The effect of Ga content on the selenization of co-evaporated CuGa/In films and their photovoltaic performance

Thin CuGa/In films with varying composition were deposited by co-evaporation and then selenized in situ with evaporated selenium. This growth process was interrupted at various stages to study the selenization behavior of metal precursors by GIXRD, SIMS, XRF, SEM, and EPMA. Precursor phase constitution and morphology were found to be similar to well-studied sputtered precursors. The phase evolution during selenization was also found to be similar to sputtered precursors, with greater Ga/(Ga+In) compositions requiring longer selenization time to completely form the chalcopyrite phase. Solar cells were fabricated with absorbers of varying composition and characterized by JV measurements. Relatively high Ga contents could be reached before photovoltaic performance degraded significantly. Champion power conversion efficiencies of 14.5, 14.4, and 12.2% were achieved with Ga/(Ga+In) ~ 30, 50, and 70%, respectively.