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.
