A solution method for preparing gradient bandgap copper indium gallium sulfur selenide solar cells

Abstract

The present invention provides a solution-based method for preparing a gradient-bandgap copper indium gallium sulfide selenide solar cell, comprising the following steps: preparing a copper indium gallium sulfide precursor solution; preparing a silver indium sulfide precursor solution; preparing a copper indium gallium sulfide precursor film containing a silver indium sulfide layer; performing a selenization treatment to obtain a copper indium gallium sulfide absorber layer; and depositing a buffer layer, a window layer, and electrodes to prepare a copper indium gallium sulfide selenide thin-film solar cell with a gradient bandgap. The solution-based method for preparing a gradient-bandgap copper indium gallium sulfide selenide solar cell employs a method of inserting an AIS interlayer during spin-coating of the precursor film, thereby selenizing to obtain an absorber layer with a gradient bandgap. This method improves crystal quality while constructing a gradient bandgap, increasing the cell's long-wavelength absorption and ultimately enhancing device performance.

Description

Technical Field

[0001] The present invention belongs to the field of application of optoelectronic device technology, and is particularly directed to the solution-processed preparation of copper-based thin-film solar cells with high-quality gradient band gaps, and lays the foundation for their further application and development in related optoelectronic devices. Specifically, it relates to a simple method for preparing gradient band gap copper indium gallium sulfur selenide solar cells using a solution-processed intermediate intercalation layer. Background Art

[0002] With growing global concern about climate change, reducing carbon emissions has become a shared mission for all nations. Against this backdrop, the photovoltaic industry, with its unique advantages, stands out as a key force in achieving sustainable development. Polycrystalline chalcopyrite copper indium gallium selenide (CIGS) material possesses excellent optoelectronic properties, including a tunable band gap, high absorption coefficient, and high stability, making it an ideal material for photovoltaic applications.

[0003] Traditional vacuum-based methods for preparing CIGS cells often require creating a gradient band gap during a three-step evaporation process. This gradient band gap creates a built-in electric field in the CIGS cell's absorber layer, promoting carrier separation and transport and reducing the probability of carrier recombination. It also broadens the absorber layer's absorption band for incident light, enhancing light utilization. Using hydrazine as a solvent to prepare CIGS cells allows for relatively easy creation of a gradient band gap within the absorber layer, as the absorber layer is directly formed through a one-step hot-plate annealing process. However, the high toxicity of hydrazine solutions and their extreme instability in air have undoubtedly limited the further large-scale development of this solution system. The use of non-hydrazine green solvent systems to prepare CIGS cells often requires a high-temperature selenization process. Under high-temperature conditions, element diffusion is relatively random, resulting in a flat-band structure in the CIGS absorber layer. The difficulties in obtaining CIGSSe thin films with a gradient band gap using non-hydrazine solution methods hinder further efficiency improvements. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing gradient band gap copper indium gallium sulfur selenide solar cells by a solution method, aiming to solve the technical problem in the prior art of difficulty in obtaining CIGSSe thin films with gradient band gaps when preparing copper indium gallium selenide cells by a non-hydrazine solution method.

[0005] To achieve the above object, the technical solution adopted by the present invention is to provide a method for preparing a gradient bandgap copper indium gallium sulfur selenide solar cell by a solution method, comprising the following steps:

[0006] Prepare copper indium gallium sulfide precursor solution;

[0007] Prepare silver indium sulfur precursor solution;

[0008] Preparation of a copper indium gallium selenide precursor film containing a silver indium sulfide layer;

[0009] After selenization treatment, a copper indium gallium selenide sulfur absorption layer is obtained;

[0010] A buffer layer, a window layer and an electrode are deposited to prepare a copper indium gallium selenide sulfur thin film solar cell.

[0011] Preferably, the preparation of the copper indium gallium sulfide precursor solution comprises the following steps:

[0012] Thiourea, copper acetate, indium trichloride tetrahydrate, and anhydrous gallium chloride are sequentially added to a dimethylformamide solvent and stirred to dissolve, thereby obtaining a CIGS precursor solution. The molar ratio of thiourea to the sum of all metal salts is 2.5-3.

[0013] Preferably, preparing the silver indium sulfide precursor solution comprises the following steps:

[0014] Thiourea, silver chloride and indium trichloride tetrahydrate are sequentially added into dimethylformamide solvent, stirred and dissolved to obtain an AIS precursor solution, wherein the molar ratio of thiourea to the sum of all metal salts is 2.5-3.

[0015] Preferably, preparing a copper indium gallium sulfide precursor film containing a silver indium sulfide layer comprises the following steps:

[0016] First, spin-coat the copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, then anneal and dry on a hot plate, repeating this process 7-9 times;

[0017] Then, the silver indium sulfide layer precursor solution was spin-coated and annealed on a hot plate for drying, which was repeated twice;

[0018] Finally, the copper indium gallium selenide precursor solution is spin-coated, annealed, and dried 1-3 times to obtain a copper indium gallium selenide precursor film containing a silver indium sulfide layer.

[0019] Preferably, the precursor solution is spin-coated and annealed at a speed of 3000-3500 rpm and an annealing temperature of 260-290°C.

[0020] Preferably, a copper indium gallium sulfur selenide absorption layer with a gradient band gap is prepared, and a precursor film obtained by spin coating is subjected to high-temperature selenization in a rapid annealing furnace, with a selenization temperature of 540-580° C. and a time of 10-15 minutes.

[0021] Preferably, a 50-80 nm cadmium sulfide buffer layer is deposited on the copper indium gallium selenide absorption layer with a gradient band gap using a chemical water bath method, an 80-100 nm intrinsic zinc oxide and a 200-400 nm aluminum-doped zinc oxide window layer are grown using a DC magnetron sputtering method, and a 1-1.5 μm silver top electrode is prepared using a thermal evaporation method, thereby obtaining the final copper indium gallium selenide sulfur thin film solar cell with a gradient band gap.

[0022] A copper indium gallium sulfide selenide solar cell, characterized in that it is prepared based on the steps of the method for preparing a gradient band gap copper indium gallium sulfide selenide solar cell by a solution method as described in any one of the above items.

[0023] The present invention provides a solution-based method for preparing gradient-bandgap copper indium gallium sulfide selenide solar cells, which has the following beneficial effects: Compared with the prior art, the present invention provides a solution-based method for preparing gradient-bandgap copper indium gallium sulfide selenide solar cells. CIGS and AIS precursor solutions are prepared using dimethylformamide as a solvent and copper acetate, silver chloride, indium trichloride tetrahydrate, anhydrous gallium chloride, and thiourea as solutes. Precursor films with varying indium-gallium gradients are obtained by adjusting the spin-coating position of the AIS. Subsequently, CIGSSe thin-film solar cells with gradient bandgap are prepared through subsequent steps such as selenization. By inserting an AIS interlayer during the spin-coating process of the precursor film, an absorption layer with a gradient bandgap is obtained by selenization. This improves crystal quality while constructing a gradient bandgap, increasing the long-wavelength absorption of the cell and ultimately improving device performance. This method provides a simple and feasible solution-based method for preparing high-efficiency CIGSSe cells with gradient bandgap. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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 embodiments or the description of the prior art. 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 paying any creative work.

[0025] Figure 1 : Schematic diagram of the process for preparing high-efficiency CIGSSe thin-film solar cells with a gradient band gap by introducing silver indium sulfide (AIS) at different locations to prepare a precursor film, and then obtaining a CIGSSe absorption layer with a gradient band gap through selenization annealing.

[0026] Figure 2 : External quantum efficiency (QE) diagram of the reference cell and the CIGSSe thin-film solar cell with an optimal gradient band gap obtained by adjusting the insertion position of silver indium sulfide (AIS) in the precursor film (a); band gap diagram obtained based on QE fitting (b); QE ratio under negative bias and no bias (c).

[0027] Figure 3 : Capacitance-voltage curves (CV) of a reference cell and a CIGSSe thin-film solar cell with an optimal gradient band gap obtained by adjusting the insertion position of silver indium sulfur (AIS) in the precursor film (a), the cell built-in voltage obtained by fitting the CV curve (b), and the cell depletion region width and interface defect density obtained from the CV and DLCP curves (c). DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] Please also refer to Figures 1 to 3 The present invention provides a method for preparing a gradient band gap copper indium gallium sulfide selenide solar cell by a solution method. The structure is SLG / Mo / CIGSSe / CdS / i-ZnO / ZnO:Al / Ag. It is a method for preparing a gradient band gap copper indium gallium sulfide selenide solar cell based on a solution method. During the spin coating process of the copper indium gallium selenide (CIGS) precursor solution, an appropriate number of layers of silver indium sulfide (AIS) are introduced at different positions to prepare a precursor film, and then the precursor film is selenized and annealed to obtain a high-quality CIGSSe absorption layer with a gradient band gap, thereby preparing a CIGSSe thin film solar cell with a gradient band gap. Specifically, the method includes the following steps:

[0030] S1. Prepare copper indium gallium sulfide precursor solution.

[0031] 2-3M thiourea (99.0%), 0.4-0.5M copper acetate (99.95%), 0.3-0.4M indium trichloride tetrahydrate (99.99%), and 0.1-0.2M anhydrous gallium chloride (99.99%) are sequentially added to dimethylformamide and stirred to dissolve, thereby obtaining a CIGS precursor solution. The molar ratio of thiourea to the sum of all metal salts is 2.5-3.

[0032] Specifically, the implementation of step 1 includes:

[0033] S1.1. Add 2-3 M thiourea (99.0%) to dimethylformamide solvent;

[0034] S1.2. After thiourea is completely dissolved in dimethylformamide solvent, add 0.4-0.5M copper acetate (99.95%) to the above clear solution;

[0035] S1.3. After the copper acetate is further dissolved, add 0.3-0.4M indium trichloride tetrahydrate (99.99%) to the above reaction solution;

[0036] S1.4. After the indium chloride tetrahydrate is dissolved, add 0.1-0.2M anhydrous gallium chloride to the above solution;

[0037] S1.5. After the anhydrous gallium chloride is further completely dissolved, a uniform and stable CIGS precursor solution is obtained.

[0038] S2. Prepare silver indium sulfur precursor solution.

[0039] 2-3M thiourea (99.0%), 0.4-0.5M silver chloride (99.95%), and 0.4-0.5M indium trichloride tetrahydrate (99.99%) are sequentially added to a dimethylformamide solvent and stirred to dissolve, thereby obtaining an AIS precursor solution. The molar ratio of thiourea to the sum of all metal salts is 2.5-3. Specifically, the implementation of step 2 includes:

[0040] S2.1. Add 2-3 M thiourea (99.0%) to dimethylformamide solvent;

[0041] S2.2. After thiourea is completely dissolved in dimethylformamide solvent, add 0.4-0.5M (99.95%) silver chloride to the clear solution;

[0042] S2.3, after the silver chloride is further dissolved, 0.4-0.5M indium trichloride tetrahydrate (99.99%) is added to the above reaction solution;

[0043] S2.4. After the indium trichloride tetrahydrate is completely dissolved, a uniform, stable and clear AIS precursor solution is obtained.

[0044] The drug to be added later needs to react after the previous raw material, and the molar ratio of thiourea to the sum of all metal salts is 3.

[0045] S3. Prepare a copper indium gallium sulfide precursor film containing a silver indium sulfide layer.

[0046] The precursor solution is spin-coated on the substrate, and then repeatedly heated and dried multiple times to obtain a copper indium gallium selenide precursor film with a silver indium sulfide layer. The precursor solution type of each spin coating is a copper indium gallium selenide precursor solution or a silver indium sulfide precursor solution.

[0047] Specifically, the precursor solution is spin-coated on a molybdenum-coated glass substrate (or a molybdenum film), and then placed on a hot stage for repeated heating and drying, and the process is repeated 12 times to achieve the required film thickness.

[0048] In this step, the thin film is repeatedly spin-coated with the precursor solution multiple times, so that the final prepared battery can fully absorb sunlight.

[0049] The preparation steps of the copper indium gallium sulfide precursor film with a silver indium sulfide layer include: spin coating a copper indium gallium sulfide or silver indium sulfide precursor solution on a molybdenum-coated glass substrate, and then heating and drying it on a hot plate, repeating the process 12 times to achieve the required film thickness.

[0050] The first method for preparing a copper indium gallium sulfide precursor film including a silver indium sulfide layer comprises the following steps: spin coating a copper indium gallium sulfide precursor solution on a molybdenum-coated glass substrate, followed by hot-plate annealing and drying, repeating the process seven times; then spin coating a silver indium sulfide precursor solution, followed by hot-plate annealing and drying, repeating the process two times; and finally spin coating a copper indium gallium selenide precursor solution, followed by annealing and drying three times.

[0051] The second preparation step of the copper indium gallium sulfide precursor film including a silver indium sulfide layer comprises: spin coating a copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, followed by hot-plate annealing and drying, repeating the process eight times, then spin coating a silver indium sulfide layer precursor solution, similarly performing hot-plate annealing and drying, repeating the process two times, and finally spin coating and annealing the copper indium gallium selenide precursor solution twice more;

[0052] The third preparation step of the copper indium gallium sulfide precursor film including a silver indium sulfide layer includes: spin coating a copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, followed by hot-plate annealing and drying, repeated 9 times, then spin coating a silver indium sulfide layer precursor solution, also hot-plate annealing and drying, repeated 2 times, and finally spin coating and annealing the copper indium gallium selenide precursor solution once more.

[0053] S4. Selenization is performed in a rapid annealing furnace to obtain a copper indium gallium selenide sulfur (CIGSSe) absorption layer with a gradient band gap.

[0054] Specifically, the absorption layer is obtained by selenization in a high-temperature annealing furnace, the selenization temperature is 540-580° C., and the time is 10-15 minutes.

[0055] S5, depositing a buffer layer, a window layer, and an electrode to prepare a copper indium gallium selenide sulfur thin film solar cell with a gradient band gap.

[0056] Specifically, a 50-80nm cadmium sulfide buffer layer is deposited on the copper indium gallium selenide absorption layer with a gradient band gap using a chemical water bath method, an 80-100nm intrinsic zinc oxide and a 200-400nm aluminum-doped zinc oxide window layer are grown using a DC magnetron sputtering method, and a 1-1.5μm silver top electrode is prepared using a thermal evaporation method, thereby obtaining the final copper indium gallium selenide sulfur thin-film solar cell with a gradient band gap.

[0057] The present invention provides a solution-based method for preparing gradient-bandgap copper indium gallium sulfide selenide solar cells. Compared to the prior art, this method uses dimethylformamide as a solvent and copper acetate, silver chloride, indium trichloride tetrahydrate, anhydrous gallium chloride, and thiourea as solutes to prepare copper indium gallium sulfide precursor solutions and silver indium sulfide precursor solutions. This method then produces a copper indium gallium selenide precursor film with a silver indium sulfide layer. Selenization and other subsequent steps are then performed to prepare a CIGSSe thin-film solar cell with a gradient bandgap. By inserting a silver indium sulfide interlayer during the spin-coating process of the precursor film, the selenization results in an absorber layer with a gradient bandgap. This improves crystal quality while constructing a gradient bandgap, increasing the cell's long-wavelength absorption and ultimately enhancing device performance. The CIGSSe device efficiency can reach 17.03%. This invention achieves the highest efficiency currently achieved using a dimethylformamide solvent system, creating a simple and feasible method for preparing high-efficiency CIGSSe cells with gradient bandgap using a solution-based method.

[0058] Example 1

[0059] A method for preparing a gradient bandgap copper indium gallium sulfur selenide solar cell by a solution process comprises the following steps:

[0060] S1. Prepare copper indium gallium sulfide precursor solution.

[0061] A stable and uniform CIGS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 1.047 g of copper acetate (Cu(CH3COO)2·H2O, 99.95%), 1.161 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%), and 0.296 g of anhydrous gallium chloride (GaCl3, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0062] In this step, the chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, so that thiourea can form a complete coordination with all metals.

[0063] S2, preparing a copper indium gallium sulfide precursor film;

[0064] The preparation steps of the copper indium gallium sulfide precursor film include: spin coating the copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, and then repeatedly heating and drying it on a hot plate, repeating this process 12 times to achieve the required film thickness.

[0065] S3. After selenization treatment at a temperature of 570° C. for 20 min, a copper indium gallium sulfur selenide (CIGSSe) absorption layer is obtained, which is the sample Control.

[0066] S4. Deposit a 50nm cadmium sulfide buffer layer, grow an 80nm intrinsic zinc oxide and a 300nm aluminum-doped zinc oxide window layer using DC magnetron sputtering, and use thermal evaporation to prepare a 1μm silver top electrode, thereby preparing a copper indium gallium selenide sulfur thin film solar cell, which is sample C-Control.

[0067] Example 2

[0068] A method for preparing a gradient bandgap copper indium gallium sulfur selenide solar cell by a solution process comprises the following steps:

[0069] S1. Prepare the precursor solution.

[0070] A stable and uniform CIGS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 1.047 g of copper acetate (Cu(CH3COO)2·H2O, 99.95%), 1.161 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%), and 0.296 g of anhydrous gallium chloride (GaCl3, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0071] In this step, the chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, so that thiourea can form a complete coordination with all metals.

[0072] S2. Prepare silver indium sulfur precursor solution.

[0073] A stable and uniform AIS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 0.75 g of silver chloride (AgCl, 99.95%), and 1.654 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0074] The chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, thereby obtaining an AIS precursor solution.

[0075] S3, preparing a copper indium gallium selenide precursor film containing two silver indium sulfide layers;

[0076] The first preparation step of a copper indium gallium sulfide precursor film including a silver indium sulfide layer includes: spin coating a copper indium gallium selenide (CIGS) precursor solution on a molybdenum-coated glass substrate, followed by hot-plate annealing and drying, repeated seven times, then spin coating a silver indium sulfide precursor solution, also hot-plate annealing and drying, repeated twice, and finally spin coating and annealing the copper indium gallium selenide precursor solution three times.

[0077] S4. After selenization treatment at 550° C. for 15 minutes, a copper indium gallium selenide sulfur (CIGSSe) absorption layer with a gradient band gap is obtained, which is sample Ch-EN.

[0078] S5. Deposit a 50nm cadmium sulfide buffer layer, grow an 80nm intrinsic zinc oxide and a 300nm aluminum-doped zinc oxide window layer using DC magnetron sputtering, and use thermal evaporation to prepare a 1μm silver top electrode to prepare a copper indium gallium selenide sulfur thin film solar cell, thereby preparing the final copper indium gallium selenide sulfur thin film solar cell, which is sample C-Ch-EN.

[0079] Example 3

[0080] A method for preparing a gradient bandgap copper indium gallium sulfur selenide solar cell by a solution process comprises the following steps:

[0081] S1. Prepare the precursor solution.

[0082] A stable and uniform CIGS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 1.047 g of copper acetate (Cu(CH3COO)2·H2O, 99.95%), 1.161 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%), and 0.296 g of anhydrous gallium chloride (GaCl3, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0083] In this step, the chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, so that thiourea can form a complete coordination with all metals.

[0084] S2. Prepare silver indium sulfur precursor solution.

[0085] A stable and uniform AIS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 0.75 g of silver chloride (AgCl, 99.95%), and 1.654 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0086] The chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, thereby obtaining an AIS precursor solution.

[0087] S3, preparing a copper indium gallium selenide precursor film containing two silver indium sulfide layers;

[0088] The second preparation step of the copper indium gallium sulfide precursor film including a silver indium sulfide layer includes: spin coating a copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, followed by hot-plate annealing and drying, repeated 8 times, then spin coating a silver indium sulfide layer precursor solution, also hot-plate annealing and drying, repeated 2 times, and finally spin coating and annealing the copper indium gallium selenide precursor solution 2 more times.

[0089] S4. After selenization treatment at 550° C. for 15 minutes, a copper indium gallium selenide sulfur (CIGSSe) absorption layer with a gradient band gap is obtained, which is sample Ch-NT.

[0090] S5. Deposit a 50nm cadmium sulfide buffer layer, grow an 80nm intrinsic zinc oxide and a 300nm aluminum-doped zinc oxide window layer using DC magnetron sputtering, and use thermal evaporation to prepare a 1μm silver top electrode to prepare a copper indium gallium selenide sulfur thin film solar cell, thereby preparing the final copper indium gallium selenide sulfur thin film solar cell, which is sample C-Ch-NT.

[0091] Example 4

[0092] A method for preparing a gradient bandgap copper indium gallium sulfur selenide solar cell by a solution process comprises the following steps:

[0093] S1. Prepare the precursor solution.

[0094] A stable and uniform CIGS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 1.047 g of copper acetate (Cu(CH3COO)2·H2O, 99.95%), 1.161 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%), and 0.296 g of anhydrous gallium chloride (GaCl3, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0095] In this step, the chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, so that thiourea can form a complete coordination with all metals.

[0096] S2. Prepare silver indium sulfur precursor solution.

[0097] A stable and uniform AIS precursor solution was prepared by sequentially adding 2.486 g of thiourea (CH4N2S, 99.0%), 0.75 g of silver chloride (AgCl, 99.95%), and 1.654 g of indium chloride tetrahydrate (InCl3·4H2O, 99.99%) to 12 mL of dimethylformamide solvent (C3H7NO, 98%).

[0098] The chemical to be added later must have reacted with the previous raw material. The molar ratio of thiourea to the sum of all metal salts is 3, thereby obtaining an AIS precursor solution.

[0099] S3, preparing a copper indium gallium selenide precursor film containing two silver indium sulfide layers;

[0100] The second preparation step of the copper indium gallium sulfide precursor film including a silver indium sulfide layer includes: spin coating a copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, followed by hot-plate annealing and drying, repeated 9 times, then spin coating a silver indium sulfide layer precursor solution, also hot-plate annealing and drying, repeated 2 times, and finally spin coating and annealing the copper indium gallium selenide precursor solution once more.

[0101] S4. After selenization treatment at 550° C. for 15 minutes, a copper indium gallium selenide sulfur (CIGSSe) absorption layer with a gradient band gap is obtained, which is sample Ch-TE.

[0102] S5. Deposit a 50nm cadmium sulfide buffer layer, grow an 80nm intrinsic zinc oxide and a 300nm aluminum-doped zinc oxide window layer using DC magnetron sputtering, and use thermal evaporation to prepare a 1μm silver top electrode to prepare a copper indium gallium selenide sulfur thin film solar cell, thereby preparing the final copper indium gallium selenide sulfur thin film solar cell, which is sample C-Ch-TE.

[0103] Data Analysis:

[0104] IV tests were performed on C-Control, C-Ch-EN, C-Ch-NT and C-Ch-TE, respectively. As shown in Table 1, compared with the reference sample, all parameters of the CIGSSe battery device with gradient band gap were improved. For the C-Ch-NT battery, the optimal device efficiency can reach 17.03%.

[0105] Table 1. Performance statistics of CIGSSe devices with different gradient band gaps

[0106]

[0107] The external quantum efficiency (QE) of the reference cell (C-Control) and the CIGSSe thin film solar cell (C-Ch-NT) with the optimal gradient band gap obtained by adjusting the insertion position of silver indium sulfur (AIS) in the precursor film were tested, and their average band gaps were obtained by fitting, as shown in Figure 5. Figure 2 (a) and (b), compared with the reference sample battery C-Control, the C-Ch-NT with gradient band gap broadens the long wavelength absorption band, and the overall absorption is enhanced, and the average band gap is reduced from 1.18eV to 1.15eV. At the same time, the reference battery (C-Control) and the C-Ch-NT with gradient band gap are subjected to negative bias QE test. Figure 2 (c), With the increase of wavelength, the QE(-1V) / QE(0V) value is smaller for C-Ch-NT with gradient band gap.

[0108] Capacitance-voltage CV tests were performed on the reference cell (C-Control) and the CIGSSe thin film solar cell (C-Ch-NT) with the optimal gradient band gap obtained by adjusting the insertion position of silver indium sulfur (AIS) in the precursor film, and their built-in voltages Vbi were obtained by fitting. Figure 3 With the introduction of gradient band gap, the built-in voltage of C-Ch-NT increases from 638mV to 847mV. As shown in Table 2, the depletion region width increases from 279nm to 400nm, and the interface defect state density increases from 7.91×10 15 / cm 3 Reduced to 3.9×10 15 / cm 3 .

[0109] Table 2. CV and DLCP test results of reference cell (C-Control) and C-Ch-NT cell with gradient band gap

[0110]

[0111] The present invention provides a method for preparing gradient-bandgap copper indium gallium selenide sulfur thin-film solar cells using a solution process. CIGS and AIS precursor solutions are prepared using dimethylformamide as the solvent and copper acetate, silver chloride, indium trichloride tetrahydrate, anhydrous gallium chloride, and thiourea as the solutes. Precursor films with varying indium-gallium gradients are obtained by adjusting the spin-coating position of the AIS. Subsequently, subsequent steps such as selenization are performed to prepare a CIGSSe thin-film solar cell with a gradient bandgap. By inserting an AIS interlayer during the spin-coating process of the precursor film, a gradient-bandgap absorption layer is obtained by selenization. This improves crystal quality while simultaneously constructing a gradient bandgap, increasing the cell's long-wavelength absorption and ultimately enhancing device performance. This method provides a simple and feasible method for preparing high-efficiency CIGSSe cells with a gradient bandgap using a solution process.

[0112] Through research and development, the present invention introduces appropriate layers of silver indium sulfide (AIS) at different positions during the spin coating of the copper indium gallium selenide precursor solution to prepare a precursor film, and then obtains a high-quality CIGSSe absorption layer with a gradient band gap through selenization annealing, thereby significantly improving the corresponding cell performance of the CIGSSe thin-film solar cell prepared based on this method. The present invention effectively solves the problem that it is difficult to obtain a CIGSSe film with a gradient band gap using a non-hydrazine solution method, thereby limiting the further improvement of its efficiency. At the same time, based on the solution method, the method of directly introducing a silver indium sulfide layer into the precursor film has a simple preparation process, which can further give play to the preparation advantages of the solution method and increase the possibility of large-scale solution method preparation of CIGSSe photovoltaic modules. It also has the characteristic that a CIGS absorption layer with a gradient band gap can be obtained even after high-temperature selenization, thereby obtaining higher device efficiency.

[0113] The technical solutions disclosed and proposed by the present invention can be realized by those skilled in the art by drawing on the contents of this article and appropriately changing the conditions, routes and other links. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, relevant technical personnel can obviously modify or re-combine the methods and technical routes described herein without departing from the content, spirit and scope of the present invention to achieve the final preparation technology. It should be pointed out in particular that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention. That is, the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing gradient bandgap copper indium gallium sulfur selenide solar cells by solution method, characterized in that: The following steps are involved: Prepare copper indium gallium sulfide precursor solution; Prepare silver indium sulfur precursor solution; Preparation of a copper indium gallium selenide precursor film containing a silver indium sulfide layer; After selenization treatment, a copper indium gallium sulfur selenide absorption layer is obtained; Depositing buffer layers, window layers, and electrodes to fabricate copper indium gallium sulfide selenide thin-film solar cells; The copper indium gallium sulfide precursor solution is prepared, comprising the following steps: Thiourea, copper acetate, indium trichloride tetrahydrate, and anhydrous gallium chloride are sequentially added to a dimethylformamide solvent and stirred to dissolve, thereby obtaining a CIGS precursor solution, wherein the molar ratio of thiourea to the sum of all metal salts is 2.5-3; The preparation of the silver indium sulfur precursor solution comprises the following steps: Sequentially adding thiourea, silver chloride, and indium trichloride tetrahydrate to a dimethylformamide solvent and stirring to dissolve, thereby obtaining an AIS precursor solution, wherein the molar ratio of thiourea to the sum of all metal salts is 2.5-3; The method for preparing a copper indium gallium sulfide precursor film containing a silver indium sulfide layer comprises the following steps: First, spin-coat the copper indium gallium selenide precursor solution on a molybdenum-coated glass substrate, then anneal and dry on a hot plate, repeating this process 7-9 times; Then, the silver indium sulfide layer precursor solution was spin-coated and annealed on a hot plate for drying, which was repeated twice; Finally, the copper indium gallium selenide precursor solution is spin-coated, annealed, and dried 1-3 times to obtain a copper indium gallium selenide precursor film containing a silver indium sulfide layer.

2. The method for preparing gradient band gap copper indium gallium sulfur selenide solar cells by solution method according to claim 1, characterized in that: The method for preparing a copper indium gallium sulfide precursor film containing a silver indium sulfide layer comprises the following steps: A silver indium sulfide intermediate layer is inserted during the spin coating process of the precursor film to obtain a copper indium gallium sulfide precursor film containing a silver indium sulfide layer. The spin coating precursor solution is annealed at a spin coating speed of 3000-3500 rpm and an annealing temperature of 260-290°C.

3. The method for preparing gradient band gap copper indium gallium sulfur selenide solar cells by solution method according to claim 2, characterized in that: Preparation of a copper indium gallium sulfide selenide absorber layer with a gradient band gap, comprising the following steps: For the precursor film obtained by spin coating, a rapid annealing furnace is used for high-temperature selenization. The selenization temperature is 540-580°C and the time is 10-15 minutes.

4. The method for preparing gradient band gap copper indium gallium sulfur selenide solar cells by solution method according to claim 3, characterized in that: Depositing a buffer layer, a window layer, and a top electrode on the gradient bandgap copper indium gallium sulfide selenide absorption layer to prepare a gradient bandgap copper indium gallium sulfide selenide thin film solar cell comprises the following steps: A 50-80 nm cadmium sulfide buffer layer is deposited on the absorption layer using a chemical water bath method, an 80-100 nm intrinsic zinc oxide and a 200-400 nm aluminum-doped zinc oxide window layer are grown using DC magnetron sputtering, and a 1-1.5 μm silver top electrode is prepared using thermal evaporation to obtain the final copper indium gallium sulfur selenide thin-film solar cell with a gradient band gap.

5. A copper indium gallium sulfur selenide solar cell, characterized in that: The method is prepared based on the steps of a solution method for preparing a gradient band gap copper indium gallium sulfur selenide solar cell as described in any one of claims 1 to 4.

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