ABSTRACT 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 (‐SO 2 ) into diaminofluorene, the ‐NH 2 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‐PbBr 2 /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.
Wang et al. (2026) studied this question.