A cztss e thin-film solar cell and a method for manufacturing the same

Abstract

The application provides a CZTSSe thin film solar cell and a preparation method thereof, and relates to the field of solar cell materials. The application introduces a CdSe thin layer between a CZTSSe absorption layer and a back electrode layer. In the selenization process, the CdSe decomposes and participates in the reaction, the local Se chemical potential is improved, and the reaction kinetics is regulated, so that the generation of Cu2SnSe3 intermediate phase is inhibited, the CZTSSe absorption layer is changed from the traditional multi-step phase change path to the direct phase formation path. At the same time, the process promotes the back interface to preferentially form a large-grained CZTSSe layer, and realizes the diffusion of Cd to the bulk phase and promotes the crystallization of the absorption layer in the late selenization stage, so as to synergistically regulate the interface and bulk phase defects. The application significantly improves the photoelectric conversion efficiency and device stability of the CZTSSe solar cell.

Description

Technical Field

[0001] This invention relates to the field of solar cell materials, and in particular to a CZTSSe thin-film solar cell and its preparation method. Background Technology

[0002] CZTSSe has a high absorption coefficient (>10) 4 cm -1 With its adjustable bandgap (1.0-1.5 eV), abundant elemental reserves, environmental friendliness, and good environmental stability, CZTSSe is widely considered one of the most promising light-absorbing layer materials for thin-film solar cells. In particular, the solution-based preparation route offers advantages such as low cost, flexible processes, and ease of scalability, demonstrating significant application prospects in novel low-cost photovoltaic technologies. In recent years, with the development of green solvent systems and continuous optimization of device fabrication processes, the efficiency of CZTSSe solar cells has been continuously improving. However, compared with its theoretical limit efficiency (approximately 32%), the performance of existing devices still lags significantly. Therefore, how to further improve the conversion efficiency of CZTSSe thin-film solar cells is an urgent problem to be solved.

[0003] Its root cause is directly related to the poor crystal quality, defect density, and interfacial recombination of the absorption layer.

[0004] While existing studies have improved the selenization process of CZTSSe through overall atmosphere regulation, precursor composition optimization, and surface Se donation, the role of the local reaction environment at the back interface in phase evolution and grain growth remains insufficiently studied. In fact, the back interface not only affects the contact quality between the film and the Mo electrode but also influences the longitudinal reaction sequence, local nucleation behavior, and grain growth process of the precursor in the early stages of selenization. Since the film surface first contacts Se vapor and preferentially grows dense grains, this top dense grain layer further hinders the diffusion of Se vapor to the bottom of the film, thus limiting the continued selenization and subsequent ripening process of the bottom CZTS precursor. Therefore, there is an urgent need to develop new strategies that can promote bottom-preferred reactions from the back interface, reconstruct the traditional phase transformation pathway, and induce more favorable longitudinal crystal growth. Summary of the Invention

[0005] To address the above problems, this invention provides a CZTSSe thin-film solar cell and its preparation method.

[0006] While existing studies have improved the selenization process of CZTSSe through overall atmosphere regulation and precursor composition optimization, the role of the local reaction environment at the back interface in phase evolution and grain growth remains insufficiently studied. This invention discovers that the back interface not only affects the contact quality between the film and the Mo electrode but also influences the longitudinal reaction sequence, local nucleation behavior, and grain growth process of the precursor in the early stages of selenization. Since the film surface first contacts Se vapor and preferentially grows dense grains, this top dense grain layer further hinders the diffusion of Se vapor to the bottom of the film, thereby limiting the continued selenization and subsequent ripening process of the bottom CZTS precursor. Therefore, this invention provides a novel strategy that promotes preferential bottom reactions starting from the back interface, reconstructs the traditional phase transformation pathway, and induces more favorable longitudinal crystal growth.

[0007] Specifically, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a CZTSSe thin-film solar cell, wherein a CdSe thin layer is disposed between the back electrode and the CZTSSe absorber layer.

[0008] Furthermore, the thickness of the CdSe layer is 1~40nm, preferably 5~30nm, and more preferably 10~20nm.

[0009] Furthermore, the CdSe thin layer can be prepared by solution method and thermal evaporation method. Specifically, the CdSe thin layer prepared by solution method is obtained by dissolving CdCl2 in an organic solvent to obtain a CdCl2 solution, and then spin-coating the solution, wherein the concentration of the CdCl2 solution is 1 mg / ml to 10 mg / ml. In this invention, the organic solvent is ethylene glycol methyl ether, dimethylformamide, or methanol; in a specific embodiment of this invention, dimethylformamide is used as the solvent. The CdSe thin layer prepared by thermal evaporation method is obtained by thermally evaporating CdSe powder, wherein the basis weight of the CdSe powder used is 0.1 g to 1 g. In a specific embodiment of this invention, the basis weight used is 0.5 g.

[0010] In a preferred embodiment of the present invention, the CdSe thin layer is obtained by thermal evaporation. The evaporation current during thermal evaporation is 120~130 A, and the evaporation time is based on the film thickness recorded by a crystal oscillator and a film thickness gauge.

[0011] Further, the battery includes: basal layer; Mo back electrode layer, wherein the Mo back electrode layer is disposed on the upper surface of the substrate layer; A CdSe thin layer is disposed on the upper surface of the Mo back electrode layer; CZTSSe absorber layer, wherein the CZTSSe absorber layer is disposed on the upper surface of the CdSe thin layer; A CdS buffer layer is disposed on the upper surface of the CZTSSe absorber layer; A first window layer is disposed on the upper surface of the CdS buffer layer; A second window layer is disposed on the upper surface of the first window layer; A top electrode is also provided on the second window layer.

[0012] Furthermore, the CZTSSe absorber layer is doped with Ag; And / or, the first window layer is made of ZnO material and the second window layer is made of ITO material.

[0013] This invention introduces a thin CdSe layer between the CZTSSe absorber layer and the back electrode layer. During selenization, CdSe decomposes and participates in the reaction, increasing the local Se chemical potential and regulating the reaction kinetics, thereby suppressing the formation of the Cu2SnSe3 intermediate phase. This transforms the CZTSSe absorber layer from a traditional multi-step phase transition path to a direct phase formation path. Simultaneously, this process promotes the preferential formation of a large-grained CZTSSe layer at the back interface and facilitates Cd diffusion into the bulk phase in the later stages of selenization, promoting absorber layer crystallization and thus synergistically controlling interface and bulk defects. This invention significantly improves the photoelectric conversion efficiency and device stability of CZTSSe solar cells.

[0014] A second aspect of the present invention is to provide a method for preparing the above-mentioned thin-film solar cell, comprising the following steps: (1) The soda-lime glass substrate is cleaned and dried to serve as the base layer; (2) Sputter deposition of a Mo back electrode layer on the substrate; (3) A CdSe thin layer is deposited on the Mo back electrode; (4) A CZTSSe absorber layer is deposited on the CdSe thin layer; (5) Deposit a CdS buffer layer on the CZTSSe absorber layer; (6) A first window layer and a second window layer are sequentially deposited on the CdS buffer layer, and then a top electrode is deposited on the second window layer.

[0015] Furthermore, in step (2), the Mo back electrode layer is prepared by DC magnetron sputtering. The Mo back electrode layer includes a Mo bottom layer and a Mo top layer; the thickness of the Mo bottom layer is 200~400nm, and the thickness of the Mo top layer is 600~800nm. When depositing the Mo bottom layer, the DC power is 180~230W; when depositing the Mo top layer, the DC power is 120~180W.

[0016] Further, in step (3), the CdSe thin layer is prepared by spin-coating a CdCl2 solution onto a Mo back electrode, followed by heat treatment and selenization to obtain a CdSe thin layer. The heat treatment temperature is 250~350℃, the heat treatment time is 1~5 minutes, and the selenization temperature is 500~600℃. Alternatively, the CdSe thin layer can be prepared by thermal evaporation. During thermal evaporation, CdSe powder is placed in an evaporation boat, and the substrate with the deposited Mo back electrode is placed in the sample holder of the thermal evaporation equipment. The vacuum is then evacuated to a level not lower than 3 × 10⁻⁶. -3 The current of the thermal evaporation equipment was increased to 100~130A, and the evaporation rate was kept at 0.15~0.3nm / s to prepare a CdSe thin layer with a thickness of 10-30 nm.

[0017] Further, in step (4), the preparation of the CZTSSe absorber layer includes: S41. Mix SC(NH2)2, copper source, and solvent, heat and stir, then add AgCl powder, and continue heating and stirring until AgCl is completely dissolved to form solution A; S42. Mix the tin source with the solvent, then add the zinc source, heat and stir to obtain a clear and transparent solution B; S43. Mix solution A and solution B and stir until homogeneous to obtain the precursor solution; S44. Treat the substrate with the deposited CdSe thin layer using an ultraviolet ozone cleaning device for 10-30 minutes; S45. After filtering the precursor solution obtained in step S43, spin-coat it onto the upper surface of the CdSe thin layer treated in step S44; then bake the adhesive. Repeated spin coating and baking were performed multiple times to obtain the precursor film; S46. The substrate with the precursor film is placed in a semi-enclosed graphite cavity containing selenium particles and placed in a rapid annealing furnace for selenization treatment to prepare the absorption layer.

[0018] In steps S41 and S42, the solvent is preferably dimethylformamide (DMF).

[0019] Furthermore, in step S46, the rapid annealing furnace further includes a nitrogen purging process before the selenization treatment. The nitrogen purging process includes evacuating the rapid annealing furnace to a vacuum level of 10. -2 Pa, then fill with sufficient high-purity nitrogen to atmospheric pressure; repeat three or more times; And / or, during the selenization treatment, the nitrogen flow rate is 80-120 sccm, the selenization program is set to raise the temperature from room temperature to 500-550°C in 1 minute and hold it at that temperature for 1200-1500 seconds; after the selenization treatment is completed, the temperature is allowed to cool naturally to room temperature.

[0020] Furthermore, in step (5), the preparation of the CdS buffer layer includes the following steps: S51. Dissolve cadmium sulfate powder in deionized water, stir well, add ammonia water, and continue stirring for 3-8 minutes to obtain a mixed solution. S52. Suspend and completely immerse the substrate with the deposited absorbent layer in the mixture obtained in step S51; S53. Add thiourea to the mixture and continue stirring for 3-8 minutes. After stirring, place the mixture in a water bath at 65-75°C, heat and stir continuously until the surface of the substrate changes from grayish-white to blue-purple. Remove the substrate and cool and dry it to obtain a substrate with a CdS buffer layer deposited on it. The thickness of the CdS buffer layer is 30-50 nm.

[0021] Further, in step (1), the cleaning includes: S11. Soak the base in detergent-deionized water, heat to 70~85℃, soak for 1~3 hours, then take it out and rinse it clean with deionized water. S12. Place the substrate on the PTFE cleaning rack and put it into a glass water tank filled with deionized water for ultrasonic cleaning. Each ultrasonic cleaning session lasts 20-40 minutes and is repeated 2-4 times. After each ultrasonic cleaning session, replace the deionized water and clean the substrate, PTFE cleaning rack and glass water tank. S13. Place the ultrasonically cleaned substrate into a glass bath, add a prepared isopropanol:acetone:methanol solution in a 1:1:1 ratio, and continue ultrasonic cleaning 2-4 times, each time lasting 20-40 minutes; S14. Then rinse the substrate with deionized water and place it in a glass water tank filled with deionized water for ultrasonic cleaning 2-4 times, each time for 20-40 minutes; the deionized water needs to be replaced after each cleaning. S15. Then, place the substrate in a glass water bath filled with anhydrous ethanol and ultrasonically clean it for 20-40 minutes. S16. Finally, place the substrate in a new glass water bath filled with anhydrous ethanol for storage. Each time it is needed, perform anhydrous ethanol ultrasonic cleaning for 5-10 minutes and dry it with a nitrogen gun.

[0022] Furthermore, intrinsic zinc oxide (i-ZnO) of 50 nm and indium tin oxide (ITO) of 200 nm were deposited by magnetron sputtering as the first and second window layers of the CZTSSe solar cell, respectively. Elemental Ag was then deposited onto the surface of the film after the second window layer was sputtered using thermal evaporation as the top electrode to obtain the solar cell.

[0023] In the method of the present invention, the preparation of the Mo back electrode layer adopts a two-layer process, including the use of a double-layer Mo plating structure during sputtering. The combination of the dense layer and the loose layer can improve the adhesion to the glass substrate, buffer the thermal stress at high temperature, provide good conductivity (reduce series resistance), and improve the interface contact with the functional layer above the Mo substrate.

[0024] In the method of this invention, a high vacuum state (10) must be maintained during the deposition of the CdSe thin layer. -3 (Pa level) By slowly adjusting the evaporation current to control the coating speed, the uniformity and continuity of the CdSe thin layer are ensured.

[0025] In the method of this invention, the rapid annealing furnace needs to undergo multiple gas washing processes, preferably at least three times, to evacuate the quartz tube to a vacuum level of 10. -2 Pa, fill with sufficient high-purity nitrogen to atmospheric pressure, repeat this operation three times to ensure that there is no air or water vapor residue in the quartz tube.

[0026] Compared with the prior art, the present invention has the following advantages: The CZTSSe thin-film solar cell provided by this invention utilizes a CdSe thin layer between the back electrode and the CZTSSe absorber layer. This CdSe thin layer, acting as a transient modulation layer at the back interface, effectively reduces carrier recombination channels, small grain layers, and voids at the back interface. During phase evolution, the decomposition of the CdSe thin layer increases the Se vapor concentration at the back interface, allowing the phase evolution to directly transition from CZTS to CZTSSe, avoiding intermediate phases such as Cu2SnSe3. In the early stages of selenization, it promotes the early formation and ripening of precursor film back interface grains, improving the overall quality of the absorber layer and significantly reducing the bulk defect concentration. When the CdSe thin layer thickness is 20 nm, the absorber layer is 10% Ag-doped, and the selenization temperature is 530℃, the photoelectric conversion efficiency of the CZTSSe solar cell increases by 31.85% (from 11.21% to 14.78%). Attached Figure Description

[0027] Figure 1The XRD patterns of a grazing incidence CdSe thin film deposited on a Mo-plated sodium-calcium glass substrate, the XRD patterns of CdSe powder, the XRD patterns of CdCl2 powder, and the XRD patterns of a CdSe thin film after spin-coating CdCl2 solution onto a Mo-plated sodium-calcium glass substrate and then drying and selenizing. Figure 2 These are photographs of CdSe thin layers of different thicknesses prepared by thermal evaporation. Figure 3 (a) XRD patterns and (b) magnified images of the (112) diffraction peaks of CZTSSe, ACZTSSe, and ACZTSSe-CdSe-x nm (x=10, 20, 30, 40) thin films; Figure 4 The cross-sectional elemental distribution diagram of the ACZTS-CdSe precursor film; Figure 5 The cross-sectional elemental distribution of the ACZTS-CdSe precursor after selenization for 30 s is shown. Figure 6 Raman scattering spectra of different samples during selenization process reveal phase evolution behavior: (a) CZTSSe thin film, (b) ACZTSSe thin film, (c) ACZTSSe-CdSe thin layer; Figure 7 SEM images of the cross-sections of (a) CZTSSe, (b) ACZTSSe, and (c) ACZTSSe-CdSe absorber films; Figure 8 JV curves for ACZTSSe and ACZTSSe-CdSe-x nm (x = 10, 20, 30, 40) solar cell devices; Figure 9 JV curves for CZTSSe solar cell devices with soda-lime glass / Mo substrate / CZTSSe, soda-lime glass / Mo / ACZTSSe, and soda-lime glass / Mo / CdSe / ACZTSSe (CdSe is 20 nm). Detailed Implementation

[0028] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0030] Unless otherwise specified, all materials and reagents used in this invention are available from commercially available products in the field.

[0031] Example 1 1. Pretreatment of soda-lime glass substrate The detergent solution was diluted with deionized water (a 1:100 volume ratio of detergent to deionized water) to prepare the cleaning agent. A 2.1 mm thick soda-lime glass (SLG) substrate was cut into 8*8 cm pieces using a desktop glass cutter. The cut SLG sheets (substrates) were placed in a glass water bath, and the detergent-deionized water solution was added. The solution was heated to 80°C and soaked for 1.5 hours. The SLG sheets were then wiped with a lint-free cloth dampened with the cleaning agent. After the surface was free of obvious stains, they were rinsed thoroughly with deionized water. The SLG sheets were then placed on a PTFE cleaning rack and placed in a glass water bath containing 1000 ml of deionized water for ultrasonic cleaning. Each ultrasonic cleaning session lasted 30 minutes and was repeated 3 times. After each ultrasonic cleaning, the deionized water needs to be replaced and the soda-lime glass, PTFE cleaning rack, and glass water tank cleaned. Then, the ultrasonically cleaned soda-lime glass slide is placed in the glass tank, and a prepared isopropanol:acetone:methanol solution (1:1:1) is added. Ultrasonic cleaning is then performed three times, each time for 30 minutes. The slide is then rinsed with deionized water and placed back into the glass water tank containing deionized water for ultrasonic cleaning, three times * 30 minutes. The deionized water needs to be replaced after each cleaning. The soda-lime glass slide is then placed in a glass water tank containing anhydrous ethanol and ultrasonically cleaned for 30 minutes. Finally, the soda-lime glass slide is stored in a new glass water tank containing anhydrous ethanol. Before each use, it undergoes 5-10 minutes of anhydrous ethanol ultrasonic cleaning and is then dried with a nitrogen gun.

[0032] 2. Fabrication of Mo back electrode on glass substrate (1) Preparation and treatment of back electrode A Mo layer, approximately 1000 nm thick, was deposited on a soda-lime glass substrate (cleaned with anhydrous ethanol using ultrasonication and dried with nitrogen) to serve as the back electrode of a CZTSSe solar cell. The Mo layer was formed in two sputtering steps: a bottom layer (approximately 300 nm) and a top layer (approximately 700 nm). Higher power was used for the bottom layer to ensure good adhesion to the glass substrate and prevent film detachment during subsequent functional layer fabrication. Lower power was used for the top layer to achieve excellent conductivity, which helps reduce the back electrode resistance and improves hole carrier transport and collection. Specific sputtering process parameters for both Mo layers are shown in Table 1.

[0033] Table 1. Mo plating process parameters

[0034] 3. A CdSe thin layer was prepared on the Mo back electrode to obtain the corresponding solar cell. (1) Preparation of CdSe thin film on Mo back electrode Weigh 0.5 g of CdSe powder using a high-precision balance under a nitrogen atmosphere and place it in an evaporation boat. Place a clean Mo-coated glass substrate in the sample holder of the thermal evaporation equipment, and evacuate the vacuum to 3 × 10⁻⁶ using a mechanical pump and a molecular pump. -3 After setting the parameters of the CdSe powder evaporation source, the current was slowly increased to 100 A, and the evaporation rate was monitored. The current was then further increased to 120-130 A, maintaining the evaporation rate at 0.2 nm / s. CdSe thin layers of 1-40 nm thickness were deposited. (2) Preparation of ACZTSSe absorber thin film with CdSe layer inserted Remove the serum bottle and magnetic stirrer from the diluted aqua regia container and rinse them thoroughly with deionized water. Dry them under nitrogen gas. Weigh 3.656 g of SC(NH2)2 reagent and 1.083 g of CuCl powder and add them sequentially to the dried serum bottle No. 1. Then, using a 10 ml pipette, add 7.8 ml of DMF solvent to the bottle. Seal the bottle and place it on a heated magnetic stirrer. Stir continuously at 60°C for 30 min to obtain a clear and transparent solution. Weigh 0.1725 g of AgCl powder and add it to serum bottle 1. Continue heating and stirring for 40 min until the AgCl is completely dissolved to obtain solution A. Weigh 1.9815 g of SnCl4 reagent and add it to serum bottle 2. Seal the bottle tightly. Use a syringe to draw up the DMF solution and puncture the cap of serum bottle 2 to add 7.8 ml of DMF solution to serum bottle 2. An exothermic reaction occurs in the bottle, producing a white precipitate. Gently shake the bottle to prevent the magnetic stir bar from being fixed to the bottom by the precipitate. Repeatedly push the syringe to avoid leaving DMF solution in the syringe. Once the exothermic reaction is complete, remove the syringe needle from serum bottle 2. Weigh 1.563 g of Zn(CH3COO)2 and add it to bottle 2. Stir continuously at 50°C for 30 min to dissolve the drug, obtaining a clear and transparent solution B. Mix solution A with solution B and stir for another 1 min to ensure complete mixing. At this point, the silver-copper-zinc-tin-sulfur (ACZTS) precursor solution is ready. To prepare the copper-zinc-tin-sulfur (CZTS) precursor solution, simply replace all molar masses of AgCl with CuCl. All of the above processes are performed in a nitrogen glove box. The total concentrations of metal ions and thiourea in the mixed solution are 1.81 M and 3.08 M, respectively. The molar ratios of Cu / (Zn+Sn), (Ag+Cu) / (Zn+Sn), Zn / Sn, and Ag / (Ag+Cu) were 0.75, 0.75, 1.12, and 0.10, respectively. Before preparing the precursor films, the 8*8cm SLG / Mo and SLG / Mo / CdSe substrates were cut into 4*4cm or 2*2cm sizes. The SLG / Mo and SLG / Mo / CdSe substrates were then treated with UV ozone for 20 minutes to remove organic matter and unpaired chemical bonds from the substrate surface, thereby increasing the wettability of the CZTS and ACZTS precursor solutions on the substrates.

[0035] In a nitrogen-atmospheric glove box (water and oxygen levels both less than 10 ppm), the prepared CZTS and ACZTS precursor solutions were filtered through a PTFE filter. The CZTS and ACZTS precursor solutions were then spin-coated onto an SLG / Mo substrate, and the ACZTS precursor solution was spin-coated onto an SLG / Mo / CdSe substrate. A desktop spin coater was used at 3000 rpm for 30 seconds to uniformly coat the precursor solutions onto the surfaces of the SLG / Mo and SLG / Mo / CdSe substrates. The spin-coated CZTS and ACZTS precursor films were then placed on a heated stage (temperature set to 300℃) for baking. After 2 minutes, the samples were removed and allowed to cool naturally before spin-coating was repeated. This process was repeated multiple times to obtain CZTS and ACZTS precursor films with a thickness of 1.2–1.5 μm and ACZTS precursor films with intercalated CdSe layers.

[0036] The precursor film was placed in a semi-enclosed graphite cavity containing 0.5g of Se particles and then placed in a rapid annealing furnace for selenization. Prior to selenization, the rapid annealing furnace required multiple high-purity nitrogen purging treatments, preferably at least three times, and the quartz tube was evacuated to a vacuum level of 10. -2 At atmospheric pressure, sufficient high-purity nitrogen was introduced, and this operation was repeated three times to ensure that no air or water vapor remained inside the quartz tube. Then, the nitrogen flow rate in the rapid annealing furnace was adjusted to 80-120 sccm, and the selenization program was set to rise from room temperature to 530℃ in 1 minute and hold for 1300 seconds. After selenization, the furnace was allowed to cool naturally to room temperature, yielding CZTSSe and ACZTSSe precursor films, and ACZTSSe absorber layer films with intercalated CdSe layers.

[0037] (3) Fabrication of solar cells Cadmium sulfide (CdS) films are used as buffer layers in CZTSSe solar cells. Approximately 40 nm thick CdS films were deposited on the surfaces of CZTSSe, ACZTSSe, and ACZTSSe-CdSe absorber layers using a chemical bath method (CBD). The specific process flow includes: placing a cleaned magnetic rotor into a beaker containing 250 ml of deionized water, and then placing the beaker on a heated magnetic stirrer at 35°C and rotating at 400 rpm, maintaining continuous stirring. Next, 0.0768 g of cadmium sulfate powder was accurately weighed using an analytical grade electronic balance and added to the beaker, stirring for 5 min until the powder was completely dissolved. Then, 13 ml of ammonia water was added dropwise using a dropper, and stirring continued for another 5 min. Afterward, a polytetrafluoroethylene sample holder containing CZTSSe, ACZTSSe, and ACZTSSe-CdSe samples was suspended in the beaker, ensuring the solution completely submerged the samples. Finally, 0.11 g of thiourea was added to the mixture, and stirring continued for 5 min. After stirring, transfer the beaker to a water bath set at 70 ℃, heat and stir continuously until the film surface changes from grayish-white to blue-purple, at which point the sample is removed, which takes about 10-11.5 min. After removing the sample, place it in a beaker filled with deionized water to cool and wash away any residue on the sample surface, and finally dry it with high-purity nitrogen gas.

[0038] Subsequently, high-resistivity intrinsic zinc oxide (i-ZnO) and low-resistivity indium tin oxide (ITO) were deposited as window layers for solar cells using radio frequency magnetron sputtering technology. Three types of samples, namely SLG / Mo / CZTSSe / CdS, SLG / Mo / ACZTSSe / CdS, and SLG / Mo / CdSe / ACZTSSe / CdS, were placed on a dedicated mask and placed into the magnetron sputtering chamber. Vacuuming, pre-sputtering, and sputtering were then performed sequentially, depositing a 50 nm thick i-ZnO layer and a 200 nm thick ITO layer. During ITO sputtering, the chamber was heated to 160°C. Other process parameters are shown in Table 2.

[0039] Table 2. Magnetron sputtering parameters for i-ZnO and ITO window layers

[0040] A thermal evaporation process was employed to deposit silver grid lines (Ag) as the top electrode onto the surface of a thin film with a pre-sputtered window layer. First, the sample was placed in a mask plate printed with a specially designed mask pattern, and a magnet was used to fix the sample in place to prevent displacement during the thermal evaporation process. The sample was then placed in the thermal evaporation apparatus, with 99.999% pure Ag wire added to the evaporation source, and the vacuum was evacuated to 10... -4At the specified level, the current was automatically increased until the Ag filament melted, and the sample baffle was opened to begin electrode deposition. The Ag electrode deposition thickness was 400 nm. After thermal evaporation, the vacuum was released, and the sample was removed after the temperature had decreased. Subsequently, the sample was divided into 9 independent cell units using mechanical scribing, each unit having an effective area of ​​0.19 cm². 2 Thus, three types of thin-film solar cells were successfully fabricated: CZTSSe, ACZTSSe, and ACZTSSe with a CdSe thin layer intercalated.

[0041] This embodiment further adjusts the thickness of the CdSe thin layer according to the method described in the above embodiment, and assembles it into a CZTSSe solar cell for performance testing. The test results are as follows: like Figure 1 As shown, different methods were explored to investigate the preparation process of CdSe thin films, including spin-coating with CdCl2 solution followed by selenization. XRD analysis showed this method was feasible, but it was abandoned due to the uncontrollable nature of the CdSe phase purity, film thickness, and MoSe2 thickness. Due to the solubility issue of CdSe, a more controllable thermal evaporation method was chosen. Phase information of CdSe films prepared by different methods is shown in [link to relevant documentation]. Figure 1 As shown. Finally, CdSe thin layers with thicknesses of 1-40 nm were thermally evaporated on the Mo-plated substrate, preferably 10 nm, 20 nm, 30 nm and 40 nm thick, and then an ACZTSe absorber layer with 10% Ag doping was prepared on top of them.

[0042] like Figure 2 The image shows CdSe thin films of different thicknesses prepared on an SLG / Mo substrate by thermal evaporation.

[0043] like Figure 3 As shown in (a), the X-ray diffraction patterns of CZTSSe, ACZTSSe absorption layers, and ACZTSSe films with CdSe layers of different thicknesses intercalated are obtained by X-ray diffraction at room temperature. Figure 3 (b) shows a magnified view of the diffraction peaks on the (112) crystal plane to determine the effect of the introduction of the CdSe thin film on the quality of the ACZTSSe absorber layer. All samples exhibited a typical kesterite phase, and no secondary phases such as Cu2Se and SnSe2 were detected, nor was any diffraction information of CdSe detected. With the increase of CdSe thickness, the position of the diffraction peaks on the (112) crystal plane of the film continued to shift to a lower angle compared to the ACZTSSe film, indicating that the lattice of the ACZTSSe-CdSe thin film expanded, which may be related to the Cd in CdSe. 2+The inference is that the CdSe thin film underwent thermal decomposition during selenization, with Cd atoms occupying Zn atom sites in the CZTSSe lattice. If the CdSe thin film did not exist in thin film form throughout the process at the back interface, it can be inferred that the Se concentration at the back interface of the CdSe thin film sample differed significantly in the early stage of the selenization reaction. The high concentration of Se atmosphere will promote the crystallization and phase evolution of ACZTSSe, which is beneficial to improving the defect state of the absorption layer. In addition, when CdSe≦20 nm, the FWHM of the (112) diffraction peak gradually narrowed, indicating that the crystallinity of the film improved. When CdSe>20 nm, the FWHM broadened significantly, accompanied by a surge in the thickness of MoSe2. Poor crystal quality and MoSe2 thickness will have a huge impact on the resistance of the film, which is obviously detrimental to the fill factor and electrical performance of the device. Through the above analysis, it can be preliminarily determined that 10 nm or 20 nm CdSe is most beneficial to improving the quality of ACZTSSe thin films.

[0044] To further describe the crystallographic differences of ACZTSSe films with different CdSe thicknesses, the diffraction angles, FWHM of the (112) crystal plane diffraction peaks, and the crystallite sizes calculated according to the Scherrer formula are summarized in Table 3. It can be seen that the introduction of CdSe significantly improves the crystallinity and crystallite size of the film, and a high-quality absorption layer film helps to achieve better light absorption and avoid high concentrations of harmful defects.

[0045] (1) In equation (1), D is the grain size, K is the Scherrer constant, λ is the wavelength, β is the full width at half maximum (FWHM) of the diffraction peak, and θ is the Bragg diffraction angle. Calculations show that the crystallite size initially increases and then decreases from CZTSSe to ACZTSSe-CdSe-40nm. CdSe-20nm exhibits superior crystallinity. As the thickness of the CdSe thin layer increases, the crystal quality of the absorption layer decreases.

[0046] Table 3. Information on the position, full width at half maximum (FWHM), and crystallite size of the (112) crystal plane diffraction peaks of different absorber layer films.

[0047]

[0048] like Figure 4 The image shows the EDS elemental scan of the ACZTS-CdSe precursor film. A continuous CdSe layer can be clearly observed between the CZTS and the Mo back electrode, with enrichment of Se and Cd elements observed in this layer. This indicates that CdSe did not undergo thermal decomposition during the spin-coating annealing process of the precursor film, and the other elements are uniformly distributed.

[0049] like Figure 5The image shows the EDS elemental scan of the ACZTS-CdSe precursor film after 30 s of selenization. It clearly shows the disappearance of the continuous CdSe layer between ACZTS and the Mo back electrode, and a significantly increased Cd concentration distribution throughout the absorber layer. This indicates that CdSe undergoes thermal decomposition during the precursor film selenization process, releasing Se and Cd, resulting in a significant increase in Se concentration at the bottom of ACZTS. This greatly promotes the crystallization behavior at the back interface of the absorber layer. The densely grown continuous ACZTSSe grains at the top hinder the diffusion of Se vapor to the bottom of the precursor film, highlighting the role and significance of Se release from the thermal decomposition of CdSe at the back interface. The fully selenized film (1300 s) was analyzed by EDS, and the elemental ratios are shown in Table 4. This also shows that the Cd / (Cd+Zn) ratio continuously increases with the increase of the CdSe layer thickness, indicating a positive proportional relationship between the CdSe thickness and the Cd content released after thermal decomposition. The Cd / (Cd+Zn) ratio of the CdSe-20nm sample was 8%. Cd substitution for Zn typically expands the optical absorption range and reduces the bandgap of devices, which is beneficial for device performance. J SC The improvement is achieved. However, excessive Cd can introduce additional band tail states or defect states, affecting the device. V OC And FF, which reduces the conversion efficiency of the device.

[0050] Table 4. Elemental ratio information for thin films under different conditions.

[0051]

[0052] like Figure 6 The figures show the Raman scattering spectra of samples (a) CZTSSe, (b) ACZTSSe, and (c) ACZTSSe-CdSe-20nm absorption layer films. The XRD results alone are insufficient to completely distinguish some intermediate phases, especially those with low content or significant overlap of characteristic vibrational peaks. To further clarify the dominant phase evolution pathways in the selenization process of different samples, Raman spectral analysis was performed on the interrupted selenization samples, and the results are discussed in conjunction with typical phase evolution reaction equations. CZTS precursors typically exhibit three main phase evolution pathways during selenization: one is the initial formation of Cu... x Se, ZnSe and SnSe xThe precursor can be converted into CZTSSe via a binary phase and then through a ternary intermediate phase Cu2SnSe3 (CTSe), corresponding to equations (1-1), (1-2), and (1-4); the precursor can be directly converted into CTSe and ZnSe, and then further reacted to form CZTSSe, corresponding to equations (1-3) and (1-4); the precursor can be directly converted from CZTS to CZTSSe without passing through a distinct intermediate phase, corresponding to equation (1-5).

[0053] Cu-Zn-Sn-S+Se→Cu x Se+ZnSe+SnSe x (1-1) Cu x Se+SnSe x +Se→Cu2SnSe3(1-2) Cu-Zn-Sn-S+Se→Cu2SnSe3+ZnSe(1-3) Cu2SnSe3+ZnSe+Se→Cu2ZnSnSe4(1-4) Cu-Zn-Sn-S+Se→Cu2ZnSnSe4(1-5) from Figure 6The Raman evolution results show that the CZTSSe sample retains obvious CZTS characteristic peaks in the early stage of selenization, followed by the gradual appearance of CTSe characteristic peaks in the 30-120 s stage, and finally the CZTSSe main phase peak gradually strengthens and tends to stabilize. This indicates that the sample underwent a multi-step transformation process during selenization, and its dominant pathway can be summarized as equations (1-3) and (1-4). For the ACZTSSe sample, the Raman evolution law is generally similar to that of the CZTSSe sample, and the formation and consumption process of the CTSe intermediate phase can also be observed, indicating that Ag doping did not fundamentally change the phase evolution path, but mainly accelerated the reaction process and shortened the residence time of the CTSe intermediate phase. Therefore, the dominant phase evolution path of the ACZTSSe sample can also be summarized as equations (1-3) and (1-4). In contrast, the ACZTSSe-CdSe sample exhibits significantly different Raman evolution characteristics. Throughout the selenization process, no CTSe characteristic peaks were observed, while the CZTSSe main phase peak appeared rapidly and continuously strengthened in the early stages, indicating that the introduction of CdSe at the back interface significantly altered the phase transformation behavior of the precursor. Combined with the aforementioned pseudo-in-situ XRD results, the transformation from precursor to main phase in this sample was more direct, and the formation of intermediate phases was significantly weakened. Therefore, the dominant phase evolution path of the ACZTSSe-CdSe sample is closer to equation (1-5), and the CZTS precursor can be more directly transformed into the CZTSSe main phase in one step during selenization. These results indicate that Ag doping and back interface CdSe play different roles in phase evolution regulation. Ag doping mainly improves the basic reactivity of the precursor, accelerating the multi-step phase transformation process, while back interface CdSe further alters the dominant phase evolution path from the perspective of the local reaction environment. This change effectively reduces the formation and residence time of unfavorable intermediate phases.

[0054] like Figure 7As shown, to investigate the effects of Ag doping and CdSe on the morphology of the absorption layer, SEM images of (a) CZTSSe, (b) ACZTSSe, and (c) ACZTSSe-CdSe-20nm absorption layers after selenization were measured. The CZTSSe film is composed of large, irregularly arranged, and uneven grains, with numerous pores on the surface that can even directly connect to the back interface. This is likely due to the continuous decrease in the vapor pressure of Se in the semi-closed graphite chamber as the reaction progresses, leading to the decomposition of the CZTSSe film. A layer of small grains with a significant thickness is formed at the bottom of the ACZTSSe film. The current in CZTSSe solar cells is mainly provided by the large grains at the top, with very little contribution from the lower grains. Therefore, it is urgent to optimize the small grain layer and pores to improve the film's absorption capacity for long-wavelength light and its carrier transport characteristics. From the perspective of the vertical growth pattern, the ACZTSSe film still mainly exhibits the characteristic of prioritizing the surface layer and subsequent improvement at the bottom, without fundamentally changing the crystal quality of the back interface. The ACZTSSe-CdSe thin film morphology is completely different from that of the CZTSSe and ACZTSSe samples, ultimately yielding an absorption layer film composed of an extremely thin bottom small grain layer and a top uniform large grain layer. Furthermore, the pores at the back interface are essentially eliminated, and the interfacial contact between the top and bottom of the small grain layer is superior.

[0055] The above results demonstrate that the introduction of CdSe at the back interface on top of Ag doping improves the overall crystallinity of the film. More importantly, it effectively removes the small grain layer in the back interface region, thereby significantly optimizing the overall vertical structure. CdSe does not function as a stable back interface modification layer but exhibits distinct staged and dynamic control characteristics. In the early stages of selenization, CdSe promotes the direct phase transition from precursor to CZTSSe and grain growth by increasing the local Se chemical potential at the back interface and regulating reactivity. In the later stages of selenization, Cd further diffuses uniformly into the bulk phase, participating in the regulation of absorber layer growth, overall composition, and defect states. Thus, CdSe plays a dual role in this system as both a transient kinetic control source and a bulk phase regulation source, synergistically reconstructing the phase evolution path, promoting grain growth and maturation, and controlling defect characteristics, resulting in a high-quality absorber layer film.

[0056] like Figure 8 As shown, ACZTSSe solar cells with 0-40 nm thick CdSe thin films on Ag-doped substrates were fabricated. The thin film samples were assembled into solar cell devices, and their JV tests were performed as follows. Figure 8 As shown in Figure 5 and Table 6, the PCE of the battery increased from 13.33% to 14.78% after the introduction of the CdSe thin layer. The ACZTSSe-CdSe-20nm layer exhibited the highest PCE, primarily due to the increase in FF from 71.72% to 73.49% and Jsc from 35.74 mA / cm². 2Increased to 37.51 mA / cm 2 The Voc value increased from 520.00 mV to 536.12 mV. The significant improvements in FF and Voc are attributed to the one-step phase evolution and improved back-interface crystal quality. The increase in Jsc is mainly due to the increased size of the large grains at the top of the absorption layer, leading to improved light absorption efficiency. As the CdSe layer thickness increases, the PCE of the cell begins to decrease. This is mainly due to a decrease in FF and Voc, but Jsc continues to rise. This is primarily because Cd substitution for Zn narrows the bandgap of the solar cell, expanding the light absorption range. Therefore, after assembling CdSe into an ACZTSSe device, the optimal cell device is ACZTSSe-CdSe-20nm.

[0057] Table 5. Performance parameters of solar cells under different conditions.

[0058]

[0059] like Figure 9 As shown, the JV curves of the optimal CZTSSe, ACZTSSe, and ACZTSSe-CdSe devices are presented. The ACZTSSe-CdSe device exhibits the best overall performance, with its Voc, FF, and Jsc all superior to those of the CZTSSe and ACZTSSe devices, at 536.12 mV, 73.49%, and 37.51 mA / cm², respectively. 2 Without using a MgF2 antireflection layer, a conversion efficiency as high as 14.78% was achieved. The PCE, Voc, FF, and Jsc of the CZTSSe device were 11.21%, 482.81 mV, 65.27%, and 35.58 mA / cm², respectively. 2 The PCE, Voc, FF, and Jsc of the ACZTSSe device are 13.33%, 520.00 mV, 71.72%, and 35.74 mA / cm, respectively. 2 This indicates that the performance improvement of the device after further introducing CdSe at the back interface on top of Ag doping does not come from a single parameter, but from the synergistic improvement of multiple photovoltaic parameters. From ACZTSSe to ACZTSSe-CdSe devices, the improvement in Jsc contributes more significantly, while Voc and FF contribute less. This stems from the one-step phase evolution, improved crystal quality, and effective control of defect states facilitated by the introduction of CdSe.

[0060] Comparative Example 1 This comparative example is an adjustment based on the optimal device fabrication (ACZTSSe-CdSe-20nm) in Example 1, with the following differences: When preparing the Mo back electrode, a Mo back electrode with a thickness of 1000 nm was directly deposited using the same power of 200W; the rest remained unchanged.

[0061] The solar cell prepared in this comparative example was tested, and its photoelectric conversion efficiency was 12.98%.

[0062] Comparative Example 2 This comparative example is an adjustment based on the optimal device fabrication (ACZTSSe-CdSe-20nm) in Example 1, with the following differences: When preparing the Mo back electrode, a Mo back electrode with a thickness of 1000 nm was directly deposited using the same power of 150W; the rest remained unchanged.

[0063] The solar cell prepared in this comparative example was tested, and its photoelectric conversion efficiency was 8.37%.

[0064] Comparative Example 3 This comparative example is an adjustment based on the optimal device fabrication (ACZTSSe-CdSe-20nm) in Example 1, with the following differences: Replace the CdSe thin-layer chromatography with a solution-based CdCl2 thin-layer chromatography, leaving everything else unchanged.

[0065] The solar cell prepared in this comparative example was tested, and its photoelectric conversion efficiency was 13.35%.

[0066] In summary, this invention prepares CdSe thin layers using a simple thermal evaporation method. The device exhibits optimal photovoltaic performance when the CdSe thin layer thickness is 20 nm. As the CdSe thin layer thickness further increases, its photovoltaic performance deteriorates.

[0067] By systematically studying CdSe thin films of different thicknesses, the optimal thickness was determined to be 20 nm. Under this condition, the crystallinity and back contact performance of the ACZTSSe film were both optimized, and the phase evolution process was transformed from multi-step phase evolution to one-step phase evolution, effectively avoiding the generation of unfavorable intermediate secondary phases. The solar cell fabricated based on this process showed an increase in photoelectric conversion efficiency from 11.21% to 14.78%, a relative improvement of 31.85%. This performance improvement is mainly attributed to three aspects: First, the thermal decomposition of the CdSe thin film releases Se elements, increasing the Se concentration at the back interface, improving the crystallinity of the back interface, and promoting one-step phase evolution; second, the Cd elements released by the thermal decomposition of CdSe can replace Zn sites, suppressing Zn-related defects, thereby improving the quality of the absorber layer; third, CdSe, as a transient modulation layer at the back interface, effectively reduces the carrier recombination probability at the back interface, promotes carrier transport, and improves the back electrode contact quality. Furthermore, this invention further ensures the photoelectric conversion efficiency of the device by optimizing the deposition of the Mo back electrode layer.

[0068] In summary, the CdSe thin film achieves bidirectional optimization of the ACZTSSe absorber layer and back electrode interface, thereby significantly improving the overall performance of the battery device.

[0069] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A CZTSSe thin-film solar cell, characterized in that... The battery has a CdSe thin layer between the back electrode layer and the CZTSSe absorber layer.

2. The CZTSSe thin-film solar cell according to claim 1, characterized in that... The thickness of the CdSe thin layer is 10-30 nm.

3. The CZTSSe thin-film solar cell according to claim 1, characterized in that... The CdSe thin layer is prepared by thermal evaporation of CdSe powder or by spin-coating a CdCl2 solution and then drying and selenizing it.

4. The CZTSSe thin-film solar cell according to claim 1, characterized in that... The battery includes: basal layer; Mo back electrode layer, wherein the Mo back electrode layer is disposed on the upper surface of the substrate layer; A CdSe thin layer is disposed on the upper surface of the Mo back electrode layer; CZTSSe absorber layer, wherein the CZTSSe absorber layer is disposed on the upper surface of the CdSe thin layer; A CdS buffer layer is disposed on the upper surface of the CZTSSe absorber layer; A first window layer is disposed on the upper surface of the CdS buffer layer; A second window layer is disposed on the upper surface of the first window layer; A top electrode is also provided on the second window layer.

5. The CZTSSe thin-film solar cell according to claim 4, characterized in that... The CZTSSe absorber layer is doped with Ag. And / or, the first window layer is made of ZnO material and the second window layer is made of ITO material.

6. A method for preparing a CZTSSe thin-film solar cell according to any one of claims 1-5, characterized in that... This includes the following steps: (1) The soda-lime glass substrate is cleaned and dried to serve as the base layer; (2) Sputter deposition of a Mo back electrode layer on the substrate; (3) A CdSe thin layer is deposited on the Mo back electrode; (4) A CZTSSe absorber layer is deposited on the CdSe thin layer; (5) Deposit a CdS buffer layer on the CZTSSe absorber layer; (6) A first window layer and a second window layer are sequentially deposited on the CdS buffer layer, and then a top electrode is deposited on the second window layer.

7. The method according to claim 6, characterized in that... In step (2), the Mo back electrode layer is prepared by DC magnetron sputtering. The Mo back electrode layer includes a Mo bottom layer and a Mo top layer; the thickness of the Mo bottom layer is 200~400nm, and the thickness of the Mo top layer is 600~800nm. When depositing the Mo bottom layer, the DC power is 180~230W; when depositing the Mo top layer, the DC power is 120~180W.

8. The method according to claim 6, characterized in that... In step (3), the CdSe thin layer is prepared by spin-coating a CdCl2 solution onto a Mo back electrode, followed by heat treatment and selenization to obtain a CdSe thin layer. The heat treatment temperature is 250~350℃, the heat treatment time is 1~5 minutes, and the selenization temperature is 500~600℃. Alternatively, the CdSe thin layer can be prepared by thermal evaporation. During thermal evaporation, CdSe powder is placed in an evaporation boat, and the substrate with the deposited Mo back electrode is placed in the sample holder of the thermal evaporation equipment. The vacuum is then evacuated to a level not lower than 3 × 10⁻⁶. -3 The current of the thermal evaporation equipment was increased to 100~130A, and the evaporation rate was kept at 0.15~0.3nm / s to prepare a CdSe thin layer with a thickness of 10-30 nm.

9. The method according to claim 6, characterized in that... In step (4), the preparation of the CZTSSe absorber layer includes: S41. Mix SC(NH2)2, copper source, and solvent, heat and stir, then add AgCl powder, and continue heating and stirring until AgCl is completely dissolved to form solution A; S42. Mix the tin source with the solvent, then add the zinc source, heat and stir to obtain a clear and transparent solution B; S43. Mix solution A and solution B and stir until homogeneous to obtain the precursor solution; S44. Treat the substrate with the deposited CdSe thin layer using an ultraviolet ozone cleaning device for 10-30 minutes; S45. After filtering the precursor solution obtained in step S43, spin-coat it onto the upper surface of the CdSe thin layer treated in step S44; then bake the adhesive. Repeated spin coating and baking were performed multiple times to obtain the precursor film; S46. The substrate with the precursor film is placed in a semi-enclosed graphite cavity containing selenium particles and placed in a rapid annealing furnace for selenization treatment to prepare the absorption layer.

10. The method according to claim 9, characterized in that... In step S46, the rapid annealing furnace further includes nitrogen gas washing treatment before selenization treatment. The nitrogen gas washing treatment includes first evacuating the rapid annealing furnace to 10-2 Pa, and then filling it with sufficient high-purity nitrogen to atmospheric pressure; repeating this process three or more times. And / or, during the selenization treatment, the nitrogen flow rate is 80-120 sccm, the selenization program is set to raise the temperature from room temperature to 500-550°C in 1 minute and hold it at that temperature for 1200-1500 seconds; after the selenization treatment is completed, the temperature is allowed to cool naturally to room temperature.

11. The method according to claim 6, characterized in that... In step (5), the preparation of the CdS buffer layer includes the following steps: S51. Dissolve cadmium sulfate powder in deionized water, stir well, add ammonia water, and continue stirring for 3-8 minutes to obtain a mixed solution. S52. Suspend and completely immerse the substrate with the deposited absorbent layer in the mixture obtained in step S51; S53. Add thiourea to the mixture and continue stirring for 3-8 minutes. After stirring, place the mixture in a water bath at 65-75°C, heat and stir continuously until the surface of the substrate changes from grayish-white to blue-purple. Remove the substrate and cool and dry it to obtain a substrate with a CdS buffer layer deposited on it.

Images