Sulfide kesterite Cu 2 ZnSnS 4 (CZTS) is a promising photovoltaic material with considerable potential for application in single-junction, multi-junction, and tandem solar cells. However, advancements in its certified power conversion efficiency (PCE) have remained slow, primarily due to severe interface recombination, which is a major limitation constraining the overall performance of CZTS solar cells. Here, we report an effective heterojunction interface engineering approach in which the CZTS/(Zn,Sn)O heterojunction is subjected to a controlled annealing treatment under dynamically flowing air atmosphere. This treatment induces Zn and Sn cation lattice diffusion to reconstruct a quasi-epitaxial contact at the intermediate interface. This reconstruction effectively suppresses defect-assisted interfacial carrier recombination and optimizes carrier dynamics by enhancing transport and collection efficiencies. Consequently, we achieved a highest certified efficiency of 11.96% for Cd-free, pure-sulfide CZTS solar cell (bandgap > 1.5 eV) without extrinsic cation alloying. This study provides insights into heterojunction interface optimization and the performance enhancement mechanism in the development of kesterite solar cells.
Luo et al. (Fri,) studied this question.