Preparation of CuGaSe2 Thin Film Solar Cells Comprising an Electrochemical Gallium Deposition Step

Abstract

Thin film CuGaSe2 solar cells were prepared from the elements using electrochemical deposition of Ga from an alkaline bath. Sputtered copper layers with a small gallium content (Cu0.86Ga0.14) on Mo/soda-lime glass served as a substrate. Subsequent reactive annealing of the thus created Cu/Ga precursor layer with selenium vapour yielded CuGaSe2. Chalcopyrite phase formation was studied with XRD, micro-Raman spectroscopy, SEM-EDX and Auger electron spectroscopy. It was concluded from these measurements that the binary phases Cu2Se and Ga2Se3 are generated prior to the formation of the favoured CuGaSe2 phase. Complete solar cell structures were fabricated by chemical bath deposition of CdS and chemical vapour deposition of ZnO onto the CuGaSe2 absorber layer. Promising 3.2% efficiency with Uoc = 542 mV, Isc = 12.0 mA/cm2 and FF = 0.49 were achieved, proving that electrochemical gallium deposition from an aqueous bath can contribute to the efficient thin film processing of chalcopyrite solar cells.