Design and Optimization of a Novel Double-Heterojunction Lead-Free Cs₂BiAgI₆ Perovskite Solar Cell with PCBM/C₆₀ Bilayer ETL and CdTe HTL: Numerical Investigation

In this study, a lead-free double perovskite solar cell structure based on Cs2BiAgI6 was simulated and optimized to enhance photovoltaic performance. The device architecture follows the configuration: ITO/PCBM/C60/Cs2BiAgI6/CdTe/Au. The thicknesses of the electron transport layer (ETL), absorber layer, and hole transport layer (HTL) are systematically optimized to evaluate their impact on key performance parameters. The results indicate that optimal performance is achieved with 600 nm thicknesses for all ETLs and HTL, and 2 μm for the Cs2BiAgl6 absorber. Under these conditions, the device exhibits a short-circuit current density of 23.23 mA/cm2, an open-circuit voltage of 1.08 V, and a fill factor of 86.35%, resulting in a power conversion efficiency exceeding 22%. The improved performance is attributed to favorable energy band alignment and enhanced charge transport, which together facilitate efficient carrier extraction and reduce recombination losses. In addition, the device demonstrates a high quantum efficiency of approximately 96% within the 200–733 nm wavelength range. These findings highlight the promise of lead-free perovskite solar cells in delivering high performance while offering a more sustainable and environmentally friendly alternative to traditional lead-based technologies.