Figure illustrates the detrimental effects of elevated defect density on cell performance. As the defect density increases, all output parameters show a consistent decline. This performance degradation is primarily due to a reduction in carrier diffusion length and carrier lifetime, as shown in the analysis. The diffusion length, which is proportional to the square root of carrier lifetime and mobility, decreases significantly with rising defect density. Consequently, fewer photogenerated carriers reach the respective contacts, leading to increased recombination within the bulk absorber material and at interfaces. For example, higher defect densities exacerbate bulk and interface recombination rates, as confirmed by numerical modeling studies. Defect states within the bandgap serve as centers for charge trapping and recombination, directly reducing carrier mobility and extraction efficiency. As a result, the effective carrier concentration within the absorber layer diminishes, further decreasing photocurrent generation and PCE Optimization of the defect density is critical for achieving high efficiency in PSCs. In this study, we selected an optimal defect density of 1×10 14 1/cm 3 , a value supported by prior experimental and simulation research indicating minimal recombination losses and sufficient carrier transport under such conditions . This optimized defect density ensures extended carrier lifetime and diffusion length, enabling more efficient charge collection and significantly enhancing the cell's overall performance.