Electron‐Deficient Amines Enable Halide‐Anchoring Hydrogen Bonding for Stable Wide‐Bandgap Perovskites Toward Perovskite/Organic Tandem Solar Cells

Perovskite/organic tandem solar cells (TSCs) represent a compelling pathway toward high-efficiency, solution-processed photovoltaics; however, their performance remains constrained by voltage losses in wide-bandgap (WBG) perovskite sub-cells due to halide phase segregation and associated ion migration. Here, we address this challenge through rational molecular design of hydrogen-bonding agents that precisely regulate crystallization dynamics. By incorporating an electron-withdrawing sulfone group (-SO₂) into diaminofluorene, the -NH₂ functionality is electronically reprogrammed from a cation-coordinating base into a halide-targeting hydrogen-bond donor that selectively stabilizes bromide via directional N─H⋯Br^- interactions. This electron-deficient architecture stabilizes Br-rich DMSO-PbBr₂/DTD intermediates, suppresses premature Br-rich nucleation, and promotes uniform vertical and horizontal halide distribution during film formation. Simultaneously, it elevates the activation barrier for halide ion migration in WBG perovskites. Consequently, single-junction 1.85 eV-WBG perovskite solar cells achieve a champion power conversion efficiency (PCE) of 19.32%, with markedly enhanced operational stability under continuous illumination. When integrated into perovskite/organic TSCs, this strategy delivers an impressive PCE of 26.76% with an open-circuit voltage (V_OC) of 2.216 V, among the highest reported for perovskite/organic tandems. This work elucidates a structure-function paradigm for molecular regulation of halide chemistry in WBG perovskites and provides a generalizable route toward phase-stable, high-voltage tandem photovoltaics.