Molecular Passivation with 2‐Aminobenzothiazole Enables Efficient and Stable Ruddlesden–Popper Tin Perovskite Solar Cells

Tin‐halide perovskite solar cells (SnPSCs) have emerged as a promising alternative to lead‐based ones due to their lower toxicity and rapidly improving photovoltaic conversion efficiency (PCE). However, high‐performance SnPSCs typically rely on three‐dimensional tin perovskites, which suffer from poor stability caused by the oxidation of Sn 2+ to Sn 4+ . Quasi‐two‐dimensional (q‐2D) tin‐halide perovskites offer improved stability due to the hydrophobic nature of bulky organic spacer cations. Nevertheless, q‐2D SnPSCs based on 2‐phenylethylamine hydroiodide (PEAI) and PC 61 BM often exhibit limited PCE, largely due to unfavorable energy‐level alignment between the perovskite absorber layer, PEDOT:PSS, and PC 61 BM. Herein, 2‐aminobenzothiazole (2‐ABZ) is introduced as an additive into a q‐2D perovskite layer with the composition (PEA 0 . 85 EA 0 . 15 ) 2 FA 4 Sn 5 I 14 . 3 Br 1 . 7 ( n = 5). The incorporation of 2‐ABZ effectively tunes the energy levels of the perovskite absorber to improve alignment with PEDOT:PSS and reduce the energy offset with PC 61 BM. Additionally, the N–H···I interaction formed by 2‐ABZ suppresses iodide migration and inhibits Sn 2+ oxidation, enhancing device stability. As a result, the optimized devices achieve a PCE of 9.07%, compared to 6.60% for the control. Furthermore, the modified devices retain 84.96% of their initial efficiency after 100 days of storage, whereas the control devices lose approximately 51% of their initial performance.