Sn‐Pb Perovskite with Strong Light and Oxygen Stability for All‐Perovskite Tandem Solar Cells

Research on mixed Sn-Pb perovskite solar cells (PSCs) is gaining significant attention due to their potential for high efficiency in all-perovskite tandem solar cells. However, Sn²⁺ in Sn-Pb perovskite is susceptible to oxidation, leading to a high defect density. The oxidation primarily occurs through two pathways: one involving a reaction with oxygen, and the other related to iodine defects, which generate I₂ and further accelerate the oxidation of Sn²⁺, greatly reducing stability. First, to tackle the photo-stability issues caused by iodine defects, amber acid (AA) is screened as the additive. The Carboxyl group on AA can strongly coordinate with Sn²⁺, reinforcing the Sn─I bond and electrostatically interacting with negatively charged defects. This interaction inhibits the photoinduced formation of I₂ and the subsequent oxidation of Sn²⁺, thereby enhancing the stability of Sn─Pb PSCs under continuous illumination. Building on the foundation of AA, a reductive sulfhydryl group is introduced to synthesize thiomalic acid (TA). It inhibits the formation of Sn⁴⁺ in both the perovskite precursor and the perovskite film, thereby improving air stability while maintaining strong photostability. Consequently, single PSCs achieved a champion efficiency of 22.7%. The best-performing two-terminal all-perovskite tandem solar cell achieved a power conversion efficiency of 28.6% with improved operational stability.