This study presents a comprehensive investigation of defect passivation strategies in perovskite thin films, with a particular focus on the incorporation of excess PbI₂ through surface and bulk treatments. A combination of experimental techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and time-resolved photoluminescence (TRPL), was employed to characterize structural integrity, chemical composition, and carrier recombination dynamics. The results demonstrate that excess PbI₂ can be introduced without compromising the perovskite crystal phase, and that passivated films exhibit prolonged carrier lifetimes, indicative of suppressed non-radiative recombination. Numerical simulations of carrier diffusion and recombination further elucidated the impact of surface recombination velocity, initial excitation profiles, and nonlinear recombination kinetics on carrier dynamics. While limitations due to material aging and instrumentation constraints are acknowledged, preliminary modeling has been successfully implemented. The findings show the potential of PbI₂-based passivation to enhance perovskite properties, and the modeling efforts provide a powerful framework for interpreting recombination dynamics based on physical parameters and guiding future passivation strategies in perovskite solar cells.