Synchronized B-site alloying for high-efficiency inorganic tin-lead perovskite solar cells

Inorganic tin-lead perovskites with low bandgap (1.2-1.4 eV) are desired absorber materials for solar cells owing to their ideal bandgap and compositional stability. However, such tin-lead perovskites are currently subject to inferior power conversion efficiency (PCE) and the origin remains unclear. Here, for the first time, we report the metal-cation-derived unsynchronized crystallization behavior of inorganic tin-lead perovskite, exemplifying by a representative composition CsPb_0.7Sn_0.3I₃. A tin-perovskite-targeted crystallization modulation agent, 1-(4-fluorophenyl) piperazine (1-4FP), is introduced to synchronize the B-site alloying through its strong targeted bonding with SnI₂, resulting in substantially enhanced film quality with better morphology and photoelectrical properties. Furthermore, first-principles molecular dynamics simulations reveal that the agent regulates the crystallization route toward the pure phase of CsPb_0.7Sn_0.3I₃ by suppressing the preforming of tin perovskite. With our proposed approach, the best device attains PCE of 17.55%, which is record-high for inorganic tin-lead perovskite solar cells. In addition, treated devices show excellent stability with only 10% and negligible loss after being exposed to 1 sun intensity for 700 h and being stored in N₂ after over 4000 h, respectively. Our findings open a new avenue of crystallization route design in inorganic tin-lead perovskites, so as to obtaining high-quality perovskite films and associated solar cells.