a schematic diagram showing the polarization degree of the perovskite nanosheet films prepared in Examples 1 to 3 of the present invention; Figure 8 The current density-voltage (JV) curves of the solar cell devices prepared in Application Examples 1 to 3 of this invention are shown. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0019] In the process of preparing solar cell devices in Application Examples 1 to 3 of this invention, the carbon paste used was purchased from Shanghai Maituowei Chemical New Material Technology Co., Ltd., named low-temperature carbon paste, with the product number MTW-CE-C-003.

[0020] Example 1 A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.31 mmol of cesium carbonate and 15.84 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 120°C, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm. Step 2: Add 1.5 mmol lead iodide and 125 mmol octadecene to a three-necked flask in sequence. First, evacuate the air, then stir and heat to 120°C. React for 1 h. Next, purge the three-necked flask with nitrogen gas, then inject 4 mL of oleic acid and 4 mL of oleylamine. React for 20 min to form a transparent lead iodide precursor solution. Cool down to 90°C and keep warm. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 2 min, transfer to an ice-water bath for quenching, and cool to 25℃ to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution and prepare a perovskite nanosheet dispersion. The specific process is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 8000 rpm for 5 min to separate the precipitate. Disperse the precipitate in 12 mL of toluene. Add ethyl acetate to the toluene containing the precipitate at a volume ratio of 2:1 (toluene to ethyl acetate). Centrifuge at 7000 rpm for 5 min to separate the precipitate. Disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 2000 rpm for 5 min to remove large particle impurities. Take the supernatant and store it at 4℃ for 24 h. Centrifuge it again at 2000 rpm for 5 min, take the supernatant and filter it with a polytetrafluoroethylene filter. Then vacuum dry it to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in n-hexane to obtain a perovskite nanosheet dispersion with a concentration of 30 mg / mL. Step 5: Pour deionized water at 4°C into the petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand for 10 seconds to allow the hexane to evaporate and the perovskite nanosheets to dissolve in the gas. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 4 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 120 nm.

[0021] Example 2 A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.31 mmol of cesium carbonate and 15.84 mmol of oleic acid to a three-necked flask, first evacuate the gas, then stir and heat to 110°C, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm. Step 2: Add 1.5 mmol lead iodide and 125 mmol octadecene to a three-necked flask in sequence. First, evacuate the air, then stir and heat to 110°C and react for 1 h. Next, introduce nitrogen gas into the three-necked flask, then inject 5 mL oleic acid and 5 mL oleylamine and react for 20 min to form a transparent lead iodide precursor solution. Cool down to 80°C and keep warm. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 3 min, transfer to an ice-water bath for quenching, and cool to 26℃ to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution and prepare a perovskite nanosheet dispersion. The specific process is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 9000 rpm for 5 min to separate the precipitate. Disperse the precipitate in 12 mL of toluene. Add ethyl acetate to the toluene containing the precipitate at a volume ratio of 2:1 (toluene to ethyl acetate). Centrifuge at 8000 rpm for 5 min to separate the precipitate. Disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 3000 rpm for 5 min to remove large particle impurities. Take the supernatant and store it at 4℃ for 24 h. Centrifuge it again at 3000 rpm for 5 min, take the supernatant and filter it with a polytetrafluoroethylene filter. Then vacuum dry to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in toluene to obtain a perovskite nanosheet dispersion with a concentration of 20 mg / mL. Step 5: Pour deionized water at 8°C into the petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand for 30 seconds to allow the toluene to evaporate and the perovskite nanosheets to dissolve in the atmosphere. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 4 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 100 nm.

[0022] Example 3 A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.31 mmol of cesium carbonate and 15.84 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 100°C, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm. Step 2: Add 1.5 mmol lead iodide and 125 mmol octadecene to a three-necked flask in sequence. First, evacuate the air, then stir and heat to 100°C. React for 1 h. Next, purge the three-necked flask with nitrogen gas, then inject 6 mL of oleic acid and 6 mL of oleylamine. React for 20 min to form a transparent lead iodide precursor solution. Cool down to 70°C and keep warm. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 2.5 min, transfer to an ice-water bath for quenching, and cool to 27°C to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution and prepare a perovskite nanosheet dispersion. The specific process is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 10,000 rpm for 5 min to separate the precipitate. Disperse the precipitate in 12 mL of toluene. Add ethyl acetate to the toluene containing the precipitate at a volume ratio of 2:1 (toluene to ethyl acetate). Centrifuge at 9,000 rpm for 5 min to separate the precipitate. Disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 4000 rpm for 5 min to remove large particle impurities. Take the supernatant and store it at 4℃ for 24 h. Centrifuge it again at 4000 rpm for 5 min, take the supernatant and filter it with a polytetrafluoroethylene filter. Then vacuum dry it to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in n-octane to obtain a perovskite nanosheet dispersion with a concentration of 30 mg / mL. Step 5: Pour deionized water at 12℃ into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand for 60 seconds to allow the n-octane to evaporate and the perovskite nanosheets to dissolve in the gas. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 4 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 120 nm.

[0023] Example 4 A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.31 mmol of cesium carbonate and 12.8 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 90°C, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm. Step 2: Add 1.5 mmol lead iodide and 84.6 mmol octadecene to a three-necked flask in sequence. First, evacuate the air, then stir and heat to 90°C. React for 1 h. Next, purge the three-necked flask with nitrogen gas, then inject 7 mL oleic acid and 4 mL oleylamine. React for 20 min to form a transparent lead iodide precursor solution. Cool down to 75°C and keep warm. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 2.5 min, transfer to an ice-water bath for quenching, and cool to 28℃ to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution and prepare a perovskite nanosheet dispersion. The specific process is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 8500 rpm for 5 min to separate the precipitate. Disperse the precipitate in 12 mL of toluene. Add ethyl acetate to the toluene containing the precipitate at a volume ratio of 2:1 (toluene to ethyl acetate). Centrifuge at 7500 rpm for 5 min to separate the precipitate. Disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 2500 rpm for 5 min to remove large particle impurities. Take the supernatant and store it at 4℃ for 24 h. Centrifuge it again at 2500 rpm for 5 min, take the supernatant and filter it with a polytetrafluoroethylene filter. Then vacuum dry it to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in n-octane to obtain a perovskite nanosheet dispersion with a concentration of 40 mg / mL. Step 5: Pour deionized water at 15℃ into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand for 60 seconds to allow the n-octane to evaporate and the perovskite nanosheets to dissolve in the gas. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 3 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 150 nm.

[0024] Example 5 A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.38 mmol of cesium carbonate and 14.32 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 80°C, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm. Step 2: Add 2 mmol lead iodide and 105 mmol octadecene to a three-necked flask in sequence. First, evacuate the air, then stir and heat to 80°C and react for 1 h. Next, introduce nitrogen gas into the three-necked flask, then inject 8 mL oleic acid and 5 mL oleylamine and react for 20 min to form a transparent lead iodide precursor solution. Cool down to 85°C and keep warm. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 3 min, transfer to an ice-water bath for quenching, and cool to 29℃ to obtain crude perovskite nanosheet solution. Step 4: Purify the crude perovskite nanosheet solution and prepare a perovskite nanosheet dispersion. The specific process is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 9500 rpm for 5 min to separate the precipitate. Disperse the precipitate in 12 mL of toluene. Add ethyl acetate to the toluene containing the precipitate at a volume ratio of 2:1 (toluene to ethyl acetate). Centrifuge at 8500 rpm for 5 min to separate the precipitate. Disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 3500 rpm for 5 min to remove large particle impurities. Take the supernatant and store it at 4℃ for 24 h. Centrifuge it again at 3500 rpm for 5 min, take the supernatant and filter it with a polytetrafluoroethylene filter. Then vacuum dry to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in n-octane to obtain a perovskite nanosheet dispersion with a concentration of 50 mg / mL. Step 5: Pour deionized water at 18℃ into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand for 60 seconds to allow the n-octane to evaporate and the perovskite nanosheets to dissolve in the gas. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 5 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 200 nm.

[0025] Example 6 A method for preparing an ordered oriented perovskite nanosheet thin film includes the following steps: Step 1: Add 0.46 mmol of cesium carbonate and 15.84 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 100°C, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm. Step 2: Add 3 mmol lead iodide and 125 mmol octadecene to a three-necked flask in sequence. First, evacuate the air, then stir and heat to 100°C and react for 1 h. Next, introduce nitrogen gas into the three-necked flask, then inject 6 mL oleic acid and 5 mL oleylamine and react for 20 min to form a transparent lead iodide precursor solution. Cool down to 70°C and keep warm. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 2 min, transfer to an ice-water bath for quenching, and cool to 30℃ to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution and prepare a perovskite nanosheet dispersion. The specific process is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 10,000 rpm for 5 min to separate the precipitate. Disperse the precipitate in 12 mL of toluene. Add ethyl acetate to the toluene containing the precipitate at a volume ratio of 2:1 (toluene to ethyl acetate). Centrifuge at 8,000 rpm for 5 min to separate the precipitate. Disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 4000 rpm for 5 min to remove large particle impurities. Take the supernatant and store it at 4℃ for 24 h. Centrifuge it again at 4000 rpm for 5 min, take the supernatant and filter it with a polytetrafluoroethylene filter. Then vacuum dry it to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in n-octane to obtain a perovskite nanosheet dispersion with a concentration of 10 mg / mL. Step 5: Pour deionized water at 20℃ into the petri dish. After the liquid surface is calm, add the perovskite nanosheet dispersion dropwise to the surface and let it stand for 60 seconds to allow the n-octane to evaporate and the perovskite nanosheets to dissolve in the gas. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process 3 times to obtain an ordered oriented perovskite nanosheet film with a thickness of 50 nm.

[0026] Application Example 1 A method for fabricating a solar cell device includes the following steps: Step 1: A 2% SnO2 aqueous solution is dropped onto the surface of an FTO conductive glass substrate and spin-coated at 3000 rpm to form a film. The film is then annealed at 150°C to form a SnO2 layer, which serves as an electron transport layer. Step 2: First, prepare the perovskite nanosheet dispersion according to steps 1-4 in Example 1. Then, pour deionized water at 10°C into a petri dish. After the liquid surface is calm, drop the perovskite nanosheet dispersion onto the liquid surface and let it stand for 10 seconds to allow the perovskite nanosheets to float in the atmosphere. The liquid interface self-assembles into a thin film. The FTO conductive glass substrate is immersed vertically into deionized water, and then the FTO conductive glass substrate is pulled out. The film is transferred to the substrate surface. The immersion and pulling are repeated 4 times to deposit an ordered oriented perovskite nanosheet film with a thickness of 120 nm on the surface of the electron transport layer, which is used as the light absorption layer. Step 3: Carbon paste is deposited on the surface of perovskite nanosheet film using screen printing process to form carbon electrode, and finally solar cell device is obtained.

[0027] Application Example 2 A method for fabricating a solar cell device includes the following steps: Step 1: A 2.25% SnO2 aqueous solution is dropped onto the surface of an FTO conductive glass substrate and spin-coated at 4000 rpm to form a film. The film is then annealed at 150°C to form a SnO2 layer, which serves as an electron transport layer. Step 2: First, prepare the perovskite nanosheet dispersion according to steps 1-4 in Example 2. Then, pour deionized water at 10°C into a petri dish. After the liquid surface is calm, drop the perovskite nanosheet dispersion onto the liquid surface and let it stand for 30 seconds to allow the perovskite nanosheets to float in the atmosphere. The liquid interface self-assembles into a thin film. The FTO conductive glass substrate is immersed vertically into deionized water, and then the FTO conductive glass substrate is pulled out. The film is transferred to the substrate surface. The immersion and pulling are repeated 4 times to deposit an ordered oriented perovskite nanosheet film with a thickness of 100 nm on the surface of the electron transport layer, which is used as the light absorption layer. Step 3: Carbon paste is deposited on the surface of perovskite nanosheet film using screen printing process to form carbon electrode, and finally solar cell device is obtained.

[0028] Application Example 3 A method for fabricating a solar cell device includes the following steps: Step 1: A 2.5% SnO2 aqueous solution is dropped onto the surface of an FTO conductive glass substrate and spin-coated at 2000 rpm to form a film. The film is then annealed at 150°C to form a SnO2 layer, which serves as an electron transport layer. Step 2: First, prepare the perovskite nanosheet dispersion according to steps 1-4 in Example 3. Then, pour deionized water at 4-20°C into a petri dish. After the liquid surface is calm, drop the perovskite nanosheet dispersion onto the liquid surface and let it stand for 60 seconds to allow the perovskite nanosheets to float in the atmosphere. The liquid interface self-assembles into a thin film. The FTO conductive glass substrate is immersed vertically into deionized water, and then the FTO conductive glass substrate is pulled out. The film is transferred to the substrate surface. The immersion and pulling are repeated 4 times to deposit an ordered oriented perovskite nanosheet film with a thickness of 120 nm on the surface of the electron transport layer, which is used as the light absorption layer. Step 3: Carbon paste is deposited on the surface of perovskite nanosheet film using screen printing process to form carbon electrode, and finally solar cell device is obtained.

[0029] Figure 1 Transmission electron microscopy (TEM) images of the perovskite nanosheet film prepared in Example 1 are shown. It can be seen that the perovskite nanosheet film has a lateral dimension of 13.68 nm and a thickness of 5.58 nm, and the nanosheets are arranged in an orderly manner with the formed edges facing upwards.

[0030] Figure 2 The UV-Vis absorption spectrum and photoluminescence fluorescence spectrum of the perovskite nanosheet film prepared in Example 1 are shown. It can be seen that the PL peak of the perovskite nanosheet film is located at 619 nm, and the exciton absorption peak at 600 nm indicates that it has a sheet-like morphology.

[0031] Figure 3 The images show physical images of perovskite nanosheet films spread on the liquid surface of different non-polar solvents in Examples 1 to 3. It can be seen that the spread effect of perovskite nanosheet films is the best when the non-polar solvent is n-hexane.

[0032] Figure 4 Transmission electron microscopy (TEM) images of the perovskite nanosheet films prepared in Examples 1-3 are shown. It can be seen that the nanosheet orientation structure of the perovskite nanosheet films is different when the nonpolar solvent is different. This is attributed to the regulatory effect of the evaporation rate of the nonpolar solvent on the orientation of the perovskite nanosheets. Specifically, the evaporation rate of n-octane is relatively slow, and the nanosheets have a mixed configuration of face-down and edge-up. The evaporation rate of n-hexane is relatively fast, and the nanosheets change from face-down arrangement to edge-up arrangement to the highest degree, forming a highly ordered edge-up configuration.

[0033] Figure 5The orientation degree of the perovskite nanosheet films prepared in Examples 1 to 3 with the nanosheets facing upward is shown. It can be seen that the orientation degree of the perovskite nanosheet films prepared in Example 1 with the nanosheets facing upward reaches 94%, while the orientation degree of the perovskite nanosheet films prepared in Examples 2 and 3 with the nanosheets facing upward reaches 91% and 74%, respectively.

[0034] Figure 6 The diagram illustrates the self-assembly mechanism of the perovskite nanosheet films prepared in Examples 1-3. It can be seen that after the perovskite nanosheet dispersion is spread on the water surface, as the non-polar solvent gradually evaporates, the nanosheets undergo an orientation change from face-down to edge-up. During the continuous evaporation of the non-polar solvent, capillary forces are generated between the layers, and the spacing between the nanosheets continuously decreases, eventually achieving a tight and orderly assembly. The evaporation rate of the non-polar solvent directly affects the degree to which the nanosheets change from face-down to edge-up.

[0035] Figure 7 The polarization degrees of the perovskite nanosheet films prepared in Examples 1 to 3 are shown. It can be seen that when the nonpolar solvents are n-hexane, toluene, and n-octane, the polarization degrees of the films are 0.41, 0.16, and 0.06, respectively.

[0036] Figure 8 The solar cell devices fabricated in Application Examples 1-3 are shown in AM 1.5 G, 100 mW / cm². 2 The current density-voltage (JV) curves under standard test conditions show that, in Application Example 1, using n-hexane as the solvent, the solar cell device exhibits the best performance, with the open-circuit voltage (VV) being optimal. OC The voltage is 0.98 V, and the short-circuit current density (J) is 0.98 V. SC The value was 11.87 mA / cm. 2 The fill factor (FF) is 46.42%, and the power conversion efficiency (PCE) reaches 5.39%. In Application Example 2, when toluene is used as the solvent, the V of the solar cell device... OC It is 0.94 V, J SC 11.04 mA / cm 2 The FF was 43.33% and the PCE was 4.49%; in Application Example 3, when n-octane was used as the solvent, the solar cell device had the lowest performance, V OC It is 0.92 V, J SC It is 9.77 mA / cm 2 The FF was 42.16%, and the PCE was only 3.78%. This is mainly attributed to the rapid volatilization of n-hexane, which caused the nanosheets to exhibit more edge-up preferred arrangement, forming a more direct vertical carrier transport channel, effectively reducing carrier transport loss, and thus achieving more efficient carrier extraction and transfer.

[0037] Table 1 shows the physical properties of the nonpolar solvents n-hexane, toluene, and n-octane. It can be seen that n-hexane has the highest evaporation rate, followed by toluene, and then n-octane. This is why the perovskite nanosheet film prepared in Example 1 exhibits the highest orientation with the nanosheet edges facing upwards.

[0038] Table 1 Physical properties of n-hexane, toluene, and n-octane Table 2 shows the photovoltaic parameters of the solar cell devices fabricated in Application Examples 1 to 3. It can be seen that the solar cell device fabricated in Application Example 1 has the best performance, with a short-circuit current density of 11.87 mA / cm². 2 The open-circuit voltage is 0.98 V, the fill factor is 46.42%, and the photoelectric conversion efficiency is 5.39%.

[0039] Table 2. Photovoltaic parameters of the solar cell devices fabricated in Application Examples 1-3

Claims

1. A method for preparing an ordered oriented perovskite nanosheet thin film, characterized in that, Includes the following steps: Step 1: Add 0.31~0.46 mmol of cesium carbonate and 12.8~15.84 mmol of oleic acid to a three-necked flask, first evacuate the air, then stir and heat to 80~120℃, react for 1 h to obtain a cesium oleate precursor solution, then purge the three-necked flask with nitrogen and keep it warm; Step 2: Add 1.5-3 mmol lead iodide and 84.6-125 mmol octadecene sequentially to a three-necked flask. First, evacuate the gas, then stir and heat to 100-120°C and react for 1 h. Next, purge the three-necked flask with nitrogen gas, then inject 4-8 mL oleic acid and 4-6 mL oleylamine. React for 20 min to form a transparent lead iodide precursor solution. Cool to 70-90°C and maintain the temperature. Step 3: Inject the cesium oleate precursor solution into the lead iodide precursor solution, react for 2-3 min, transfer to an ice-water bath for quenching, and cool to 25-30℃ to obtain a crude solution of perovskite nanosheets. Step 4: Purify the crude perovskite nanosheet solution to obtain pure perovskite nanosheets, and disperse them in a non-polar solvent to obtain a perovskite nanosheet dispersion with a concentration of 10~50 mg / mL. Step 5: Pour deionized water into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand to allow the non-polar solvent to evaporate and the perovskite nanosheets to float in the atmosphere. Liquid interfaces self-assemble into thin films; Step 6: Immerse the clean substrate perpendicularly into deionized water, then pull the substrate out and transfer the film to the substrate surface. Repeat the immersion and pull-out process several times to obtain an ordered oriented perovskite nanosheet film of the desired thickness.

2. The method for preparing ordered oriented perovskite nanosheet thin films according to claim 1, characterized in that, The specific process of step 4 is as follows: Step 4.1: Centrifuge the crude perovskite nanosheet solution at 8000~10000 rpm for 5 min to separate the precipitate. Disperse the precipitate in toluene, then add ethyl acetate at twice the volume of toluene, centrifuge at 7000~9000 rpm for 5 min to separate the precipitate, and disperse the precipitate in n-hexane to obtain a perovskite nanosheet solution. Step 4.2: Centrifuge the perovskite nanosheet solution at 2000-4000 rpm for 5 min, collect the supernatant and store it at 4℃ for 24 h, then centrifuge it at 2000-4000 rpm for 5 min, collect the supernatant and filter it with a polytetrafluoroethylene filter, and then vacuum dry it to obtain pure perovskite nanosheets. Step 4.3: Disperse the pure perovskite nanosheets in a non-polar solvent to obtain a perovskite nanosheet dispersion with a concentration of 10~50 mg / mL.

3. The method for preparing ordered oriented perovskite nanosheet thin films according to claim 1 or 2, characterized in that, The nonpolar solvent is n-hexane, toluene, or n-octane.

4. The method for preparing ordered oriented perovskite nanosheet thin films according to claim 1, characterized in that, The temperature of the deionized water in step 5 is 4~20℃.

5. The method for preparing ordered oriented perovskite nanosheet thin films according to claim 1, characterized in that, The settling time in step 5 is 10~60 s.

6. An ordered oriented perovskite nanosheet thin film prepared by the method according to any one of claims 1 to 5, characterized in that, The degree of polarization is 0.06~0.41, and the degree of orientation is 74%~94%.

7. A solar cell device, characterized in that, Including the ordered-oriented perovskite nanosheet thin film as described in claim 6.

8. The solar cell device according to claim 7, characterized in that, It is prepared by the following method: Step 1: Deposit a SnO2 layer onto the FTO conductive glass substrate as an electron transport layer; Step 2: Pour deionized water into a petri dish. After the liquid surface has calmed, add the perovskite nanosheet dispersion dropwise to the surface and let it stand. The perovskite nanosheets will then... The liquid interface self-assembles into a thin film. The FTO conductive glass substrate is immersed vertically into deionized water, and then pulled out of the FTO conductive glass substrate. The thin film is transferred to the substrate surface. The immersion and pulling are repeated several times to deposit an ordered oriented perovskite nanosheet thin film of the required thickness on the surface of the FTO conductive glass substrate. Step 3: Deposit carbon electrodes on the surface of perovskite nanosheet films to finally obtain solar cell devices.

9. The solar cell device according to claim 8, characterized in that, The specific process of step 1 is as follows: a SnO2 aqueous solution with a mass fraction of 2%~2.5% is dropped onto the surface of an FTO conductive glass substrate, and a film is formed by spin coating at a speed of 3000~4000 rpm. The film is then annealed at 150°C to form a SnO2 layer.

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