Potassium Fluoride Ex Situ Treatment on Both Cu-Rich and Cu-Poor CuInSe2 Thin Film Solar Cells

In this paper, we show that CuInSe
₂
(CIS) absorbers grown under Cu-excess have better collection efficiencies compared to Cu-poor ones. We also show that an ex situ potassium fluoride postdeposition treatment leads to an improvement in V
_OC
for CIS absorbers grown under both Cu-excess and Cu-poor conditions. Additionally, for absorbers grown under Cu-excess, the junction breakdown, which is observed in reverse bias of untreated cells, is removed. This improvement is based mainly on improving the interface of the CIS absorber grown under Cu-excess to the cadmium sulphide buffer layer through moving the dominant recombination from the interface to the bulk. In contrast to observations in the literature, the treated surface is not completely Cu-free.