A method for preparing an inorganic perovskite thin film

Abstract

The application discloses a method for preparing an inorganic perovskite film, which comprises the following steps: A: weighing a certain proportion of cesium halide and lead halide, dissolving the cesium halide and the lead halide in a mixed solution of dimethyl sulfoxide and dimethylformamide, adding acetate or oxalate after complete dissolution, and obtaining a precursor solution; B: coating the precursor solution on a substrate to obtain a pre-prepared layer film, and then annealing to obtain a perovskite film; C: dissolving a certain amount of methylamine iodide and cesium halide in a specific solvent to configure a post-processing solution, or adding methylamine iodide to a hole transport layer solution; D: spin-coating the post-processing solution in the step C or the hole transport layer solution to which the methylamine iodide has been added on the perovskite film obtained in the step B, and completing post-processing of the film after annealing. The method can effectively reduce the annealing temperature, can realize preparation of the inorganic perovskite film under the condition of a maximum relative humidity of 80%, and the prepared film has high quality and good stability in air.

Description

Technical Field

[0001] This invention relates to the field of perovskite solar cells, and more particularly to a method for preparing inorganic perovskite thin films for solar cells. Background Technology

[0002] Perovskite solar cells have attracted worldwide attention from researchers due to their high theoretical limit efficiency, simple fabrication methods, compatibility with solvation, and ease of large-scale production, resulting in rapid development in recent years. Currently, the latest laboratory-certified efficiency of perovskite solar cells has reached 25.8%, demonstrating a broad application prospect. The efficiency of large-scale modules has also exceeded 20%, and industrialization is progressing steadily. However, high-efficiency perovskite solar cells typically use large-radius organic cations such as formamidinium and methylamine as A-site cations. The high-temperature insensitivity of organic materials leads to the problem of easy decomposition of perovskite solar cells under high-temperature conditions. Therefore, the all-inorganic CsPbX3 perovskite solar cell has been proposed, exhibiting better thermal stability, and its photoelectric conversion efficiency has recently exceeded 20%.

[0003] The most important factor affecting the photoelectric conversion efficiency of inorganic perovskite solar cells is the quality of the perovskite thin film's light-absorbing layer, and the preparation method of the film has the most significant impact on the film quality. Currently, inorganic perovskite thin films are usually prepared using a one-step solution method: cesium halides, lead halides, etc., are mixed and dissolved in an organic solvent in a certain proportion, coated, and then annealed at high temperature to obtain the perovskite thin film.

[0004] In one-step solution processing, small amounts of additives, such as hydroiodide (HPbI3), are typically added to control the crystallization process of the film. However, whether the film remains an inorganic perovskite after the addition of hydroiodide is controversial, and high-temperature thermal stability issues persist. Subsequent annealing typically requires temperatures exceeding 250°C to reach the transformation temperature of the black-phase inorganic perovskite, increasing preparation costs and energy consumption. Furthermore, rapid solvent evaporation makes the film highly susceptible to defects, making it difficult to control film quality and morphology. In addition, even trace amounts of water and oxygen can severely damage the quality of inorganic perovskite films, necessitating the use of expensive inert atmosphere glove boxes for precise control of water and oxygen conditions. This hinders the large-scale production of inorganic perovskite solar cells. Therefore, developing a high-temperature annealing method that eliminates the need for humidity control is urgently needed to prepare high-quality inorganic perovskite films. Summary of the Invention

[0005] The purpose of this invention is to optimize the preparation process of inorganic perovskite thin films to achieve the preparation of high-quality inorganic perovskite thin films without humidity control and high-temperature annealing, so as to meet the requirements of low energy consumption and easy large-scale production in the preparation process, and maximize the potential of inorganic perovskite materials in the field of photoelectric conversion.

[0006] To achieve the above objectives, the present invention provides a method for preparing inorganic perovskite thin films, comprising the following steps:

[0007] A: Weigh out cesium halide and lead halide in a certain proportion, dissolve them in a mixed solution of dimethyl sulfoxide and dimethyl imide to prepare a solution with a designed stoichiometric ratio, and add a certain amount of acetate or oxalate after complete dissolution to obtain the precursor solution;

[0008] B: The above precursor solution is coated on the substrate to obtain a pre-coated thin film, and then annealed for a certain time to obtain a perovskite thin film.

[0009] C: Dissolve a certain amount of methylamine iodide and cesium halide in a specific solvent to prepare a post-treatment solution, or add methylamine iodide to the hole transport layer solution;

[0010] D: Spin-coat a layer of the post-treatment solution from step C or a hole transport layer solution containing methyl halide onto the perovskite film obtained in step B, and complete the film post-treatment after annealing.

[0011] Preferably, the added acetate or oxalate is one or more of lead acetate, lead acetate trihydrate, cesium acetate, cesium acetate dihydrate, and lead oxalate.

[0012] Preferably, the total amount of acetate or oxalate added is 5% to 25% relative to the amount of lead halide in the precursor solution.

[0013] Preferably, the annealing temperature of the preformed film is 80–150°C, and the annealing time is 5–25 minutes.

[0014] Preferably, the cesium halide is one or more of cesium iodide, cesium bromide, and cesium chloride.

[0015] Preferably, the concentration of the post-treatment solution is calculated based on halogen anions and is 0.1–2 g / L, and the specific solvent is one of isopropanol, methanol, and ethanol.

[0016] Preferably, the amount of methyl iodide added to the hole transport layer solution is 0.1–0.7 g / L, and the hole transport layer solution is Spiro-OMeTAD (2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene) or PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) or P3HT (3-hexyl-substituted polythiophene), and the solvent used is one of chlorobenzene and chloroform.

[0017] Preferably, the spin coating process in the post-treatment step should be dynamic spin coating, with a rotation speed of 5000-8000 rpm and a spin coating time of 20-40 seconds.

[0018] Preferably, the post-treatment annealing temperature is 50–100°C, and the annealing time is 4–15 minutes.

[0019] The technical principles employed in this invention are as follows:

[0020] Adding a certain amount of acetate or oxalate to the precursor solution can reduce the formation energy of stable black perovskite, thereby lowering the annealing temperature. Acetate or oxalate ions will exist at the interface between the film and air during spin coating and annealing, which greatly inhibits the erosion of the film by moisture and oxygen. Acetate or oxalate ions have a strong binding effect with DMSO, which slows down the solvent evaporation rate, significantly slows down the crystallization rate, and thus increases the grain size.

[0021] However, the formation of large grains in the thin film leads to the expansion of grain boundaries, resulting in severe recombination of charge carriers at the grain boundaries and affecting the performance of perovskite solar cells. Furthermore, the excess lead or cesium added cannot enter the crystal lattice and remains on the film surface, causing numerous surface defects. Simultaneously, lower annealing temperatures cannot completely remove acetate or oxalate ions, affecting the thermal stability of the film. Post-treatment using a solution containing methylamine iodide achieves the simultaneous reconstruction of a smooth, defect-free film and removal of excess acetate ions. Acetate ions and methylamine cations combine to form a methylamine acetate ionic liquid, which is rapidly removed. Excess lead in the film combines with iodide and cesium ions to form a two-dimensional perovskite layer, protecting the top of the perovskite film from water and oxygen corrosion.

[0022] Compared with existing perovskite material preparation technologies, this invention has the following advantages:

[0023] 1. This method effectively reduces the annealing temperature of the thin film. Inorganic perovskite thin films typically require annealing at 250℃, but this method only requires a maximum annealing temperature of 150℃. 2. It can resist the influence of humidity conditions on thin film preparation, enabling the preparation of high-quality inorganic perovskite thin films under conditions of up to 80% relative humidity. 3. The thin films prepared by this method are of very high quality, with small grain boundaries, few surface defects, large grains, good crystallinity, and good stability. The prepared inorganic perovskite thin films are very suitable as the absorber layer of perovskite solar cells, playing a significant role in improving the photoelectric conversion efficiency of inorganic perovskite solar cells. Attached Figure Description

[0024] Figure 1 The X-ray diffraction pattern of the perovskite thin film prepared in Example 1 after post-treatment;

[0025] Figure 2 This is a scanning electron microscope image of the surface of the perovskite thin film prepared in Example 1 after post-treatment;

[0026] Figure 3This is a scanning electron microscope (SEM) image of the surface of the perovskite thin film prepared in Example 1 before post-treatment.

[0027] Figure 4 The image shows the UV-Vis absorption spectrum of the perovskite thin film prepared in Example 3. Detailed Implementation

[0028] Example 1:

[0029] A: Weigh 20.7 g of cesium iodide and 36.8 g of lead iodide into 100 mL of a DMSO / DMF mixed solvent with a solvent ratio of DMSO:DMF = 4:1. After stirring for 12 hours, add 1.5 g of lead acetate trihydrate to the solution and continue stirring for 1 hour until completely dissolved.

[0030] B: On an ITO substrate with a pre-prepared tin oxide electron transport layer, a pre-coated thin film is obtained by spin coating using the precursor solution obtained in step A; the relative humidity is 50-60%, the room temperature is 21℃, and there is no humidity control during the preparation process; the pre-coated thin film is placed on a 100℃ hot stage and annealed for 10 minutes to obtain a perovskite thin film.

[0031] C: Dissolve 1 gram of methylamine iodide and 0.5 grams of cesium iodide in 500 ml of isopropanol and stir for 1 hour to obtain the post-treatment solution.

[0032] D: The post-treatment solution obtained in step C was dynamically spin-coated onto the perovskite film at a speed of 5000 rpm for 30 seconds; the film was then placed on a 70°C hot plate and annealed for 5 minutes to complete the post-treatment optimization of the CsPbI3 perovskite film.

[0033] The X-ray diffraction pattern of the obtained CsPbI3 perovskite film is shown in the figure. Figure 1 The strong intensity and small half-width of the diffraction peaks of the thin film indicate that the film has good crystallinity, no impurity peaks, and no secondary phase.

[0034] The surface morphology of the film changed significantly before and after post-processing optimization. A scanning electron microscope image of the CsPbI3 film surface after post-processing optimization is shown below. Figure 2 The film is flat and dense, with small grain boundaries, few surface defects, large grains, and no obvious voids or gaps.

[0035] The unprocessed scanning electron microscope image of the thin film is shown below. Figure 3 The addition of lead acetate slows down the crystallization of the film and prolongs the grain growth time, resulting in more voids between the perovskite grains and poor film quality. When used as an absorber layer in a solar cell, this film can cause very serious non-radiative recombination, affecting the efficiency of the solar cell.

[0036] Example 2:

[0037] A: Weigh 90 mg of cesium iodide and 161 mg of lead iodide and dissolve them in 0.5 mL of a DMSO / DMF mixed solvent with a solvent ratio of DMSO:DMF = 4:1. After stirring for 2 hours, add 7 mg of lead acetate trihydrate to the solution and continue stirring for 1 hour until completely dissolved.

[0038] B: On an ITO substrate with a pre-prepared SnO2 electron transport layer, a pre-coated thin film is obtained by spin coating using the precursor solution obtained in step A; the relative humidity is 10-20% and the room temperature is 25℃; the pre-coated thin film is placed on a hot plate at 120℃ and annealed for 5 minutes to obtain a perovskite thin film.

[0039] C: Dissolve 1 mg of methyl iodide in 1 ml of a pre-prepared Spiro-OMeTAD hole transport layer solution (the solvent used is chlorobenzene), and stir for 1 hour to obtain the post-treatment solution.

[0040] D: Dynamically spin-coat the hole transport layer solution obtained in step C onto the perovskite film at a spin speed of 6000 rpm for 30 seconds; place the film on a 50°C hot plate and anneal for 5 minutes to complete the post-processing optimization of the perovskite film.

[0041] The obtained ITO / SnO2 / CsPbI3 perovskite / Spiro-OMeTAD was deposited with silver in vacuum evaporation to fabricate a perovskite solar cell device, achieving a photoelectric conversion efficiency of 16.1% under one solar intensity. In this example, a Spiro-OMeTAD hole transport layer solution with added methylamine iodide was used for thin film post-processing, achieving simultaneous one-step fabrication of the hole transport layer and optimized thin film post-processing, simplifying the device fabrication process and resulting in a solar cell device with high photoelectric conversion efficiency.

[0042] Example 3:

[0043] A: Weigh 90.9 mg of cesium iodide, 100.9 mg of lead iodide, and 48.4 mg of lead bromide into 0.5 mL of DMSO / DMF mixed solvent, with a solvent ratio of DMSO:DMF = 1:4. After stirring for 1 hour, add 7 mg of lead acetate trihydrate to the solution and continue stirring for 0.5 hours until completely dissolved.

[0044] B: On an ITO substrate with a pre-prepared tin oxide / zinc oxide electron transport layer, a pre-coated thin film is obtained by spin coating using the precursor solution obtained in step A (relative humidity greater than 80%, room temperature 23℃); the pre-coated thin film is placed on a hot plate at 150℃ and annealed for 10 minutes to obtain a black perovskite thin film.

[0045] C: Dissolve 2 mg of methyl iodide and 1 mg of cesium iodide in 1 ml of isopropanol and stir for 1 hour to obtain the post-treatment solution.

[0046] D: The post-treatment solution obtained in step C was dynamically spin-coated onto the perovskite film at a speed of 8000 rpm for 40 seconds; the film was then placed on a 100°C hot plate and annealed for 5 minutes to complete the post-treatment optimization of the perovskite film.

[0047] This perovskite film was prepared in an environment without humidity control. A stable perovskite film could be obtained simply by annealing at 150℃, and it could maintain its black phase for approximately 48 hours; after 48 hours, CsPbI... 2.25 Br 0.75 The UV-Vis absorption spectrum of the thin film is shown in the figure. Figure 4 As can be seen, the thin film has good light absorption and no phase transition has occurred.

[0048] Comparative Example 1:

[0049] 90.9 mg of cesium iodide, 100.9 mg of lead iodide, and 48.4 mg of lead bromide were weighed into 0.5 mL of a DMSO / DMF mixed solvent with a solvent ratio of DMSO:DMF = 1:4 to obtain a precursor solution. The precursor solution was then spin-coated onto an ITO substrate with a pre-prepared tin oxide / zinc oxide electron transport layer to obtain a pre-formed thin film (ambient relative humidity greater than 80%, room temperature 23℃).

[0050] The pre-formed film was placed on a 150°C hot plate. The film turned dark brown within 30 seconds, and after maintaining this temperature for 1 minute, it turned yellow. Because the film failed to completely transform into the black perovskite phase at 150°C, the metastable perovskite film completely degraded after solvent evaporation, transforming into the optically inactive yellow CsPbI phase. 2.25 Br 0.75 Perovskite.

[0051] Meanwhile, the pre-formed film was placed on a 250°C hot plate. The film turned dark brown within 5 seconds, and after holding it for 10 minutes, the film annealing was completed, yielding CsPbI. 2.25 Br 0.75 Perovskite thin films; upon cooling to room temperature, the films degrade into a yellow perovskite phase within 30 seconds. Inorganic perovskites are unstable in high humidity environments, leading to rapid decomposition and making their preparation under high humidity conditions difficult.

Claims

1. A method for preparing inorganic perovskite thin films, characterized in that, Includes the following steps: A: Weigh out cesium halide and lead halide in a certain proportion, dissolve them in a mixed solution of dimethyl sulfoxide and dimethyl imide to prepare a solution with a designed stoichiometric ratio, and add a certain amount of acetate or oxalate after complete dissolution to obtain a precursor solution; B: The above precursor solution is coated on the substrate to obtain a pre-coated thin film, and then annealed for a certain time to obtain a perovskite thin film. C: A certain amount of methylamine iodide and cesium halide are dissolved in a specific solvent to prepare a post-treatment solution, or methylamine iodide is added to the hole transport layer solution, wherein the specific solvent is one of isopropanol, methanol, and ethanol; D: Spin-coat a layer of the post-treatment solution from step C or a hole transport layer solution containing methyl halide onto the perovskite film obtained in step B, and complete the film post-treatment after annealing. The amount of methyl iodide added to the hole transport layer solution is 0.1~0.7 g / L, and the hole transport layer solution is Spiro-OMeTAD, PTAA, or P3HT, and the solvent used is one of chlorobenzene and chloroform. The post-treatment annealing temperature is 50~100°C, and the annealing time is 4~15 minutes.

2. The method as described in claim 1, characterized in that, The added acetate or oxalate is one or more of lead acetate, lead acetate trihydrate, cesium acetate, cesium acetate dihydrate, and lead oxalate.

3. The method as described in claim 2, characterized in that, The total amount of acetate or oxalate added is 5% to 25% relative to the amount of lead halide in the precursor solution.

4. The method as described in claim 1, characterized in that, The annealing temperature of the preformed film is 80~150°C, and the annealing time is 5~25 minutes.

5. The method as described in claim 1, characterized in that, Cesium halides are one or more of cesium iodide, cesium bromide, and cesium chloride.

6. The method as described in claim 1, characterized in that, The concentration of the post-treatment solution is calculated based on halogen anions, and the concentration is 0.1~2 g / L.

7. The method as described in claim 1, characterized in that, The spin coating process in the post-processing stage needs to be dynamic, with a spin speed of 5000~8000 rpm and a spin coating time of 20~40 seconds.

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