A method for improving the environmental stability of inorganic CsPbI3 perovskite thin films

Abstract

The application relates to a method for improving the environmental stability of inorganic CsPbI3 perovskite films, and the specific steps are as follows: 1) dissolving powder raw materials for preparing CsPbI3 perovskite in N,N-dimethylformamide to prepare a perovskite precursor solution; 2) dissolving methylamine iodine powder in isopropyl alcohol to prepare an MAI solution; 3) performing ultraviolet ozone treatment on FTO conductive glass covered with a TiO2 electron transport layer, coating the surface of the FTO conductive glass with the perovskite precursor solution, and then performing first annealing treatment, so that a perovskite film is obtained after cooling; 4) using a spin coating method to spin coat the MAI solution on the perovskite film, and then performing second annealing treatment to obtain a CsPbI3 perovskite solid film with good stability. The method provided by the application can perform surface passivation on the grain boundary and other defects of the inorganic CsPbI3 perovskite film by using MAI, and the environmental stability of the inorganic CsPbI3 perovskite film is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device material selection technology, specifically relating to a method for improving the environmental stability of inorganic CsPbI3 perovskite thin films. Background Technology

[0002] Perovskite materials are increasingly favored in the photovoltaic field due to their long carrier diffusion length, precisely tunable bandgap, high light absorption coefficient, and high defect tolerance. Since Kojima et al. (J. Am. Chem. Soc., 2009, 131, 6050-6051) first applied synthesized methylamine lead iodide (MAPbI3) to solar cells in 2009, achieving a power conversion efficiency of 3.8%, research on perovskite solar cells has experienced explosive growth in just 13 years, with a certified efficiency of 25.5% currently achieved (Nature, 2021, 598, 444–450). However, the instability of organic cations in conventional organic-inorganic hybrid perovskite solar cells limits the commercial application of perovskites. Therefore, all-inorganic perovskites have attracted widespread attention due to their excellent thermal stability at high temperatures (330℃).

[0003] Among them, the CsPbI3 system in all-inorganic perovskites has attracted researchers' attention due to its optical bandgap of ~1.70 eV, which is suitable for use as the top cell in perovskite-silicon tandem solar cells (Science, 2020, 370, 1300-1309; Joule, 2021, 5, 183-196). However, CsPbI3 perovskite materials also have drawbacks. Because the formation energy of the optically active black CsPbI3 phase is higher than that of the non-optically active yellow CsPbI3 phase, the black phase perovskite film is prone to phase transformation to the yellow phase in the environment, thus hindering the industrial application of inorganic CsPbI3 perovskite. To address this problem, this invention provides a method for improving the environmental stability of inorganic CsPbI3 perovskite films, which is of great significance to the development of perovskite solar cells. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, one of the objectives of this invention is to provide a method for improving the environmental stability of inorganic CsPbI3 perovskite thin films.

[0005] To achieve the above-mentioned objectives, the specific technical solution is as follows:

[0006] A method for improving the environmental stability of inorganic CsPbI3 perovskite thin films, the specific steps of which are as follows:

[0007] 1) Dissolve the powder raw material for preparing CsPbI3 perovskite in N,N-dimethylformamide to prepare a perovskite precursor solution;

[0008] 2) Prepare an MAI solution by dissolving methylamine iodine (MAI) powder in isopropanol (IPA);

[0009] 3) The FTO conductive glass coated with TiO2 electron transport layer is subjected to ultraviolet ozone treatment, and the perovskite precursor solution obtained in step 1) is coated on its surface. Then, the first annealing treatment is performed, and after cooling, a perovskite film is obtained.

[0010] 4) The MAI solution obtained in step 2) is spin-coated onto the perovskite film obtained in step 3) by spin coating, and then a second annealing treatment is performed to obtain a CsPbI3 perovskite solid film with good stability.

[0011] According to the above scheme, the powder raw materials for preparing CsPbI3 perovskite in step 1) are cesium iodide (CsI), lead iodide (PbI2), and dimethylamine hydroiodate (DMAI). Preferably, the molar ratio of cesium iodide, lead iodide, and dimethylamine hydroiodate is 1:1:1.

[0012] According to the above scheme, the molar volume ratio of cesium iodide to N,N-dimethylformamide in step 1) is 0.6 to 0.7 mmol / mL.

[0013] According to the above scheme, the molar concentration of the MAI solution in step 2) is 5-15 mM (mmol / L).

[0014] According to the above scheme, the process conditions for coating the perovskite precursor solution on the FTO conductive glass surface in step 3) are: spin coating at a speed of 3000 rpm / min for 30-40 seconds.

[0015] According to the above scheme, the process conditions for the first annealing treatment in step 3) are: annealing at 210℃ for 5 minutes. The first annealing treatment causes the perovskite precursor solution to form a solid film.

[0016] According to the above scheme, in step 4), the amount of MAI solution coated on the perovskite film surface is 14–18 μL / cm. 2 .

[0017] According to the above scheme, the process conditions for spin-coating the MAI solution onto the perovskite film in step 4) are: spin-coating at a speed of 3500 rpm / min for 30 to 40 seconds.

[0018] According to the above scheme, the process conditions for the second annealing in step 4) are: annealing at 120℃ for 10 minutes. The purpose of the second annealing is to remove residual solvent.

[0019] The second objective of this invention is to provide an inorganic CsPbI3 perovskite thin film with good stability prepared according to the above method.

[0020] The specific technical solution is as follows:

[0021] An inorganic CsPbI3 perovskite film with good stability prepared according to the above method is provided. The inorganic CsPbI3 perovskite film can be stably stored for more than 1 hour at room temperature (15-35°C) and relative humidity of 60-70%.

[0022] The third objective of this invention is to provide applications of the aforementioned inorganic CsPbI3 perovskite thin films.

[0023] The specific technical solution is as follows:

[0024] Application of the above-mentioned inorganic CsPbI3 perovskite thin film in perovskite / silicon-based tandem solar cells.

[0025] The principle of this invention is as follows: A layer of MAI solution is spin-coated onto a perovskite solid film. MAI passivates defects such as grain boundaries in the inorganic CsPbI3 perovskite film. When MAI accumulates at the grain boundaries of the inorganic perovskite, it applies stress to inhibit the transformation of the CsPbI3 from the black phase to the yellow phase, thereby improving the stability of the film. Experimental results show that when the concentration of the MAI solution is 5–15 mM, the obtained perovskite grain size is larger, the film particle size distribution is more uniform, and the film stability is also improved.

[0026] The beneficial effects of this invention are as follows: 1. The method provided by this invention enables MAI to passivate defects such as grain boundaries in inorganic CsPbI3 perovskite films, thereby improving the environmental stability of inorganic CsPbI3 perovskite films; 2. The inorganic CsPbI3 perovskite films provided by this invention have excellent characteristics such as uniform grain size, good crystallinity, and strong stability. Attached Figure Description

[0027] Figure 1 Scanning electron microscope images and particle size distributions of four inorganic CsPbI3 perovskite films prepared by treating with MAI solutions of different concentrations in Example 1 of this invention.

[0028] Figure 2 X-ray diffraction patterns of four inorganic CsPbI3 perovskite films prepared by treatment with MAI solutions of different concentrations in Example 1.

[0029] Figure 3 Atomic force microscopy images of four inorganic CsPbI3 perovskite films prepared by treating with MAI solutions of different concentrations in Example 1.

[0030] Figure 4 The image shows the UV-Vis spectrum of the inorganic CsPbI3 perovskite film prepared in Example 1 by treatment with MAI solutions of concentrations of 0 mM and 15 mM, as it is placed in the environment over time. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] All raw materials used in the embodiments of the present invention are weighed in a glove box, and the stirring process is carried out by shaking in the glove box.

[0033] Example 1

[0034] A method for improving the environmental stability of inorganic CsPbI3 perovskite thin films includes the following steps:

[0035] 1) The FTO conductive glass substrate (2.5cm×2.5cm) was cleaned with cleaning agent, ultrapure water and alcohol respectively. After the cleaned FTO conductive glass substrate was treated with ultraviolet ozone for 15 minutes, a 0.2M bis(acetylacetonyl)diisopropyl titanate solution (commercial raw material) was spin-coated onto the FTO conductive glass by spin coating at a rate of 4000rpm / s for 30s and annealed at 100℃ for 10min to prepare a TiO2 electron transport layer on the surface of FTO conductive glass.

[0036] 2) Weigh 0.6 mmol of cesium iodide, lead iodide and dimethylamine hydroiodate respectively, dissolve them in 1 mL of N,N-dimethylformamide to prepare a perovskite precursor solution;

[0037] 3) Dissolve different amounts of MAI powder in 1 ml of isopropanol to prepare MAI solutions of different molar concentrations (0 mM, 5 mM, 15 mM, 30 mM).

[0038] 4) The FTO conductive glass with TiO2 electron transport layer obtained in step 1) was subjected to ultraviolet ozone treatment for 15 minutes. Then, 50 μL of the perovskite precursor solution prepared in step 2) was spin-coated onto the FTO conductive glass by spin coating at a speed of 3000 rpm / min for 30 s. After annealing at 210℃ for 5 min, it was allowed to cool naturally to room temperature.

[0039] 5) On the perovskite film obtained in step 4), spin-coat 100 μL of the MAI solution prepared in step 3) within the first 3 seconds of spin coating, spin-coat at 3500 rpm / min for 35 seconds, then anneal at 120℃ for 10 min and cool naturally to room temperature to obtain an inorganic CsPbI3 perovskite film (the sample with MAI solution concentration of 0 mM is designated as the Control sample).

[0040] Figure 1 Scanning electron microscope (SEM) images and particle size distributions of four inorganic CsPbI3 perovskite films prepared by treatment with MAI solutions of different concentrations in this embodiment are shown. Comparison of the images reveals that the Control sample perovskite film, without MAI solution surface treatment, exhibits poor density and porosity, with an average particle size of 586 nm. Perovskite crystal uniformity gradually improves after surface treatment with appropriate concentrations of MAI solution, and the average particle size increases (612 nm and 627 nm after surface treatment with 5 mM and 15 mM MAI solutions, respectively). Porosity within the film also gradually disappears, and the film morphology is significantly improved. However, when the MAI solution concentration is further increased to 30 mM, the film particle size decreases significantly, with an average particle size of 571 nm, and a large amount of unreacted white material (MAI) accumulates on the film surface. This indicates that controlling the MAI solution concentration can influence the morphology of the all-inorganic perovskite film to a certain extent; the preferred MAI solution concentration range is 5–15 mM.

[0041] Figure 2 The X-ray diffraction patterns are shown for four inorganic CsPbI3 perovskite films prepared by treatment with MAI solutions of different concentrations in this embodiment. Compared with the Control sample perovskite film without MAI solution treatment, the film treated with a 5 mM MAI solution exhibits the highest diffraction peak intensity and the best preferred orientation. However, further increasing the concentration of the MAI solution leads to a significant decrease in the intensity of the diffraction peaks, and the crystallinity also gradually deteriorates.

[0042] Figure 3 Atomic force microscopy (AFM) images of four inorganic CsPbI3 perovskite films prepared by treatment with MAI solutions of different concentrations in this embodiment. The images show that the surface roughness of the films first decreases and then increases with increasing MAI solution concentration. The films treated with 5 mM and 15 mM MAI solutions exhibit the lowest roughness, which is consistent with... Figure 1 The results are consistent with those obtained from scanning electron microscopy.

[0043] Figure 4This figure shows the UV-Vis stability changes of inorganic CsPbI3 perovskite films prepared by treatment with 0mM and 15mM MAI solutions in this embodiment. The film samples were stored at room temperature and relative humidity of 60-70% for a certain period, and their stability was tested using UV-Vis. The comparison in the figure shows that the UV-Vis absorption intensity of the Control sample film decreased significantly within 1 hour, and the absorption peak of the black perovskite phase (~730nm) was no longer detectable in the film at 60 minutes, indicating that the Control sample film rapidly degraded from the black photoactive perovskite phase to the yellow non-photoactive perovskite phase within 1 hour. In contrast, the film treated with MAI solution, after being placed in the environment for 1 hour, still showed a detectable absorption peak of the black perovskite phase (~730nm), confirming that the film could still exist in the black phase form of photoactive perovskite. This indicates that the stability of the film treated with MAI solution is significantly better than that of the untreated Control sample film.

[0044] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for improving environmental stability of inorganic CsPbI 3 perovskite thin film, characterized in that, The specific steps are as follows: 1) Dissolve the powder raw material for preparing the CsPbI3 perovskite in N,N-dimethylformamide to prepare a perovskite precursor solution; 2) Dissolve methylamine iodide powder in isopropanol to prepare an MAI solution; 3) Perform ultraviolet ozone treatment on the FTO conductive glass coated with a TiO2 electron transport layer, and coat the surface of the FTO conductive glass with the perovskite precursor solution prepared in step 1), and then perform a first annealing treatment, and obtain a perovskite thin film after cooling; 4) Use a spin coating method to spin coat the MAI solution prepared in step 2) on the perovskite thin film obtained in step 3), and then perform a second annealing treatment to obtain a CsPbI3 perovskite solid-state thin film with good stability, and the second annealing treatment process conditions are: annealing at 120℃ for 10 min.

2. The method for improving the environmental stability of inorganic CsPbI3 perovskite thin films according to claim 1, characterized in that, The powder raw material for preparing the CsPbI3 perovskite in step 1) is cesium iodide, lead iodide, and dimethylamine hydroiodide.

3. The method for improving the environmental stability of inorganic CsPbI3 perovskite thin films according to claim 2, characterized in that, The molar volume ratio of the cesium iodide to N,N-dimethylformamide in step 1) is 0.6-0.7 mmol / mL.

4. The method for improving the environmental stability of inorganic CsPbI3 perovskite thin films according to claim 1, characterized in that, The molar concentration of the MAI solution in step 2) is 5-15 mM.

5. The method for improving the environmental stability of inorganic CsPbI3 perovskite thin films according to claim 1, characterized in that, The process conditions for coating the perovskite precursor solution on the surface of the FTO conductive glass in step 3) are: spin coating at a speed of 3000 rpm / min for 30-40 s; and the first annealing treatment process conditions in step 3) are: annealing at 210℃ for 5 min. 6.The method of claim 1, wherein the inorganic CsPbI 3 perovskite thin film is a perovskite thin film having a structure of ABX 6 (A: Cs, Rb, or FA; B: Pb; X: I, Br, or Cl). Step 4) MAI solution is coated on the surface of the perovskite film at a coating amount of 14-18 μL / cm 2 .

7. The method for improving the environmental stability of inorganic CsPbI3 perovskite thin films according to claim 1, characterized in that, The process conditions for spin coating the MAI solution on the perovskite thin film in step 4) are: spin coating at a speed of 3500 rpm / min for 30-40 s.

8. A stable inorganic CsPbl3 perovskite thin film prepared according to the method of any one of claims 1-7, characterized in that, The inorganic CsPbI3 perovskite thin film can be stored stably for more than 1 h under the condition of room temperature and a relative humidity of 60-70%.

9. Use of the inorganic CsPbI3 perovskite thin film of claim 8 in a perovskite / silicon-based stacked solar cell.

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