LAUSR

Abstract The α-HC(NH 2 ) 2 PbI 3 (FAPbI 3 ) perovskite with narrower band gap and higher thermal stability is a promising candidate for high performance perovskite optoelectronic applications. However, it is difficult to achieve fast growth of a phase pure α-FAPbI 3 perovskite because the unwanted δ-FAPbI 3 usually first forms at lower temperature then converted into the wanted α-FAPbI 3 at higher temperature. It takes long time annealing to complete the conversion of δ-FAPbI 3 to α-FAPbI 3 , which could also lead to uncontrollable degradation of α-FAPbI 3. Here we report a facile flash deposition of large grain phase pure α-FAPbI 3 without any δ-FAPbI 3 impurity by inhibiting the δ phase crystallization. In this method, a simple PMMA sealing to synchronize a flash α-crystallization process at appropriate temperature with the unwanted δ phase crystallization. Consequently, a high quality phase pure α-FAPbI 3 with large grain size was fabricated into high performance perovskite solar cells. The strategy of flash crystallization would be a promising method for deposition of phase pure perovskite in future.