Especially, strong non-radiative recombination in all reported FA-Cs based PSCs limited the open-circuit voltage (Voc) of the resulting devices . The FA1-xCsxPbI3 perovskite films are firstly prepared by the crystallization decoupling engineering. A FAPbI3 precursor film is firstly deposited by a typical anti-solvent method. The Cs is sequentially introduced onto the FA perovskite film. For comparison, we employed different content of Cs to fabricate FA1-xCsxPbI3 perovskites. The final ratios of Cs in the FA1-xCsxPbI3 perovskite films, i.e., the value of x, are 0.05, 0.09 and 0.16, as confirmed by inductively coupled plasma-mass spectrometry (ICP-MS) analysis (Table ). The corresponding FA1-xCsxPbI3 perovskite films are noted as x=0.05, x=0.09, x=0. .