A facile deposition of large grain and phase pure α-FAPbI3 for perovskite solar cells via a flash crystallization

The α-HC(NH2)2PbI3 (FAPbI3) 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-FAPbI3 perovskite because the unwanted δ-FAPbI3 usually first forms at lower temperature then converted into the wanted α-FAPbI3 at higher temperature. It takes long time annealing to complete the conversion of δ-FAPbI3 to α-FAPbI3, which could also lead to uncontrollable degradation of α-FAPbI3. Here we report a facile flash deposition of large grain phase pure α-FAPbI3 without any δ-FAPbI3 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-FAPbI3 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.