Multifaceted Reductant for Buried Interface Modification of Tin‐Based Perovskite Solar Cells by Concurrently Suppressing Sn‐Oxidation and Facilitating Energy‐Alignment

Advancing environmentally‐benign tin halide perovskite solar cells (Sn‐PSCs) has encountered numerous critical obstacles, leading to severe efficiency and stability losses. Both the Sn 2+ oxidation triggered by the corrosion of hole‐transporting layers (HTLs) and the energy‐level mismatch at the perovskites/HTL interfaces seem to be less investigated. This study introduces dopamine hydrochloride (DACl) as a dual‐functional reductant for buried interface modification. When deposited onto the HTL surface, DACl forms multiple hydrogen and coordination bonds with both the perovskite and HTLs through −NH 3 + and −OH groups, concurrently suppressing Sn 2+ oxidation, neutralizing HTL corrosiveness, and aligning energy levels. Intriguingly, when applicable to PEDOT:PSS and NiO x HTLs in Sn‐PSCs, they present distinct mechanisms yet comparable efficiencies of 14.18% and 14.11%, respectively. Both unencapsulated devices retain > 80% initial efficiency after 1000 h in Ar atmosphere. This work manifests a universal approach to strengthen interfacial stability and hole extraction in Sn‐PSCs regardless of the HTL types, with new insights into designing appropriate HTLs for lead‐free perovskite optoelectronics.