Stabilization of PN heterojunction between Cu(InGa)Se2 thin-film absorber and ZnO window with Zn(O, S, OH)x buffer

Dramatic improvement of current-voltage (I-V) performance, especially the fill factor (FF) observed in the Cu(InGa)Se-2-based thin-film circuits with Zn(O, S, OH)(x) buffer after postdeposition light soaking is discussed in this study. Considering the composition of Zn(O, S, OH)(x) buffer and the reversible behavior with respect to postdeposition light soaking, a model is proposed, in which H2O molecules released by the dehydration of Zn(OH)(2) in the Zn(O, S,OH)(x) buffer are considered to play a dominant role in this behavior. Based upon this model, attempts to stabilize the pn heterojunction by making the reversible behavior irreversible are, for the first time, successfully achieved by adjusting the postdeposition light-soaking conditions. The reduction of the Zn(OH)(2) concentration in the Zn(O, S, OH)(x) buffer through the combination of heating at 130 degrees C for at least 40 min and irradiation using a constant-light solar simulator contributes to stabilizing the pn heterojunction and improving the I-V performance as well as the electrical yield.