FA/Cs-based mixed Pb–Sn perovskite solar cells: A review of recent advances in stability and efficiency

Perovskite solar cells (PSCs) have gained widespread attention due to their impressive optoelectronic properties, extraordinarily high efficiency, and low-cost manufacturing processes. PSCs are poised to usher in a new era of clean energy production. However, the use of methylammonium (MA) as the A-site cation in PSCs may result in poor thermal and atmospheric stability, limiting their potential for widespread commercialization. On the other hand, the most extensively studied perovskite systems with respect to B-site cations are pure Pb-based compositions due to their high device performance demonstrated to date. However, mixed Pb–Sn compositions can offer optimal bandgap energies for single-junction solar cells, suggesting the promise of future efficiency improvements. Thus, this review focuses on mixed Pb–Sn perovskite solar cells that use formamidinium (FA) or mixed cations of FA and cesium (Cs) without MA. These materials have bandgap energies suitable for use in either single-junction or multi-junction solar cells and show improved stability compared to their MA-based counterparts. We discuss the structural and optoelectronic properties of FA/Cs-based Pb–Sn perovskites and the efforts to improve their solar cell performance and stability through additive engineering, process optimization, and structural modifications. Our review highlights the potential for FA/Cs-based mixed Pb–Sn perovskites as a more stable and efficient alternative for future commercial applications of PSCs.