Stability of formamidinium tin triiodide-based inverted perovskite solar cells

Enormous progress has been made in formamidinium tin triiodide (FASnI3)-based inverted perovskite solar cells (IPSCs). However, the instability issue remains a significant obstacle in both the fabrication and evaluation of the entire device. According to the lessons learned from lead-based PSCs, stability is difficult to address compared to other performance metrics during the optimization process. Therefore, it is imperative to explore the sources of instability and the underlying pathways of device degradation, especially in PSCs incorporating sensitive Sn2+. This review begins by introducing the prevalent light absorber and device structure in lead-free Sn-based IPSCs. The rationale behind the widespread utilization of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in Sn-based PSCs is thoroughly examined. Then, the principal degradation mechanisms and potential reactions are assessed under different stress conditions. Based on the International Summit on Organic Photovoltaic Stability protocols, recent strategies for improving device stability are systematically summarized, including the engineering of solvents, components, additives, and passivation on perovskite or PEDOT:PSS. The final section offers insights into addressing current challenges and provides perspectives about the future development of stable Sn-based IPSCs.