Losses in CuInSe2-based thin film monolithic tandem solar cells
ABSTRACT Two critical aspects for the development of tandem solar cells using CuInSe2-alloy materials are addressed. First a structure for monolithic tandem solar cells using wide and narrow bandgap Cu(InGa)Se2-alloys in the top and bottom cells is demonstrated. This structure uses an ITO layer as both back contact to the wide bandgap Cu(InGa)Se2 and interconnect to the bottom cell. Three different options for the emitter in the bottom cell are compared. Second, progress on the wide bandgap cell using the Cu(InGa)(SeS)2 system is presented, and different loss mechanisms in Cu(InGa)Se2 and CuInS2 based devices are identified. Efficiency with Cu(InGa)Se2 is reduced by lower optical absorption and poor current collection while with CuInS2, it is reduced by interface recombination.