Composite film for perovskite solar cell and preparation method thereof

Abstract

The invention belongs to the technical field of solar cells, and discloses a composite film for a perovskite solar cell and a preparation method of the composite film. The composite film comprises a CaF2 substrate and a composite film layer arranged on the surface of the CaF2 substrate, and the composite film layer comprises ZnS layers and MgF2 layers which are sequentially and alternately arranged from inside to outside. According to the CaF2 / ZnS / MgF2 composite film disclosed by the invention, the core problems of temperature rise and thermalization loss of the perovskite solar cell are closely solved, the optical performance of a film material is fully utilized, and high transmission of visible light and high reflection of near-infrared light by the film are simultaneously realized through specific laminated structure arrangement. On one hand, high-energy near-infrared light is intercepted from the source, and thermalization loss is remarkably reduced; on the other hand, sufficient visible light is ensured to participate in photoelectric conversion, the energy utilization efficiency is improved, and dual optimization of thermal management and photoelectric performance of the battery is formed.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and particularly relates to a composite thin film for perovskite solar cells and its preparation method. Background Technology

[0002] Perovskite solar cells (PSCs), as a new generation of photovoltaic cells, have attracted much attention in the renewable energy field due to their high photoelectric conversion efficiency and low-cost fabrication. However, in practical applications, perovskite solar cells face many challenges, among which the temperature rise during operation is particularly prominent. Increased temperature leads to changes in the properties of the internal materials, such as increased carrier recombination probability and decreased open-circuit voltage, thereby reducing the photoelectric conversion efficiency and stability of the cell and shortening its lifespan. Simultaneously, with the expansion of applications such as building-integrated photovoltaics (BIPV), the requirements for the optical performance and thermal management of solar cells are becoming increasingly stringent, necessitating effective heat management while ensuring efficient absorption of visible light for photoelectric conversion.

[0003] In the structure of perovskite solar cells, the glass encapsulation material plays a crucial role in protecting the internal structure and ensuring light transmission. However, traditional tempered glass has relatively limited optical properties and its ability to control incident light is limited, remaining at a basic level of light transmission and unable to selectively process visible and near-infrared light. Therefore, thermal loss is one of the key issues restricting the performance improvement and stable operation of perovskite solar cells. When the photon energy absorbed by a perovskite solar cell exceeds the band gap of the perovskite material, the excess energy is dissipated as heat, resulting in thermal loss and severely affecting the photoelectric conversion efficiency and lifespan of the cell. Existing optical thin-film structures mostly focus on improving light utilization, such as some multilayer film designs for organic solar cells. While these designs offer spectral modulation capabilities, they are not specifically designed for the cooling needs of perovskite solar cells and lack specificity in adjusting the light wavelength to reduce cell temperature. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a composite thin film for perovskite solar cells and its preparation method. The composite thin film has the characteristics of high visible light transmission and high near-infrared reflectance. On the one hand, by reflecting near-infrared light, the input of high-energy photons is reduced at the source, thus reducing thermal losses caused by absorbing excess energy photons. On the other hand, by transmitting visible light, sufficient visible light is ensured for photoelectric conversion in the perovskite solar cell, improving energy utilization efficiency and reducing thermal losses caused by insufficient energy utilization. This improves the photoelectric conversion efficiency and stability of the cell and extends its service life.

[0005] The inventive concept of this invention is as follows: This invention provides a CaF2 / ZnS / MgF2 multilayer composite film with high visible light transmission and high near-infrared reflectance, which can be used to replace ordinary tempered glass in perovskite solar cells with double-layer glass encapsulation. By precisely controlling the reflection and transmission characteristics of the multilayer film on incident light, the purpose of reducing the temperature of perovskite solar cells and improving photoelectric conversion efficiency and stability can be achieved.

[0006] Specifically, from an optical principle perspective, CaF2 possesses excellent optical transmittance, particularly high transmittance in the mid-infrared band, enabling effective radiative cooling. As a substrate layer, CaF2 provides a stable base for subsequent composite thin film deposition. By alternately stacking ZnS and MgF2 to form a multilayer composite thin film structure, the optical properties of the film can be effectively controlled, achieving specific reflection and transmission effects for different wavelengths of light, thus achieving efficient photothermal management. Simultaneously, the high mid-infrared transmittance of the CaF2 substrate facilitates radiative cooling, further reducing the operating temperature of the perovskite solar cell and improving its photoelectric conversion efficiency and stability. From a thermal management perspective, near-infrared light carries high energy; its effective reflection significantly reduces thermal losses caused by the absorption of high-energy photons during operation, thereby improving the cell's photoelectric conversion efficiency and stability. Furthermore, the high transmittance of visible light ensures that the perovskite solar cell can fully absorb and convert light energy, further enhancing energy utilization efficiency. In addition, the high transmittance of CaF2 substrate to mid-infrared light allows solar cells to be cooled by radiation, further reducing the operating temperature of the cells and improving their performance.

[0007] To address the aforementioned technical problems, a first aspect of the present invention provides a composite film comprising a CaF2 substrate and a composite film layer disposed on the surface of the CaF2 substrate, wherein the composite film layer comprises alternating ZnS layers and MgF2 layers disposed from the inside out.

[0008] Specifically, the composite film of this invention uses CaF2 as the substrate layer, providing excellent optical transmittance and a stable substrate for the ZnS and MgF2 composite film, especially its high transmittance to mid-infrared light, which is beneficial for radiative cooling. The stacking order of the ZnS and MgF2 layers from the inside out achieves dual optimization of high transmittance of visible light and high reflectance of near-infrared light. Simultaneously, the optical transmittance of CaF2 allows visible light to pass smoothly through the substrate layer, providing a foundation for subsequent photothermal management; and the high transmittance of the CaF2 substrate to mid-infrared light is beneficial for radiative cooling, further reducing the operating temperature of the solar cell and improving cell performance. ZnS has high transmittance to visible light, allowing most visible light to pass through, thereby reducing light loss and improving light utilization. MgF2 has relatively high reflectance to near-infrared light, reflecting some high-energy near-infrared light and reducing thermal loss. Alternating stacking of ZnS and MgF2 layers to form a multilayer composite film structure can achieve specific reflection and transmission effects for different wavelengths of light, thereby achieving efficient photothermal management. This multi-layered composite structure has superior overall performance compared to a single ZnS layer or MgF2 layer.

[0009] In some embodiments of the present invention, the composite film layer comprises 16-20 layers; for example, 16 layers, 18 layers, 20 layers, etc.

[0010] Research has found that the composite film, employing a multilayer structure with alternating ZnS and MgF2 layers, offers greater flexibility in precisely controlling the film's optical properties compared to single-material deposition or simple stacking of multiple materials. MgF2 exhibits high reflectivity for near-infrared light, while ZnS demonstrates good transmittance for visible light. This alternating stacking method endows the film with specific reflection and transmission characteristics across different wavelength ranges, achieving a dual optimization of high transmittance for visible light and high reflectivity for near-infrared light. Simultaneously, the alternating multilayer structure more effectively intercepts high-energy near-infrared light, reducing thermal losses in perovskite solar cells, while ensuring sufficient visible light participation in photoelectric conversion, thus improving energy utilization efficiency. Furthermore, the alternating ZnS and MgF2 layers enhance the film's stability, ensuring overall quality and performance, and ultimately improving the reliability and durability of perovskite solar cells.

[0011] In some embodiments of the present invention, the total thickness of the composite film is 1050-1100 nm; for example, 1050 nm, 1073 nm, 1100 nm, etc.

[0012] In some embodiments of the present invention, the thickness of the ZnS layer is 47-63 nm (single layer), and the thickness of the MgF2 layer is 57-75 nm (single layer).

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned composite film, comprising the following steps:

[0014] A composite film is obtained by depositing a ZnS layer and a MgF2 layer alternately from the inside to the outside of the CaF2 substrate.

[0015] In some embodiments of the present invention, the coating is deposited using a magnetron sputtering process to deposit ZnS and MgF2.

[0016] In some embodiments of the present invention, the magnetron sputtering process has a power of 50-80W and is performed with an argon flow rate of 10-15 sccm.

[0017] In some embodiments of the present invention, after the magnetron sputtering process is completed, the composite film is further annealed at 200-300°C for 1-2 hours.

[0018] In some embodiments of the present invention, the CaF2 substrate is further subjected to a cleaning and drying step before the magnetron sputtering process.

[0019] In some embodiments of the present invention, the cleaning process is as follows: first, ultrasonic cleaning is performed for 10-15 minutes with acetone and anhydrous ethanol to remove oil and impurities; then, deionized water is used for rinsing and ultrasonic cleaning for 5-10 minutes.

[0020] In some embodiments of the present invention, the drying process is carried out using high-purity nitrogen gas.

[0021] A third aspect of the present invention provides a perovskite solar cell comprising the above-described composite thin film.

[0022] In some embodiments of the present invention, the perovskite solar cell further includes, from bottom to top, ITO glass, a functional layer, a perovskite active layer, an Au electrode, an encapsulating film, and a top glass layer disposed on the surface of the composite film.

[0023] Specifically, the composite thin film structure of the present invention can replace the tempered glass used for encapsulation in traditional commercial double-layer glass-encapsulated perovskite solar cells, optimize the cell's encapsulation structure, and solve the shortcomings of traditional encapsulation glass in photothermal management through optical improvements without changing the basic working principle and structural framework of the cell, thereby improving the performance of perovskite solar cells in practical applications.

[0024] In some embodiments of the present invention, the functional layer includes an electron transport layer (ETL) and a hole transport layer (HTL).

[0025] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0026] (1) The CaF2 / ZnS / MgF2 composite thin film of the present invention closely addresses the core issues of temperature rise and thermal loss in perovskite solar cells. It fully utilizes the optical properties of the thin film material and achieves high transmittance of visible light and high reflectance of near-infrared light through a specific stacked structure. On the one hand, it intercepts high-energy near-infrared light at the source, significantly reducing thermal loss; on the other hand, it ensures sufficient visible light to participate in photoelectric conversion, improving energy utilization efficiency and forming a dual optimization of battery thermal management and photoelectric performance.

[0027] (2) The CaF2 / ZnS / MgF2 composite film of the present invention can replace the ordinary tempered glass in traditional commercially packaged perovskite solar cells, and achieve performance improvement without changing the main structure of the cell, providing a better solution for the commercial promotion and performance breakthrough of perovskite solar cells.

[0028] (3) The CaF2 / ZnS / MgF2 composite thin film of the present invention has the characteristics of high visible light transmittance and high near-infrared reflectance, achieving a visible light transmittance of up to 90% and a near-infrared reflectance of up to 93.6%, which significantly reduces heat input while ensuring photoelectric conversion efficiency. When this composite thin film is applied to perovskite solar cells, the short-circuit current can reach 73mA at a voltage of 0V, exhibiting high current output. Attached Figure Description

[0029] Figure 1 This is a comparative structural diagram of the perovskite solar cells prepared in Example 1 and Comparative Example 1 of the present invention.

[0030] Figure 2 This is a schematic diagram of the photothermal management of the CaF2 / ZnS / MgF2 composite thin film of the present invention;

[0031] Figure 3 This is a comparison of the simulated and experimental spectra of the CaF2 / ZnS / MgF2 composite thin film prepared in Example 1 of this invention;

[0032] Figure 4 This is a comparison of simulated spectra of the thin films prepared in Example 1 and Comparative Examples 1-3 of the present invention;

[0033] Figure 5 This is a thermal imaging comparison of the perovskite solar cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0034] Figure 6 This is a comparison diagram of the current-voltage characteristics of the perovskite solar cells prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0036] Example 1

[0037] A method for preparing a CaF2 / ZnS / MgF2 composite thin film includes the following steps:

[0038] First, prepare high-purity CaF2 substrate, ZnS and MgF2 targets, and cleaning reagents such as acetone and anhydrous ethanol. Also, debug the magnetron sputtering equipment and calibrate the film thickness monitor. First, ultrasonically clean the CaF2 substrate sequentially in acetone and anhydrous ethanol for 10-15 minutes to remove oil and impurities. Then rinse with deionized water and ultrasonically clean for 5-10 minutes. Dry with high-purity nitrogen gas before use. Place the cleaned CaF2 substrate into the vacuum chamber of the magnetron sputtering equipment and evacuate to 10 °C. -5 The deposition process involved ZnS and MgF2 targets, measured in Pa. First, a MgF2 layer was deposited at 65W power and 12sccm argon flow rate. The deposition was stopped once the designed thickness (65nm) was achieved, based on film thickness monitoring. After adjusting the parameters, ZnS (54nm thick) was deposited. ZnS and MgF2 were then deposited alternately in sequence to ensure precise thickness for each layer, resulting in 18 layers with a total thickness of 1071nm. After deposition, the film was annealed at 200-300℃ for 1-2 hours to obtain the CaF2 / ZnS / MgF2 composite film of this embodiment.

[0039] A schematic diagram of a perovskite solar cell is shown below. Figure 1 As shown in -a, from bottom to top, it includes a cooling layer (CaF2 / ZnS / MgF2 composite film prepared in Example 1), ITO glass, electron transport layer (ETL), hole transport layer (HTL), perovskite active layer, Au electrode (Au), encapsulating film (EVA), and top glass.

[0040] The above perovskite solar cells were prepared using methods commonly used in the field, wherein: ITO glass was ultrasonically cleaned and treated with UV-O3; a SnO2 electron transport layer was formed by spin coating at a rotation speed of 3000 rpm / 30 s, and annealed at 150 °C for 30 min; a perovskite active layer was formed by dropwise addition of chlorobenzene at a rotation speed of 4000 rpm / 30 s using anti-solvent-assisted spin coating with MAPbI3 as a precursor solution, and annealed at 100 °C for 10 min; an Au electrode with a thickness of 80-100 nm was deposited by thermal evaporation; and the EVA film and the top glass were vacuum laminated and encapsulated at 150 °C for 15 min to complete the sealing.

[0041] Example 2

[0042] A method for preparing a CaF2 / ZnS / MgF2 composite thin film includes the following steps:

[0043] First, prepare high-purity CaF2 substrate, ZnS and MgF2 targets, and cleaning reagents such as acetone and anhydrous ethanol. Also, debug the magnetron sputtering equipment and calibrate the film thickness monitor. First, ultrasonically clean the CaF2 substrate sequentially in acetone and anhydrous ethanol for 10-15 minutes to remove oil and impurities. Then rinse with deionized water and ultrasonically clean for 5-10 minutes. Dry with high-purity nitrogen gas before use. Place the cleaned CaF2 substrate into the vacuum chamber of the magnetron sputtering equipment and evacuate to 10 °C. -5 The deposition process involved ZnS and MgF2 targets, measured in Pa. First, a MgF2 layer was deposited at 55W power and 14sccm argon flow rate. The deposition was stopped once the designed thickness (72nm) was reached, based on film thickness monitoring. After adjusting the parameters, ZnS (60nm thick) was deposited. ZnS and MgF2 were deposited alternately in sequence to ensure precise thickness for each layer, resulting in 16 layers with a total thickness of 1056nm. After deposition, the film was annealed at 200-300℃ for 1-2 hours to obtain the CaF2 / ZnS / MgF2 composite film of this embodiment.

[0044] The structure and fabrication method of the perovskite solar cell in Example 2 are the same as those in Example 1.

[0045] Example 3

[0046] A method for preparing a CaF2 / ZnS / MgF2 composite thin film includes the following steps:

[0047] First, prepare high-purity CaF2 substrate, ZnS and MgF2 targets, and cleaning reagents such as acetone and anhydrous ethanol. Also, debug the magnetron sputtering equipment and calibrate the film thickness monitor. First, ultrasonically clean the CaF2 substrate sequentially in acetone and anhydrous ethanol for 10-15 minutes to remove oil and impurities. Then rinse with deionized water and ultrasonically clean for 5-10 minutes. Dry with high-purity nitrogen gas before use. Place the cleaned CaF2 substrate into the vacuum chamber of the magnetron sputtering equipment and evacuate to 10 °C.-5 The deposition process involved ZnS and MgF2 targets, measured in Pa. First, a MgF2 layer was deposited at 75W power and 10sccm argon flow rate. The deposition was stopped once the designed thickness (60nm) was reached, based on film thickness monitoring. After adjusting the parameters, ZnS (50nm thick) was deposited. ZnS and MgF2 were then deposited alternately in sequence to ensure precise thickness for each layer, for a total of 20 layers and a total thickness of 1100nm. After deposition, the film was annealed at 200-300℃ for 1-2 hours to obtain the CaF2 / ZnS / MgF2 composite film of this embodiment.

[0048] The structure and fabrication method of the perovskite solar cell in Example 3 are the same as those in Example 1.

[0049] Comparative Example 1

[0050] The difference between Comparative Example 1 and Example 1 is that tempered glass is used instead of the CaF2 / ZnS / MgF2 composite film in Example 1. A schematic diagram of the perovskite solar cell structure of Comparative Example 1 is shown below. Figure 1 -b is shown.

[0051] Comparative Example 2

[0052] The difference between Comparative Example 2 and Example 1 is that a CaF2 / MgF2 film is used instead of the CaF2 / ZnS / MgF2 composite film in Example 1.

[0053] The method for preparing the CaF2 / MgF2 thin film of Comparative Example 2 includes the following steps:

[0054] First, prepare high-purity CaF2 substrate, MgF2 target, and cleaning reagents such as acetone and anhydrous ethanol. Then, debug the magnetron sputtering equipment and calibrate the film thickness monitor. First, immerse the CaF2 substrate sequentially in acetone and anhydrous ethanol for ultrasonic cleaning for 10-15 minutes to remove oil and impurities. Next, rinse with deionized water and ultrasonically clean for 5-10 minutes. Dry with high-purity nitrogen gas before use. Place the cleaned CaF2 substrate into the vacuum chamber of the magnetron sputtering equipment and evacuate to 10 °C. -5 The Pa level was used to install a MgF2 target. MgF2 layers were deposited at 65 W power and 12 sccm argon flow rate, achieving the designed thickness (59.5 nm) based on film thickness monitoring. A total of 18 layers were deposited, with a total thickness of 1071 nm. After deposition, the films were annealed at 200-300 °C for 1-2 hours to obtain the CaF2 / MgF2 film of this comparative example.

[0055] Comparative Example 3

[0056] The difference between Comparative Example 3 and Example 1 is that CaF2 / ZnS film is used instead of CaF2 / ZnS / MgF2 composite film in Example 1.

[0057] The method for preparing the CaF2 / ZnS thin film of Comparative Example 3 includes the following steps:

[0058] First, prepare a high-purity CaF2 substrate, a ZnS target, and cleaning reagents such as acetone and anhydrous ethanol. Also, debug the magnetron sputtering equipment and calibrate the film thickness monitor. First, immerse the CaF2 substrate sequentially in acetone and anhydrous ethanol for ultrasonic cleaning for 10-15 minutes to remove oil and impurities. Then rinse with deionized water and sonicate for 5-10 minutes. Dry with high-purity nitrogen gas before use. Place the cleaned CaF2 substrate into the vacuum chamber of the magnetron sputtering equipment and evacuate to 10 °C. -5 The ZnS target was mounted on a Pa scale. ZnS layers were deposited at 65 W power and 12 sccm argon flow rate. Deposition was stopped once the designed thickness (59.5 nm) was reached, based on film thickness monitoring. A total of 18 layers were deposited, with a total thickness of 1071 nm. After deposition, the films were annealed at 200-300 °C for 1-2 hours to obtain the CaF2 / ZnS film of this comparative example.

[0059] Performance testing and characterization

[0060] 1. Photothermal management performance

[0061] like Figure 2 This diagram illustrates the photothermal management of the CaF2 / ZnS / MgF2 composite thin film of the present invention. Visible light (0.3-0.8 μm) is indicated by a yellow arrow pointing downwards towards the photonic cooler and perovskite solar cell (PSC), showing that visible light is allowed to pass through for photoelectric conversion in the perovskite solar cell. Near-infrared light (0.8-2.5 μm) is indicated by a red U-shaped arrow, meaning that near-infrared light is reflected back to avoid being absorbed by the perovskite solar cell and generating excessive heat, thus reducing thermal loss. Mid-infrared light (8-13 μm) is indicated by a blue arrow pointing upwards from the perovskite solar cell, indicating that the perovskite solar cell emits mid-infrared light, which can carry away some heat and assist in heat dissipation.

[0062] like Figure 3 The image shows a comparison of the simulated and experimental spectra of the CaF2 / ZnS / MgF2 composite thin film prepared in Example 1, specifically a curve illustrating the reflection of the film as a function of wavelength, demonstrating the experimental and simulated reflectance data. Figure 3As can be seen, the average transmittance is 90% in the visible light band (approximately 400-810 nm), indicating that the composite film allows light to pass through well in the visible light band, meeting the high transmittance requirement for visible light. In the near-infrared band (810-2500 nm), the reflectance can reach up to 93.6%, indicating that the composite film has a good reflective effect on near-infrared light, which can significantly reduce heat input while ensuring photoelectric conversion efficiency. The experimental data and simulation data show a basically consistent trend, indicating that the simulation results can reflect the actual situation well.

[0063] Figure 4 This is a comparison of simulated spectra of the thin films prepared in Example 1 and Comparative Examples 1-3 of the present invention. Figure 4 As can be seen, Comparative Example 1 (conventional glass) has an average transmittance of approximately 95% in the visible light band (400-810nm) and a reflectance of only 4% in the near-infrared band (810-2500nm). Comparative Example 2 (MgF2 monolayer) achieves a visible light transmittance of 97% (anti-reflection effect), but its near-infrared reflectance is only a maximum of 3% (no targeted reflection of near-infrared light). Comparative Example 3 (ZnS monolayer) has a visible light transmittance of 80% and a near-infrared reflectance of approximately 15%. This demonstrates that the CaF2 / ZnS / MgF2 composite film of the present invention, while ensuring high transmittance of visible light, also exhibits high reflectivity for near-infrared light.

[0064] Figure 5 This is a thermal imaging comparison of the perovskite solar cells prepared in Example 1 and Comparative Example 1 of the present invention, showing the perovskite solar cells prepared in Example 1. Figure 5 -a) compared to traditional commercial perovskite solar cells ( Figure 5 -b) Temperature conditions. From Figure 5 It can be seen that the perovskite solar cell prepared in Example 1, due to the use of the CaF2 / ZnS / MgF2 composite thin film, reduces thermal loss by reflecting near-infrared light in the cooling layer, resulting in a temperature of 43.2℃. In contrast, the conventional commercial perovskite solar cell in Comparative Example 1, due to the absorption of more near-infrared light and the resulting thermal loss, has a higher temperature of 53.5℃, which is 10.3℃ higher than that of Example 1. This demonstrates that the CaF2 / ZnS / MgF2 composite thin film of the present invention has a significant cooling effect.

[0065] Figure 6 This is a comparison diagram of the current-voltage characteristics of the perovskite solar cells prepared in Example 1 and Comparative Example 1 of the present invention. Figure 6It is evident that the CaF2 / ZnS / MgF2 composite film of this invention exhibits significant advantages over traditional glass in perovskite solar cell encapsulation applications. At 0V, the perovskite solar cell encapsulated with traditional glass (Comparative Example 1) exhibits a short-circuit current of 67mA, while the short-circuit current of Example 1 is 73mA. This is mainly because the high visible light transmission ensures light absorption, significantly improving current output.

[0066] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A composite film, characterized in that, It includes a CaF2 substrate and a composite film layer disposed on the surface of the CaF2 substrate, wherein the composite film layer includes alternating ZnS layers and MgF2 layers arranged sequentially from the inside to the outside.

2. The composite film according to claim 1, characterized in that, The composite membrane consists of 16-20 layers.

3. The composite film according to claim 1 or 2, characterized in that, The total thickness of the composite film is 1050-1100 nm.

4. The composite film according to claim 3, characterized in that, The thickness of the ZnS layer is 47-63 nm, and the thickness of the MgF2 layer is 57-75 nm.

5. A method for preparing a composite thin film as described in any one of claims 1-4, characterized in that, Includes the following steps: A composite film is obtained by depositing a ZnS layer and a MgF2 layer alternately from the inside to the outside of the CaF2 substrate.

6. The method for preparing the composite thin film according to claim 5, characterized in that, The coating is achieved by depositing ZnS and MgF2 using a magnetron sputtering process.

7. The method for preparing the composite thin film according to claim 6, characterized in that, The magnetron sputtering process uses a power of 50-80W and deposits argon gas at a flow rate of 10-15 sccm.

8. The method for preparing the composite thin film according to claim 6, characterized in that, After the magnetron sputtering process is completed, the composite film is further annealed at 200-300°C for 1-2 hours.

9. A perovskite solar cell, characterized in that, The perovskite solar cell includes the composite thin film according to any one of claims 1-4.

10. The perovskite solar cell according to claim 9, characterized in that, The perovskite solar cell further includes, from bottom to top, ITO glass, a functional layer, a perovskite active layer, an Au electrode, an encapsulating film, and a top glass layer disposed on the surface of the composite film.

Images