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 CH₃NH₃SnIxBr3-x (0 ≤ x ≤ 3)-based solar cell, with the primary study focusing on the impact of the "I" concentration in CH₃NH₃SnIxBr3-x material on the device output parameters in terms of short circuit current density (JSC), open circuit potential (VOC), 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 CH₃NH₃SnIxBr3-x 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 JSC of 34.69 mA/cm², a VOC of 1.13 V, and a FF of 82.23%. Introducing interfacial defects (10¹⁵ cm⁻²) led to adjustments in the values, such as JSC = 34.05 mA/cm², VOC = 1.038 V, FF = 86.72%, and PCE = 30.66%.