Halogen Bonding Networks Regulate Bromide Crystallization and Stabilize Phase Homogeneity in Efficient All‐Perovskite Tandem Solar Cells

Wide‐bandgap (WBG) mixed‐halide perovskites (>20% bromine) are critical top‐cells for high‐efficiency all‐perovskite tandem solar cells (APTSCs), yet mismatched crystallization kinetics and photothermal‐driven halide migration cause severe halide segregation during both film formation and operation. Herein, we introduce a halogen‐bonding‐network strategy using 1,2‐diiodotetrafluorobenzene (1,2‐DITFB) that preferentially binds bromide over iodide, selectively retarding its rapid crystallization and defect formation during halogen homogenization while constructing robust I···Br networks that kinetically lock in compositional homogeneity. This dual‐action mechanism suppresses phase separation across both initial solidification and long‐term photothermal stress. Consequently, single‐junction WBG devices achieve a champion efficiency of 20.25% with an impressive open‐circuit voltage (V OC ) of 1.34V, and retain 90% of initial efficiency after 500 h of continuous maximum power point (MPP) tracking under 1 sun illumination and at 65°C. Applied in APTSCs, this approach delivers an outstanding V OC of 2.13 V and a power‐conversion efficiency (PCE) of 28.58%, with unencapsulated devices maintaining 85% performance after 1000 h MPP operation at 55°C. This work demonstrates kinetic halogen bonding as a versatile approach for stabilizing WBG perovskites.