Charge loss investigations in kesterite solar cells (Invited Paper)

Kesterite Cu2ZnSn(S, Se)4 (CZTSSe) solar cells are highly promising low-cost thin-film photovoltaics. However, the efficiency of these solar cells is challenged by severe charge losses and complex defects. Here, we firstly reveal through a data-driven correlation analysis that the dominant deep defect in CZTSSe exhibits a donor character. We further propose that incomplete cation exchange in the multi-step crystallization reactions of CZTSSe is the kinetic mechanism responsible for the defect formation. To facilitate the cation exchange, we introduce a multi-elemental alloying approach aimed at weakening the metal-chalcogen bond strength and the stability of intermediate phases. This strategy leads to a significant reduction in charge losses within the CZTSSe absorber. Overall, these results not only present a significant advancement for kesterite solar cells but could also help identify and regulate defects in photovoltaic materials.