Sequential Deposition Strategy Enabling High‐Performance Wide‐Bandgap Perovskite Solar Cells With Fill Factor Exceeding 85%

ABSTRACT For wide‐bandgap perovskite solar cells (WBG PSCs), significant non‐radiative recombination at the self‐assembled monolayers (SAM)/perovskite interface, along with high bulk defect densities, severely limit device performance and stability. Hence, defect suppression is critical to boost the fill factor (FF), representing a key challenge in developing high‐performance devices. Herein, an innovative bilayer SAM (BL‐SAM) interface engineering strategy is proposed via sequentially depositing [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) butyl] phosphonic acid (Me‐4PACz) and (4‐(3,11‐dimethoxy‐7H‐dibenzo[ c,g ]carbazol‐7‐yl) butyl) phosphonic acid (MeO‐4PADCB) as hole selective layers (HSLs). Theoretical and experimental evidence demonstrate that MeO‐4PADCB not only passivates the defects caused by incomplete coverage at buried surface, but also interacts with the perovskite lattice. The BL‐SAM strategy operates by orchestrating three synergistic effects: interfacial vacancy passivation, energy level alignment optimization, and residual lattice strain release. Consequently, the champion power conversion efficiency (PCE) of 20.35% is obtained with an exceptional FF of 85.18% and an open‐circuit voltage ( V OC ) of 1.33 V for 1.79 eV PSCs, representing one of the highest performance values reported in this category. The general applicability of this strategy is validated in 1.85 eV PSCs, delivering a PCE of 19.24% and an outstanding V OC of 1.39 V. This work offers a versatile strategy for achieving high‐performance and stable PSCs.