Ultrafast Light‐Driven Molecular Engineering for Dynamic Elimination of Buried Interfacial DMSO Residuals in Two‐Step Fabricated Perovskite Solar Cells

Residual dimethyl sulfoxide (DMSO) trapped at buried interfaces severely limits the performance of two‐step processed perovskite solar cells (PSCs). Conventional interfacial modifications fail to fully remove these residuals due to their limited effective range. Here, a light‐responsive molecular engineering strategy is introduced using 4′‐aminoazobenzene‐4‐sulfonic acid (AABSA) at the SnO 2 /perovskite interface. AABSA serves as a photoactive switch capable of ultrafast (sub‐picosecond) UV‐triggered reversible isomerization. This dynamic approach enables in situ, continuous removal of residual DMSO while simultaneously enhancing crystallization, reducing interfacial strain, and improving charge transport, overcoming the spatial constraints of static interfacial modifications. As a result, n‐i‐p PSCs achieve a champion power conversion efficiency of 26.01%, while retaining >91% of their initial performance after >4500 h in ambient air and >700 h under continuous 1‐sun illumination. This work pioneers dynamic interfacial control via light‐driven molecular engineering, offering a universal pathway toward stable, high‐efficiency photovoltaics.