Interfacial Electronic Reconstruction in Defect‐Engineered Heterojunctions for Programming β Phase and Dielectric Permittivity in Flexible Piezoelectric Polymers

ABSTRACT Flexible piezoelectric polymers are promising for self‐powered electronics, artificial skins, and wearable human‐machine interfaces, but their performance is limited by insufficient electroactive phase formation, dipole orientation, and interfacial stress transfer. Herein, we propose a defect‐engineered heterointerface strategy to regulate chain conformation, interfacial polarization, and electromechanical coupling in P(VDF‐TrFE)‐based composites. Sulfur‐vacancy‐rich BaTiO 3 /SnS 2 ‐S v heterojunctions with tunable defect concentrations are designed as multifunctional fillers. The BaTiO 3 /SnS 2 heterointerface enhances dielectric polarization and generates built‐in local electric fields, while sulfur vacancies expose uncoordinated Sn sites that strongly interact with F atoms in P(VDF‐TrFE). Such vacancy‐mediated Sn···F coupling promotes ordered ‐CF 2 dipole alignment, increases the electroactive β‐phase content from 59.67% to 89.37%, and strengthens filler‐polymer stress transfer. Experimental characterizations and theoretical calculations reveal that sulfur vacancies regulate interfacial electronic distribution and charge redistribution. Consequently, the optimized 8 wt.% BaTiO 3 /SnS 2 ‐10/P(VDF‐TrFE) composite delivers an output voltage of 29 V, an output current of 0.48 µA, and a power density of 16.3 µW cm −2 . The device further enables self‐charging energy storage and wireless control of intelligent vehicle motion.