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# Thin-Film Photovoltaics

CuGaSe2 with its band gap of 1.68 eV is a promising material for thin-film photovoltaics, since it can act as the top cell in a PV tandem device with CuInSe2 as the bottom cell.

CuGaSe2 was synthesized from Cu, Ga, and Se taken in stoichiometric amounts.

At 450°C, the evaporation of Se3 is detected by means of the isotope distribution between m/z 230 and m/z 245, which indicates a nonstoichiometric material.

The presence of iodine shows that it was used as a mineralizer for synthesis. The presence of Se at temperatures higher than 900°C is due to the thermal degradation of CuGaSe2.
Regulation of the Se vapor pressure is required to control the stoichiometry. (measurement with QMS 403/5 SKIMMER®)