Alleviating the Crystallization Dynamics and Suppressing the Oxidation Process for Tin‐Based Perovskite Solar Cells with Fill Factors Exceeding 80 Percent

Abstract The low toxicity and a near‐ideal bandgap endow tin (Sn)‐based perovskite solar cells (TPSCs) a promising future in photovoltaic technologies. However, in general the Sn‐based perovskites suffer from poor resistance to oxidation and fast crystallization dynamics, resulting in low fill factors (FFs) and power conversion efficiencies (PCEs). Herein, a strategy to improve the performance of TPSCs by incorporating 2‐(2‐aminoethyl)–2‐thiopseudourea dihydrobromide (AET) into the Sn‐based perovskites is proposed. AET interacts strongly with the Sn‐based perovskites, and thus effectively inhibits the oxidation from Sn2+ to Sn4+ and slows down the crystallization process. As a result, the TPSCs with AET achieve a high FF of 80.26% and a high PCE of 13.55%. Notably, this FF value represents the highest reported in the field of TPSCs with narrow bandgaps. Furthermore, encapsulated TPSCs demonstrate good stability, maintaining 80% of their initial performance over the course of 700 h.