Narrow bandgap Sn-Pb perovskite solar cells with high operational stability modulated by imidazoline derivative

Sn-Pb mixed perovskites with narrow bandgap (NBG) are important for high-performance single- and multi-junction perovskite solar cells (PSCs). However, the inherent Sn2+ oxidation and ion migration lead to inferior stability. Herein, 2-hydrazino-2-imidazoline hydrobromide (2H2I) is employed as a coordinating additive to regulate the film crystallization and inhibit Sn2+ oxidation. Meanwhile, 2H2I can form hydrogen bonds with I− ions to suppress ion migration, thereby improving photovoltaic stability. The target FA0.8Cs0.2Sn0.5Pb0.5I3:2H2I PSC exhibits a champion power conversion efficiency (PCE) of 22.44 %, higher than that of the control device (19.16 %). The target devices retain 90 % (T90) and 80 % (T80) of the initial PCE under maximum power point (MPP) tracking for 1360 h at room temperature and for 436 h at 65 °C, respectively, the highest values for NBG Sn-Pb PSCs. This work demonstrates an effective strategy toward photothermally stable Sn-Pb PSCs.