Influence of NaF addition on Cu2ZnSn(S,Se)4 thin film solar cells

The Cu₂ZnSn(S,Se)₄ (CZTSSe) absorbers were fabricated by two step process which consists of deposited stacking precursor followed by selenization. We investigated the influence of adding sodium into CZTSSe absorbers via sputtering NaF layer during the fabrication of precursor, or evaporating NaF layer on top of CZTSSe absorbers followed by vacuum annealing. We discovered that the NaF layer at the bottom of precursor can change the morphological properties of CZTSSe absorbers; on the contrary, the NaF layer on the top of precursor show no significant change. The increasing thickness of NaF layer revealed positive dependence on crystallinity of CZTSSe absorbers and increased the carrier concentration. However, we found device performance to be worse than those without NaF addition.