Investigation of “I” Variations in CH ₃ NH ₃ SnI _x Br _{3– x} Perovskite Solar Cells: Simulation-Driven Selection and Optimization of CH ₃ NH ₃ SnI ₃

This work reports the design and optimization of a CH 3 NH 3 SnI x Br 3– x (0 ≤ x ≤ 3)-based solar cell, with the primary study focusing on the impact of the “I” concentration in CH 3 NH 3 SnI x Br 3– x material on the device output parameters in terms of short circuit current density ( J SC ), open circuit potential ( V OC ), fill factor (FF), and power conversion efficiency (PCE). This study is backed by a brief discussion using density functional theory (DFT) analysis of the structural and electronic properties of the perovskite material. The solar cell achieved optimal performance when the value of x in CH 3 NH 3 SnI x Br 3– x was set to 3, meaning that CH 3 NH 3 SnI 3 served as the absorber layer. With CH 3 NH 3 SnI 3 as the absorber, the solar cell was further refined by adjusting the absorber thickness, doping density, and both internal and interfacial defect densities. The optimized solar cell attained a PCE of ∼34.05% at a thickness of 1 μm and a doping density of 3.2 × 10 15 cm –3, assuming no defects. When internal defects were factored in, the PCE decreased to ∼32.33%, with a J SC of 34.69 mA/cm 2, a V OC of 1.13 V, and a FF of 82.23%. Introducing interfacial defects (10 15 cm –2 ) led to adjustments in the values, such as J SC = 34.05 mA/cm 2, V OC = 1.038 V, FF = 86.72%, and PCE = 30.66%.