Control of the thin film properties of Cu(In,Ga)Se2 using water vapor introduction during growth

The effects of water vapor introduction during growth on $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{Se}}_2$ (CIGSe) thin film properties, specifically the electrical and photoluminescence (PL) properties have been studied. Increases in the hole carrier density and conductivity with water vapor introduction were observed for all $\left[\mathrm{Ga}\right]∕[\mathrm{In}+\mathrm{Ga}]$ composition ratios. The PL spectra observed from $\mathrm{Cu}\mathrm{Ga}{\mathrm{Se}}_2$ (CGSe) showed an annihilation of deep donor-acceptor pair emissions related to Se vacancies with water vapor introduction. In addition, the Na content in the CIGSe layers as well as the O content was found to increase. These results suggest that the mechanism behind the variation observed in the electrical and PL properties and consequent cell improvement is largely attributable to a decrease in the Se-vacancies-induced donor defect density and an enhancement of Na effects.