Robust Defect Passivation for Stable Tin Perovskite Solar Cells via Suppression of Sn²⁺ Oxidation and I– Loss

Tin halide perovskites (THPs) have sparked considerable research interest in the field of photovoltaics, photodetectors, light-emitting diodes, lasers, and transistors. However, the advancements of efficiency and stability in tin perovskite solar cells (TPSCs) are impeded by severe Sn2+ oxidation and stuctual imperfections. Here, we report sodium triacetoxyborohydride (BNa3Ac) as a multifunctional defect passivator for THPs. The strong chemical interaction between THPs and BNa3Ac groups (C═O, B–H and Na+) not only inhibited the oxidation of Sn2+ and the migration of I– and passivated the corresponding defects but also promoted the deposition of high-quality films. Meantime, it also has a strong N–H···O hydrogen bond interaction with FAI and MABr, which can stabilize the perovskite structure. As a consequence, perovskite films with BNa3Ac exhibit increased carrier lifetime and reduced nonradiative recombination. The oxidation level is also substantially reduced in BNa3Ac films, leading to restrained p-type doping in THPs. Accordingly, the BNa3Ac films demonstrate a notable reduction in electron trap density (from 1.30 × 1016 cm–3 to 9.19 × 1015 cm–3) and hole trap density (from 2.24 × 1016 cm–3 to 1.83 × 1016 cm–3), respectively. Therefore, the open-circuit voltage of the BNa3Ac device exhibits a significant increase from 857 to 906 mV, generating a champion power conversion efficiency of 13.33%. The unencapsulated BNa3Ac device also exhibits outstanding stability over 2200 h in an N2 atmosphere.