Performance-Optimized Lead-Free Double Perovskites: A Comparative Study of (FA)2BiCuI6 and Cs2BiCuI6 Solar Cells

The toxicity and instability of lead-based perovskite solar cells (PSCs) have intensified the need for eco-friendly alternatives that have driven research into lead-free options such as (FA)₂BiCuI₆ and Cs₂BiCuI₆-based double perovskites. An extensive computational analysis and performance optimization are executed via SCAPS-1D simulations. The photovoltaic performance of (FA)₂BiCuI₆ and Cs₂BiCuI₆-based solar cells has been evaluated using different electron and hole transport layer combinations. In this work, the photovoltaic performance optimization has been simulated across different HTL (CBTS, CFTS, GO) and ETL (SnS₂, In₂S₃₃, WS₂) combinations in the proposed device design to optimize power conversion efficiency. According to simulations, the optimized FTO/WS₂/Cs₂BiCuI₆/CBTS/Au architecture achieves a PCE of 27.57%, significantly higher than the 20.32% efficiency of the FTO/WS₂/(FA)₂BiCuI₆/CBTS/Au design. The implementation of bandgap grading in absorber layers boosts cell efficiencies to 20.61% and 27.94% by suppressing interfacial recombination. The investigation has been further analyzed for several critical parameters, focusing on absorber defect concentrations, generation-recombination rates, and temperature effects. These findings have driven significant progress in eco-friendly double perovskite solar cells (PSCs), improving efficiency and paving the way for widespread adoption.