Synergistic effects of the zinc acetate additive on the performance enhancement of Sn-based perovskite solar cells

Tin-based perovskites are promising candidates for preparing lead-free perovskite solar cells due to the optimal bandgap and excellent optoelectronic properties, while the low formation energy of Sn2+ vacancy and facile oxidation of Sn2+ to Sn4+ lead to low efficiency and poor air instability of tin-based PSCs. Here, zinc acetate (ZnAc2) is employed as an additive to form a FAI·SnI2·ZnAc2 intermediate phase in the as-deposited films and control the crystallization process. Besides, the presence of Zn ions could favor the crystal growth by modifying the nucleation process. These synergistic effects lead to high-quality tin-based perovskite films with a large grain size and a low density of Sn2+ vacancies. Moreover, ZnAc2 could form a complex with SnCl2 and an antioxidant to uniformly encapsulate the grains and further improve the air stability of the perovskite layers. As a result, the efficiency of tin-based perovskite solar cells is improved from 6.70% to 8.38%. This work demonstrates a viable strategy to fabricate highly efficient and air-stable Sn PSCs by simultaneously suppressing the formation of Sn2+ vacancy and oxidation of Sn2+ in perovskite films.