Composition and morphology of partially selenized CuIn1−XGaXSe2 thin films prepared using diethylselenide (DESe) as selenium source

CuIn1−xGaxSe2 (CIGS) thin films are being prepared by selenization of Cu-In-Ga precursors using diethylselenide, (C2H5)2Se, (DESe) as selenium source in place of H2Se gas because of lower toxicity and ease of handling. Rough estimates indicate that selenization process using DESe would cost approximately same or slightly less compared to that using H2Se. Price of DESe per mole is approximately five times that of H2Se. However, partial pressure of DESe, which reflects source material consumption, is approximately three to four times less than that of H2Se, due to higher decomposition rate of DESe compared to that of H2Se. The actual DESe consumption would be four to ten times less compared to that of H2Se. A selenization set-up using DESe as selenium source has been designed, fabricated and installed at FSEC Photovoltaic Materials Lab. Initial characterization of CIGS thin films have been carried out using electron probe microanalysis (EPMA), X-ray diffraction (XRD), scanning electron microscopy, secondary ion mass spectroscopy and Auger electron spectroscopy. EPMA showed elemental ratios of film to be near stoichiometric composition CuInSe2 with very low gallium content mainly because of tendency of gallium to diffuse towards back contact. XRD data shows formation of high crystalline CuInSe2 phase consistent with the EPMA data.