Method for preparing perovskite thin film by using gas-phase molecules

Abstract

The invention relates to a method for preparing a perovskite thin film by using gas-phase molecules, and belongs to the technical field of thin film preparation and solar cell preparation. The method comprises the following steps: preparing a perovskite liquid film from a perovskite layer precursor solution by adopting a solution method; the liquid film is moved into a reaction cavity, the reaction cavity is vacuumized, and pre-annealing / annealing treatment is carried out in the cavity; two gas-phase molecules are introduced in the pre-annealing / annealing process, one gas-phase molecule is used for adjusting the crystallization process of the perovskite thin film, the other gas-phase molecule is used for carrying out solid-gas phase reaction with the perovskite thin film under thermal excitation, and the defect density of the thin film is controlled by passivating defects. By loading two gas-phase molecules, the crystallization process of the perovskite thin film is regulated and controlled at the same time, the defects of the perovskite thin film are modified, the annealing passivation effect of the perovskite thin film is enhanced, and application and construction of an efficient perovskite solar cell are facilitated. The method has the advantages of controllable conditions, high repetition accuracy and the like.

Description

Technical Field

[0001] The present invention relates to thin film preparation technology and solar cell preparation technology, and in particular to a method for preparing a perovskite thin film by using gas phase molecules. Background Art

[0002] In recent years, organic-inorganic hybrid perovskite materials have attracted much attention from researchers due to their advantages such as high light absorption coefficient, adjustable band gap, and long carrier diffusion length. The conversion efficiency of perovskite solar cells based on perovskite films has made great progress in recent years and has reached 26.7%. The quality of perovskite films directly affects the performance parameters of solar cells. In order to improve the quality of the film and obtain better photoelectric conversion efficiency, the commonly used strategy is to use interface / surface layer engineering, additive engineering and other methods to regulate perovskite crystallization and passivate the defect states of perovskite films, such as patents CN111029463A, CN112382725A, CN112582544A, etc. The perovskite film defect state regulation strategy developed by it is mainly to add additives to the perovskite film-forming solution, or to perform solution phase post-treatment on the film surface. It is difficult to achieve good control of the passivation modification of the defect states of perovskite films by liquid phase methods.

[0003] Recently, the inventor has reported the application of gas phase method to realize the passivation of defective states of perovskite film, by the solid-gas phase reaction of gas phase molecules such as perovskite film and CO, NO2 under electric field induction, the defective state quantity of film can be significantly reduced, and film quality is improved (patent CN113540363A). In addition, there are also inventors who use 4-tert-butylbenzylamine iodine to carry out solid-gas phase reaction with perovskite film, realize the passivation of defective states of film, and improve solar cell device performance (patent CN113421979A). The above perovskite film defective state gas phase passivation strategy is based on the film after perovskite film formation to carry out gas phase post-processing to film, owing to not improving film quality during perovskite crystallization film formation, its defective state passivation effect still needs to be further improved. Therefore, it is urgent to develop novel perovskite film gas phase passivation method, promote the application development of this method on perovskite solar cell device.

[0004] Based on this, the inventors have developed an integrated high-quality perovskite preparation method that realizes thin film crystallization regulation and defect state passivation by utilizing the fact that the crystallization film of the perovskite precursor solution after coating requires pre-annealing / annealing treatment. That is, during the pre-annealing / annealing process of the coated perovskite liquid film, two gas phase molecules are introduced, one gas phase molecule is used to regulate the crystallization process of the perovskite film, and the other gas phase molecule is used to react with the perovskite film in a solid-gas phase under thermal excitation to passivate defects and obtain a low defect density perovskite film. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a perovskite film using gas phase molecules, by which the crystallization process of the perovskite film and the passivation of film defects are regulated by two gas phase molecules to obtain a high-quality perovskite film.

[0006] To achieve the above purpose, the specific technical solution adopted by the present invention is as follows:

[0007] A method for preparing a perovskite film using gas phase molecules, the method comprising the following steps:

[0008] (1) preparing a perovskite precursor solution and preparing a perovskite liquid film on a FTO glass substrate;

[0009] (2) placing the FTO glass substrate covered with the perovskite liquid film in step (1) on a heatable substrate in a reaction chamber, sealing the reaction chamber, and evacuating the chamber to a vacuum using a vacuum pump;

[0010] (3) In the heating step (2), the substrate is heated to a certain temperature to perform pre-annealing and annealing treatment on the film. At the same time, two gas phase molecules are introduced simultaneously to regulate the crystallization process of the perovskite film during the pre-annealing / annealing process and to react with the solid-gas phase of the perovskite film to obtain the perovskite film; the process of gas phase molecules treating the perovskite film is monitored by an impedance analysis in-situ system.

[0011] The present application obtains a high-quality perovskite film by introducing specific gas-phase molecules into a perovskite liquid film undergoing pre-annealing / annealing treatment, regulating the crystallization process of the perovskite film, and inducing the gas-phase molecules to react with defect structures in the perovskite film under thermal excitation.

[0012] According to the present invention, in the step (1), after the perovskite precursor solution is prepared, the perovskite liquid film is prepared by a one-step spin coating method or a two-step spin coating method.

[0013] According to the present invention, in step (1), the thin film is an organic-inorganic hybrid perovskite liquid film.

[0014] According to the present invention, the specific steps of step (2) are: transferring the prepared thin film to a heatable substrate in the reaction chamber, sealing the reaction chamber, and evacuating the reaction chamber with a dry vacuum pump.

[0015] According to the present invention, the specific steps of step (3) are: heating the heated substrate in the reaction chamber to 50-80°C, pre-annealing for 3-6 minutes, and then continuing to heat the heated substrate to 110-160°C and annealing for 8-12 minutes; during pre-annealing and annealing, introducing gas phase molecules to regulate the crystallization process of the perovskite film and react with the perovskite film in a solid-gas phase, and using an impedance analysis in-situ system to continuously monitor the performance of the perovskite film. The most preferred pre-annealing temperature is 70°C and the pre-annealing time is 5 minutes; the annealing temperature is 120°C and the annealing time is 10 minutes.

[0016] According to the present invention, in step (3), the two gas phase molecules introduced are methanol, tetrahydrofuran or acetonitrile, and acetylacetone or acetic anhydride, and their concentrations are 0.5% to 8% by volume in the buffer gas helium.

[0017] Beneficial effects of the present invention:

[0018] The advantages of the present invention are that two gas phase molecules are used, one of which is used to regulate the crystallization process of the perovskite film, and the other is used to react with the thermally excited perovskite film in the pre-annealing / annealing process to undergo solid-gas phase reaction, to modify the defect structure and passivate the defects, and to prepare a high-quality perovskite film with low defect density. By adjusting the chemical properties of the reaction gas, the passivation modification of different types of defects in the film can be achieved, which not only achieves the purpose of regulating the crystallization of the perovskite film, but also improves the passivation ability of the annealing process on the film defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of a device for preparing a perovskite film using gas phase molecules according to the present invention;

[0020] Figure 2 The graphs are the variable frequency impedance graph of the perovskite film prepared by the gas phase molecular method in Example 1 of the present invention and the variable frequency impedance graph of the perovskite film prepared without the gas phase molecular method in Example 2. DETAILED DESCRIPTION

[0021] The method of the present invention will be described in further detail below in conjunction with specific embodiments. The following embodiments are only for exemplary purposes to illustrate and explain the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0022] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0023] Example 1

[0024] This embodiment is completed in a glove box with a reaction chamber. The reaction chamber has a gas loading function and the temperature of the heating substrate in the chamber is controllable. The reaction chamber is made of 316 stainless steel. The impedance analyzer is used to monitor the impedance changes of the film in the reaction chamber in real time. Figure 1 The specific steps are as follows:

[0025] (1) Add methylammonium iodide (CH3NH3I, i.e., MAI) and lead iodide (PbI2) in a molar ratio of 1:1 to a solvent in which the volume ratio of anhydrous N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is 4:1, and stir for 6 hours to fully dissolve to obtain a perovskite precursor solution. Using a one-step spin coating method, 45 μL of the precursor solution is dropped onto a fluorine-doped tin oxide (FTO)-coated glass substrate at a speed of 4000 rpm, and the coating is rotated for 20 seconds. At 8 seconds after the precursor solution is added, 980 μL of ether is used for back extraction to obtain a perovskite liquid film.

[0026] (2) The FTO substrate coated with the perovskite liquid film was transferred to a heated substrate in a reaction chamber (62 mm × 45 mm × 33.7 mm) placed in a glove box, the reaction chamber was sealed, and then a dry vacuum pump was turned on to evacuate the reaction chamber and maintain the vacuum for 1 minute.

[0027] (3) The substrate is quickly heated to 70°C and the perovskite liquid film is pre-annealed for 5 minutes. Then, the substrate is further heated to 120°C and annealed for 10 minutes. At the same time, the air inlet valve is opened to introduce tetrahydrofuran / helium and acetylacetone / helium. The volume concentration of tetrahydrofuran in helium is 5%, and the volume concentration of acetylacetone in helium is 1%. During the air intake, the gas pressure in the reaction chamber is monitored by a vacuum gauge. When the pressure in the chamber reaches 1 atmosphere, the air intake is stopped. The pressure of tetrahydrofuran / helium is 0.4 atmospheres, and the pressure of acetylacetone / helium is 0.6 atmospheres. The perovskite film is treated with gas phase molecules until the annealing is completed to obtain a MAPbI3 perovskite film. The impedance analysis in-situ system measures the results of the obtained perovskite film as shown below. Figure 2 shown.

[0028] Example 2

[0029] In this embodiment, the MAPbI3 liquid film was prepared in the same manner as in Example 1, and the film was pre-annealed / annealed under the same temperature and time conditions. The difference is that during the pre-annealing / annealing of the MAPbI3 liquid film, the gas phase molecules in Example 1 were not introduced into the perovskite film, but the liquid film was directly pre-annealed / annealed in the nitrogen environment in the glove box. The impedance analysis system characterization results are shown in Figure 1. Figure 2 shown.

[0030] By comparing the impedance analysis results of Examples 1 and 2, it can be seen that the impedance value of the MAPbI3 perovskite film obtained by using two types of gas phase molecular treatments during the pre-annealing / annealing process is significantly lower than that of the perovskite film obtained by the conventional annealing method, indicating that the perovskite film obtained by gas phase molecular treatment has less defect density and higher quality.

[0031] The perovskite solar cells prepared in the above two embodiments were subjected to photoelectric testing to obtain comparative data as shown in Table 1 below.

[0032] Table 1. Comparison of photoelectric test data of perovskite solar cells prepared in two embodiments of the present invention

[0033] Open circuit voltage(V) <![CDATA[Short-circuit current density (mA·cm -2 )]]> Fill factor (%) Photoelectric conversion efficiency (%) Example 1 1.09 22.48 78.37 19.32 Example 2 1.07 22.25 78.83 17.01

[0034] As can be seen from Table 1, the perovskite solar cell prepared in Example 1 of the present invention has a high photoelectric conversion efficiency, and the open circuit voltage and short circuit current density of the cell are higher than those of the perovskite film cell that has not been treated with gas phase molecules, indicating that the perovskite film obtained by the gas phase molecule treatment strategy of the present invention has high quality and few surface defects. Therefore, the method of the present invention can prepare a perovskite film with few defects and high crystal quality, and the solar cell prepared therefrom has good performance and can obtain a high photoelectric conversion efficiency.

[0035] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a perovskite film using gas phase molecules, characterized in that: The method comprises the following steps: (1) preparing a perovskite precursor solution and preparing a perovskite liquid film on a FTO glass substrate; (2) placing the FTO glass substrate covered with the perovskite liquid film in step (1) on a heatable substrate in a reaction chamber, sealing the reaction chamber, and evacuating the chamber to a vacuum using a vacuum pump; (3) In the heating step (2), the substrate is heated to a certain temperature to perform pre-annealing and annealing treatment on the film. At the same time, two gas phase molecules are introduced simultaneously to regulate the crystallization process of the perovskite film during the pre-annealing / annealing process and to react with the solid-gas phase of the perovskite film to obtain the perovskite film; the process of gas phase molecules treating the perovskite film is monitored by an impedance analysis in-situ system.

2. The method for preparing a perovskite film using gas phase molecules according to claim 1, characterized in that: In the step (1), after the perovskite precursor solution is prepared, the perovskite liquid film is prepared by a one-step spin coating method or a two-step spin coating method.

3. The method for preparing a perovskite film using gas phase molecules according to claim 1, characterized in that: In the step (1), the perovskite liquid film is an organic-inorganic hybrid perovskite liquid film.

4. The method for preparing a perovskite film using gas phase molecules according to claim 1, characterized in that: The specific steps of step (2) are: moving the prepared liquid film onto a heatable substrate in the reaction chamber, sealing the reaction chamber, and evacuating the reaction chamber with a dry vacuum pump.

5. The method for preparing a perovskite film using gas phase molecules according to claim 1, characterized in that: The specific steps of step (3) are: heating the heated substrate in the reaction chamber to 50-80° C., pre-annealing for 3-6 minutes, and then continuing to heat the heated substrate to 110-160° C. and annealing for 8-12 minutes; during the pre-annealing and annealing, introducing gas phase molecules to regulate the crystallization process of the perovskite film and conduct solid-gas phase reaction with the perovskite film, and using an impedance analysis in-situ system to continuously monitor the performance of the perovskite film.

6. The method for preparing a perovskite film using gas phase molecules according to claim 1, characterized in that: The two gas phase molecules introduced in step (3) are methanol, tetrahydrofuran or acetonitrile, and acetylacetone or acetic anhydride, with a volume concentration of 0.5% to 8% in the buffer gas helium.

7. A perovskite solar cell, comprising a perovskite thin film layer, characterized in that: The perovskite film layer is a perovskite film prepared by the perovskite preparation method according to any one of claims 1 to 6.

Images