Thermally Evaporated Methylammonium Tin Triiodide Thin Films for Lead-Free Perovskite Solar Cell Fabrication

We report on the synthesis of methylammonium tin triiodide (MASnI₃) 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 MASnI₃ 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 MASnI₃ 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 MASnI₃ perovskite thin films which can be used to fabricate efficient Pb-free perovskite solar cells.