Preparation of copper-zinc-tin-sulfur precursor film by low-temperature heat treatment method and copper-zinc-tin-sulfur-selenium solar cell containing the same

Abstract

The present invention belongs to the field of new energy technology of optoelectronic materials, and relates to a low-temperature heat treatment method for preparing a copper-zinc-tin-sulfur precursor film and a copper-zinc-tin-sulfur-selenide solar cell containing the same, comprising the following steps: (1) preparing a Cu-Zn-Sn-S precursor solution; (2) spin coating-baking-low-temperature heat treatment to prepare a Cu-Zn-Sn-S precursor film; (3) subjecting the Cu-Zn-Sn-S precursor film described in step (2) to high-temperature sulfur-selenide to prepare a copper-zinc-tin-sulfur-selenide (Cu2ZnSn(S,Se)4, CZTSSe) absorption layer film. That is, in the experiment of preparing the precursor film, the present invention uses low-temperature heat treatment instead of the cooling step, significantly changing the surface morphology of the Cu-Zn-Sn-S precursor film, thereby promoting the downward diffusion of Se elements in the subsequent sulfur-selenide process, resulting in the top-down grain growth mode dominating the grain growth, thereby obtaining a single-layer CZTSSe absorption layer film with a large grain structure, and further preparing a CZTSSe thin film solar cell with an efficiency of 11.8% based on the absorption layer film.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy of optoelectronic materials, and in particular relates to a method for preparing a copper-zinc-tin-sulfur precursor film and a copper-zinc-tin-sulfur-selenium solar cell by a low-temperature heat treatment process. Background Art

[0002] CZTSSe thin-film solar cells (CZTSSe) offer promising development prospects due to their rich composition, lack of toxic components, environmental friendliness, and low cost. The absorber layer, a thin film with a single-layer crystalline structure, is a crucial component of high-efficiency solar cells. Among CZTSSe thin film preparation methods, the chemical solution method leads the way in device efficiency. This method involves three key steps: 1. preparing a precursor solution; 2. spin coating and baking the precursor film; and 3. high-temperature sulfur-selenization to obtain the CZTSSe absorber layer. Researchers have extensively studied steps 1 and 3, and step 2, as a bridge between the two, warrants further investigation and optimization.

[0003] During the high-temperature sulfur-selenization process of a precursor film to prepare a copper-zinc-tin-sulfur-selenide absorber layer film, the morphology and elemental distribution of the precursor film have a significant impact on the crystal quality and film structure of the copper-zinc-tin-sulfur-selenide absorber layer. Baking the precursor wet film not only evaporates the organic solvent in the film, but also causes the compounds in the solution to undergo a decomposition and resynthesis step to form the precursor film. Almost all films must wait for the film prepared in the previous cycle to cool before the next spin coating cycle. Generally speaking, after heat treatment at 300°C, the film requires 4 minutes to cool to room temperature, and then the absorber layer film is prepared. The film surface usually has a large number of holes, showing a double-layer grain structure and low device efficiency. Summary of the Invention

[0004] In light of this, the present invention discloses a low-temperature heat treatment method for preparing a copper-zinc-tin-sulfur (CZTSSe) precursor film and a CZTSSe solar cell containing the same. The low-temperature heat treatment process, which alters the surface morphology of the precursor film and promotes the diffusion of Se during the subsequent high-temperature sulfur-selenization process, results in a CZTSSe absorber layer with a smooth surface and minimal pores. This film was used as the absorber layer of a solar cell, ultimately producing a CZTSSe thin-film solar cell with a device efficiency of 11.8%.

[0005] It should be noted that the present invention explores the use of low-temperature heat treatment at 50°C during the cooling process of the Cu-Zn-Sn-S precursor film to modify the surface morphology of the precursor film and thereby improve the crystal quality of the CZTSSe absorber layer film. After low-temperature heat treatment, the crystallinity of the Cu-Zn-Sn-S precursor film is significantly improved, the grain size is significantly increased, and the surface becomes loose and porous, which facilitates the downward diffusion of Se during the sulfur-selenization process. The top-down grain growth pattern dominates the grain growth, ultimately resulting in a single-layer CZTSSe absorber layer film with large grains.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The first technical purpose of the present invention is to provide a method for preparing a copper-zinc-tin-sulfur precursor film by a low-temperature heat treatment process, the operating steps of which are:

[0008] (1) Preparation of copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor solution:

[0009] Zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), cuprous chloride (CuCl), thiourea (CH4N2S, Tu), and tin tetrachloride pentahydrate (SnCl4·5H2O) were mixed, and then ethylene glycol monomethyl ether (MOE) and dimethyl sulfoxide (DMSO) were added to react in a water bath to obtain a Cu-Zn-Sn-S precursor solution;

[0010] (2) Preparation of Cu-Zn-Sn-S precursor film by spin coating-baking-low temperature heat treatment:

[0011] The Cu-Zn-Sn-S precursor solution is dropped on the four corners and the middle of the molybdenum glass, and spin coating is performed after the solution completely covers the surface; after the spin coating is completed, the wet film is baked and then subjected to low-temperature heat treatment, and the spin coating-baking-low-temperature heat treatment steps are repeated 10 times to obtain a Cu-Zn-Sn-S precursor film.

[0012] Preferably, the element ratio of the precursor solution is designed to follow the principle of copper-poor and zinc-rich, and the molar ratios of the constituent elements Cu / (Zn+Sn) and Zn / Sn are designed to be 0.72 and 1.14; the water bath reaction temperature is 66°C, and the reaction time is 3 hours to obtain a fully dissolved precursor solution.

[0013] Preferably, the size of the molybdenum glass is 2×2 cm, including a 2 mm thick soda-lime glass and a 1 μm thick molybdenum layer; the parameters for the spin coating setting are: a rotation speed of 3600 r / min and a time of 36 s; baking parameters: a time of 2 min and a temperature of 300°C; low-temperature heat treatment parameters after baking: a time of 5 min and a temperature of 50°C. After the low-temperature treatment, the next cycle of spin coating can be carried out directly without waiting for the film to cool to room temperature.

[0014] The second technical purpose of the present invention is to provide a copper-zinc-tin-sulfur-selenium absorption layer film, which is prepared by high-temperature sulfur-selenization of a copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor film prepared by the above method; the method is as follows:

[0015] The copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor film, stannous sulfide (SnS) and selenium pellets are subjected to high-temperature sulfur-selenization to obtain the copper-zinc-tin-sulfur-selenium absorption layer film (CZTSSe film).

[0016] Optionally, there is a specific quantitative relationship between the mass ratio of the copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor film, stannous sulfide (SnS), and selenium pills, which is 4 pieces: 10 mg: 350 mg.

[0017] Optionally, the sulfur-selenide operation is as follows: heating the temperature from room temperature to 280° C. and maintaining for 10 minutes for soft sulfur-selenide, with a heating rate of 28.3° C. / min; continuing to heat the temperature to 510° C. to start high-temperature sulfur-selenide and timing, with a heating rate of 25.5° C. / min during this process;

[0018] Among them, high-temperature sulfur-selenide was repeated twice between 510℃ and 570℃, and the heating and cooling rates were both 17.1℃ / min. The specific operations were: heating from 510℃ to 570℃ for 3.5min, cooling from 570℃ to 510℃ for 3.5min, heating from 510℃ to 570℃ for 3.5min, and cooling from 570℃ to 510℃ for 3.5min. The heating and cooling rates were both 17.1℃ / min, thus completing the entire sulfur-selenide process.

[0019] The third technical purpose of the present invention is to provide a copper-zinc-tin-sulfur-selenium solar cell, which comprises the copper-zinc-tin-sulfur-selenium absorption layer thin film as described above.

[0020] Preferably, the preparation process of the copper-zinc-tin-sulfur-selenium solar cell is as follows:

[0021] A 50nm thick CdS buffer layer is first deposited on the copper zinc tin sulfur selenide absorber layer thin film (CZTSSe thin film) to form a pn junction with CZTSSe and reduce the lattice mismatch and band gap mismatch between the absorber layer and the window layer. Then, a 50nm thick intrinsic zinc oxide (i-ZnO) and a 230nm thick tin-doped indium oxide (ITO) window layer are deposited by magnetron sputtering as the upper surface structure of the solar cell. Finally, a 100nm thick Ag electrode is thermally evaporated to collect photogenerated current. In summary, the preparation of the copper zinc tin sulfur selenide solar cell (CZTSSe thin film solar cell) is completed.

[0022] Furthermore, the CdS film was deposited by a chemical water bath method, with a water bath temperature of 70°C and a rotation speed of 600 r / min; the background vacuum of the magnetron sputtering was 5×10 -4 Pa, the working gas pressure for sputtering i-ZnO is 0.5Pa, and the sputtering power is 35W-20min, 60W-5min; the working gas pressure for sputtering ITO is 0.3Pa, and the sputtering power is 80W-90min.

[0023] Preferably, the copper-zinc-tin-sulfur-selenium solar cell has a structure of SLG / Mo / CZTSSe / CdS / i-ZnO / ITO / Ag.

[0024] The technology of the present invention can be used to prepare a complete copper-zinc-tin-sulfur-selenium thin film solar cell with an efficiency of 11.8%, an open circuit voltage of 523.49 mV, and a short circuit current density of 35.53 mA / cm 2 , the filling factor is 63.67%.

[0025] Through the above technical solution, compared with the prior art, it can be seen that the present invention uses a low-temperature heat treatment method to prepare a copper-zinc-tin-sulfur precursor film and a copper-zinc-tin-sulfur-selenium solar cell containing the same. It has the following technical effects:

[0026] Compared to a Cu-Zn-Sn-S precursor film that had not undergone low-temperature heat treatment, the precursor film had a looser surface, with significantly expanded grains and more pronounced inter-grain gaps. The resulting loose, porous surface structure facilitated downward diffusion of Se elements. The porous structure of the Cu-Zn-Sn-S precursor film accelerated grain growth, ultimately resulting in a single, large-grain CZTSSe absorber layer. Using this film as the absorber layer for solar cells, the fill factor and efficiency of the resulting CZTSSe thin-film solar cells increased from 54% and 9.03% to 63.67% and 11.8%, respectively.

[0027] That is, the present invention prepares a Cu-Zn-Sn-S precursor film through low-temperature heat treatment, optimizes the surface morphology of the precursor film, obtains a CZTSSe absorption layer with a single-layer grain structure, and obtains a CZTSSe thin-film solar cell with an efficiency of 11.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0029] Figure 1Surface SEM image of the Cu-Zn-Sn-S precursor film prepared in Example 1;

[0030] Figure 2 Surface SEM image of the Cu-Zn-Sn-S precursor film prepared in Comparative Example 1;

[0031] Figure 3 Surface SEM image of the Cu-Zn-Sn-S precursor film prepared in Comparative Example 2;

[0032] Figure 4 Surface SEM image of the Cu-Zn-Sn-S precursor film prepared in Comparative Example 3;

[0033] Figure 5 This is a surface SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Example 1;

[0034] Figure 6 This is a surface SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Comparative Example 1;

[0035] Figure 7 This is a surface SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Comparative Example 2;

[0036] Figure 8 This is a surface SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Comparative Example 3;

[0037] Figure 9 This is a cross-sectional SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Example 1;

[0038] Figure 10 This is a cross-sectional SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Comparative Example 1;

[0039] Figure 11 This is a cross-sectional SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Comparative Example 2;

[0040] Figure 12 This is a cross-sectional SEM image of the copper-zinc-tin-sulfur-selenium absorption layer film prepared in Comparative Example 3;

[0041] Figure 13 This is a JV curve of the copper-zinc-tin-sulfur-selenium thin film solar cell prepared in Example 2;

[0042] Figure 14 This is a JV curve of the copper-zinc-tin-sulfur-selenium thin film solar cell prepared in Comparative Example 4;

[0043] Figure 15 This is an EQE curve of the copper-zinc-tin-sulfur-selenium thin film solar cell prepared in Example 2;

[0044] Figure 16 This is the EQE curve of the copper-zinc-tin-sulfur-selenium thin film solar cell prepared in Comparative Example 4. DETAILED DESCRIPTION

[0045] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0046] The term "embodiment" is used herein specifically to describe any embodiment as "exemplary," and should not be construed as superior or preferable to other embodiments. Performance indicators in the embodiments of this application were tested using conventional testing methods in the art, unless otherwise specified. It should be understood that the terms used in this application are intended solely to describe specific implementations and are not intended to limit the disclosure herein.

[0047] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

[0048] In order to better illustrate the content of this application, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that this application can be implemented without certain specific details. In the examples, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of this application.

[0049] Under the premise of no conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solutions belong to the contents disclosed in the embodiments of this application.

[0050] The present invention discloses a method for preparing a Cu-Zn-Sn-S precursor film by a low-temperature heat treatment process, wherein the specific preparation steps are as follows:

[0051] (1) Preparation of Cu-Zn-Sn-S precursor solution:

[0052] 0.8166 g of zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), 0.4989 g of cuprous chloride (CuCl), 1.6991 g of thiourea (CH4N2S), and 1.1412 g of tin tetrachloride pentahydrate (SnCl4·5H2O) were weighed in sequence and added into a clean transparent glass bottle (volume 10 mL), and then 3 mL of ethylene glycol methyl ether (MOE) and 3 mL of dimethyl sulfoxide (DMSO) were added thereto and tightly sealed with a bottle cap. Finally, the solution was placed in a constant temperature water bath (temperature: 66°C, speed: 666 r / min) and stirred for 3 hours to obtain a Cu-Zn-Sn-S precursor solution.

[0053] (2) Preparation of precursor film by spin coating-baking-low temperature heat treatment:

[0054] First, use a disposable syringe (capacity: 2.5mL) to absorb the filtered solution for later use. Then, place the cleaned molybdenum glass on the suction cup of the spin coater and fix it. Add the solution dropwise to the four corners and the middle of the molybdenum glass. Wait until the solution completely covers the surface before spin coating. After spin coating, place the wet film on a 300℃ heating table and bake it for 2 minutes. Then, move the sample to a 50℃ heating table for low-temperature heat treatment for 5 minutes. Repeat the spin coating-baking-low-temperature heat treatment steps 10 times to obtain a Cu-Zn-Sn-S precursor film.

[0055] (3) Preparation of CZTSSe absorption layer film by high temperature sulfur selenization:

[0056] Place 10 mg of tin sulfide (SnS), 350 mg of selenium pellets and the Cu-Zn-Sn-S precursor film obtained in step (2) in the graphite box in sequence, then place the graphite box in the middle position of the quartz tube of the single-temperature zone tubular furnace, clean the quartz tube with high-purity argon (Ar) three times and seal the quartz tube. After high-temperature sulfur-selenization, wait for the sample to cool to room temperature and then take it out.

[0057] (4) A 50 nm thick CdS buffer layer was deposited on the CZTSSe thin film obtained in step (3), followed by sputtering a 50 nm thick intrinsic zinc oxide (i-ZnO) and a 230 nm thick tin-doped indium oxide (ITO) window layer, and finally a 100 nm thick Ag electrode was deposited by thermal evaporation to complete the preparation of the CZTSSe thin film solar cell.

[0058] Preferably, the Zn(CH3COOH)2·2H2O in step (1) is purchased with a purity of 99.99%; the CuCl is purchased with a purity of 99.9%; the SnCl4·5H2O is purchased with a purity of 99.995%; the DMSO is purchased with a purity of 99.9%; and the MOE is purchased with a purity of 99.8%. All of the above drugs are purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. CH4N2S is purchased from Beijing Inokai Technology Co., Ltd. with a purity of 99%. The element ratio design of the precursor solution follows the principle of copper-poor and zinc-rich, and the molar ratios of Cu / (Zn+Sn) and Zn / Sn are designed to be 0.72 and 1.14. All experimental operations for the preparation of the Cu-Zn-Sn-S precursor solution are completed in an air environment.

[0059] Preferably, the size of the molybdenum glass in step (2) is 2×2 cm, comprising a 2 mm thick soda-lime glass and a 1 μm thick molybdenum layer; the parameters set for the spin coater are 3600 r / min and the time is 36 s; the thickness of the Cu-Zn-Sn-S precursor film obtained by spin coating-baking-low temperature heat treatment 10 times is 1.2 μm, and the precursor film is prepared in an air environment.

[0060] Preferably, the specific operation of the high-temperature sulfur-selenide in step (3) is: first, the temperature is raised from room temperature to 280°C over 9 minutes and maintained for 10 minutes for soft sulfur-selenide, and the heating rate of this process is 28.3°C / min; then the temperature is raised to 510°C for 9 minutes to start high-temperature sulfur-selenide and timing is performed, and the heating rate of this process is 25.5°C / min; the temperature is raised from 510°C to 570°C for 3.5 minutes, and the temperature is lowered from 570°C to 510°C for 3.5 minutes, and ... heating and cooling rates are both 17.1°C / min, thereby completing the entire sulfur-selenide process.

[0061] Preferably, the specific steps of the method for preparing the copper-zinc-tin-sulfur-selenium thin film solar cell are:

[0062] 1) Prepare a 50 nm thick n-type CdS buffer layer from the copper-zinc-tin-sulfur-selenium absorber film by chemical bath deposition. The specific steps are as follows:

[0063] The absorber layer film was picked up with processed tweezers and soaked in ultrapure water for 15 minutes to remove oxides from the CZTSSe film surface. 22 mL of ultrapure water was then measured and placed in numbered small beakers. 1.256 g of Tu and 0.847 g of CdSO₄·8 / 3H₂O were weighed and added to the beakers, followed by sonication to promote dissolution. A constant-temperature water bath was set at 70°C and 600 rpm. The soaked sample was transferred to a sedimentation beaker containing 150 mL of ultrapure water and equipped with a rotor. First, a cadmium sulfate solution was added. After 40 seconds, ammonia solution was added, followed by a thiourea solution after 1 minute and 40 seconds. After 8 minutes and 30 seconds, the sample was removed and rinsed three times with ultrapure water. Finally, it was dried on a hot plate.

[0064] 2) On the basis of the buffer layer, a 50nm thick i-ZnO film and a 230nm thick ITO film are deposited as a window layer by magnetron sputtering and radio frequency sputtering. The specific operation is as follows:

[0065] The sample of the deposited buffer layer was placed in the window layer chamber of the magnetron sputtering, and the pressure was pumped from atmospheric pressure to 10 Pa using a mechanical pump, and then to 5×10 -4 When sputtering i-ZnO, the working pressure is 0.5Pa, the high-purity argon flow rate is 13sccm, and the sputtering power is 35W-20min, 60W-5min; when sputtering ITO, the working pressure is 0.3Pa, the high-purity argon flow rate is 7sccm, and the sputtering power is 80W-90min.

[0066] 3) Finally, an Ag electrode is evaporated on the window layer to obtain a copper-zinc-tin-sulfur-selenium thin film solar cell.

[0067] Preferably, the copper-zinc-tin-sulfur-selenide thin-film solar cell has a complete structure of SLG / Mo / CZTSSe / CdS / i-ZnO / ITO / Ag.

[0068] For a better understanding of the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as limiting the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content are also considered to fall within the scope of protection of the present invention.

[0069] Example 1

[0070] (1) Preparation of Cu-Zn-Sn-S precursor solution: 0.8166 g zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), 0.4989 g cuprous chloride (CuCl), 1.6991 g thiourea (CH4N2S, Tu), and 1.1412 g tin tetrachloride pentahydrate (SnCl4·5H2O) were weighed in sequence and added into a clean transparent glass bottle (volume 10 mL). Then, 3 mL ethylene glycol methyl ether (MOE) and 3 mL dimethyl sulfoxide (DMSO) were added and the solution was tightly sealed with a bottle cap. Finally, the solution was placed in a constant temperature water bath (temperature: 66 °C, speed: 666 r / min) and stirred for 3 hours to obtain a Cu-Zn-Sn-S precursor solution.

[0071] (2) Preparation of Cu-Zn-Sn-S precursor film by spin coating-baking-low temperature heat treatment: First, use a disposable syringe (capacity: 2.5 mL) to absorb the filtered solution for later use. Then, place the cleaned molybdenum glass on the spin coater suction cup and fix it. Add the solution dropwise to the four corners and the middle of the molybdenum glass. After the solution completely covers the surface, spin coating is performed. After spin coating is completed, the wet film is placed on a 300°C heating table and baked for 2 minutes. Then, the sample is moved to a 50°C heating table and low temperature heat treatment is performed for 5 minutes. Repeat the spin coating-baking-low temperature heat treatment steps 10 times to obtain a Cu-Zn-Sn-S precursor film.

[0072] (3) Preparation of copper-zinc-tin-sulfur-selenide absorption layer film by high-temperature sulfur-selenide treatment: 10 mg of stannous sulfide (SnS), 350 mg of selenium pellets and the precursor film obtained in step (2) were placed in a graphite box in sequence. The graphite box was then placed in the middle of the quartz tube of a single-temperature zone tubular furnace. The quartz tube was cleaned three times with high-purity argon (Ar) and sealed. The high-temperature sulfur-selenide treatment was then started. Finally, the sample was cooled to room temperature and then taken out.

[0073] from Figure 1 From the SEM image of the precursor Cu-Zn-Sn-S film surface, it can be seen that the grain size of the film surface obtained in Example 1 is significantly increased, the gaps between the grains are more prominent, and there are more pores on the surface, which is conducive to the diffusion of Se elements during the sulfur-selenization process. Figure 5 and Figure 9 It can be seen that the CZTSSe absorption layer film prepared by the Cu-Zn-Sn-S precursor after low-temperature heat treatment at 50°C has fewer holes on the surface and the cross-section is an absorption layer film with a single-layer grain structure.

[0074] Example 2

[0075] The specific steps of preparing a copper-zinc-tin-sulfur-selenide thin-film solar cell according to the copper-zinc-tin-sulfur-selenide absorption layer film described in Example 1 are as follows: a 50 nm thick cadmium sulfide (CdS) buffer layer is prepared on the CZTSSe thin film obtained by temperature-variable sulfur-selenization by chemical water bath deposition, followed by magnetron sputtering of a 50 nm thick intrinsic zinc oxide (i-ZnO) and a 230 nm thick tin-doped indium oxide (ITO) window layer, and finally a 100 nm thick Ag electrode is evaporated by thermal evaporation (current of 60 A, time of 15 min) to complete the preparation of the CZTSSe solar cell.

[0076] The JV curve of the copper-zinc-tin-sulfur-selenium thin film solar cell prepared according to Example 2 is as follows: Figure 13 As shown, the efficiency is 11.8%, the open circuit voltage is 523.49mV, and the short circuit current density is 35.53mA / cm 2 , the filling factor is 63.67%. Figure 15 As shown in the figure, the maximum EQE is greater than 90%, and the EQE is greatly improved in the long-wave range, indicating that the crystal quality of the absorption layer thin film is good.

[0077] In order to further demonstrate the beneficial effects of the present invention and to better understand the present invention, the following comparative examples are provided to further illustrate the technical features disclosed in the present invention, but they should not be construed as limiting the present invention. Other improvements made by those skilled in the art based on the above invention without inventive work are also considered to fall within the scope of protection of the present invention.

[0078] Comparative Example 1

[0079] (1) Preparation of Cu-Zn-Sn-S precursor solution: 0.8166 g zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), 0.4989 g cuprous chloride (CuCl), 1.6991 g thiourea (CH4N2S, Tu), and 1.1412 g tin tetrachloride pentahydrate (SnCl4·5H2O) were weighed in sequence and added into a clean transparent glass bottle (volume 10 mL). Then, 3 mL ethylene glycol methyl ether (MOE) and 3 mL dimethyl sulfoxide (DMSO) were added and the solution was tightly sealed with a bottle cap. Finally, the solution was placed in a constant temperature water bath (temperature: 66 °C, speed: 666 r / min) and stirred for 3 hours to obtain a Cu-Zn-Sn-S precursor solution.

[0080] (2) Spin coating-baking treatment to prepare the precursor film: First, use a disposable syringe (capacity: 2.5mL) to absorb the filtered solution for later use. Then, place the cleaned molybdenum glass on the spin coater suction cup and fix it. Add the solution to the four corners and the middle of the molybdenum glass. After the solution completely covers the surface, spin coating is performed. After the spin coating is completed, the wet film is placed on a 300℃ heating table and baked for 2 minutes. Then, wait for the sample to cool before the next spin coating cycle. Repeat the spin coating-baking step 10 times to obtain the precursor film.

[0081] (3) Preparation of absorption layer film by high-temperature sulfur-selenide treatment: 10 mg of tin sulfide (SnS), 350 mg of selenium pellets and the precursor film obtained in step (2) were placed in a graphite box in sequence. The graphite box was then placed in the middle of the quartz tube of a single-temperature zone tubular furnace. The quartz tube was cleaned three times with high-purity argon (Ar) and sealed. The high-temperature sulfur-selenide treatment was then started. Finally, the sample was taken out after cooling to room temperature.

[0082] from Figure 2 From the surface SEM image of the precursor film, it can be seen that the precursor film obtained in Comparative Example 1 has obvious agglomeration phenomenon, the grain outline is relatively fuzzy, and the grain gap is small, which is not conducive to the diffusion of Se elements in the subsequent high-temperature sulfur-selenization process. Figure 6 and Figure 10 It can be seen that there are many holes on the surface of the copper-zinc-tin-sulfur-selenium absorption layer film prepared from the precursor that has not undergone low-temperature heat treatment, and the cross-section is a double-layer grain structure with obvious boundaries.

[0083] Comparative Example 2

[0084] (1) Preparation of Cu-Zn-Sn-S precursor solution: 0.8166 g zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), 0.4989 g cuprous chloride (CuCl), 1.6991 g thiourea (CH4N2S, Tu), and 1.1412 g tin tetrachloride pentahydrate (SnCl4·5H2O) were weighed in sequence and added into a clean transparent glass bottle (volume 10 mL). Then, 3 mL ethylene glycol methyl ether (MOE) and 3 mL dimethyl sulfoxide (DMSO) were added and the solution was tightly sealed with a bottle cap. Finally, the solution was placed in a constant temperature water bath (temperature: 66 °C, speed: 666 r / min) and stirred for 3 hours to obtain a Cu-Zn-Sn-S precursor solution.

[0085] (2) Preparation of Cu-Zn-Sn-S precursor film by spin coating-baking-low temperature heat treatment: First, use a disposable syringe (capacity: 2.5 mL) to absorb the filtered solution for later use. Then, place the cleaned molybdenum glass on the spin coater suction cup and fix it. The solution is dripped onto the four corners and the middle of the molybdenum glass. After the solution completely covers the surface, spin coating is performed. After spin coating is completed, the wet film is placed on a 300°C heating table and baked for 2 minutes. Then, the sample is moved to a 40°C heating table and low temperature heat treatment is performed for 5 minutes. Repeat the spin coating-baking-low temperature heat treatment steps 10 times to obtain a Cu-Zn-Sn-S precursor film.

[0086] (3) Preparation of copper-zinc-tin-sulfur-selenide absorption layer film by high-temperature sulfur-selenide treatment: 10 mg of stannous sulfide (SnS), 350 mg of selenium pellets and the precursor film obtained in step (2) were placed in a graphite box in sequence. The graphite box was then placed in the middle of the quartz tube of a single-temperature zone tubular furnace. The quartz tube was cleaned three times with high-purity argon (Ar) and sealed. The high-temperature sulfur-selenide treatment was then started. Finally, the sample was cooled to room temperature and then taken out.

[0087] from Figure 3 From the SEM image of the precursor Cu-Zn-Sn-S film surface, it can be seen that the grain size of the film surface obtained in Comparative Example 2 is increased, and the gaps between the grains are increased, which is conducive to the diffusion of Se elements during the sulfur-selenization process. Figure 7 and Figure 11 It can be seen that the surface holes of the CZTSSe absorption layer film prepared by the Cu-Zn-Sn-S precursor after low-temperature heat treatment at 40°C are reduced, and the cross-sectional morphology is improved to a certain extent, but it still has a double-layer grain structure.

[0088] Comparative Example 3

[0089] (1) Preparation of Cu-Zn-Sn-S precursor solution: 0.8166 g zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), 0.4989 g cuprous chloride (CuCl), 1.6991 g thiourea (CH4N2S, Tu), and 1.1412 g tin tetrachloride pentahydrate (SnCl4·5H2O) were weighed in sequence and added into a clean transparent glass bottle (volume 10 mL). Then, 3 mL ethylene glycol methyl ether (MOE) and 3 mL dimethyl sulfoxide (DMSO) were added and the solution was tightly sealed with a bottle cap. Finally, the solution was placed in a constant temperature water bath (temperature: 66 °C, speed: 666 r / min) and stirred for 3 hours to obtain a Cu-Zn-Sn-S precursor solution.

[0090] (2) Preparation of Cu-Zn-Sn-S precursor film by spin coating-baking-low temperature heat treatment: First, use a disposable syringe (capacity: 2.5 mL) to absorb the filtered solution for later use. Then, place the cleaned molybdenum glass on the spin coater suction cup and fix it. The solution is dripped onto the four corners and the middle of the molybdenum glass. After the solution completely covers the surface, spin coating is performed. After spin coating is completed, the wet film is placed on a 300°C heating table and baked for 2 minutes. Then, the sample is moved to a 60°C heating table and low temperature heat treatment is performed for 5 minutes. Repeat the spin coating-baking-low temperature heat treatment steps 10 times to obtain a Cu-Zn-Sn-S precursor film.

[0091] (3) Preparation of copper-zinc-tin-sulfur-selenide absorption layer film by high-temperature sulfur-selenide treatment: 10 mg of stannous sulfide (SnS), 350 mg of selenium pellets and the precursor film obtained in step (2) were placed in a graphite box in sequence. The graphite box was then placed in the middle of the quartz tube of a single-temperature zone tubular furnace. The quartz tube was cleaned three times with high-purity argon (Ar) and sealed. The high-temperature sulfur-selenide treatment was then started. Finally, the sample was cooled to room temperature and then taken out.

[0092] from Figure 4 From the SEM image of the precursor Cu-Zn-Sn-S film surface, it can be seen that the film surface obtained in Comparative Example 3 has more gaps and holes, which is conducive to the diffusion of Se elements during the sulfur-selenization process. Figure 8 and Figure 12 It can be seen that the surface grains of the CZTSSe absorption layer film prepared by the Cu-Zn-Sn-S precursor after low-temperature heat treatment at 60°C are relatively large, but there are many small holes on the surface of the film probably due to the loss of elements, and the cross section is an absorption layer film with an obvious single-layer grain structure.

[0093] Comparative Example 4

[0094] The specific steps for preparing a copper-zinc-tin-sulfur-selenide thin-film solar cell using the copper-zinc-tin-sulfur-selenide absorber layer described in Comparative Example 1 are as follows: a 50nm thick cadmium sulfide (CdS) buffer layer is deposited on the CZTSSe thin film obtained by constant-temperature sulfur-selenization using chemical water bath deposition, followed by magnetron sputtering of a 50nm thick intrinsic zinc oxide (i-ZnO) and a 230nm thick tin-doped indium oxide (ITO) window layer. Finally, a 100nm thick Ag electrode is deposited by thermal evaporation to complete the CZTSSe solar cell.

[0095] The JV curve of the copper-zinc-tin-sulfur-selenium thin film solar cell prepared in Comparative Example 2 is as follows: Figure 14 As shown, the efficiency is 9.03%, the open circuit voltage is 504.99mV, and the short circuit current density is 33.13mA / cm 2 , the filling factor is 54.00%. EQE Figure 16As shown, compared with the device prepared by the low-temperature heat treatment method, the solar cell has a poor collection efficiency in the long-wave range, which may be related to the double-layer grains of the absorption layer film, which is also one of the main reasons for the low short-circuit current density.

[0096] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a copper-zinc-tin-sulfur precursor thin film by a low-temperature heat treatment process, characterized in that: The steps are: (1) Preparation of copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor solution: Zinc acetate dihydrate (Zn(CH3COOH)2·2H2O), cuprous chloride (CuCl), thiourea (CH4N2S, Tu), and tin tetrachloride pentahydrate (SnCl4·5H2O) were mixed, and then ethylene glycol monomethyl ether (MOE) and dimethyl sulfoxide (DMSO) were added to react in a water bath to obtain a Cu-Zn-Sn-S precursor solution; The element ratio design of the precursor solution follows the principle of being copper-poor and zinc-rich. The molar ratios of the constituent elements Cu / (Zn+Sn) and Zn / Sn are designed to be 0.72 and 1.

14. (2) Preparation of Cu-Zn-Sn-S precursor film by spin coating-baking-low temperature heat treatment: The Cu-Zn-Sn-S precursor solution is dropped on the four corners and the middle of the molybdenum glass, and spin-coated after the solution completely covers the surface; after the spin coating is completed, the wet film is baked and then subjected to low-temperature heat treatment, and the spin coating-baking-low-temperature heat treatment steps are repeated 10 times to obtain a Cu-Zn-Sn-S precursor film; Baking parameters: time is 2 minutes, temperature is 300℃; low temperature heat treatment parameters: time is 5 minutes, temperature is 50℃.

2. The method for preparing a copper-zinc-tin-sulfur precursor thin film by a low-temperature heat treatment process according to claim 1, characterized in that: The water bath reaction temperature was 66°C and the reaction time was 3 hours.

3. The method for preparing a copper-zinc-tin-sulfur precursor thin film by a low-temperature heat treatment process according to claim 2, characterized in that: The molybdenum glass has a size of 2×2 cm and includes a 2 mm thick soda-lime glass and a 1 μm thick molybdenum layer; the spin coating parameters are: a rotation speed of 3600 r / min and a time of 36 s.

4. A copper-zinc-tin-sulfur-selenium absorption layer film, characterized in that: The absorption layer film is prepared by high-temperature sulfur-selenization of a copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor film prepared by the method of claim 1; the method is as follows: The copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor film, stannous sulfide (SnS), and selenium pellets are subjected to high-temperature sulfur-selenization to obtain the copper-zinc-tin-sulfur-selenium absorption layer film (CZTSSe film); The sulfur-selenide operation is as follows: heating the temperature from room temperature to 280°C and maintaining it for 10 minutes for soft sulfur-selenide, with a heating rate of 28.3°C / min; continuing to heat the temperature to 510°C to start high-temperature sulfur-selenide and timing, with a heating rate of 25.5°C / min during this process; The high-temperature sulfur-selenide process was repeated twice between 510°C and 570°C, with both the heating and cooling rates being 17.1°C / min, thus completing the entire sulfur-selenide process.

5. The copper-zinc-tin-sulfur-selenium absorption layer thin film according to claim 4, characterized in that: There is a specific quantitative relationship between the copper-zinc-tin-sulfur (Cu-Zn-Sn-S) precursor film, stannous sulfide (SnS), and selenium pills, with the ratio being 4 pieces: 10 mg: 350 mg.

6. A copper-zinc-tin-sulfur-selenium solar cell, characterized in that: The solar cell comprises the copper-zinc-tin-sulfur-selenium absorption layer thin film as claimed in claim 4.

7. The copper-zinc-tin-sulfur-selenium solar cell according to claim 6, characterized in that: The preparation operation is as follows: A 50nm thick CdS buffer layer is first deposited on the copper zinc tin sulfur selenide absorption layer thin film (CZTSSe thin film), and then a 50nm thick intrinsic zinc oxide (i-ZnO) and a 230nm thick tin-doped indium oxide (ITO) window layer are deposited by magnetron sputtering. Finally, a 100nm thick Ag electrode is thermally evaporated to complete the preparation of the copper zinc tin sulfur selenide solar cell (CZTSSe thin film solar cell).

8. The copper-zinc-tin-sulfur-selenium solar cell according to claim 7, characterized in that: The CdS film was deposited by a chemical water bath method, with a water bath temperature of 70°C and a rotation speed of 600 r / min; the background vacuum of the magnetron sputtering was 5×10 -4 Pa, the working pressure of sputtering i-ZnO is 0.5Pa, the sputtering power is 35W-20min, 60W-5min; the working pressure of sputtering ITO is 0.3Pa, the power is 80W-90min.

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