An inorganic perovskite thin film, its preparation method and a solar cell

Abstract

This invention relates to an inorganic perovskite thin film, its preparation method, and a solar cell. The method includes the following steps: S1: forming a first thin film through a first vapor deposition process; S2: annealing the first thin film to obtain a second thin film; S3: forming a third thin film on the second thin film through a second vapor deposition process; and S4: annealing the second thin film and the third thin film to obtain the inorganic perovskite thin film; wherein, in the first vapor deposition process, the raw materials used for evaporation include cesium bromide and lead iodide; and in the second vapor deposition process, the raw materials used for evaporation include cesium iodide and lead iodide. The inorganic perovskite thin film prepared by the method of one embodiment of this invention, compared with existing inorganic perovskite thin films, improves the phase stability of the perovskite structure without affecting the light absorption range of the prepared solar cell, and simultaneously improves the photoelectric conversion efficiency of the cell.

Description

Technical Field

[0001] This invention relates to perovskite thin films, and more particularly to an inorganic perovskite thin film that can be used in solar cells and a method for preparing the same. Background Technology

[0002] A solar cell is a device that uses the photovoltaic effect to convert light energy into electrical energy. As an emerging photovoltaic material, metal halide perovskite was first used in solar cells in 2009. Due to its versatility and ease of manufacturing, it has brought about a revolutionary change in the photovoltaic field.

[0003] CsPbI3 inorganic perovskite, with its high chemical stability and wide band gap (1.73-1.77 eV), meets the requirements for the perovskite top cell in perovskite-perovskite-silicon triple-junction tandem solar cells, thus becoming the preferred top-layer light-absorbing material in triple-junction solar cells. However, the phase stability of inorganic perovskite remains a key issue to be solved in the field. At room temperature, the stable phase of CsPbI3 perovskite is usually a yellow phase without photoelectric effect, making it difficult to use in photovoltaic devices. Furthermore, CsPbI3 perovskite readily undergoes a phase transition to the yellow phase when exposed to moisture, resulting in poor phase stability.

[0004] Existing technologies improve the structure tolerance factor of CsPbI3 perovskites by using halide anion substitution, such as using bromine to partially or completely replace iodine to prepare bromine-containing inorganic perovskites. However, when the substitution amount is too high, not only is the optical band gap increased, but phase separation is also prone to occur, affecting the photoelectric conversion efficiency of the final battery device.

[0005] On the other hand, while traditional solution methods can prepare mixed anionic inorganic perovskites in any proportion, they easily introduce organic components from the solvent and suffer from poor solubility of the CsBr precursor components. Therefore, vapor deposition can completely avoid the use of organic solvents and eliminate the impact of large differences in the solubility of precursor components. However, traditional two-source co-vapor deposition processes cannot prepare low-Br content perovskites. - Mixed anionic inorganic perovskites with a content of <20% are prone to severe phase separation and blue shift of the optical bandgap. At the same time, multi-source deposition increases the difficulty of controlling the evaporation rate due to cross-influence. Summary of the Invention

[0006] Based on the above analysis, one embodiment of the present invention aims to provide an inorganic perovskite thin film to solve the problems of poor phase stability, wide optical bandgap, or low photoelectric conversion efficiency of existing inorganic perovskite thin films when used in solar cells.

[0007] In a first aspect, an embodiment of the present invention provides a method for preparing an inorganic perovskite thin film, comprising the following steps:

[0008] S1: A first thin film is formed by a first vapor deposition process;

[0009] S2: Anneal the first film to obtain the second film;

[0010] S3: Forming a third film on the second film by a second vapor deposition process; and

[0011] S4: Anneal the second film and the third film to obtain the inorganic perovskite film;

[0012] In the first vapor deposition process, the raw materials used for evaporation include cesium bromide and lead iodide; in the second vapor deposition process, the raw materials used for evaporation include cesium iodide and lead iodide.

[0013] According to one embodiment of the present invention, the annealing process in step S2 includes a first annealing process and a second annealing process, wherein the first annealing process is performed in an air environment and the second annealing process is performed in a nitrogen atmosphere.

[0014] According to one embodiment of the present invention, the temperatures of the first annealing treatment and the second annealing treatment are 250 to 270°C.

[0015] According to one embodiment of the present invention, the first annealing process takes 30 to 60 seconds, and the second annealing process takes 40 to 60 seconds.

[0016] According to one embodiment of the present invention, the annealing process in step S4 includes a third annealing process and a fourth annealing process, wherein the third annealing process is performed in an air environment and the fourth annealing process is performed in a nitrogen atmosphere.

[0017] According to one embodiment of the present invention, the temperatures of the third annealing treatment and the fourth annealing treatment are 320 to 370°C.

[0018] According to one embodiment of the present invention, the time for the third annealing process is 30 to 60 seconds, and the time for the fourth annealing process is 40 to 60 seconds.

[0019] According to one embodiment of the present invention, the thickness of the first thin film is 20 to 150 nm.

[0020] According to one embodiment of the present invention, the thickness of the first thin film is 80-150 nm.

[0021] According to one embodiment of the present invention, the inorganic perovskite thin film comprises the compound CsPbI 3-x Brx .

[0022] According to one embodiment of the present invention, the inorganic perovskite thin film comprises the compound CsPbI 3-x Br x and Cs4PbI 6- x Br x .

[0023] Secondly, one embodiment of the present invention provides an inorganic perovskite thin film, which is prepared by the method described above.

[0024] Thirdly, one embodiment of the present invention provides a solar cell comprising the aforementioned inorganic perovskite thin film.

[0025] According to one embodiment of the present invention, the solar cell includes:

[0026] Electron transport layer;

[0027] An absorption layer is disposed on the electron transport layer; and

[0028] A hole transport layer is disposed on the absorption layer;

[0029] The absorber layer includes the inorganic perovskite thin film.

[0030] Fourthly, one embodiment of the present invention provides a tandem solar cell comprising the aforementioned inorganic perovskite thin film.

[0031] The inorganic perovskite thin film prepared by the method of one embodiment of the present invention improves the phase stability of the perovskite structure compared with existing inorganic perovskite thin films, without affecting the light absorption range of the prepared solar cell, and can improve the photoelectric conversion efficiency of the cell.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention. Wherein:

[0034] Figure 1 This is a schematic flowchart of a method for preparing an inorganic perovskite thin film according to an embodiment of the present invention.

[0035] Figure 2AThis is a schematic diagram of the structure of CsPbI2Br;

[0036] Figure 2B This is a schematic diagram of the structure of CsPbI3;

[0037] Figure 3 This is a schematic diagram of the structure of a solar cell according to an embodiment of the present invention;

[0038] Figure 4 This is an XRD phase analysis diagram of the inorganic perovskite thin film of Example 1 of the present invention;

[0039] Figure 5A The XRD phase detection images are of the inorganic perovskite thin films of Example 1 and Comparative Example 1 of this invention.

[0040] Figure 5B The XRD phase development patterns of the inorganic perovskite thin films of Examples 1 (1) and Comparative Examples 1 (2) of this invention are shown in the range of 19° to 25°.

[0041] Figure 5C The XRD phase development patterns of the inorganic perovskite thin films of Examples 1 (1) and Comparative Examples 1 (2) of the present invention are in the range of 28° to 29.5°.

[0042] Figure 6 This is a UV-vis image of the stability tracking test of the inorganic perovskite thin film of Example 1 of the present invention in a dry room temperature air environment;

[0043] Figure 7 This is a cross-sectional scanning electron microscope image of the solar cell of Embodiment 2 of the present invention;

[0044] Figure 8 The JV scan curve of the inorganic perovskite solar cell of Example 2 of the present invention;

[0045] Figure 9 Box plots showing the photoelectric conversion efficiency of the solar cell devices prepared in Examples 2 (120nm) and 3 (20nm, 80nm, 150nm) of this invention;

[0046] Figure 10 Box plots showing the photoelectric conversion efficiency performance of the solar cell devices prepared in Embodiment 2 and Comparative Example 3 of this invention;

[0047] Figure 11 CsPbI in Embodiment 2 of the present invention 3-x Br x A comparison of the stability of inorganic perovskite solar cells and Comparative Example 2's CsPbI3 inorganic perovskite solar cells in a dry, room-temperature air environment.

[0048] The annotations in the attached figures are explained as follows:

[0049] 10. Substrate; 20. First electrode; 30. Electron transport layer; 40. Absorption layer; 50. Hole transport layer; 60. Second electrode. Detailed Implementation

[0050] The preferred embodiments of the present invention will be described in detail below. The accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0051] Reference Figure 1 As shown, one embodiment of the present invention provides a method for preparing an inorganic perovskite thin film, comprising the following steps:

[0052] S1: A first thin film is formed by a first vapor deposition process;

[0053] S2: Anneal the first film to obtain the second film;

[0054] S3: A third thin film is formed on the second thin film by a second vapor deposition process; and

[0055] S4: Anneal the second and third films to obtain an inorganic perovskite film.

[0056] In the first vapor deposition process, the raw materials used for evaporation include cesium bromide (CsBr) and lead iodide (PbI2); in the second vapor deposition process, the raw materials used for evaporation include cesium iodide (CsI) and lead iodide (PbI2).

[0057] In one embodiment, the inorganic perovskite thin film obtained includes the compound CsPbI. 3-x Br x .

[0058] In one embodiment, the second thin film comprises the compound CsPbI2Br, and the third thin film comprises the compound CsPbI3, wherein the structures of CsPbI2Br and CsPbI3 are as follows: Figure 2A , 2B .

[0059] In one embodiment, the chemical composition of the crystal structure of the obtained inorganic perovskite thin film includes CsPbI. 3- x Br x Where x can be less than 1, that is, Br - with I - The molar ratio is less than 1 / 2.

[0060] The preparation method of one embodiment of the present invention uses a two-stage vapor-phase co-evaporation deposition process to prepare an inorganic perovskite thin film, and then performs co-annealing treatment on the second and third films to allow Br to... - Uniform diffusion from bottom to top from the second film to the third film helps Br - The appropriate introduction of certain amounts of evaporation feedstocks also contributes to Br. - The appropriate introduction of Br avoids - The optical bandgap widening caused by excessive content (resulting in excessive blue shift) and the effect of this bandgap change on the light absorption range resulted in an inorganic perovskite thin film with a light absorption bandgap (1.73 eV to 1.77 eV) suitable for the top cell of a tandem solar cell.

[0061] On the other hand, the introduced Br - Promotes zero-dimensional Cs4PbI with low formation energy 6-x Br x The increased content of zero-dimensional Cs4PbI 6-x Br x The structure surrounding the three-dimensional perovskite structure increases the surface energy of the three-dimensional bulk perovskite, forming a highly stable "molecular lock," thus suppressing the phase transition of the three-dimensional perovskite and improving the phase stability of the inorganic perovskite structure. Simultaneously, zero-dimensional Cs₄PbI₄... 6-x Br x The (004) crystal plane of perovskite and three-dimensional CsPbI 3-x Br x The (200) crystal plane of perovskite has a low lattice mismatch (<10%), allowing for eutectic growth. Therefore, zero-dimensional Cs₄PbI₄... 6-x Br x The increased content promoted the three-dimensional CsPbI 3-x Br x The preferred orientation of the (200) crystal plane of perovskite is beneficial to the transmission of longitudinal photocurrent, which can further improve the stability and photoelectric conversion efficiency of inorganic perovskite solar cells.

[0062] In one embodiment, the chemical composition of the crystal structure of the obtained inorganic perovskite thin film includes CsPbI. 3- x Br x and Cs4PbI 6-x Br x .

[0063] In one embodiment, the first thin film is prepared by a vapor-phase co-evaporation process in step S1; step S1 may include: placing a substrate and two evaporation sources, cesium bromide and lead iodide, in an evaporation chamber, and then evacuating the chamber; waiting for the chamber vacuum level to reach 10 - 4When the temperature is below Pa, the substrate temperature is set, and the evaporation rates of lead iodide and cesium bromide are adjusted to stabilize. After the evaporation source rate stabilizes, the substrate is turned on and kept rotating, the substrate baffle is opened, and a vapor-phase co-evaporation deposition film is performed to form a first film on the substrate, resulting in a "substrate / first film" structure.

[0064] In one embodiment, the evaporation rate of lead iodide in step S1 can be... For example The evaporation rate of cesium bromide can be For example

[0065] In one embodiment, the evaporation temperature of lead iodide in step S1 is 300-315°C, for example 305°C, 310°C, 313°C, or 315°C; and the evaporation current of lead bromide is 102A-108A, for example 103A, 105A, or 107A.

[0066] In one embodiment, the molar ratio M1 of cesium bromide to lead iodide in step S1 is 0 < M1 ≤ 1, for example, M1 is 0.01, 0.1, 0.2, 0.5, 0.8, 0.9 or 1.

[0067] In one embodiment, the thickness of the first thin film formed in step S1 can be 20–150 nm, further 80–150 nm, even further 110–130 nm, and still further 115–125 nm. When the thickness of the first thin film is in the range of 80–150 nm, using the prepared inorganic perovskite thin film as the absorber layer of the solar cell can enable the solar cell to have a higher photoelectric conversion efficiency.

[0068] In one embodiment, the thickness of the first thin film can be, for example, 30nm, 50nm, 60nm, 70nm, 85nm, 90nm, 100nm, 110nm, 115nm, 120nm, 125nm, 130nm, or 140nm.

[0069] In one embodiment, the annealing process in step S2 includes two annealing processes, namely a first annealing process and a second annealing process; the temperature of both the first and second annealing processes can be 250-270°C, for example 255°C, 258°C, 260°C, 262°C, 265°C, and 268°C; the time of the first annealing process can be 30-60 seconds, for example 35 seconds, 40 seconds, 45 seconds, 50 seconds, and 55 seconds; the time of the second annealing process can be 40-60 seconds, for example 45 seconds, 50 seconds, and 55 seconds.

[0070] In one embodiment, step S2 includes: performing a first annealing treatment on the "substrate / first thin film" structure in an air environment; after the first annealing treatment, placing the thin film in a nitrogen atmosphere for a second annealing treatment to obtain a "substrate / second thin film" structure. The second thin film can be a CsPbI2Br perovskite thin film. The two annealing treatments can improve crystallinity and purify the perovskite black phase.

[0071] In one embodiment, step S3 includes: placing the "substrate / second thin film" structure obtained in step S2 into the evaporation chamber, simultaneously placing cesium iodide and lead iodide evaporation sources in the evaporation chamber, and then evacuating the chamber; waiting for the chamber vacuum level to reach 10... -4 When the temperature is below Pa, the substrate temperature is set, and the evaporation rates of lead iodide and cesium iodide are adjusted to stabilize. After the evaporation source rate stabilizes, the substrate is turned on and kept rotating, the substrate baffle is opened, and a second vapor-phase co-evaporation deposition of the thin film is performed to obtain the third thin film, forming a "substrate / second thin film / third thin film" structure.

[0072] In one embodiment, the evaporation rate of lead iodide in step S3 can be... For example The evaporation rate of cesium iodide can be For example

[0073] In one embodiment, the evaporation temperature of lead iodide in step S3 is 290 to 298°C, for example 292°C, 294°C, 295°C, 296°C, or 298°C; and the evaporation current of lead iodide is 102A to 105A, for example 103A or 104A.

[0074] In one embodiment, the molar ratio M2 of lead iodide and cesium iodide in step S3 is 1:1.

[0075] In one embodiment, the thickness of the third film can be 300-400 nm, for example 320 nm, 330 nm, 350 nm, 360 nm, 380 nm, or 400 nm.

[0076] In step S4 of one embodiment, Br - Driven by high-temperature annealing, perovskite diffuses into the crystal lattice, simultaneously promoting zero-dimensional Cs4PbI. 6-x Br x The formation of "molecular locks" leads to the formation of CsPbI based on a zero-dimensional structurally stable structure. 3- x Br x Inorganic perovskite thin films.

[0077] In one embodiment, the annealing process in step S4 includes two annealing processes, namely a third annealing process and a fourth annealing process; the temperature of both the third and fourth annealing processes can be 320-370°C, for example 330°C, 340°C, 345°C, 348°C, 350°C, 352°C, 355°C, 358°C, 360°C, and 365°C; the time of the third annealing process can be 30-60 seconds, for example 35 seconds, 40 seconds, 45 seconds, 50 seconds, and 55 seconds; the time of the fourth annealing process can be 40-60 seconds, for example 45 seconds, 50 seconds, and 55 seconds.

[0078] In one embodiment, step S4 includes: placing the "substrate / second thin film / third thin film" structure in an air environment for a third annealing treatment; after the third annealing treatment, placing the obtained structure in a nitrogen atmosphere for a fourth annealing treatment to obtain CsPbI 3-x Br x Inorganic perovskite thin films.

[0079] One embodiment of the present invention provides a perovskite thin film prepared by the method described above.

[0080] In one embodiment, the thickness of the inorganic perovskite film can be 500–520 nm, for example, 505 nm, 510 nm, or 515 nm.

[0081] The perovskite thin film of one embodiment of the present invention can be used in solar cells, particularly as an absorber layer in solar cells.

[0082] One embodiment of the present invention provides a solar cell comprising the perovskite thin film described above.

[0083] Reference Figure 3 As shown, a solar cell according to one embodiment of the present invention includes:

[0084] Base 10;

[0085] The first electrode 20 is disposed on the substrate 10;

[0086] An electron transport layer 30 is disposed on the first electrode 20;

[0087] An absorption layer 40 is disposed on the electron transport layer 30;

[0088] Hole transport layer 50 is disposed on absorber layer 40; and

[0089] The second electrode 60 is disposed on the hole transport layer 50;

[0090] The absorber layer 40 is the aforementioned inorganic perovskite thin film.

[0091] In one embodiment, the substrate 10 may be a glass substrate, the first electrode 20 may be a transparent conductive electrode, and the second electrode 60 may be a metal electrode, such as a gold electrode, with a thickness of 100-120 nm.

[0092] In one embodiment, the electron transport layer 30 can be a dense TiO2 layer with a thickness of 20-40 nm; the hole transport layer 50 can be a Spiro-OMeTAD layer (2,2',7,7'-tetratetraN,N-di(4-methoxyphenyl)amino-9,9'-spirodifluorene) with a thickness of 150-250 nm.

[0093] One embodiment of the present invention provides a tandem solar cell comprising the above-mentioned inorganic perovskite thin film.

[0094] In one embodiment, the tandem solar cell is a perovskite-perovskite-silicon tandem solar cell, comprising CsPbI₂ cells stacked in series. 3-x Br x Solar cells, Cs x FA 1-x PbI3 solar cells and silicon solar cells.

[0095] The inorganic perovskite thin film of one embodiment of the present invention is prepared by a two-stage vapor-phase co-evaporation deposition process. Since the vapor-phase deposition process does not introduce organic solvents, the inorganic perovskite thin film does not contain the organic components commonly found in solution-based synthesis, thus contributing to the material's excellent carrier transport properties. Furthermore, the vapor-phase deposition process for preparing perovskite thin films achieves the goal of uniformly covering a textured silicon substrate while maintaining the integrity of the textured silicon's pyramidal structure. Therefore, it contributes to achieving silicon tandem solar cells with excellent photovoltaic performance and provides an effective pathway for developing high-efficiency photovoltaic technologies that can be industrialized on a large scale.

[0096] An inorganic perovskite thin film according to one embodiment of the present invention, by introducing an appropriate amount of Br - This promotes a more stable zero-dimensional Cs4PbI 6-x Br x The in-situ formation of the "molecular lock" structure improves the phase stability of inorganic perovskite without affecting the light absorption range of the fabricated solar cell, while also enhancing the photoelectric conversion efficiency. In particular, the fabricated inorganic perovskite thin film possesses an optical bandgap of 1.73–1.77 eV, facilitating the tandem application of inorganic perovskite solar cells with silicon-based perovskite cells. For example, it can be used to fabricate perovskite-perovskite-silicon tandem solar cells. By replacing traditional III-V group semiconductor cells with perovskite solar cells, expensive manufacturing costs can be avoided.

[0097] A solar cell according to one embodiment of the present invention, due to the presence of Br in its inorganic perovskite thin film absorber layer... - The appropriate content avoids the effects of Br - The excessive introduction of phase separation eliminates the obstruction to effective photocurrent transmission caused by severe phase separation, thereby improving the stability and photoelectric conversion efficiency of the battery. Simultaneously, the eutectic growth of the zero-dimensional (400) crystal plane and the three-dimensional (200) crystal plane promotes the preferred orientation of the inorganic perovskite (200) crystal plane, which is beneficial for photocurrent transmission; for example, it can enable the photoelectric conversion efficiency of the fabricated single-cell photovoltaic device to reach 15.60%.

[0098] The preparation of an inorganic perovskite thin film and solar cell according to an embodiment of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, all raw materials used are commercially available.

[0099] Example 1 Inorganic perovskite thin film (CsPbI) 3-x Br x Preparation of )

[0100] S1: Preparation of the first thin film

[0101] (1) Electronic-grade glass was selected as the substrate. First, the electronic-grade glass was rinsed several times with deionized water. Then, the rinsed substrate was ultrasonically treated with deionized water, acetone and ethanol as solvents in sequence, and ultrasonicated at room temperature for 10 minutes each. The ultrasonically treated electronic-grade glass was dried with nitrogen gas and then treated with oxygen plasma to enhance the bonding force and adhesion of the substrate material surface.

[0102] (2) Place cesium bromide and lead iodide powder in the evaporation source inside the vacuum evaporation chamber, and place the substrate obtained in step (1) on the sample holder inside the vacuum chamber. Close the chamber door and evacuate the vacuum.

[0103] (3) Wait until the vacuum degree reaches 10 -4 At the Pa level, the substrate temperature was set to 150°C, and the lead iodide evaporation rate was adjusted to... The rate of cesium bromide is

[0104] (4) After the evaporation source rate stabilizes, the substrate baffle is opened to begin depositing a thin film with a thickness of 120 nm. The substrate is rotated during the deposition process, and a “substrate / first thin film” structure is obtained after the deposition is completed.

[0105] S2: Preparation of the second thin film

[0106] The "substrate / first thin film" structure obtained in step S1 is placed in an air environment and subjected to a first annealing at 260°C for 40 seconds. After the first annealing, the obtained structure is placed in a nitrogen atmosphere for a second annealing at 260°C for 60 seconds. After the annealing, a "substrate / second thin film" structure is obtained, and the second thin film is a CsPbI2Br thin film.

[0107] S3: Preparation of the third thin film

[0108] (1) Place cesium iodide and lead iodide powder in the evaporation source inside the vacuum evaporation chamber, and place the “substrate / second thin film” structure obtained in step S2 on the sample holder inside the vacuum chamber. Close the chamber door and evacuate the vacuum.

[0109] (2) Wait until the vacuum degree reaches 10 -4 At the Pa level, the substrate temperature was set to 150°C, and the lead iodide evaporation rate was adjusted to... The rate of cesium iodide is

[0110] (3) After the evaporation source rate stabilizes, the substrate baffle is opened to start the deposition of a thin film with a thickness of 400 nm. The substrate is rotated during the deposition process. After the deposition is completed, a “substrate / second thin film / third thin film” structure is obtained.

[0111] S4: Formation of all-inorganic perovskite thin films

[0112] The "substrate / second thin film / third thin film" structure obtained in step S3 is placed in an air environment and subjected to a first annealing at 350°C for 40 seconds. After the first annealing, the resulting structure is placed in a nitrogen atmosphere for a second annealing at 350°C for 60 seconds. After the second annealing, CsPbI₂ is obtained. 3-x Br x All-inorganic perovskite thin films.

[0113] Comparative Example 1: Preparation of Inorganic Perovskite Thin Film (CsPbI3)

[0114] (1) The substrate is prepared in the same manner as step (1) in S1 of Example 1;

[0115] (2) Place cesium iodide and lead iodide powder in the evaporation source inside the vacuum evaporation chamber, and place the substrate obtained in step (1) on the sample holder inside the vacuum chamber. Close the chamber door and evacuate the vacuum.

[0116] (3) Wait until the vacuum degree reaches 10 -4 At the Pa level, the substrate temperature was set to 150°C, and the lead iodide evaporation rate was adjusted to... The rate of cesium iodide is

[0117] (4) After the evaporation source rate stabilizes, open the substrate baffle to start depositing a thin film with a thickness of 520 nm. Keep the substrate rotating during the deposition process.

[0118] (5) After deposition, the obtained film was placed in the air environment and annealed for the first time at 350°C for 40 seconds.

[0119] (6) After the first annealing, the obtained film is placed in a nitrogen atmosphere for a second annealing at 350°C for 60s. After the annealing, the CsPbI3 inorganic perovskite film can be obtained.

[0120] Example 2 Inorganic perovskite (CsPbI) 3-x Br x Preparation of solar cells

[0121] Substrate preparation

[0122] Fluorine-doped tin dioxide (FTO) conductive glass was selected as the substrate. First, the FTO conductive glass was rinsed several times with deionized water. Then, the rinsed substrate was ultrasonically treated sequentially with deionized water, acetone, and ethanol as solvents, each for 10 minutes. The ultrasonically treated FTO conductive glass was dried with nitrogen gas, and then treated with oxygen plasma to enhance the bonding and adhesion of the substrate surface.

[0123] Fabrication of electron transport layer

[0124] Tetrabutyl titanate was dissolved in ethanol to prepare an ethanol solution of tetrabutyl titanate, which was used as a precursor solution for preparing a dense TiO2 thin film. The volume percentage of tetrabutyl titanate in the precursor solution was 10%. The precursor solution was deposited on the above-treated FTO conductive glass substrate by spin coating, and then sintered at 500°C for 30 minutes to form a dense TiO2 thin film, thus obtaining a "substrate / electron transport layer" structure.

[0125] Preparation of the absorption layer

[0126] An inorganic perovskite thin film (CsPbI) was prepared on the surface of the electron transport layer in the "substrate / electron transport layer" structure using the same steps and raw materials as in Example 1. 3-x Br x This yields a "substrate / electron transport layer / absorption layer" structure.

[0127] Preparation of hole transport layer

[0128] 73.4 mg of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene, 17.5 μL of lithium bis(trifluoromethanesulfonyl)imide acetonitrile solution, 16 μL of cobalt bis(trifluoromethanesulfonyl)imide acetonitrile solution, and 28 μL of 4-tert-butylpyridine were dissolved in chlorobenzene to form a mixed solution system. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the lithium bis(trifluoromethanesulfonyl)imide acetonitrile solution was 500 mg / mL, and the concentration of cobalt bis(trifluoromethanesulfonyl)imide in the cobalt bis(trifluoromethanesulfonyl)imide acetonitrile solution was 375 mg / mL. 40 μL of this mixed solution was spin-coated onto the surface of the absorber layer of the "substrate / electron transport layer / absorber layer" structure to form a hole transport layer on the absorber layer, thus obtaining the "substrate / electron transport layer / absorber layer / hole transport layer" structure.

[0129] Preparation of electrode layer

[0130] A 100 nm thick layer of metallic Au was deposited as an electrode layer on the hole transport layer of the aforementioned "substrate / electron transport layer / absorption layer / hole transport layer" structure using a vapor deposition method to obtain CsPbI. 3-x Br x Inorganic perovskite solar cells.

[0131] Example 3 contains different inorganic perovskites (CsPbI) 3-x Br x Fabrication of multiple solar cells

[0132] This embodiment uses the same steps and raw materials as Example 2 to prepare three types of solar cells. The only difference is that in the preparation of the absorption layer, the thickness of the first film deposited in step S1(4) of Example 2 is 120 nm, while the thicknesses of the first films deposited in step S1(4) of the three types prepared in Example 3 are 20 nm, 80 nm and 150 nm, respectively.

[0133] Comparative Example 2: Fabrication of Inorganic Perovskite (CsPbI3) Solar Cells

[0134] This example uses essentially the same steps and raw materials as Example 2 to prepare a solar cell, the only difference being that the same steps and raw materials are used in the preparation of the absorber layer as in Comparative Example 1 to prepare an inorganic perovskite thin film (CsPbI3).

[0135] Comparative Example 3 Inorganic perovskite (CsPbI) 3-x Br x Preparation of solar cells

[0136] This example uses essentially the same steps and raw materials as Example 2 to prepare a solar cell, the only difference being that the absorber layer, perovskite (CsPbI), is prepared using the following method. 3-x Br x)film.

[0137] (1) Electronic grade glass is selected as the substrate. First, the electronic grade glass is rinsed several times with deionized water. Then, the rinsed substrate is ultrasonically treated with deionized water, acetone and ethanol as solvents in sequence, and each is ultrasonicated at room temperature for 10 minutes. The ultrasonically treated electronic grade glass is dried with nitrogen and then treated with oxygen plasma to enhance the bonding force and adhesion of the substrate material surface.

[0138] (2) Place cesium bromide and lead iodide powder with the same molar ratio as in Example 2 into the evaporation source in the vacuum evaporation chamber, and place the substrate obtained in step (1) on the sample holder in the vacuum chamber, close the chamber door, and evacuate the vacuum.

[0139] (3) Wait until the vacuum degree reaches 10 -4 At the Pa level, the substrate temperature was set to 150°C, and the lead iodide evaporation rate was adjusted to... The rate of cesium bromide is

[0140] (4) After the evaporation source rate stabilizes, open the substrate baffle to start depositing a thin film with a thickness of 520 nm. Keep the substrate rotating during the deposition process.

[0141] (5) After deposition, the film is placed in the air environment and annealed for the first time at 260°C for 40 seconds.

[0142] (6) After the first annealing, the obtained film was placed in a nitrogen atmosphere for a second annealing at 260°C for 60 seconds. After annealing, CsPbI was obtained. 3-x Br x Inorganic perovskite thin films.

[0143] The perovskite films prepared in Example 1 and Comparative Example 1 were subjected to XRD phase analysis, and the detection spectra are shown below. Figure 4 , 5A As shown in 5C. Figure 4 The results show that the perovskite film prepared in Example 1 has high crystallinity; Figure 4 , 5B The "*" peak in the 5C ((1) curve) represents Cs4PbI 6-x Br x The peak indicates that Cs4PbI has formed in the perovskite film prepared in Example 1. 6-x Br x The structure can improve the phase stability of the perovskite structure. Additionally, Figure 5B , 5C This indicates that the CsPbI prepared in Example 1 3-x Br xThe all-inorganic perovskite thin film ((1) curve) has a preferred orientation of the (200) crystal plane, which will ultimately be beneficial to the effective transmission of photocurrent in the device.

[0144] The perovskite film prepared in Example 1 was further stored at room temperature in a dry air environment for phase stability monitoring. The UV-vis detection results are as follows: Figure 6 As shown. Figure 6 The results show that the CsPbI prepared in Example 1 3-x Br x The perovskite film exhibits high phase stability, which also indicates that the light absorption initiation band edge of the perovskite film is located between 700 nm and 720 nm. The corresponding light absorption band gap is calculated by the Tauc-plot method, which is between 1.73 eV and 1.77 eV, matching the optical band gap of the top cell in a perovskite-perovskite-silicon tandem solar cell.

[0145] In addition, from Figure 6 It can also be seen that the final formed inorganic perovskite thin film CsPbI 3-x Br x The molar ratio of Br to I in the film is less than 1:2. Since the optical band gap in the thin film increases with increasing bromine content, according to... Figure 6 It can be seen that the absorption band edge of the final perovskite film is located between 700 nm and 720 nm, which is smaller than the absorption initiation band edge of CsPbI2Br (which is generally accepted in the literature to be located at 646 nm). Therefore, the optical band gap of the final inorganic perovskite film is smaller than that of CsPbI2Br, and its bromine content will also be smaller than that of CsPbI2Br.

[0146] Figure 7 This is a cross-sectional scanning electron microscope image of the solar cell of Embodiment 2 of the present invention. Figure 7 It can be seen that the obtained solar cell consists of a total of 5 thin film structures, and the inorganic perovskite thin film, which serves as the light-absorbing layer, has a flat and dense film morphology, which ensures good photoelectric conversion efficiency.

[0147] The CsPbI obtained in Example 2 3-x Br x The photoelectric conversion efficiency of the inorganic perovskite solar cell was tested, and the test results are as follows: Figure 8 As shown. Figure 8 The results show that the solar cell prepared in Example 2 has a high photoelectric conversion efficiency, up to 15.60%.

[0148] Multiple solar cells were prepared using the same methods as in Examples 2 and 3, and the resulting solar cells were subjected to relevant tests. Figure 9Box plots show the photoelectric conversion efficiency of solar cell devices prepared according to the methods of Example 2 (120nm) and Example 3 (20nm, 80nm, 150nm). By comparison, it can be seen that by keeping the thickness of the first thin film in the range of 80 to 150nm during the preparation of the inorganic perovskite thin film, the resulting solar cell has a higher photoelectric conversion efficiency.

[0149] Multiple solar cells were prepared using the same methods as in Example 2 and Comparative Example 3, and the resulting solar cells were subjected to relevant tests. Figure 10 Box plots showing the photoelectric conversion efficiency of solar cell devices prepared according to the methods of Example 2 and Comparative Example 3. A comparison shows that the CsPbI prepared using a secondary vapor-phase co-evaporation deposition process in Example 2... 3- x Br x The thin-film solar cell formed is superior to the CsPbI solar cell of Comparative Example 3, which was prepared using a single vapor-phase co-evaporation deposition process. 3-x Br x Thin-film solar cells have higher photoelectric conversion efficiency.

[0150] The CsPbI obtained in Example 2 3-x Br x Inorganic perovskite solar cells and the CsPbI3 inorganic perovskite solar cells prepared in Comparative Example 2 were simultaneously stored in a dry room temperature air environment (RH < 10%, RT) to track and compare the phase transition of inorganic perovskite cells obtained by the two deposition processes. The results are as follows: Figure 11 As shown. The non-perovskite phase (yellow phase) without photovoltaic effect has a higher optical band gap (greater than 2.8 eV), and the optical photographs of the film appear yellow; while the perovskite phase (black phase) with good photovoltaic effect has a narrower band gap (close to 1.76 eV), and the optical photographs of the film appear almost black. According to... Figure 11 The optical photographs of Comparative Example 2's CsPbI3 inorganic perovskite solar cell showed that within 4 days, the optical photographs of the latter had completely approached a yellowish color. Figure 11 The light-absorbing layer of perovskite appears light-colored or colorless, indicating that it is in a nearly completely yellow phase and does not have a light-absorbing effect; while the CsPbI in Example 2... 3-x Br x Optical photographs of inorganic perovskite solar cells are nearly black. Figure 11 The light-absorbing layer appears dark or black, indicating that it remains in a black phase and maintains good light absorption. These results demonstrate that the cell in Example 2 possesses higher phase stability, providing material-level assurance for the efficient and stable photovoltaic performance of perovskite-perovskite-silicon tandem solar cells.

[0151] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an inorganic perovskite thin film, comprising the following steps: S1: A first thin film is formed by a first vapor deposition process; S2: Anneal the first film to obtain the second film; S3: Forming a third film on the second film by a second vapor deposition process; and S4: Anneal the second film and the third film to obtain the inorganic perovskite film; wherein, In the first vapor deposition process, the raw materials used for evaporation include cesium bromide and lead iodide; in the second vapor deposition process, the raw materials used for evaporation include cesium iodide and lead iodide. The inorganic perovskite thin film is prepared by a two-step gas phase co-deposition process. Through co-annealing of the second thin film and the third thin film, Br - is uniformly diffused from the second thin film to the third thin film.

2. The method of claim 1, wherein, The annealing process in step S2 includes a first annealing process and a second annealing process. The first annealing process is carried out in an air environment, and the second annealing process is carried out in a nitrogen atmosphere.

3. The method of claim 2, wherein, The temperatures for the first and second annealing treatments are 250–270°C; and / or, The first annealing process takes 30 to 60 seconds, and the second annealing process takes 40 to 60 seconds.

4. The method of claim 1, wherein, The annealing process in step S4 includes a third annealing process and a fourth annealing process. The third annealing process is carried out in an air environment, and the fourth annealing process is carried out in a nitrogen atmosphere.

5. The method of claim 4, wherein, The temperatures for the third and fourth annealing processes are 320–370°C; and / or, The third annealing process takes 30 to 60 seconds, and the fourth annealing process takes 40 to 60 seconds.

6. The method of claim 1, wherein, The thickness of the first thin film is 20–150 nm.

7. The method according to claim 6, wherein the thickness of the first film is 80-150 nm.

8. An inorganic perovskite thin film, prepared by the method according to any one of claims 1 to 7.

9. A solar cell comprising the inorganic perovskite thin film of claim 8.

10. A tandem solar cell comprising the inorganic perovskite thin film of claim 8.

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