Fabrication And Characterization Of CuInS₂ And ZnS Thin Films Materials For Solar Cells By Electrodeposition

CuInS2 is one kind of direct band gap semiconductor material, its band gap is 1.5eV at room temperature and optical absorption coefficient is up to 105cm-1. CuInS2 is very suitable to be used as absorption layer material for solar cells due to its high theoretical photoelectric conversion efficiency, and is currently the research hotspot of photovoltaic materials. CdS was usually used as buffer layers material for initial compound thin film solar cells, this material is harmful for both environment and humans. In the pursuit of low cost, high efficiency solar cells, development of non-toxic, environmentally friendly, cadmium-free ZnS buffer layer material to replace CdS material is another research focus of solar cells.Electrodeposition is a low-temperature, non-vacuum coating technology for fabricating CuInS2 thin films, which can achieve low-cost and large-area thin films deposition. It can simplify the processing of vacuum evaporation method and magnetron sputtering method and ensure the large-area uniformity of thin films to continuously fabricate CuInS2 absorption layers and ZnS buffer layers by electrodeposition, which has important significance not only for the fabrication of large-area CuInS2 solar cells but also for the realization of low-cost, large-scale commercial production of solar cells.In this paper, CuInS2 and ZnS thin films for solar cells were deposited onto Ti foils and transparent ITO conductive glasses respectively by electrodeposition method. The effects of relevant electrodeposition parameters such as electrodeposition potentials, electrolyte concentration and annealing parameters such as annealing temperature, annealing time on the phase composition, crystalline state, surface morphology, optical property and electrical property of thin films were studied. The thin films were characterized with X-ray diffractometer, optical microscope, scanning electron microscope, Raman microscope, UV-Vis-NIR spectrophotometer, four-probe meter and Hall Effect measurement system. The main results were as follows:(1) The potentiostatic electrodeposition method for fabricating CuInS2 thin films was studied, p-type chalcopyrite structure CuInS2 thin film with smooth surface and uniformly distributed crystal grains was obtained under the electrolyte component of 12.5 mmol/L CuCl2,12.5 mmol/L InCl3,125 mmol/L Na2S2O3,0.05 mol/L citrate. Its band gap was 1.6eV and carrier concentration was 3.737×1017 cm-3.(2) The optimum annealing temperature for the CuInS2 thin films deposited on Ti foils was studied, the results showed that the CuInS2 thin films would crack and break off from Ti foils due to different thermal expansion coefficients between CuInS2 thin films and Ti foils, which would degrade the quality of thin films.(3) ZnS thin films were fabricated by two-electrode electrodeposition method, they were treated by sulfurization of solid sulfur source. It was found that pure ZnS thin films were obtained after sulfurization for 4 hours. The band gaps of ZnS thin films were about 4.0eV with visible light transmittance of 50%.