“…7 CuInS 2 is a wide band gap chalcopyrite, and it is a promising material for thin film solar cells because of its near optimum direct band gap of 1.5 eV, and its possible use as a top cell in a tandem structure with CIGS. 8 Although the best thin film solar cell efficiency reported was set by a CIGS heterojunction cell (18.8 percent) made at the National Renewable Energy Laboratory (NREL), CuInS 2 solar cells are theoretically expected to show efficiencies superior to those of CIGS cells. 9 However, total area efficiency of only 11.4 percent has been achieved thus far for CuInS 2 cells.…”