open-circuit voltage loss and instability from surface sn(ii) oxidation and high-density sn vacancies pose great hurdles for developing high-performance sn-based perovskite solar cells (pscs). turning attention from the bulk microstructure to surface reconstruction is promising to push the performance enhancement of sn-based pscs. herein, a surface-modulation strategy based on 6-maleimidohexanehydrazide trifluoroacetate is rationally designed to reconstruct the surface structure of fasni3 films to manage the fermi level and passivate defects. the electronic state evolution results in an n-type fermi level shift of the shallow surface, thereby forming an extra back-surface field for electron extraction. meanwhile, the ion-pairing agent affords passivating cationic and anionic defects, thereby nullifying the charged-defect-rich surface. in particular, the reductive hydrazide group and carboxyl groups alleviate superficial sn(iv) and inhibit sn(iv) formation, homogenizing surface potential and prolonging carrier lifetime. accordingly, devices deliver a champion power conversion efficiency (pce) of 13.64% and an elongated lifespan, with over 75% of the original pce after 1000 h of illumination (o2 < 50 ppm). this work presents a new insight on the surface reconstruction strategy for developing high-performance sn-based pscs.
