Group III Elemental Composition Dependence of RbF Postdeposition Treatment Effects on Cu(In,Ga)Se2 Thin Films and Solar Cells

Abstract

The effects of RbF postdeposition treatment (RbF-PDT) on Cu(In,Ga)Se2, CuInSe2, and CuGaSe2 thin films and solar cell devices are comparatively studied. Similar to the effect of the KF postdeposition treatment (KF-PDT), Cu(In,Ga)Se2 and CuInSe2 film surfaces show significant pore formation resulting in a rough surface morphology with RbF-PDT, whereas this is not the case for In-free CuGaSe2. The device properties of the In-containing and In-free Cu(In,Ga)Se2 solar cells also show contrasting results, namely, Cu(In,Ga)Se2 or CuInSe2 devices show an increase in the open circuit voltage (Voc) and fill factor (FF) values and almost constant or a slight decrease in the short-circuit current density (Jsc) values with RbF-PDT, whereas CuGaSe2 devices show no significant improvements in the Voc and FF values but a substantial increase in the Jsc values. These results suggest that the alkali effects on the Cu(In,Ga)Se2 film and device properties strongly depend on the group III elemental composition in the Cu(In,G...