Preparation of Cu(In,Ga)Se₂ Thin Film Solar Cells by Selenization of Metallic Precursors in an Ar Atmosphere

Cu(In,Ga)Se₂ thin films are deposited on Mo-coated glass substrates by Se vapour selenization of sputtered metallic precursors in the atmosphere of Ar gas flow under a pressure of about 10Pa. The it in situ heat treatment of as-grown precursor leads to the formation of a better alloy. During selenization, the growth of CuInSe₂ phase preferably proceeds through Se-poor phases as CuSe and InSe at relatively low substrate temperature of 250°C, due to the absence of In₂Se₃ at intermediate stage at low reactor pressure. Subsequently, the Cu(In,Ga)Se₂ phase is produced by the reactive diffusion of CuInSe₂ with a Se-poor GaSe phase at high temperature of up to 560°C. The final film exhibits smooth surface and large grain size. The absorber is used to fabricate a glass/Mo/Cu(In,Ga)Se₂/CdS/ZnO cell with the total-area efficiency of about 7%. The low open-circuit voltage value of the cell fabricated should result from the nonuniform distribution of In and Ga in the absorber, due to the diffusion-controlled reaction during the phase formation. The films, as well as devices, are characterized.