Sulfamethoxazole-Induced Synergistic Interfacial Passivation for Efficient and Stable Perovskite Solar Cells

Interfacial defects remain one of the critical bottleneck restricting further enhancements in the efficiency and stability of perovskite solar cells (PSCs). Here, we report sulfamethoxazole (SMX), a commercially available sulfonamide antibiotic, as a multidentate Lewis base interfacial modifier for FA/MA mixed-cation n-i-p PSCs. The SMX molecule contains multiple N- and O-based binding sites that simultaneously passivate undercoordinated Pb2+, organic-cation vacancies, and halide vacancies through synergistic coordination, hydrogen bonding, and electrostatic interaction. The device with optimized SMX concentration (0.5 mg mL-1) achieves an average power conversion efficiency (PCE) of 20.31% (champion 21.05%), outperforming the reference device (18.01%), and exhibits a reduced hysteresis index from 5.33% to 2.58%. Comprehensive carrier-dynamics analyses reveal that SMX passivation decreases trap density, reduces nonradiative recombination losses, facilitates charge extraction, and reinforces the built-in electric field, thereby contributing to the improved VOC. Moreover, the unencapsulated SMX-modified device retains 93.45% of its initial PCE after storage in ambient air for 800 h. Therefore, this study provides a practical strategy of using multifunctional Lewis bases for synergistic interfacial passivation, ion migration suppression, and stability improvement in PSCs.