Self‐Segregated Buried‐Interface Regulation Resolves Kinetic–Environmental Coupling for Ambient Flexible Perovskite Solar Cells

ABSTRACT Ambient fabrication of flexible perovskite solar cells is fundamentally limited by a detrimental kinetic–environmental coupling at the buried interface, where moisture ingress and nonoptimal crystallization mutually compromise film quality—yet the underlying mechanism remains elusive. Using dual‐side in situ photoluminescence, we overturn the conventional top–down model by revealing simultaneous nucleation at both gas–liquid and liquid–solid interfaces during antisolvent‐assisted solution processing, but find that outward solvent evaporation delays α‐phase conversion at the buried interface relative to the surface, creating kinetic mismatch that exacerbates moisture attack and defect accumulation. To address these kinetic and environmental constraints, we design a self‐segregating multifunctional molecule, 2‐[(3‐trifluoromethyl)phenyl]amino‐3‐pyridinecarboxylic acid (NFA), which spontaneously enriches at the buried interface to synchronize dual‐interface crystallization while simultaneously passivating defects, optimizing energy‐level alignment, and constructing a hydrophobic barrier against moisture ingress. Consequently, this self‐segregated kinetic–environmental regulation yields record ambient flexible photovoltaic performance with power‐conversion efficiencies of 24.84% (0.09 cm 2 , certified at 23.75%) and 21.46% on mini‐modules (13.8 cm 2 ). The optimized devices maintain 96.26% of their starting efficiency following 1000 h damp aging at 85 ± 5% RH. Our work establishes self‐segregated interfacial regulation as a rational route to address kinetic and environmental constraints in scalable flexible photovoltaics.