The perovskite film-manufactured via a one-step method-was superficially improved through an anti-solvent process to increase solar cell efficiency. Although perovskite synthesis proceeds rapidly, a significant amount of lead iodide residue remains. Well-placed lead iodide in perovskite grains prevents electron-hole recombination; however, when irregularly placed, it interferes with the movement of electron and holes. In this study, we focused on improving the crystallinity of the perovskite layer, as well as reducing lead iodide residues by adding a methylammonium halide material to the anti-solvent. Methylammonium iodide in chlorobenzene used as an anti-solvent reduces lead iodide residues and improves the crystallinity of formamidinium lead iodide perovskite. The improved crystallinity of the perovskite layer increased the absorbance and, with reduced lead iodide residues, increased the efficiency of the perovskite solar cell by 1.914%.