Thermally evaporated methylammonium tin triiodide thin films for lead-free perovskite solar cell fabrication

We report on the synthesis of methylammonium tin triiodide (MASnI(3)) thin films at room temperature by a hybrid thermal evaporation method and their application in fabricating lead (Pb)-free perovskite solar cells. The as-deposited MASnI(3) thin films exhibit smooth surfaces, uniform coverage across the entire substrate, and strong crystallographic preferred orientation along the < 100 > direction. By incorporating this film with an inverted planar device architecture, our Pb-free perovskite solar cells are able to achieve an open-circuit voltage (V-OC) up to 494 mV. The relatively high V-OC is mainly ascribed to the excellent surface coverage, the compact morphology, the good stoichiometry control of the MASnI(3) thin films, and the effective passivation of the electron-blocking and hole-blocking layers. Our results demonstrate the potential capability of the hybrid evaporation method to prepare high-quality Pb-free MASnI(3) perovskite thin films which can be used to fabricate efficient Pb-free perovskite solar cells.