Evolution of Na-S(-O) compounds on Cu2ZnSnS4 absorber surface and its effect on CdS growth

Na-containing surface compounds is likely to form during the formation of CZTS absorber. Still, the understanding of any potential influence on buffer layer growth and device performance is limited. In this work, we observed that NaxS compound can possibly form on the CZTS surface after annealing, and negatively affect the growth of the subsequent CdS buffer. The Na
_x
S compound is oxidized to Na
₂
SO
₄
via air exposing the annealed CZTS surface, which allows greatly improved quality of the CdS layer. This provides new insights for improving the CdS/CZTS interface during the fabrication of CZTS solar cells.