Recognizing that no photovoltaic device can entirely eliminate series resistance, a practical value of Rs=1Ω was chosen for further optimization. For MAPbI3-based cells, the optimized parameters at Rs=1Ω are Voc=1.10V, Jsc=28.47 mA, FF = 86.42%, and η=27.10%. Similarly, MASnI3-based cells show optimized performance with Rs=1Ω, where Voc=0.97V, Jsc=34.89mA/cm2, FF = 82.51%, and η=27.98%. Fig. highlights the device behavior under ideal and non-ideal conditions. When Rs=0Ω, the device achieves a maximum efficiency of 29.1%. However, with Rs=6Ω, the efficiency declines sharply to 22.45%. This confirms that higher series resistance significantly impacts the device performance, even though Voc remains relatively constant. The simulation results further demonstrate that both Jsc and FF reach minimal values as Rs increases from 1 Ω to 6 Ω.