CHARACTERIZATION OF POLYCRYSTALLINE CU(IN,GA)SE-2 THIN-FILMS PRODUCEDBY RAPID THERMAL-PROCESSING

In this study a simple, tolerant and reproducible process has been dev eloped to produce device quality Cu(ln,Ga)Se-2 thin films. These films were prepared by the rapid thermal processing (RTP) of thermally evap orated Cu-In-Ga-Se metallic precursors. All precursors used in this st udy were prepared by a new growth process in which all metals (Cu, In and Ga) were evaporated from one single crucible in a Se atmosphere. I n this process, developed at Stuttgart University, the stoichiometry o f the precursor films was fixed by the amount of material in the cruci ble and the substrate temperature was kept constant at 200 degrees C. Various rapid thermal processes were considered to optimize the materi al properties (adhesion, surface morphologies and uniformity) of the c ompound films. In the case of relatively slow rapid thermal processes (RTP) which involved various ramping steps, films with poor structural properties (inhomogeneous film morphologies and presence of secondary phases) were obtained. A significant improvement in material properti es was obtained in the case of rapid heating (in 10s from 200 degrees C to 550 degrees C) of samples. However, these films were still charac terized by the presence of secondary phases. Optimum material properti es (homogeneous and dense films) were obtained when the heating profil e followed a root function in the critical temperature range around 30 0 degrees C. Preliminary solar cell devices were fabricated with conve rsion efficiencies above 6% (total area).