Guest effect of N-butylammonium iodide for stable α-phase formamidinium perovskite via sequential deposition method

Formamidinium lead iodide perovskite (FAPbI₃) is widely employed in photovoltaic area because of its better stability and high potential of efficiency compared to methylammonium lead iodide (MAPbI₃). However, the α-phase FAPbI₃ that is beneficial for high performance solar cells is not stable in air. Here, N-butylammonium Iodide (BAI) was used to slice PbI₂ precursor via guest effect. Subsequently, this BAI-PbI₂ film transforms to FAPbI₃ through the reaction with FAI solution. Meanwhile, the existence of BA accelerates the formation of α-phase FAPbI₃. We find the α-phase FAPbI₃ film based on BAI-PbI₂ precursor film shows much better stability in air, the better surface morphology and crystallization than those of the control FAPbI₃ film based on normal PbI₂ precursor. The obtained stable α-phase FAPbI₃ films are potential excellent materials for stable and high performance perovskite optoelectronic derives.