Annealing method and application of CdS / Sb2S3 film

Abstract

The invention provides an annealing method and application of a CdS / Sb2S3 film, and relates to the technical field of photovoltaic materials. The invention provides an annealing method of a CdS / Sb2S3 film, which is a double-sided annealing method, one surface is annealed for 10-20 minutes on a first platform preheated to 350-400 DEG C, and the other surface is continuously annealed for 2-3 hours on a second platform preheated to 150-180 DEG C. The annealing method has the advantages of being easy to operate, remarkable in effect, low in practice cost and the like, effectively improves the back interface crystallinity of the Sb2S3 thin film, ensures the quality of CdS / Sb2S3 heterojunction, and effectively improves the carrier transport performance of the Sb2S3 thin film solar cell.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic materials technology, and relates to an annealing method for CdS / Sb2S3 thin films and their applications. Background Technology

[0002] Sb₂S₃ is considered a photovoltaic material with great development potential. The quality of the Sb₂S₃ thin film is a crucial factor determining the photoelectric performance of Sb₂S₃ solar cells, and this quality mainly depends on its lattice orientation, crystallinity, compactness, and lattice defects. Currently, Sb₂S₃ solar cells are all based on CdS / Sb₂S₃ heterojunctions. However, the poor thermal stability of this heterojunction structure limits the annealing temperature of the Sb₂S₃ thin film, and traditional tube furnace annealing technology cannot obtain Sb₂S₃ thin films with high crystallinity. Glovebox annealing technology is currently the main method for preparing high-quality Sb₂S₃ thin films due to its advantages of convenient operation, uniform heating, and rapid temperature rise and fall. However, there is significant heat loss near the upper surface of the Sb₂S₃ film during annealing, resulting in a large temperature gradient and causing the back interface of the Sb₂S₃ film to have significantly less crystallinity compared to the front interface.

[0003] Therefore, it is necessary to further optimize the annealing process of CdS / Sb2S3 heterojunction. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an annealing method for CdS / Sb2S3 thin films and its application.

[0005] The technical solution of the present invention is as follows:

[0006] An annealing method for CdS / Sb2S3 thin films, wherein the annealing is double-sided annealing: one side is annealed on a first platform preheated to 350-400℃ for 10-20 min, and the other side is annealed on a second platform preheated to 150-180℃ for 2-3 h.

[0007] Preferably, during the double-sided annealing, the sample to be annealed is placed in a sealed quartz tube under an inert gas atmosphere.

[0008] More preferably, the inert gas atmosphere is purged for 2-3 minutes, and then the gas flow rate is controlled at 50±10 sccm.

[0009] More preferably, the bottom surface of the quartz tube is a plane, and the bottom surface is in contact with the heating surfaces of the first platform and the second platform, respectively.

[0010] More preferably, the quartz tube is covered with an insulation cover for heat preservation.

[0011] Preferably, the method for preparing the CdS / Sb2S3 thin film is as follows: CdCl2 was deposited on a CdS film, and a first annealing was performed to obtain a first film. A mixed solution consisting of potassium antimony tartrate aqueous solution and sodium thiosulfate aqueous solution is subjected to a hydrothermal reaction with the first membrane. After the reaction is completed, the membrane is rinsed with deionized water and dried to obtain the final product.

[0012] More preferably, the first annealing is annealing at 380-400℃ for 10-15 minutes; The concentration of the potassium antimony tartrate aqueous solution is 0.005-0.02 g / mL; The concentration of the sodium thiosulfate aqueous solution is 0.04-0.12 g / mL.

[0013] More preferably, the first film is fixed on a glass slide; The molar ratio of potassium antimony tartrate in the potassium antimony tartrate aqueous solution to sodium thiosulfate in the sodium thiosulfate aqueous solution is 1:12-18. The mixed solution also contains 200-300 ppm of concentrated hydrochloric acid in the volume of the potassium antimony tartrate aqueous solution.

[0014] More preferably, the mixed solution submerges the first film; The conditions for the hydrothermal reaction are: 120-150℃ for 1.5-4 hours.

[0015] An application of a CdS / Sb2S3 heterojunction obtained by the annealing method described in any of the above embodiments, for use in indoor photovoltaics, photocatalytic water splitting, photodetectors, or solar cells.

[0016] The beneficial effects of this invention are: (1) This invention proposes a double-sided annealing technique for preparing high-quality Sb2S3 thin films, which solves the problem of insufficient crystallization at the back interface of the absorber layer of Sb2S3 solar cells prepared by hydrothermal method, and effectively improves the longitudinal crystallization uniformity and carrier transport performance of Sb2S3 thin films prepared by hydrothermal method. (2) The double-sided annealing technology proposed in this invention is convenient to operate, simple to use, and low in cost, making it suitable for industrial production. Attached Figure Description

[0017] Figure 1 This is a comparison of the morphology of the CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1.

[0018] Figure 2 This is a comparison of the GIXRD results of the CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1.

[0019] Figure 3 This is a comparison of the AFM morphology, conductivity distribution, and conductivity statistics of the CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1.

[0020] Figure 4 A comparison of the IV characteristics of FTO / Sb2S3 / Au devices composed of CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1.

[0021] Figure 5 A comparison of the JV characteristics of FTO / Sb2S3 / Au devices composed of CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1.

[0022] Figure 6 The EQE of the FTO / Sb2S3 / Au devices composed of CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1 is compared. Detailed Implementation

[0023] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0024] On the one hand, the present invention proposes an annealing method for CdS / Sb2S3 thin films, wherein the annealing is double-sided annealing: one side is annealed on a first platform preheated to 350-400℃ for 10-20 min, and the other side is annealed on a second platform preheated to 150-180℃ for 2-3 h.

[0025] This invention employs a double-sided annealing method for CdS / Sb2S3 thin films: First, conventional single-step annealing on the front side (heating of the front interface) promotes effective crystallization of the Sb2S3 thin film and reduces S loss during the annealing process; then, low-temperature annealing on the reverse side (heating of the back interface) improves the crystallinity of the back interface, providing longitudinal crystallization uniformity of the Sb2S3 thin film and ensuring the integrity and performance matching of the CdS / Sb2S3 heterojunction.

[0026] The aforementioned double-sided annealing with single-step annealing of the front side, employing a preheated first platform, achieves moderate heating and cooling rates, improves annealing uniformity, shortens process time, and establishes a suitable temperature gradient. Annealing of the first side can be performed at 350℃ for 10 min, 350℃ for 15 min, 350℃ for 20 min, 360℃ for 10 min, 360℃ for 15 min, 360℃ for 20 min, 380℃ for 10 min, 380℃ for 15 min, 380℃ for 20 min, 400℃ for 10 min, 400℃ for 15 min, 400℃ for 20 min, etc. Furthermore, the annealing of the first platform can be performed at 360-380℃ for 10-15 min. For the annealing of the other side, it can be annealed at 150℃ for 2 hours, 150℃ for 2.5 hours, 150℃ for 3 hours, 160℃ for 2 hours, 160℃ for 2.5 hours, 160℃ for 3 hours, 180℃ for 2 hours, 180℃ for 2.5 hours, 180℃ for 3 hours, etc.

[0027] In some embodiments, during double-sided annealing, the sample to be annealed is placed in a sealed quartz tube under an inert gas atmosphere. The sealed quartz tube and inert gas atmosphere prevent oxidation of the CdS / Sb₂S₃ heterojunction. There are no particular limitations on the inert gas atmosphere; it can be argon and / or helium.

[0028] In some embodiments, the inert gas atmosphere is maintained by purging for 2-3 minutes, followed by controlling the gas flow rate to 50±10 sccm. This technical solution can continuously maintain the inert gas atmosphere during double-sided annealing.

[0029] In some embodiments, the bottom surface of the quartz tube is a plane, which is attached to the heating surfaces of the first platform and the second platform, respectively. The plane bottom surface of the quartz tube ensures good adhesion to the first and second platforms, allowing heat to be conducted more quickly and evenly from the heating platforms into the quartz tube for double-sided annealing of the CdS / Sb2S3 thin film, thereby obtaining a CdS / Sb2S3 thin film heterojunction with better performance.

[0030] In some embodiments, the quartz tube is covered and insulated with a heat-insulating cover. Covering the quartz tube with a heat-insulating cover can prevent heat loss between the first and second platforms, allowing more and faster heat from the platforms to be conducted into the quartz tube. Furthermore, the heat-insulating cover can also cover the first and second platforms, forming a complete enclosure of the first and second platforms and the quartz tube.

[0031] In some embodiments, the method for preparing CdS / Sb2S3 thin films is as follows: CdCl2 was deposited on a CdS film, and a first annealing was performed to obtain a first film. A mixed solution consisting of potassium antimony tartrate aqueous solution and sodium thiosulfate aqueous solution is subjected to a hydrothermal reaction with the first thin film. After the reaction is completed, the film is rinsed with deionized water and dried to obtain the final product.

[0032] There are no particular limitations on the preparation method of CdS thin films. For example, one method is to put 32 mL of 15 mmol / L CdSO4 solution, 16 mL of 1.5 mol / L thiourea solution, 40 mL of ammonia water and 220 mL of deionized water into a beaker, preheat it in a 66°C water bath for 2 min, then add 16 mL of thiourea and place it in a clean FTO glass. After deposition in a 66°C water bath for 22 min, remove it, rinse and dry it to obtain a CdS thin film, which is then loaded onto an FTO glass.

[0033] For example, one method for depositing CdCl2 on a CdS film is to prepare a CdCl2 methanol solution with a concentration of 15 mg / mL, and then spin-coat it onto the deposited CdS film using a spin coater.

[0034] In some embodiments, the first annealing is annealing at 380-400°C for 10-15 minutes; The concentration of potassium antimony tartrate aqueous solution is 0.005-0.02 g / mL; The concentration of sodium thiosulfate aqueous solution is 0.04-0.12 g / mL.

[0035] For example, the first annealing can be annealing at 380℃ for 10 min, 380℃ for 12 min, 380℃ for 15 min, 400℃ for 10 min, 400℃ for 11 min, 400℃ for 15 min, etc.; the concentration of the potassium antimony tartrate aqueous solution can be 0.005 g / mL, 0.01 g / mL, 0.015 g / mL, 0.02 g / mL, etc., and can be prepared by dissolving potassium antimony tartrate trihydrate in deionized water, for example, 0. 2671g (0.4mmol) of potassium antimony tartrate trihydrate was dissolved in 20ml of deionized water; the concentration of sodium thiosulfate aqueous solution can be 0.04g / mL, 0.06g / mL, 0.08g / mL, 0.09g / mL, 0.10g / mL, 0.12g / mL, etc. It can be prepared by dissolving sodium thiosulfate pentahydrate in deionized water, for example, 1.5884g (6mmol) of sodium thiosulfate pentahydrate was dissolved in 20ml of deionized water.

[0036] In some embodiments, the first film is fixed on a glass slide, and there are no particular restrictions on the fixing method. For example, high-temperature resistant double-sided adhesive can be used to fix the first film on the glass slide. The molar ratio of potassium antimony tartrate in an aqueous solution to sodium thiosulfate in an aqueous solution is 1:12-18. For example, the molar ratio can be 1:12, 1:14, 1:15, 1:16, 1:18, etc. The mixed solution also contains 200-300 ppm of concentrated hydrochloric acid in a potassium antimony tartrate aqueous solution. For example, add 5 μL of concentrated hydrochloric acid to 20 ml of potassium antimony tartrate aqueous solution.

[0037] In some embodiments, the mixed solution floods the first film, which can ensure that the surface of the first film forms an Sb2S3 absorption layer as completely as possible. The conditions for hydrothermal reaction are: 120-150℃ for 1.5-4 hours. For example, the conditions for hydrothermal reaction can be 120℃ for 4 hours, 130℃ for 3 hours, 140℃ for 2.5 hours, 150℃ for 1.5 hours, etc.

[0038] On the other hand, the present invention also proposes an application of the CdS / Sb2S3 heterojunction obtained by the annealing method described in any of the above embodiments for use in indoor photovoltaics, photocatalytic water splitting, photodetectors or solar cells.

[0039] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0040] Example 1 32 mL of 15 mmol / L CdSO4 solution, 16 mL of 1.5 mol / L thiourea solution, 40 mL of ammonia water, and 220 mL of deionized water were placed in a beaker and preheated in a 66°C water bath for 2 min. Then, 16 mL of thiourea was added, and a clean FTO glass was placed in the beaker. After deposition in a 66°C water bath for 22 min, the beaker was removed, rinsed, and dried to obtain a CdS film, which was then loaded onto the FTO glass.

[0041] A CdCl2 methanol solution with a concentration of 15 mg / mL was prepared and then spin-coated onto the deposited CdS film using a spin coater. The film was then air-annealed on a hot stage at 400 °C for 11 min and rapidly cooled to room temperature to obtain the CdS contact layer.

[0042] 0.2671 g of potassium antimony tartrate trihydrate was dissolved in 20 mL of deionized water to prepare an aqueous solution of potassium antimony tartrate, and 1.5884 g of sodium thiosulfate pentahydrate was dissolved in 20 mL of deionized water to prepare an aqueous solution of sodium thiosulfate. The two aqueous solutions were then mixed and stirred on a magnetic stirrer until the solution turned yellow. 5 μL of concentrated hydrochloric acid was then added, and the mixture was stirred until homogeneous to obtain a mixed solution. The FTO glass with the CdS contact layer was attached to a glass slide using high-temperature double-sided adhesive tape, and a PTFE liner was placed inside. The mixed solution was then added to submerge the FTO glass. The PTFE liner was placed in a hydrothermal reactor and then placed in an oven at 130°C for 135 min. After the reaction, the sample was cooled, removed, rinsed with deionized water, and dried to obtain the first thin film.

[0043] The first thin film was placed in a sealed quartz tube (back surface facing upwards), with the bottom surface of the quartz tube flat. It was then purged with inert Ar gas for 2 minutes, followed by a continuous flow of Ar gas at a flow rate of 50 sccm. The quartz tube was then placed on a preheated platform (bottom surface of the quartz tube in contact with the platform) and covered with an insulation cover for annealing for 10 minutes. After annealing, the quartz tube was removed and allowed to cool to room temperature. The first thin film was then removed and placed back into a sealed quartz tube (back surface facing downwards and raised 1 mm), with the bottom surface of the quartz tube flat. It was purged with inert Ar gas for 2 minutes, followed by a continuous flow of Ar gas at a flow rate of 50 sccm. The quartz tube was then placed on a preheated platform (preheated to 160°C). o The quartz tube was placed on the mesa (with the bottom surface of the quartz tube in contact with the mesa) and covered with an insulation cover, and annealed for 2.5 h. After the annealing time was over, the quartz tube was removed and allowed to cool to room temperature to obtain a CdS / Sb2S3 heterojunction.

[0044] Example 2 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, annealing at 360°C for 10 minutes is changed to annealing at 380°C for 10 minutes, and annealing at 160°C for 2.5 hours is changed to annealing at 180°C for 2 hours. The remaining steps remain unchanged.

[0045] Example 3 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, annealing at 360°C for 10 minutes is changed to annealing at 360°C for 15 minutes, and annealing at 160°C for 2.5 hours is changed to annealing at 150°C for 3 hours. The remaining steps remain unchanged.

[0046] Example 4 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, annealing at 360°C for 10 minutes is changed to annealing at 350°C for 15 minutes, and annealing at 160°C for 2.5 hours is changed to annealing at 160°C for 2 hours. The remaining steps remain unchanged.

[0047] Comparative Example 1 This comparative example is the CdS / Sb2S3 heterojunction obtained by annealing at 360°C for 10 min in Example 1.

[0048] A comparison of the morphology (SEM) of the CdS / Sb2S3 heterojunctions obtained in Example 1 and Comparative Example 1 is attached. Figure 1 As shown, the left image (a) is Comparative Example 1, labeled Control; the right image (b) is Example 1, labeled 2.5h. The thickness of the Sb2S3 film was controlled at around 350 nm. After conventional single-sided annealing (Comparative Example 1), the surface morphology of the film was smooth and the grain boundaries were clear, indicating that the Sb2S3 film had good crystallinity. However, from the SEM morphology of its cross-section, it can be observed that there is a significant difference and boundary between the morphology of the back interface and the front interface of the film. This indicates that under conventional single-sided annealing, due to the large temperature gradient, there is a difference in crystallinity between the front and back interfaces of the obtained Sb2S3 film. After double-sided annealing (Example 1), that is, on the basis of conventional single-sided annealing, the back interface was brought close to the heating stage for low-temperature secondary annealing. The grains of the Sb2S3 film became larger, and from the cross-sectional SEM image of the film, it can be seen that the Sb2S3 film achieved uniform crystallinity from top to bottom. This demonstrates that the double-sided annealing technique proposed in this invention can effectively improve the longitudinal crystallization uniformity of Sb2S3 films.

[0049] Figure 2 Grazing incidence X-ray diffraction (GIXRD, grazing incidence angle 0.3°) of the CdS / Sb₂S₃ heterojunctions obtained in Example 1 and Comparative Example 1. o In comparison, the comparative example is labeled Control, and Example 1 is labeled BIA. It can be seen that both Example 1 and Comparative Example 1 can achieve the preparation of orthorhombic Sb₂S₃ thin films with good crystallinity, and the Sb₂S₃ thin films as a whole exhibit the characteristic of preferred growth of the (hk₀) crystal plane. Figure 2 As shown in (b), magnified analysis of the strongest (130) crystal plane reveals that the Sb2S3 film back interface of Example 1 has a smaller full width at half maximum (FWHM) and the peak position shifts to a lower angle in the opposite direction. Combined with the SEM analysis results, it can be seen that the double-sided annealing technique of Example 1 can effectively enhance the crystallinity of the Sb2S3 film back interface.

[0050] Figure 3This paper compares the AFM morphology, conductivity distribution, and conductivity statistics of the CdS / Sb2S3 heterojunctions of Example 1 and Comparative Example 1. Figures (a)-(c) show the AFM morphology, conductivity distribution, and conductivity statistics of the CdS / Sb2S3 heterojunction of Comparative Example 1, while Figures (d)-(f) show the same data. Therefore, the double-sided annealing technique proposed in this invention can effectively reduce the roughness of the Sb2S3 thin film. When applied to solar cells, it helps improve carrier recombination loss at the back interface of the Sb2S3 thin film solar cell, reduces the series short resistance of the device, and thus improves the open-circuit voltage. Furthermore, under a 5 V tunneling voltage, the Sb2S3 thin films obtained under the two different annealing techniques exhibit different tunneling current distributions, such as... Figure 3 Comparing (b) and 3(e), the Sb2S3 thin film obtained in Example 1 exhibits a higher tunneling current, a result that can be seen from... Figure 3 The results are validated in the tunneling current statistics in (c) and 3(f).

[0051] To verify the C-AFM results, based on the FTO / Sb2S3 / Au device structure, tests were conducted and the following results were obtained: Figure 4 The IV characteristics shown are as follows. Calculations show that the conductivity of the Sb₂S₃ thin films obtained in Comparative Example 1 and Example 1 are 3.24 × 10⁻⁶. - 5 S / cm and 6.80×10 -5 S / cm. This indicates that the Sb2S3 film obtained by the double-sided annealing technique of the present invention has better conductivity, and the crystallinity of the film is significantly improved. The above results further verify that the double-sided annealing technique proposed in this invention can effectively enhance the crystallinity uniformity of Sb2S3 film, thereby enhancing the conductivity of the film.

[0052] To further investigate the effects of conventional single-sided and double-sided annealing on the performance of Sb₂S₃ thin films, a top-mass Sb₂S₃ solar cell was assembled according to the device structure of FTO / CdS / Sb₂S₃ / Spiro-OMeTAD / Au. The results are shown in Table 1 below. A comparison between Example 1 and Comparative Example 1 is attached. Figure 5 (Comparison of JV characteristic curves) and appendix Figure 6 (Comparison of external quantum efficiency EQE) is shown, where Comparative Example 1 is labeled Control and Example 1 is labeled BIA.

[0053] Table 1

[0054] Therefore, compared to single-sided annealing, double-sided annealing slightly reduces the open-circuit voltage of the device, but significantly improves the fill factor and short-circuit current density, resulting in a certain increase in PCE. The reduction in open-circuit voltage is attributed to the fact that the second-step back-side annealing facilitates element migration within the Sb₂S₃ thin film, filling donor-type S-vacancy defects and thus reducing the bandgap value of the Sb₂S₃ thin film, thereby lowering the open-circuit voltage. However, the improved crystallinity of the back interface significantly enhances the conductivity and carrier transport performance of the film, effectively suppressing carrier recombination losses, increasing the short-circuit current density (JSC) and fill factor (FF), and ultimately improving the photoelectric conversion efficiency of the Sb₂S₃ solar cell. Figure 6 As shown, Example 1 effectively improved the EQE performance of Sb2S3 solar cells in the 550–750 nm range. This result demonstrates that double-sided annealing can effectively suppress bulk recombination and back-interface recombination losses of charge carriers in Sb2S3 solar cells. This is attributed to the fact that double-sided annealing enhances the crystallinity of the Sb2S3 film's back interface, thereby effectively improving the overall crystallinity uniformity of the film and promoting its charge carrier transport performance. Furthermore, the integral JSC extracted from the EQE data shows good agreement with the JV results, proving the accuracy of the results. Therefore, the novel double-sided annealing technique proposed in this invention can effectively solve the problem of insufficient crystallinity at the back interface of Sb2S3 films, thereby improving the conductivity of the Sb2S3 film and enhancing the overall charge carrier transport performance of the device. It can significantly improve the short-circuit current density and fill factor of Sb2S3 solar cells, thus significantly improving the photoelectric conversion efficiency of Sb2S3 solar cells.

[0055] Therefore, the annealing process plays a crucial role in regulating the crystallinity of Sb₂S₃ thin films and determines the photoelectric conversion efficiency of Sb₂S₃ thin-film solar cells. This invention proposes a double-sided annealing technique, which has the following advantages: 1) simple operation, significant effects, and low implementation cost; 2) effectively improving the crystallinity of the Sb₂S₃ thin film back interface while ensuring the quality of the CdS / Sb₂S₃ heterojunction; 3) effectively improving the carrier transport performance of Sb₂S₃ thin-film solar cells.

[0056] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An annealing method for CdS / Sb2S3 thin films, characterized in that, The annealing is double-sided annealing: one side is annealed on a first platform preheated to 350-400℃ for 10-20 minutes, and the other side is annealed on a second platform preheated to 150-180℃ for 2-3 hours.

2. The annealing method according to claim 1, characterized in that, During the double-sided annealing, the sample to be annealed is placed in a sealed quartz tube under an inert gas atmosphere.

3. The annealing method according to claim 2, characterized in that, The inert gas atmosphere is purged for 2-3 minutes, and then the gas flow rate is controlled at 50±10 sccm.

4. The annealing method according to claim 2, characterized in that, The bottom surface of the quartz tube is flat, and the bottom surface is in contact with the heating surfaces of the first platform and the second platform, respectively.

5. The annealing method according to claim 2, characterized in that, The quartz tube is covered with an insulation cover for heat preservation.

6. The annealing method according to claim 1, characterized in that, The method for preparing the CdS / Sb2S3 thin film is as follows: CdCl2 was deposited on a CdS film, and a first annealing was performed to obtain a first film. A mixed solution consisting of potassium antimony tartrate aqueous solution and sodium thiosulfate aqueous solution is subjected to a hydrothermal reaction with the first membrane. After the reaction is completed, the membrane is rinsed with deionized water and dried to obtain the final product.

7. The annealing method according to claim 6, characterized in that, The first annealing is performed at 380-400℃ for 10-15 minutes; The concentration of the potassium antimony tartrate aqueous solution is 0.005-0.02 g / mL; The concentration of the sodium thiosulfate aqueous solution is 0.04-0.12 g / mL.

8. The annealing method according to claim 6, characterized in that, The first film is fixed on the glass slide; The molar ratio of potassium antimony tartrate in the potassium antimony tartrate aqueous solution to sodium thiosulfate in the sodium thiosulfate aqueous solution is 1:12-18. The mixed solution also contains 200-300 ppm of concentrated hydrochloric acid in the volume of the potassium antimony tartrate aqueous solution.

9. The annealing method according to claim 6, characterized in that, The mixed solution submerges the first film; The conditions for the hydrothermal reaction are: 120-150℃ for 1.5-4 hours.

10. An application of a CdS / Sb2S3 heterojunction obtained by the annealing method according to any one of claims 1-9, characterized in that, Used in indoor photovoltaics, photocatalytic water splitting, photodetectors, or solar cells.

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