Improved performance in CuInSe2 and Surface-modified CuGaSe2 solar cells

In this paper, we present an update and review on the progress made in the development of low-bandgap CuInSe2 (CIS) and wide-bandgap CuGaSe2 (CGS) solar cells. Our research project is primarily concerned with the optimization of the bottom and top cells of the tandem solar cell. This past year, we established new record total-area efficiencies of 15.0% and 10.2% for CIS and surface-modified CGS solar cells, respectively. These achievements were possible by modifying the growth process for CIS and CGS absorbers. We attempt to modify the surface region of the CGS absorber to be CIGS-like in composition. We also have designed a mechanical-stacked tandem solar cell where the 15% CIS cell serves as the bottom cell and transparent CdTe cell serves as the top cell. The NREL-confirmed total-area efficiency for this CdTe/CIS tandem device is 15.31%.