Highly Efficient Tin Perovskite Solar Cells Based on a Triple Reactant Strategy

Tin perovskite is rising as the most promising lead-free perovskite for photovoltaic applications. However, the uncontrollable kinetics of crystal growth brings poor crystal quality with a poor orientation and large defect density. In this work, we explored formamidine acetate (FAAc) and ammonium iodide (NH 4 I) to replace the generally used formamidinium iodide (FAI) in the growth of a tin perovskite film. This triple reagent (FAAc + NH 4 I + SnI 2 ) method prolongs the reaction path for the growth of the tin perovskite film. It impedes the growth of a three-dimensional (3D) perovskite structure at room temperature while having less impact on the growth of a low-dimensional structure. As a result, the low-dimensional structure formed at room temperature serves as a seed structure for 3D structure growth in subsequent annealing. The tin perovskite film grown using this triple reactant source hence shows enhanced orientation and long carrier lifetimes, leading to an efficiency of 14.6% for tin perovskite solar cells.