CuInSe₂ And Cuin(S_xSe_1-x)₂ Thin Films Prepared By Solvothermal Method

The compound semiconductor CIS(CuInSe₂,CuIn(S_xSe_1-x)₂,CuInS₂) has been attracted interest for use in photovoltaic solar cells since 1976 [1]. As a chalcopyrite semiconductor, CuInSe₂, CuIn(S_xSe_1-x)₂ and CuInS₂ had band gaps range from 1.04eV to 1.55eV. The theoretical optimum value for photovoltaic's applications is 1.45eV, so CIS is suitable for preparing high conversion efficiency solar cell. What'more, CIS thin film solar cells have other advantages, such as long-term stability and nontoxic.In this paper, we studied CIS prepared by solvothermal method. CuInSe₂ nanoparticles which were synthesized by solvothermal method can be made as solar cells. Using this method, solar cells with efficiency of 6.7% have been fabricated [2]. Be differ from vacuum-based methods, such as evaporation [5-7] and sputtering [8-13], solvothermal method was used here due to its relatively simple procedures and low cost. These two advantages made solvothermal method suited for large-scale industrialization of solar cells.There were differences in specific process routes of preparing CuInSe₂, CuIn(S_xSe_1-x)₂ and CuInS₂ by solvothermal method. CuInSe₂ and CuInS₂ thin films can be prepared by reacting CuInSe₂/CuInS₂ nanoparticles in Se/H2S, and CuInSe₂ and CuInS₂ nanoparticles can be synthesized by solvothermal method directly. Two routes to CuIn(S_xSe_1-x)₂ thin films had been reported. First route was the reaction of CuInSe₂ which were synthesized by solvothermal method with H2S. The other route was selenization or sulphurization of CuIn(S_xSe_1-x)₂ prepared by solvothermal method. In this paper, only the process of synthesizing CuIn(S_xSe_1-x)₂ nanoparticles was studied in the second route.There were three main factors which affected the product prepared by solvothermal method: ratio of elements in precursor, temperature of the reaction and time of the reaction. By controlling these three factors, we can synthesize nanoparticles with high quality, and the ratio of Se and S of CuIn(S_xSe_1-x)₂ nanoparticles can also be controlled. On the other hand, temperature and time of the selenization or sulphurization were main factors on making thin films. It was found that the compositions, degree of crystallinity, homogeneity and ratio of Se and S of the final CuIn(S_xSe_1-x)₂ thin films were controlled by temperature and time of the selenization or sulphurization.XRD, SEM, EDS, Raman are used to characterized the property of the CIS thin film.