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 about 1 m. The deterioration of the transparency of the ITO was observed after deposition of the CGS film. A distinct second diode could not be seen in the current voltage curve of the CGS cells at room temperature. The CGS solar cells were electrically connected in series with Cu In,Ga Se2 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 AM 1.5, total are