Single-source evaporation of CH3NH3SnI3 for Pb-free perovskite solar cells

Sn-based perovskite is the most promising candidate as environmentally benign and Pb-free perovskite; however, the nonuniform morphology of Sn-based perovskite thin films caused by rapid crystallization is a major issue. We demonstrate how pure CH3NH3SnI3 (CH3NH3 = methylammonium, MA) thin films can be uniformly deposited by the single-source evaporation of presynthesized MASnI(3) crystals. The perovskite crystals are synthesized by cooling crystallization under an ambient atmosphere and sublimed without decomposition by controlling the heating rate. The evaporated thin films were postannealed at various temperatures and times, which resulted in a pinhole-free microstructure with an average grain size of 423 nm. The average power conversion efficiency (PCE) of planar-type solar cells based on the optimized perovskite thin films was 1.7% +/- 0.1%.