Sulfonic‐Derivative Side Group Modulation for Perovskite Solar Cells: A Synergistic Role in Promoting Defect Passivation and Carrier Transport

Introducing interfacial molecules with tailored side groups represents a critical strategy for passivating defects and enhancing carrier transport at the buried interface in perovskite solar cells (PSCs). However, precisely modulating side groups and elucidating the corresponding structure–property correlation remain insufficiently explored. Herein, three sulfonic‐derivative molecules bearing distinct side groups are investigated to modify the buried SnO 2 /perovskite interface, i.e., sodium cyclohexanesulfonate (SCSA), sodium benzenesulfonate (SBSA), and sodium pyridine‐3‐sulfonate (SPy3SA). The molecular design is based on an “anchoring group + functional side group” strategy. The sulfonate group (–SO 3 ‐ ) serves as a common anchoring group, strongly chelating uncoordinated Sn 4+ on the SnO 2 surface to ensure stable adsorption, while the varying side groups interact with the overlying perovskite layer. Among them, SPy3SA featuring a pyridine group showcases superior defect passivation and carrier transport due to the favorable coordination between nitrogen atoms and undercoordinated Pb 2+ . Hence, the SPy3SA‐modified PSC yields a boosted power conversion efficiency (PCE) from 21.84% to 23.81%, along with remarkable stability by remaining 77.6% (unmodified, 53.5%) of its initial PCE after 1000 h aging under ambient conditions. This study provides a valuable guide for the rational design of side groups in functional interfacial molecules for efficient and stable PSCs.