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

Tin perovskite is rising as the mostpromising lead-freeperovskitefor photovoltaic applications. However, the uncontrollable kineticsof crystal growth brings poor crystal quality with a poor orientationand large defect density. In this work, we explored formamidine acetate(FAAc) and ammonium iodide (NH4I) to replace the generallyused formamidinium iodide (FAI) in the growth of a tin perovskitefilm. This triple reagent (FAAc + NH4I + SnI2) method prolongs the reaction path for the growth of the tin perovskitefilm. It impedes the growth of a three-dimensional (3D) perovskitestructure at room temperature while having less impact on the growthof a low-dimensional structure. As a result, the low-dimensional structureformed at room temperature serves as a seed structure for 3D structuregrowth in subsequent annealing. The tin perovskite film grown usingthis triple reactant source hence shows enhanced orientation and longcarrier lifetimes, leading to an efficiency of 14.6% for tin perovskitesolar cells.