Synergistic Effect of Sodium Cyanoborohydride in Pb‐Sn Perovskite Solar Cells

Abstract Pb‐Sn mixed perovskite has received extensive attention because of its high research value in environmental protection and theoretical prospects. However, the film defects brought on by the quick crystallization of Pb‐Sn mixed perovskites and the facile oxidation of Sn 2+ to Sn 4+ are detrimental to the performance of Pb‐Sn perovskite solar cells (PSCs). Here, aiming at the interface of Pb‐Sn PSCs, which has been less studied, a reducing agent is first introduced on the top of Pb‐Sn mixed perovskite interface. The results show that in NaBH 3 CN(SC), B─H can suppress the oxidation of Sn 2+ and C≡N can enhance the perovskite crystallinity and passivate the surface defects. Benefitting from this synergistic effect, a champion power conversion efficiency of 21.3% is obtained for Pb‐Sn PSCs. In addition, the encapsulated device can maintain good stability under maximum power point tracking conditions.