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

The effects of RbF postdeposition treatment (RbF-PDT) on Cu(In,Ga)Se 2, CuInSe 2, and CuGaSe 2 thin films and solar cell devices are comparatively studied. Similar to the effect of the KF postdeposition treatment (KF-PDT), Cu(In,Ga)Se 2 and CuInSe 2 film surfaces show significant pore formation resulting in a rough surface morphology with RbF-PDT, whereas this is not the case for In-free CuGaSe 2 . The device properties of the In-containing and In-free Cu(In,Ga)Se 2 solar cells also show contrasting results, namely, Cu(In,Ga)Se 2 or CuInSe 2 devices show an increase in the open circuit voltage ( V oc ) and fill factor (FF) values and almost constant or a slight decrease in the short-circuit current density ( J sc ) values with RbF-PDT, whereas CuGaSe 2 devices show no significant improvements in the V oc and FF values but a substantial increase in the J sc values. These results suggest that the alkali effects on the Cu(In,Ga)Se 2 film and device properties strongly depend on the group III elemental composition in the Cu(In,Ga)Se 2 films as well as alkali-metal species.