Synergistic Passivation of Buried Interface and Grain Boundary of Tin–Lead Mixed Perovskite Films for Efficient Solar Cells

Abstract Due to its extreme susceptibility of tin to oxidation, the power conversion efficiency (PCE) of tin–lead mixed perovskite (TLP) solar cells still lags far behind the pure lead halides perovskite solar cells (PSCs). More than the endeavors of the suppression of tin‐oxidation in the bulk TLP films, the synergistic interface engineering of both grain boundaries and interfaces turns more and more important. Here, a synergistic co‐passivation strategy is reported by modulating poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) substrate with p‐guanidinobenzonitrile hydrochloride (CG) and grain boundary passivation of TLP film with 3‐cyano‐4‐hydrazinylbenzoic acid (3C‐HBA), realizing a competitive device PCE of 23.3%, positioning it at the forefront of reported literature. Strikingly, the discovery of CG modifications for such important PEDOT:PSS layer. Moreover, relying on the comprehensive spectroscopies, 3C‐HBA is revealed to effectively modulate the crystallization process of TLP films. This co‐passivation strategy obviously reduces trap density and suppresses Sn²⁺ oxidation of TLP devices.