A stacked chalcopyrite thin-film tandem solar cell with 1.2 V open-circuit voltage

CuGaSe2 (CGS) thin films were prepared on tin-doped indium oxide (ITO) coated soda-lime glass substrates by thermal co-evaporation to fabricate transparent solar cells. The films consisted of columnar grains with a diameter of approximately 1 mum. Some deterioration of the transparency of the ITO was observed after deposition of the CGS film. The CGS solar cells were electrically connected in series with Cu(In,Ga)Se-2 (CIGS) solar cells and mechanically stacked on the CIGS cells to construct tandem cells. The tandem solar cell with the CGS cell as the top cell showed an efficiency of 7.4% and an open-circuit voltage of 1.18 V (AM 1.5, total area). Copyright (C) 2003 John Wiley Sons, Ltd.