Preparation and characterization of Cu-Ga-Se films of ordered vacancy compound

Cu-Ga-Se films with an orderd vacancy compound (OVC) structure were prepared at substrate temperature about 500degreesC by thermal co-deposition. With a preparation under extremely Se excess condition, films of the OVC were synthesized within the compositional ratio of 0.73 less than or equal to [Ga]/([Cu]+[Ga]) less than or equal to 0.86 along Cu2Se-Ga2Se3 pseudo binary system. The growth on soda-lime glass substrates improves the crystallinity compared to that on alkali-free glass. An increase in the optical bandgaps of OVC films from 1.85 eV to 1.94 eV was observed with an increase in the Ga content of the films. The deposition of Cu and Se onto Ga2Se3 films resulted in a vertically inhomogeneous film: the bottom layer with the OVC structure and the top layer with the chalcopyrite structure. A solar cell using the CuGa5.0Se8.1 film within a ZnO/CdS/Cu-Ga-Se/Mo/soda-lime glass substrate structure showed an open circuit voltage of 947 mV, an efficiency of 2.2%, a short circuit current density of 4.5 mA/cm(2), and a fill factor of 0.52 (Air Mass 1.5, 0.5 cm(2), total area).