Preparation method of cztss e thin film material and solar cell

Abstract

The application belongs to the technical field of solar cells, and particularly relates to a preparation method of a CZTSSe thin film material and a solar cell. The cell structure comprises, from bottom to top, a sodium-calcium glass substrate layer, a Mo back electrode layer, a CZTSSe absorption layer, a CdS buffer layer, a ZnO first window layer, an ITO second window layer and a metal Ag electrode. The preparation method of the CZTSSe absorption layer is multiple spin coating and annealing to obtain a pre-prepared layer film, bath annealing of the CZTS pre-prepared layer solvent, and selenization of the pre-prepared layer to obtain the CZTSSe absorption layer. The method can more completely decompose and remove residual organic matter in the pre-prepared layer, reduce internal pores and interface defects of the absorption layer, improve the crystallization quality and density of the CZTSSe absorption layer, and effectively improve the photoelectric conversion efficiency of the CZTSSe thin film solar cell.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a method for preparing CZTSSe thin film material and a solar cell. Background Technology

[0002] With its advantages of unlimited reserves, wide distribution, and zero emissions, solar energy has become the renewable energy form with the greatest potential for large-scale application. As the mainstream technology for solar energy utilization, photovoltaic power generation has undergone technological iterations such as crystalline silicon cells, cadmium telluride, and copper indium gallium selenide, and is developing towards a direction of resource-unrestricted, environmentally friendly, low-cost, and large-area fabrication.

[0003] Copper-zinc-tin-sulfur-selenium (CuZnSn(S,Se)4, CZTSSe) is a class of direct bandgap semiconductor materials with a zinc-stampedite structure. It possesses excellent photoelectric properties, including an tunable bandgap (1.0–1.5 eV) adapted to the solar spectrum, ultra-high light absorption coefficient, and a theoretical photoelectric conversion efficiency approaching the Shockley-Queisser limit. Its constituent elements—copper, zinc, tin, sulfur, and selenium—are all abundant and environmentally friendly elements. The raw material cost is significantly lower than CIGS and CdTe, and it is non-toxic and does not face resource bottlenecks. It is widely recognized as a core absorber layer material for next-generation low-cost, scalable, and environmentally friendly thin-film solar cells, with broad application prospects in distributed photovoltaics, flexible devices, tandem cells, and space energy.

[0004] Currently, solution-based CZTS film preparation leaves behind a large amount of organic solvents and organic ligands. These organic substances are divided into free solvent carbon that can volatilize at high temperatures and pyrolysis residue carbon that cannot volatilize at high temperatures. Residual carbon can cause film porosity and elemental segregation, reducing battery performance. Increasing the annealing temperature during the pre-layer preparation process can effectively remove solvent carbon from the pre-layer film, but this method cannot remove pyrolysis residue carbon and will also accelerate the crystallization rate of the pre-layer, leading to a reduction in crystal size, which further affects the uniformity and crystal quality of the selenized CTZSSe film. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for constructing a low-carbon, high-efficiency CZTSSe solar cell absorber layer using solvent bath annealing. After spin-coating the CZTS precursor, a solvent bath annealing treatment is added. This annealing process is carried out in a solvent, allowing free solvent carbon and pyrolysis residue carbon in the preform film to be slowly and thoroughly decomposed and dissolved in a selected good solvent, achieving deep carbon removal. Simultaneously, the selected solvent is a poor solvent for the preform film, maintaining its structural integrity and stable interfacial bonding, preventing cracks, peeling, or localized shrinkage, significantly improving the crystallinity quality of the absorber layer and the photoelectric performance of the cell.

[0006] To achieve the above objectives, the present invention provides a method for preparing CZTSSe thin film material, the method comprising the following steps: S1. Dissolve copper salt, zinc salt, tin salt and sulfur-containing organic compound in ethylene glycol methyl ether solution and stir until completely dissolved to obtain precursor solution; S2. Drop the precursor solution onto Mo-coated sodium-calcium glass and spin-coat it using a spin coater. After the spin-coating step is completed, place the sample on a hot plate for annealing. Repeat the above spin-coating and annealing steps multiple times to obtain the CZTS preform film. S3. Place the CZTS preform film in a solvent and heat the solvent for solvent bath annealing to obtain a low-carbon CZTS preform film. The solvent is deionized water, methanol, ethanol, acetone, DMF, DMSO, chlorobenzene, ethanolamine, ethylenediamine or isopropanol. S4. Place the low-carbon CZTS pre-coated film in a graphite box containing selenium particles, put it into a rapid thermal annealing selenization furnace with nitrogen flow, heat it up and hold it for a certain time, and then cool it naturally to obtain the CZTSSe absorber film.

[0007] Preferably, in step S1, the copper salt includes one or more of copper sulfate octahydrate, copper nitrate, cuprous chloride, cuprous sulfide, cuprous iodide, cuprous acetate, and cuprous selenide; the zinc salt includes one or more of zinc acetate dihydrate, anhydrous zinc acetate, and zinc oxalate dihydrate; the tin salt includes one or more of tin tetrachloride pentahydrate, anhydrous tin tetrachloride, and stannous sulfate; and the sulfur-containing organic compound includes one or more of thiourea, benzyl thiourea, and ethylene thiourea.

[0008] Preferably, in step S2, the spin coating speed is 3000rpm-5000rpm, the rotation time is 10-70s, and the annealing temperature is 90-300℃.

[0009] Preferably, in step S3, the solvent bath annealing temperature is 50-300℃ and the time is 0.1-20min.

[0010] Preferably, in step S4, the temperature is raised to 300-800℃ and held for 5-40 minutes.

[0011] The present invention also provides a solar cell, wherein the cell structure from top to bottom comprises: a soda-lime glass substrate layer, a Mo back electrode layer, a CZTSSe absorber layer, a CdS buffer layer, a ZnO first window layer, an ITO second window layer, and a metal Ag electrode, wherein the CZTSSe absorber layer is prepared by any of the above methods.

[0012] The beneficial effects of this invention are reflected in: (1) Solvent bath annealing can more thoroughly remove free solvent carbon and pyrolysis residue carbon, reduce carbon impurity content, reduce defect state density, and avoid carbon-related short circuits and leakage. (2) Compared with increasing the annealing temperature to remove organic matter during the preparation of the preform, adding an extra solvent bath annealing after the preform is fully prepared can ensure the crystal quality of the preform, prevent film cracking and pore formation, and improve film density. (3) Organic matter is removed in solvent after the preform is fully prepared, which avoids the preform crystallization caused by high temperature annealing, maintains the uniformity of grains and the continuity of film, and optimizes the subsequent growth of selenized grains. (4) The process steps are simple, only adding an annealing step to the existing spin coating process. It is highly compatible with conventional solution spin coating process, does not require new complex equipment, and is suitable for continuous and large-scale production. (5) The short-circuit current density (Jsc) and fill factor (FF) of CZTSSe thin-film solar cells were improved, thus effectively improving the photoelectric conversion efficiency. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 A process flow diagram of the CTZSSe absorber layer preparation method provided by the present invention; Figure 2 The images show a comparison of the SEM cross-sections of the CZTSSe prefabricated layer provided in Embodiment 1 and Comparative Example 1 of the present invention, where (a) is Embodiment 1 and (b) is Comparative Example 1. Figure 3 The images show a comparison of the SEM planar images of the CZTSSe prefabricated layer provided in Embodiment 1 and Comparative Example 1 of the present invention, where (a) is Embodiment 1 and (b) is Comparative Example 1. Figure 4 PCE, V of the CZTSSe device provided in Embodiment 1 and Comparative Example 1 of the present invention OC FF, J SC A comparison of box plots. Detailed Implementation

[0015] This invention provides a method for constructing low-carbon, high-efficiency CZTSSe thin film materials by solvent bath annealing. After spin-coating the CZTS precursor, an additional solvent bath annealing treatment is added to more thoroughly remove residual organic matter in the preform, reduce internal pores and interface defects in the absorber layer, and improve the crystallinity and density of the CZTSSe absorber layer.

[0016] Example 1: (1) Clean the substrate and dry it for later use. The substrate is Mo-plated sodium calcium glass, a metal foil sputtered with a Mo film, or a polyimide film sputtered with a Mo film.

[0017] (2) Add 0.6492g CuCl and 0.7928g Zn(Ac)2 2H₂O, 1.0728g SnCl₄ 5H2O and 1.9223g of thiourea were dissolved in 10ml of ethylene glycol methyl ether solution and stirred until completely dissolved. Stirring was continued until completely dissolved to prepare a precursor solution. (3) Drop the CZTS precursor solution onto Mo-coated sodium-calcium glass. Spin coat the sample using a spin coater, setting the rotation speed to 3000 r / min and the rotation time to 30 s. After spin coating, place the sample on a hot plate at 280°C and bake for 2 min. Repeat the spin coating and annealing steps 8 times to obtain the CZTS preform film.

[0018] (4) Place the CZTS preform film in 100ml of acetone, heat the acetone to 60℃, and perform solvent bath annealing for 2min to obtain the low carbon CZTS preform film.

[0019] (5) The low-carbon pre-fabricated film is placed in a graphite box containing selenium particles, and then placed in a rapid thermal annealing furnace with nitrogen flow. The temperature is raised to 550°C and held for 1000s. After natural cooling, the CZTSSe absorber film is obtained. The CZTSSe absorber film has a zinc steric ore structure and a film thickness of 1-3μm.

[0020] (6) The obtained CZTSSe absorber layer film is then processed into a CZTSSe solar cell through subsequent steps for performance testing. The specific steps are as follows: A. A CdS film is deposited on the surface of the CZTSSe film obtained in step (5) using a chemical bath method as a buffer layer. The thickness of the CdS film is 50 nm.

[0021] B. An intrinsic zinc oxide (i-ZnO) thin film was deposited on the buffer layer obtained in step A using a sputtering method. The sputtering power was 80 W, the time was 16 min, and the thickness of the resulting i-ZnO thin film was 50 nm.

[0022] C. An indium-doped zinc oxide (ITO) film is deposited on the i-ZnO film obtained in step B using a sputtering method. The sputtering power is 80 W, the time is 25 min, and the thickness of the resulting ITO film is 200 nm.

[0023] D. Cover the ITO thin film obtained in step C with a mask, and deposit a metallic silver electrode using a vacuum thermal evaporation method.

[0024] Comparative Example 1: Unlike Example 1, step (4) is omitted. The other steps are exactly the same.

[0025] The morphology of the low-carbon preform film obtained in Example 1 (solvent bath annealing group) and the preform film obtained in Comparative Example 1 (control group) was observed using scanning electron microscopy (SEM), and the cross-sectional images are shown below. Figure 2 As shown in the figure, the solvent bath annealing group ( Figure 2 In film a), the film thickness decreases accordingly with solvent evaporation, resulting in fewer defect particles and higher film uniformity. The SEM planar image is shown below. Figure 3 As shown, it can be seen that the solvent bath annealing group ( Figure 3 Thin film contrast control group (a) Figure 3 (b) shows higher uniformity and fewer pores. Furthermore, the box plots of the CTZSSe devices obtained in Comparative Example 1 and Comparative Example 1 (b) are compared. Figure 4 As can be seen, the short-circuit current density (Jsc), fill factor (FF), and photoelectric conversion efficiency of Example 1 are all effectively improved.

[0026] Example 2: The difference in Example 1 is that step (4) is changed to placing the CZTS pre-coated film in 100ml of deionized water, heating the deionized water to 90°C, and annealing it in a solvent bath for 2 minutes to obtain a low-carbon CZTS pre-coated film. The other steps are exactly the same.

[0027] Compared with Comparative Example 1, the short-circuit current density (Jsc), fill factor (FF), and photoelectric conversion efficiency of the CTZSSe device obtained in Example 2 are all effectively improved.

[0028] Compared with Example 1, the efficiency and fill factor of the CZTSSe device obtained in Example 2 were reduced. This is attributed to the fact that deionized water could not effectively dissolve the pyrolysis carbon residue in the preform, leading to the introduction of series resistance.

[0029] Comparative Example 2: Unlike Example 1, the temperature of the hot plate in step (3) is changed to 350°C, and step (4) is omitted. The other steps are exactly the same.

[0030] Compared with Example 1, Comparative Example 2 removes carbon from the preform film by increasing the spin coating annealing temperature. This method leads to a reduction in the crystal size of the preform, affecting the uniformity of the selenized CTZSSe film and resulting in a decrease in device efficiency.

Claims

1. A method for preparing a CZTSSe thin film material, characterized in that, Includes the following steps: S1. Dissolve copper salt, zinc salt, tin salt and sulfur-containing organic compound in ethylene glycol methyl ether solution and stir until completely dissolved to obtain precursor solution; S2. Drop the precursor solution onto Mo-coated sodium-calcium glass and spin-coat it using a spin coater. After the spin-coating step is completed, place the sample on a hot plate for annealing. Repeat the above spin-coating and annealing steps multiple times to obtain the CZTS preform film. S3. Place the CZTS preform film in a solvent and heat the solvent for solvent bath annealing to obtain a low-carbon CZTS preform film. The solvent is deionized water, methanol, ethanol, acetone, DMF, DMSO, chlorobenzene, ethanolamine, ethylenediamine or isopropanol. S4. Place the low-carbon CZTS pre-coated film in a graphite box containing selenium particles, put it into a rapid thermal annealing selenization furnace with nitrogen flow, heat it up and hold it for a certain time, and then cool it naturally to obtain the CZTSSe absorber film.

2. The production method according to claim 1, characterized by, In step S1, the copper salt includes one or more of copper sulfate octahydrate, copper nitrate, cuprous chloride, cuprous sulfide, cuprous iodide, cuprous acetate, and cuprous selenide; the zinc salt includes one or more of zinc acetate dihydrate, anhydrous zinc acetate, and zinc oxalate dihydrate; the tin salt includes one or more of tin tetrachloride pentahydrate, anhydrous tin tetrachloride, and stannous sulfate; and the sulfur-containing organic compound includes one or more of thiourea, benzyl thiourea, and ethylene thiourea.

3. The preparation method according to claim 1, characterized in that, In step S2, the spin coating speed is 3000rpm-5000rpm, the rotation time is 10-70s, and the annealing temperature is 90-300℃.

4. The preparation method according to claim 1, characterized in that, In step S3, the solvent bath annealing temperature is 50-300℃ and the time is 0.1-20min.

5. The preparation method according to claim 1, characterized in that, In step S4, the temperature is raised to 300-800℃ and held for 5-40 minutes.

6. A solar cell, characterized in that, The battery structure, from top to bottom, consists of: a soda-lime glass substrate, a Mo back electrode layer, a CZTSSe absorber layer, a CdS buffer layer, a ZnO first window layer, an ITO second window layer, and a metal Ag electrode, wherein the CZTSSe absorber layer is prepared by any one of the methods in claims 1-5.

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