Durable all inorganic perovskite tandem photovoltaics

All-inorganic perovskites prepared by substituting the organic cations (e.g. methylammonium (MA + ) and formamidinium (FA + )) with inorganic cations (e.g. Cs + ) are effective concepts to enhance the long-term photo- and thermal-stability of perovskite solar cells (PSCs) 1,2 . Hence, inorganic perovskite tandem solar cells (IPTSCs) are promising candidates for breaking the efficiency bottleneck and addressing the stability issue as well 3,4 . However, challenges remain in fabricating 2-terminal (2T) IPTSCs due to the inferior film formation and deep trap states induced by tin cations 5-7 . Herein, a ligand evolution (LE) strategy with p-toluenesulfonyl hydrazide (PTSH) is employed to regulate film formation and eliminate deep traps in inorganic narrow bandgap (NBG) perovskite, enabling the successful development of 2T IPTSCs. Accordingly, the 1.31 eV CsPb 0.4 Sn 0.6 I 3 :LE device delivers a record efficiency of 17.41%. Combined with the 1.92 eV CsPbI 2 Br top-cell, 2T IPTSCs exhibit a champion efficiency of 22.57% (certified 21.92%). Additionally, IPTSCs are engineered to deliver remarkable durability under maximum power point (MPP) tracking, maintaining 80% of the initial efficiency at 65 °C for 1510 h and at 85°C for 800 h, respectively. We elucidate that LE deliberately leverages multiple roles for inorganic NBG perovskite growth and anticipate our study provides insightful guideline for developing high-efficiency and stable IPTSCs.