PFN‐Br Modified Buried Interface Enhanced Charge Extraction in Inverted Wide‐Bandgap Perovskite Solar Cells

In recent years, tandem solar cells (TSCs) have achieved remarkable progress. Nevertheless, wide‐bandgap perovskite solar cells (WBG PSCs), typically employed as the top cell, still suffer from significant open‐circuit voltage ( V OC ) losses. One contributing factor is the deeper valence band of WBG PSCs compared with conventional bandgap counterparts, which results in energy‐level mismatch when conventional hole transport materials are used in p–i–n structured PSCs. Moreover, the top‐down crystallization process of perovskite films frequently induces defect states at the buried interface, underscoring the urgent need for advanced passivation strategies. Here, we introduce poly[9,9‐bis(3′‐(N,N‐dimethyl)‐N‐ethylammoniumpropyl)‐2,7‐fluorene‐alt‐2,7‐(9,9‐dioctylfluorene)] dibromide (PFN‐Br) as an interlayer between 2PACz and the perovskite absorber. The bromide‐counterion ammonium groups in PFN‐Br effectively suppress non‐radiative recombination, while simultaneously tuning the energy‐level alignment, thereby facilitating more efficient hole extraction in WBG PSCs. As a result, the PFN‐Br–modified devices deliver a champion power conversion efficiency of 23.15% and a high V OC of 1.281 V for perovskite cells with a bandgap of 1.67 eV.