Incorporating multiple cations of the IA alkali metal column of the periodic table (K + /Rb + /Cs +) to prepare perovskite films is promising for boosting the photovoltaic properties. However, contrary to K + , both Cs + and Rb + suffer from non-uniformity at the origin of performance and stability losses. In this paper, Ammonium chloride (NH4Cl) additive is shown to address this concern. We analyze step-by-step the effects of NH4Cl Additive and Alkali Metal Cations (K + /Rb + /Cs +) on the one-step film formation process of methylammoniumfree, formamidinium-based, halide perovskites. First, we highlight the action of NH4Cl additive on the spincoating and the anti-solvent dripping processes. We show that it improves the solubility of PbI2 in solution by forming an intermediate and then favor the perovskite phase formation. Then, we investigate the annealing process, showing the increased grain size, improved crystallinity and PbI2 suppression by adding NH4Cl.