Mechanistic insights into performance limitation and optimization of lead-free double perovskite Cs2BiAgI6 solar cells

Lead-free double perovskites have emerged as promising alternatives to lead-based absorbers in perovskite solar cells due to their enhanced stability and environmentally benign nature. This study systematically investigates the key parameters influencing the performance of the FTO/ZnO/Cs2BiAgI6/CuSCN/Au solar cell, with a primary focus on optimizing its power conversion efficiency (PCE) using the SCAPS-1D software. Variations in electron affinity, impurity concentration, and defect density are found to impact device performance significantly. A lower electron affinity facilitates improved charge transport, thereby enhancing overall device efficiency. An optimal impurity concentration of Cs2BiAgI6 at 1 × 1018 cm–3 yields a maximum PCE of 18.95%. Additionally, increasing the ambient temperature from 300 K to 400 K leads to a decline in PCE from 16.77% to 11.89%. To evaluate the effect of series resistance, its value was varied from 1 to 5 Ω.cm2, resulting in a decrease in PCE from 21.20% to 19.21%. The highest quantum efficiency is observed at a short wavelength of 370 nm. The optimized PCE of 21.20% achieved in this study exceeds previously reported values, highlighting the significant potential of Cs2BiAgI6-based devices in the development of high-performance, lead-free photovoltaic technologies.