Different concentrations of NH4Cl are introduced to MAPbI3 precursor solution, planar MAPbI3 perovskite films, and solar cells’ performance with or without NH4Cl have been studied. The NH4Cl/MAPbI3 films exhibit increased grain size and narrowed grain boundaries. The light absorption of perovskite films with different concentrations of NH4Cl was also evaluated. To understand the growth of perovskite films with NH4Cl added to perovskite precursor solutions, XRD and XPS spectroscopy were conducted on different perovskite film samples. By adding NH4Cl, the MAPbI3 film shows good crystal quality and the shift of Pb peaks indicates that NH4Cl is not physically mixed but chemically incorporated into MAPbI3 films. We attribute the effect to Cl ions of NH4Cl combining with free lead ions of MAPbI3 so as to fill the vacancy of volatile I ions in the NH4Cl–MAPbI3 films. The 20 mg NH4Cl-based device showed an enhanced performance of a PCE of 13.67% compared to the device without adding NH4Cl with a PCE of 10.24%. The introduction of 20 mg NH4Cl achieved the best passivation effect. Using a 20 mg NH4Cl device, the trap density can be reduced to 0.84 × 1016 cm−3, resulting in more efficient charge removal from the surface and improved performance.