The use of layered perovskites is an important strategy to stabilize a formamidinium (FA) based photoactive α-FAPbI₃ phase. However, the growth mechanism of FA-based layered perovskites and its influence on their physical properties have not yet been reported. Herein, we demonstrate an inclusive study on the growth, structure and optoelectronic properties of FA-based Ruddlesden–Popper (RP) type perovskites M₂FA_n−1Pb_nI_3n+1 (M = benzylamine (PMA) or FA) during two-step sequential deposition, revealing the transformation of dominant layered perovskites from PMA₂FA_n−1Pb_nI_3n+1 to novel FA₂FA_n−1Pb_nI_3n+1 with increasing FA : PMA ratios in precursors, and increased n values from top to bottom for the former case while a uniform distribution for the latter case. Moreover, we investigated the charge transport kinetics between quantum wells and illustrate the application of these structures in perovskite solar cells with a power conversion efficiency that exceeds 19%, accompanied by enhanced film stability in contrast to 3D analogs.