Role of formamidinium in the crystallization of FAxMA1-xPbI3-yCly perovskite via recrystallization-assisted bath-immersion sequential ambient deposition

Abstract Crystallization control plays a key role in the preparation of high-quality perovskite absorbers, which is particularly critical in ambient-process fabrications. FA/MA (FA+ = formamidinium, MA+ = methylammonium) mixed perovskite solar cells (PVSCs) have been reported to exhibit a higher performance than MA-based devices. Here, we systematically study the role of FA in the sequential crystallization of FAxMA1-xPbI3-yCly mixed-ion perovskite prepared by recrystallization-assisted bath-immersion method. A dramatic different morphology of bath-immersed perovskite films is observed when using FA and MA based bath solutions, while it is consistently reconstructed after recrystallization. A considerably enhanced selective growth of (110) and (220) domains toward out-of-plane orientation is observed when involving FA into MA-based perovskite. The morphology and efficiency evolution are systematically studied while changing the FA-involvement ratio. Benefiting from improved crystal quality and extended absorption edge, an enhancement in device efficiency has been observed.