Design and Performance Analysis of Lead-Free CsGeI3/ Cs2AgBiBr6 Double Perovskite Solar Cell with Interfacial Layers for Enhanced Efficiency

Perovskite solar cells (PSCs) have garnered considerable attention due to their rapidly advancing power conversion efficiencies. Among them, inorganic perovskite-based devices have shown remarkable performance and improved durability, making them promising candidates for next-generation solar technologies. This study offers a comprehensive analysis and design of a novel, lead-free double perovskite solar cell (DPSC) that employs $\text{CsGeI}_{3}$ and $\text{Cs}_{2} \text{AgBi} \text{Br}_{6}$ as absorber materials. To enhance both the efficiency and stability of the device, graphene and 3C-silicon carbide (3C-SiC) are introduced as interfacial layers. The device configuration is carefully optimized by reducing defect densities, adjusting layer thicknesses and doping levels, and selecting appropriate hole and electron transport layers with well-aligned energy bands. This uniquely designed, lead-free, and highly stable double perovskite solar cell structure, FTO/CdS/3C-SiC/ CsGeI ${ }_{3} / \mathrm{C} \mathrm{s}_{2} \text{AgBi} \text{Br}_{6} / \text{Graphene}^{-} / \text{CNTS} / \text{Pt}$, demonstrates outstanding performance with a fill factor (FF) of 90.84 %, a power conversion efficiency (PCE) of 30.03 %, an open-circuit voltage (Voc) of 1.44 V, and a short-circuit current density (Jsc) of $22.97 \text{mA} / \text{cm}^{2}$. This design demonstrates a strategic combination of materials engineering and interface optimization, paving the way for efficient, environmentfriendly, and lead-free materials for developing highperformance DPSCs, supporting their potential for future deployment and commercialization.