Halide‐Cation Interactions Enable Controlled Crystallization and Defect Minimization in High‐Performance All‐Perovskite Tandems

This work demonstrates that synergistic passivation using Cl-salt or F-salt significantly enhances the performance of wide-bandgap (WBG) perovskite subcells and all-perovskite tandem solar cells (TSCs). The improved performance is attributed to the dual mechanisms of PF₆ ⁻ coordination with Pb² ⁺ and the formation of N─H···Cl/F hydrogen bonds, which collectively promote ordered crystal growth, suppress phase segregation in WBG perovskites, and improve overall film quality. Consequently, the modified WBG subcells achieve power conversion efficiencies (PCEs) of up to 20.5% (Cl-salt) and 20.3% (F-salt), with notable enhancements in open-circuit voltage (VOC) and fill factor (FF). When integrated into tandem devices, the treated cells yield remarkable PCEs of 29.2% (Cl-salt) and 29.3% (F-salt), and maintain 87% of the initial PCE after maximum power point tracking (MPP) under 1 sun illumination for 700 h.