Copper bismuth sulpho-chloro thin films, method for their preparation, solar cells and photovoltaic modules

Abstract

A copper bismuth sulfide chloride film includes a plurality of CuBiSCl2 grains. The CuBiSCl2 grains are platelet-shaped and have a length, a width and a thickness, wherein the length is greater than the width and the thickness. The length of the CuBiSCl2 grain refers to the widest one of the dimensions of the projection of the CuBiSCl2 grain along its thickness direction, and the width refers to the dimension of the projection of the CuBiSCl2 grain along its thickness direction in a direction perpendicular to the length direction. In the copper bismuth sulfide chloride film, the plurality of CuBiSCl2 grains are stacked layer by layer, and the angle between the thickness direction of 80% to 90% of the CuBiSCl2 grains and the thickness direction of the copper bismuth sulfide chloride film is 0 to 10 degrees. The application also provides a preparation method of the copper bismuth sulfide chloride film, a solar cell containing the copper bismuth sulfide chloride film and a photovoltaic module. The film morphology of the application is compact, the film forming quality is high, the charge transport is facilitated, the conductivity is increased, and the stability can be greatly improved.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and more specifically, to a copper bismuth sulfur chloride thin film and its preparation method, including solar cells and photovoltaic modules using the copper bismuth sulfur chloride thin film. Background Technology

[0002] Perovskite solar cells have attracted much attention due to their rapidly improving power conversion efficiency, but their inherent poor long-term stability limits their commercialization. One reason for the low stability of halide perovskites is the weak ionic binding energy between monovalent halides and divalent lead ions. Compared with high-efficiency halide inorganic thin-film solar cells, chalcogenide inorganic thin-film solar cells have attracted much attention due to their excellent long-term water and oxygen stability. Therefore, it is essential to develop ideal photovoltaic materials based on chalcogenide-halide hybrid compounds that are stable, lead-free, and have few defects. Summary of the Invention

[0003] In view of this, this application provides a copper bismuth sulfur chloride thin film that is lead-free, stable, and has defect-tolerant properties similar to those of halide perovskites. That is, the main defects in copper bismuth sulfur chloride are shallow and do not act as strong non-radiative recombination centers, thus helping to maintain high photoelectric conversion efficiency. Moreover, the preparation process is simple.

[0004] A copper-bismuth-sulfur-chloride thin film includes a plurality of CuBiSCl2 grains. The CuBiSCl2 grains are plate-shaped and have a length, width, and thickness, wherein the length is greater than the width and the thickness. The length of the CuBiSCl2 grain refers to the widest dimension of the projection of the CuBiSCl2 grain along its thickness direction, and the width of the CuBiSCl2 grain is the dimension of the projection of the CuBiSCl2 grain along its thickness direction in the direction perpendicular to the length direction. In the copper-bismuth-sulfur-chloride thin film, the plurality of CuBiSCl2 grains are stacked layer by layer, and the angle between the thickness direction of most of the CuBiSCl2 grains and the thickness direction of the copper-bismuth-sulfur-chloride thin film is 0-10 degrees.

[0005] In this application, the copper-bismuth-sulfur-chloride thin film is characterized by a predominantly flat CuBiSCl2 grain arrangement on the substrate, closely adjacent in the horizontal direction. Simultaneously, along the thickness direction of the film, the grains exhibit a stacking fault arrangement, with overlapping grains. This means that in certain areas, the grains may completely contact and fuse, forming gapless connections. Consequently, the copper-bismuth-sulfur-chloride thin film is dense, exhibiting high film quality, which is beneficial for charge transport, increases conductivity, and significantly improves stability.

[0006] As one possible implementation, along the thickness direction of the copper-bismuth-sulfur-chloride thin film, the plurality of CuBiSCl2 grains are arranged in a stacked fault pattern, and the projections of adjacent CuBiSCl2 grains along the thickness direction of the copper-bismuth-sulfur-chloride thin film will at least partially overlap.

[0007] As one possible implementation, the angle between the thickness direction of 10%-20% of the CuBiSCl2 grains and the thickness direction of the copper bismuth sulfur chloride film is greater than 10 degrees and less than or equal to 90 degrees.

[0008] As one possible implementation, the length of the CuBiSCl2 grains is distributed between 0.2 and 3 μm, and the thickness of the CuBiSCl2 grains is distributed between 0.2 and 0.5 μm.

[0009] In one possible implementation, the plurality of CuBiSCl2 grains are divided into large-sized grains, small-sized grains, and intermediate-sized grains. The large-sized grains have a length of 1 to 2 μm, the small-sized grains have a length of 0.2 to 0.5 μm, and the intermediate-sized grains have a length of 0.5 to 1 μm, excluding 0.5 μm and 1 μm. The large-sized grains account for 75% to 85% of the total number of grains, the small-sized grains account for 10% to 20% of the total number of grains, and the remainder are the intermediate-sized grains.

[0010] Secondly, this application provides a method for preparing a copper-bismuth-sulfur-chloride thin film, comprising: Bi2S3 powder and CuCl2 powder are mixed with a solvent and then ground to form a slurry. The solvent is an organic alcohol. The slurry is placed on a substrate and annealed at a temperature of 100℃~400℃ to form a copper bismuth sulfur chloride film.

[0011] The conventional preparation process involves first sintering Bi₂S₃ powder and CuCl₂ powder at high temperatures to form CuBiSCl₂ (this high-temperature sintering process is both time-consuming and involves high temperatures), then coating the CuBiSCl₂ slurry to form a CuBiSCl₂ thin film. The conventional high-temperature sintering process requires stringent reaction conditions to form a high-quality bulk material. Precise control of reaction conditions, such as temperature and time, is necessary during synthesis to ensure the formation of the correct phase. Temperature control is challenging during rapid thermal annealing (RTP) curing. This process can lead to the formation of secondary phases, which negatively impact the film's quality and optical properties. Excessively high annealing temperatures can also promote the formation of pores / holes in the film. During slurry formation, the physically dispersed powder exhibits poor grain size uniformity, resulting in lower film density, less grain overlap, poor conductivity, and numerous defects. As a light-absorbing layer, this leads to severe carrier recombination, resulting in low photoelectric conversion performance of the fabricated solar cell.

[0012] This application uses a mixture of Bi₂S₃ powder and CuCl₂ powder (or Bi₂S₃ powder, CuCl₂ powder, and BiCl₃ powder) to form a slurry, which is then coated and annealed to form a CuBiSCl₂ thin film. During the annealing process, Bi₂S₃ reacts with CuCl₂ to form CuBiSCl₂, or Bi₂S₃, CuCl₂, and BiCl₃ react to form CuBiSCl₂. Thus, the preparation method of the copper-bismuth-sulfur-chloride thin film in this application uses raw materials to form a slurry, and then directly forms a film and anneals it, avoiding the conventional lengthy and high-temperature sintering process. This method is simple and time-saving. Furthermore, the copper-bismuth-sulfur-chloride thin film prepared using this method is dense, has high film quality, is beneficial for charge transport, increases conductivity, and significantly improves stability.

[0013] As one possible implementation, the molar ratio of the Bi₂S₃ powder to the CuCl₂ powder is 1:(1~3); or, The slurry also contains BiCl3 powder, wherein the molar ratio of Bi2S3 powder, CuCl2 powder, and BiCl3 powder is 1:(1~4):(1~3); or The mass ratio of the solvent to all powders is (5~7):1.

[0014] Thirdly, this application provides a solar cell, including a substrate and a light-absorbing layer located on the substrate, wherein the light-absorbing layer is the aforementioned copper-bismuth-sulfur-chloride thin film.

[0015] As one possible implementation, the solar cell further includes a hole transport layer, an electron transport layer, a transparent conductive oxide layer, and an electrode, wherein the hole transport layer, the copper-bismuth-sulfur-chloride thin film, the electron transport layer, the transparent conductive oxide layer, and the electrode are sequentially stacked on the substrate.

[0016] Fourthly, this application provides a photovoltaic module including a plurality of the aforementioned solar cells. Attached Figure Description

[0017] Figure 1 Scanning electron microscope (SEM) images of copper-bismuth-sulfur-chloride thin films according to embodiments of this application. Figure 1 .

[0018] Figure 2 Scanning electron microscope (SEM) images of copper-bismuth-sulfur-chloride thin films according to embodiments of this application. Figure 2 .

[0019] Figure 3 The X-ray diffraction patterns are of copper-bismuth-sulfur-chloride thin films according to three embodiments of this application.

[0020] Figure 4 This is a schematic diagram of the optical bandgap calculation based on the optical absorption spectrum fitting of a copper-bismuth-sulfur-chlorine thin film according to an embodiment of this application.

[0021] Figure 5 This is a cross-sectional schematic diagram of a solar cell according to an embodiment of this application.

[0022] Explanation of key component symbols: Solar cell 100, substrate 10, hole transport layer 20, copper-bismuth-sulfur-chloride thin film 30, electron transport layer 40. Transparent conductive oxide layer 50, electrode 60, SnO2 thin film 51, indium zinc oxide thin film 53. Detailed Implementation

[0023] The copper-bismuth-sulfur-chloride thin film of this application is used as a light-absorbing layer in a solar cell. This copper-bismuth-sulfur-chloride thin film is typically attached to a substrate, usually a glass substrate. Furthermore, other layers, such as a hole transport layer, are disposed between the light-absorbing layer and the substrate.

[0024] Please refer to the following: Figure 1 and Figure 2 Scanning electron microscope (SEM) images of copper-bismuth-sulfur-chloride thin films from embodiments of this application. From Figure 1 and Figure 2It is evident that the copper-bismuth-sulfur-chloride thin film comprises multiple CuBiSCl2 grains. These CuBiSCl2 grains are plate-like. The multiple CuBiSCl2 grains are densely packed to form a compact film. Each CuBiSCl2 grain has a length, width, and thickness, with the length being greater than both the width and thickness. The length of the grain refers to the widest dimension projected along its thickness direction, and the width is the dimension of the CuBiSCl2 grain projected along its thickness direction in the direction perpendicular to the length direction.

[0025] The projection shape of CuBiSCl2 grains along their thickness direction is not limited; for example, they can be circular, elliptical, rectangular, triangular, or other irregular shapes.

[0026] In this embodiment, the copper-bismuth-sulfur-chloride thin film is mostly stacked on the substrate in a manner where the grains are laid flat on the substrate, with the thickness direction of the grains perpendicular to the substrate. The plate-like grains are stacked layer by layer along the thickness direction of the copper-bismuth-sulfur-chloride thin film to form a film of a certain thickness, with the thickness direction of most of the plate-like grains consistent with the thickness direction of the film. In this application, the consistency between the thickness direction of the grains and the thickness direction of the film is defined as follows: the angle between the thickness direction of the grains and the thickness direction of the film is greater than or equal to 0 degrees and less than or equal to 10 degrees. In this embodiment, 80%-90% of the grains have the thickness direction consistent with the thickness direction of the film.

[0027] Because most of the grains are arranged in a flat, planar manner on the substrate—meaning the grains are closely adjacent with almost no gaps in a two-dimensional plane—the copper-bismuth-sulfur-chloride thin film is relatively dense. For example... Figure 2 As shown, along the thickness direction of the copper-bismuth-sulfur-chloride thin film, the grains are arranged in a stacked fault pattern, wherein the projections of adjacent grains along the thickness direction of the copper-bismuth-sulfur-chloride thin film overlap at least partially.

[0028] In copper-bismuth-sulfur-chloride thin films, a small portion of the grains are inclined or perpendicular to the substrate, meaning their thickness direction is inclined or parallel to the substrate. The minimum angle between the grains and the substrate is 0~90°. Alternatively, a small portion of the grains have a thickness direction inconsistent with the thickness direction of the copper-bismuth-sulfur-chloride thin film; for example, a small portion of the grains have a thickness direction perpendicular to or inclined relative to the thickness direction of the copper-bismuth-sulfur-chloride thin film. In this application, the inconsistency between the grain thickness direction and the film thickness direction is defined as an angle greater than 10 degrees and less than or equal to 90 degrees. In the embodiments of this application, 10%~20% of the grains have a thickness direction consistent with the film thickness direction.

[0029] In this way, a small number of grains that are tilted or perpendicular to the substrate can be inserted between the gaps between the flat grains, making the copper-bismuth-sulfur-chloride film more dense.

[0030] In some embodiments, the grain length is mainly distributed between 0.2 and 3 μm, and the thickness is distributed between 0.2 and 0.5 μm.

[0031] In some embodiments, CuBiSCl2 grains are divided into large-sized grains, small-sized grains, and intermediate-sized grains based on their grain length, wherein the length of large-sized grains is 1~2 μm > the length of intermediate-sized grains is 0.5~1 μm > the length of small-sized grains is 0.2~0.5 μm. The length of intermediate-sized grains does not include 0.5 μm and 1 μm.

[0032] Large-sized grains account for 75%–85% of the total grain count, small-sized grains account for 10%–20%, and the remainder are medium-sized grains. It is evident that CuBiSCl2 grains are predominantly large-sized. These large grains are stacked flat, while smaller grains fill the spaces between them, resulting in a relatively dense copper-bismuth-sulfur-chloride film.

[0033] In some embodiments, the thickness of the copper-bismuth-sulfur-chloride thin film is 0.5–5 μm. As a light-absorbing layer, the copper-bismuth-sulfur-chloride thin film cannot be too thick. Generally, the greater the thickness of the light-absorbing layer, the higher its light absorption efficiency. This is because a thicker absorption layer can provide more light paths, thereby increasing the interaction time between light and the material, allowing more light to be absorbed. However, when the thickness of the light-absorbing layer exceeds a certain range, the absorption efficiency will begin to decrease because an excessively thick absorption layer increases the light propagation distance, causing some light to not be completely absorbed, thus reducing the absorption efficiency.

[0034] This application also provides a method for preparing the above-mentioned copper bismuth sulfur chloride thin film, including the following steps (1) and (2).

[0035] (1) Mix Bi2S3 powder with CuCl2 powder and solvent and grind to form a slurry. The molar ratio of Bi2S3 powder to CuCl2 powder is 1:(1~3), and the solvent can be an organic alcohol, such as ethanol, butylcarbazol, etc.

[0036] In some embodiments, Bi2S3 powder and CuCl2 powder are first thoroughly mixed, then a solvent is added and the mixture is thoroughly mixed again, wherein the mass ratio of solvent to powder is (5~7):1. The mixture is then thoroughly ground in a three-roll mill to form a slurry. In one embodiment, the mass ratio of solvent to powder is 6:1.

[0037] (2) Place the slurry on the substrate and anneal it at a temperature of 100℃~400℃ for 15-60 minutes.

[0038] In some embodiments, the slurry can be applied to the substrate using methods such as blade coating, screen printing, or spin coating. The substrate is FTO glass with a hole transport layer (NiO layer) already deposited. Annealing is performed in a glove box. In one embodiment, the annealing temperature is 300°C and the annealing time is 30 min. During annealing, the solvent is removed, and Bi₂S₃ and CuCl₂ react to form CuBiSCl₂ grains.

[0039] This application also provides another method for preparing the aforementioned copper-bismuth-sulfur-chloride thin film. The difference between this method and the previous method is that BiCl3 powder is added to the raw materials of the slurry. That is, in the method for preparing the copper-bismuth-sulfur-chloride thin film, the BiCl3 powder is selectively added.

[0040] (1) Mix Bi2S3 powder, CuCl2 powder, BiCl3 powder and solvent and grind them to form a slurry. The molar ratio of Bi2S3 powder, CuCl2 powder and BiCl3 powder is 1:(1~4):(1~3). The solvent can be an organic alcohol, such as ethanol, butylcarbamate, etc.

[0041] In some embodiments, Bi₂S₃ powder, CuCl₂ powder, and BiCl₃ powder are first thoroughly mixed, then a solvent is added and the mixture is thoroughly mixed again, wherein the mass ratio of solvent to powder is (5~7):1. The mixture is then thoroughly ground in a three-roll mill to form a slurry. In one embodiment, the molar ratio of Bi₂S₃ powder, CuCl₂ powder, and BiCl₃ powder is 1:3:1; the mass ratio of solvent to powder is 6:1.

[0042] (2) Place the slurry on the substrate and anneal it at a temperature of 100℃~400℃ for 15-60 minutes.

[0043] In some embodiments, the slurry can be applied to the substrate using methods such as blade coating or screen printing. The substrate is FTO glass with a pre-deposited hole transport layer (NiO layer). Annealing is performed in a glove box. In some embodiments, the annealing temperature is 300°C and the annealing time is 30 min. During annealing, the solvent is removed, and Bi₂S₃, CuCl₂, and BiCl₃ react to form CuBiSCl₂ grains.

[0044] In some embodiments, a glass plate is covered on the surface of the slurry film during annealing to prevent elemental diffusion loss in the copper-bismuth-sulfur-chlorine film.

[0045] Figure 3 The X-ray diffraction patterns of copper-bismuth-sulfur-chloride thin films obtained by annealing at different temperatures (200℃, 250℃, and 300℃) for 30 min are shown. Comparison with relevant literature shows that the characteristic peaks of the copper-bismuth-sulfur-chloride thin films are in the same positions as those recorded in the literature. Figure 3 As can be seen, the diffraction characteristic peaks of CuBiSCl2 can be observed at all three annealing temperatures. Moreover, the intensity of the diffraction characteristic peaks of CuBiSCl2 increases significantly with the increase of annealing temperature, indicating that the crystallization of CuBiSCl2 becomes more complete with the increase of annealing temperature.

[0046] Conventional preparation processes involve first sintering Bi₂S₃ powder and CuCl₂ powder at high temperatures to form CuBiSCl₂ (high-temperature sintering is time-consuming and involves high temperatures), then coating the CuBiSCl₂ slurry to form a CuBiSCl₂ thin film. This application, however, uses a mixture of Bi₂S₃ powder and CuCl₂ powder (or Bi₂S₃, CuCl₂, and BiCl₃ powder) to form a slurry, which is then coated and annealed to form the CuBiSCl₂ thin film. During annealing, Bi₂S₃ reacts with CuCl₂ to form CuBiSCl₂, or Bi₂S₃, CuCl₂, and BiCl₃ react to form CuBiSCl₂. Thus, the preparation method of the copper-bismuth-sulfur-chloride thin film in this application uses raw materials to form a slurry, followed by direct film formation and annealing, avoiding the conventional lengthy high-temperature sintering process. This method is simple and time-efficient.

[0047] Conventional preparation processes for CuBiSCl2 thin films often result in the formation of secondary phases during sintering and annealing. These secondary phases negatively impact the film's quality and optical properties. Furthermore, the resulting films contain numerous pores, resulting in a small area of ​​intergranular bonding, low film density, numerous defects, and increased carrier recombination. Consequently, the films exhibit poor conductivity and low carrier extraction efficiency, ultimately leading to low photoelectric conversion efficiency in the solar cells.

[0048] In conventional high-temperature sintering processes, the reaction conditions for forming high-quality bulk materials are demanding. Precise control of reaction conditions, such as temperature and time, is required during synthesis to ensure the formation of the correct phase. Temperature control is particularly challenging during rapid thermal treatment (RTP) vulcanization. Furthermore, the synthesis process generates secondary phases, which can negatively impact the film's quality and optical properties. Excessively high annealing temperatures can also promote the formation of pores / holes in the film. During slurry formation, the physically dispersed powder exhibits poor grain size uniformity, resulting in lower film density, less grain overlap, poor conductivity, and numerous defects. As a light-absorbing layer, severe carrier recombination leads to low photoelectric conversion performance in the fabricated solar cell.

[0049] Furthermore, different preparation processes result in variations in the internal microstructure of the obtained CuBiSCl2 thin films. In the copper-bismuth-sulfur-chloride thin films prepared using the method described in this application, most of the CuBiSCl2 grains are plate-like, and most of the grains are arranged in a flat manner on the substrate. The grains are closely adjacent in the horizontal direction, and along the thickness direction of the film, there is a stacking fault arrangement between the grains. This means that in some areas, the grains may be in complete contact and fused, forming gapless connections. Thus, the copper-bismuth-sulfur-chloride thin film is dense, with high film quality, which is beneficial for charge transport, increases conductivity, and significantly improves stability. Typically, in CuBiSCl2 thin films formed by coating a slurry, the CuBiSCl2 grains are mainly spherical, and the arrangement and connection of these spherical particles are significantly different from the flat and stacking fault arrangement of most of the plate-like CuBiSCl2 grains in the copper-bismuth-sulfur-chloride thin film of this application.

[0050] Please see Figure 4 The optical absorption spectrum of a copper-bismuth-sulfur-chloride thin film according to an embodiment of this application. Figure 4 As shown, the optical band gap Eg of the copper bismuth sulfur chloride thin film is approximately 1.35 eV, obtained by fitting the optical absorption spectrum. This indicates that the optical band gap of the copper bismuth sulfur chloride thin film is relatively small.

[0051] This application also provides a solar cell containing the aforementioned copper-bismuth-sulfur-chloride thin film. For example... Figure 5 As shown, the solar cell 100 includes a substrate 10, a hole transport layer 20, a copper bismuth sulfur chloride thin film 30, an electron transport layer 40, and a transparent conductive oxide layer 50, which are sequentially stacked on the substrate 10. An electrode 60 is also disposed on the side of the transparent conductive oxide layer 50 facing away from the substrate. The copper bismuth sulfur chloride thin film 30 serves as a light absorption layer.

[0052] In some embodiments, substrate 10 is an FTO substrate, i.e., fluorine-doped SnO2 transparent conductive glass. Hole transport layer 20 is a NiO layer with a thickness of approximately 20 nm. Electron transport layer 40 is C 60 The thin film has a thickness of approximately 20 nm. The transparent conductive oxide 50 comprises a stacked SnO2 thin film 51 and an indium zinc oxide (IZO) thin film 53, wherein the SnO2 thin film is located between the electron transport layer and the IZO thin film. The SnO2 thin film 51 has a thickness of approximately 30 nm, and the IZO thin film 53 has a thickness of approximately 110 nm.

[0053] This application also provides a method for preparing a solar cell containing the above-mentioned copper-bismuth-sulfur-chloride thin film, comprising the following steps.

[0054] Step 1: Provide and clean the FTO substrate.

[0055] The FTO substrate was sequentially cleaned with glass cleaner, deionized water, and anhydrous ethanol for 0–20 min, and then dried with nitrogen at room temperature.

[0056] Step 2: Form a hole transport layer on the FTO substrate.

[0057] In some embodiments, the hole transport layer may be prepared as a NiO layer using a solution method, with a thickness of approximately 20 nm.

[0058] Step 3: Form a copper-bismuth-sulfur-chloride thin film on the hole transport layer.

[0059] This step can be performed using the above-described preparation method to prepare copper-bismuth-sulfur-chloride thin films. First, a slurry is prepared, and then a slurry coating + annealing method or a slurry spin coating + annealing method is used to form the copper-bismuth-sulfur-chloride thin film.

[0060] Step 4: Form an electron transport layer on the copper-bismuth-sulfur-chloride thin film.

[0061] In some embodiments, this step may employ physical vapor deposition to prepare C 60 The film has a thickness of approximately 20 nm.

[0062] Step 5: Form a transparent conductive oxide layer in the electron transport layer.

[0063] In some embodiments, the five steps include step (1): preparing an i-SnO2 thin film with a thickness of about 30 nm by atomic layer deposition; and step (2): preparing an IZO thin film with a thickness of about 110 nm by physical vapor deposition.

[0064] Step 6: Form an electrode on the transparent conductive oxide layer.

[0065] In some embodiments, step six involves forming an electrode by vapor deposition, and the electrode material can be Ag with a thickness of 700 nm.

[0066] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A copper-bismuth-sulfur-chloride thin film, characterized in that, The film comprises multiple CuBiSCl2 grains, each CuBiSCl2 grain being plate-shaped and having length, width, and thickness, wherein the length is greater than the width and the thickness. The length of the CuBiSCl2 grain refers to the widest dimension of its projection along its thickness direction, and the width of the CuBiSCl2 grain is the dimension of its projection along its thickness direction in the direction perpendicular to the length direction. In the copper-bismuth-sulfur-chloride thin film, the multiple CuBiSCl2 grains are stacked layer by layer, and the angle between the thickness direction of 80% to 90% of the CuBiSCl2 grains and the thickness direction of the copper-bismuth-sulfur-chloride thin film is 0 to 10 degrees.

2. The copper-bismuth-sulfur-chlorine thin film according to claim 1, characterized in that, Along the thickness direction of the copper-bismuth-sulfur-chloride thin film, the projections of adjacent CuBiSCl2 grains along the thickness direction will at least partially overlap.

3. The copper-bismuth-sulfur-chlorine thin film according to claim 1, characterized in that, The angle between the thickness direction of 10% to 20% of the CuBiSCl2 grains and the thickness direction of the copper bismuth sulfur chloride film is greater than 10 degrees and less than or equal to 90 degrees.

4. The copper-bismuth-sulfur-chlorine thin film according to claim 1, characterized in that, The length of the CuBiSCl2 grains is distributed between 0.2 and 3 μm, and the thickness of the CuBiSCl2 grains is distributed between 0.2 and 0.5 μm.

5. The copper-bismuth-sulfur-chloride thin film according to claim 1, characterized in that, The plurality of CuBiSCl2 grains are divided into large-sized grains, small-sized grains, and intermediate-sized grains. The length of the large-sized grains is 1-2 μm, the length of the small-sized grains is 0.2-0.5 μm, and the length of the intermediate-sized grains is 0.5-1 μm, excluding 0.5 μm and 1 μm. The large-sized grains account for 75%-85% of the total number of grains, the small-sized grains account for 10%-20% of the total number of grains, and the remainder are the intermediate-sized grains.

6. A method for preparing a copper-bismuth-sulfur-chloride thin film, characterized in that: include: Bi2S3 powder and CuCl2 powder are mixed with a solvent and then ground to form a slurry. The solvent is an organic alcohol. as well as The slurry is placed on a substrate and annealed at a temperature of 100℃~400℃ to form a copper bismuth sulfur chloride film.

7. The method for preparing a copper-bismuth-sulfur-chloride thin film according to claim 6, characterized in that, The molar ratio of Bi₂S₃ powder to CuCl₂ powder is 1:(1~3); or, The slurry also contains BiCl3 powder, wherein the molar ratio of Bi2S3 powder, CuCl2 powder, and BiCl3 powder is 1:(1~4):(1~3); or The mass ratio of the solvent to all powders is (5~7):

1.

8. A solar cell, comprising a substrate and a light-absorbing layer located on the substrate, characterized in that, The light-absorbing layer is a copper-bismuth-sulfur-chlorine thin film as described in any one of claims 1 to 5.

9. The solar cell according to claim 8, characterized in that, The solar cell further includes a hole transport layer, an electron transport layer, a transparent conductive oxide layer, and an electrode, wherein the hole transport layer, the copper-bismuth-sulfur-chloride thin film, the electron transport layer, the transparent conductive oxide layer, and the electrode are sequentially stacked on the substrate.

10. A photovoltaic module, characterized in that, It includes multiple solar cells as described in claim 8 or 9.

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