OPTIMIZING LEAD-FREE CsGeI<sub>3</sub> PEROVSKITE SOLAR CELLS: SCAPS-1D SIMULATION ACHIEVING 27.34% EFFICIENCY THROUGH LAYER THICKNESS AND BAND ALIGNMENT TUNING

Lead-free perovskite solar cells (PSCs) present a sustainable alternative to conventional lead-based devices by mitigating toxicity concerns. In this work, we use SCAPS-1D numerical simulations to optimize an all-inorganic CsGeI3-based PSC structure incorporating TiO2 as the ETL and CuSCN as the HTL. The study systematically explores the influence of absorber thickness (300-700 nm), ETL thickness (50-250 nm), HTL thickness (100-500 nm), and the electron affinities of each layer (CsGeI3; 3.9-4.1 eV; TiO2: 4.18-4.34 eV; CuSCN: 1.6-1.8 eV) on device performance. Key photovoltaic parameters VOC, JSC, FF, and PCE are analyzed under these variations. The optimized device achieves a PCE of 27.34%, with VOC ≈ 1.33 V, JSC ≈ 23.59 mAcm-2, and FF ≈ 86.89%. These enhancements are attributed to efficient charge carrier generation, reduced recombination, and favorable band alignment. The external quantum efficiency approaches 100% across the 390-700 nm wavelength range, indicating strong visible-light absorption. Overall, the results demonstrate the high potential of CsGeI3 for environmentally friendly, high-performance PSCs and provide valuable design guidelines to support experimental realization in renewable energy applications.