Preparation of Cu(In,Ga)Se2 thin film solar cells by selenization of metallic precursors in an Ar atmosphere

Cu(In,Ga)Se-2 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 10 Pa. The 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 degrees C, due to the absence of In2Se3 at intermediate stage at low reactor pressure. Subsequently, the Cu(In,Ga)Se-2 phase is produced by the reactive diffusion of CuInSe2 with a Se-poor GaSe phase at high temperature of up to 560 degrees C. The final film exhibits smooth surface and large grain size. The absorber us used to fabricate a glass/Mo/Cu(In,Ga)Se-2/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.