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.