LAUSR

Abstract Enhancement of photovoltaic performance due to alkali-metal doping in various thin-film compound solar cells such as chalcogenide Cu(In,Ga)Se2 (CIGS), Cu2ZnSnS4 (CZTS), and organic–inorganic hybrid perovskite, is significant in the development of photovoltaic technologies. In this work, the effects of light Li- and heavy Cs-doping in ternary CuGaSe2 (CGS) and quaternary CIGS thin-films and devices are compared. The new findings are: (i) heavy alkali-metal halide CsF postdeposition treatment (PDT) modifies the CGS film surface morphology and increases the carrier density; however, the beneficial effects of Cs on the CGS photovoltaic performance are low when compared to the results observed from quaternary CIGS devices; (ii) LiF-PDT leads to no significant CGS and CIGS film surface (hetero p-n junction interface) modifications; thus, the use of a thin (approximately 30 nm) CdS buffer layer is not effective in enhancing photovoltaic performance; and (iii) the beneficial effects of either light Li or heavy Cs on ternary CGS devices are modest; nonetheless, Li may be more effective than Cs, unlike quaternary CIGS devices.