Abstract
The low toxicity, narrow bandgaps, and high charge-carrier mobilities make tin perovskites the most promising light absorbers for low-cost perovskite solar cells (PSCs). However, the development of the Sn-based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn(2+) to Sn(4+) and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI(3)) film via ion exchange/insertion reactions between solid-state SnF(2) and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI(3) can be well controlled, and a highly uniform pinhole-free MASnI(3) perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI(3) film due to the presence of a large amount of remaining SnF(2). This high-quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI(3)-based solar cells. Moreover, the MASnI(3) solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low-cost and lead-free tin-based halide perovskite solar cells.