P–N Junction Passivation in Kesterite Solar Cells by Use of Solution-Processed TiO2 Layer

In this work, we used a solution-processed TiO
₂
layer between Cu
₂
ZnSnSe
₄
and CdS buffer layer to reduce the recombination at the p-n junction. Introducing the TiO
₂
layer showed a positive impact on VOC but fill factor and efficiency decreased. Using a KCN treatment, we could create openings in the TiO
₂
layer, as confirmed by transmission electron microscopy measurements. Formation of these openings in the TiO
₂
layer led to the improvement of the short-circuit current, fill factor, and the efficiency of the modified solar cells.