Addressing challenges related to the structural defects, ion migration, and instability in perovskite solar cells, this study investigates the impact of incorporating methylammonium chloride (MACl) into the perovskite precursor solution. The optimal addition of MACl (10 mg/mL) resulted in perovskite films with grain growth improvement and fewer grain boundaries, as observed by field emission scanning electron microscopy. Furthermore, X-ray diffraction analysis showed an increased preferential orientation along the (001) and (002) crystal planes, while UV-Vis and photoluminescence spectroscopy data indicated smooth surface and reduced defects induced recombination. Consequently, the fabricated PSCs with the optimized composition achieved a power conversion efficiency of 14.56%, representing a significant improvement over the control device (12.81%) and the sample with excess MACl (20 mg/mL, 13.43%). This enhanced performance was attributed to improvements in all photovoltaic parameters, along with a notable reduction in the hysteresis index, indicating suppressed ion migration. Electrochemical impedance spectroscopy analysis further supported these improvements by revealing reduced charge transfer resistance and enhanced recombination resistance. Importantly, the optimized devices demonstrated enhanced power output, retaining 85% of their initial performance after 120 s light soaking. These results indicate that optimized MACl incorporation is an effective strategy for simultaneously improving the efficiency and stability of PSCs by enhancing crystallinity, suppressing ion migration, and promoting defect passivation.