Ga-grading and Solar Cell Capacitance Simulation of an industrial Cu(In,Ga)Se2 solar cell produced by an in-line vacuum, all-sputtering process

Cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells are fabricated on stainless steel substrate using an industrial, in-line vacuum, all sputtering process. The absorber layer is deposited from compound CIGS targets and crystallized simultaneously by high temperature processing. In-depth compositional and structural characterization of the chalcopyrite material is conducted and a Solar Cell Capacitance Simulator (SCAPS) model for the complete device is set-up. Ga-grading of the absorber through the successive use of different CIGS target compositions and resulting in solar cell performance enhancement is shown. At the research and development scale, efficiency values of 15.1% and 13.2% are reported for 1 cm2 and 225 cm2 total area solar cells, respectively. Successful transfer to production is also demonstrated. A series of a hundred 225 cm2 solar cells produced following an optimized process including the Ga grading studied in the present contribution average at 14.8% total area efficiency.