Selenization of Co-Sputtered CuInAl Precursor Films

CuInAl precursor films with varying Al/(In+Al) ratios were co-sputtered onto Mo coated soda-lime glass substrates. Metal precursor films were then selenized under vacuum conditions using thermally evaporated elemental selenium. Both precursor films and selenized samples were characterized for composition, crystalline phases, morphology, and compositional depth uniformity. Selenized films show low Al incorporation and phase separation when selenized at both 500 and 525 °C. Films selenized with a Se deposition rate of 12 Å/s showed poor adhesion compared with samples selenized at 4 Å/s. The segregation of aluminum towards the back contact as well as oxygen incorporation appears to cause adhesive loss in extreme cases, and poor interface electrical characteristics in others. The maximum device efficiency measured was 5.2% under AM1.5 for a device with ∼2 at% aluminum.