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

This work reports the design and optimization of a CH₃NH₃SnI_<i>x</i>Br_3-<i>x</i> (0 ≤ <i>x</i> ≤ 3)-based solar cell, with the primary study focusing on the impact of the "I" concentration in CH₃NH₃SnI_<i>x</i>Br_3-<i>x</i> material on the device output parameters in terms of short circuit current density (<i>J</i>_SC), open circuit potential (<i>V</i>_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 <i>x</i> in CH₃NH₃SnI_<i>x</i>Br_3-<i>x</i> was set to 3, meaning that CH₃NH₃SnI₃ served as the absorber layer. With CH₃NH₃SnI₃ 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 × 10¹⁵ cm^-3, assuming no defects. When internal defects were factored in, the PCE decreased to ∼32.33%, with a <i>J</i>_SC of 34.69 mA/cm², a <i>V</i>_OC of 1.13 V, and a FF of 82.23%. Introducing interfacial defects (10¹⁵ cm^-2) led to adjustments in the values, such as <i>J</i>_SC = 34.05 mA/cm², <i>V</i>_OC = 1.038 V, FF = 86.72%, and PCE = 30.66%.