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, 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)Se-2 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)Se-2 solar cells also show contrasting results, namely, Cu(In,Ga)Se-2 or CuInSe2 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 CuGaSe2 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.