Photoelectric‐Coupled Ferroelectric Heterojunctions for Ultrahigh NO ₂ Sensing With Polarization‐Memory‐Assisted Interfacial Modulation

ABSTRACT Ferroelectric oxide heterostructures coupling optical, electrical, and chemical stimuli offer a compelling pathway toward multimodal artificial sensory systems mimicking biological perception. We report all‐Aurivillius‐phase Bi ₂ WO ₆ /SrBi ₂ Ta ₂ O ₉ (BWO/SBT) heterojunction that integrates light‐driven ferroelectric polarization switching, photoelectric memory, and gas sensing within a single architecture. Epitaxial BWO (∼65 nm) and ultrathin SBT (∼5 nm) films were grown in situ by laser molecular beam epitaxy, forming a coherent interface that enables visible‐light–induced polarization reversal and persistent photoconductivity (PPC). The interfacial band bending, photoinduced charge screening, and polarization realignment dramatically enhance gas‐sensing performance, achieving 530% (301%) NO ₂ –response at 10 ppm (0.3 ppm) —approximately 300‐fold higher than the electrically pre‐polarized counterpart. The PPC‐enhanced sensor delivers a 0.46 ppb detection limit and 129.7% ppm ⁻¹ sensitivity, representing one‐ and two‐order‐of‐magnitude enhancements over electrically polarized (5.2 ppb, 11.5% ppm ⁻¹ ) and unpoled (17.5 ppb, 3.42% ppm ⁻¹ ) devices, respectively. It also exhibits exceptional stability, maintaining strong responses at 10°C–100°C and robust humidity tolerance (coefficient of variation < 4% from 5%–86% RH). This work provides experimental evidence supporting a non‐linear interaction consistent with optoelectronic memory–mediated ferroelectric coupling, as a powerful strategy to modulate charge‐transfer kinetics, offering a universal framework for self‐adaptive gas sensors and multimodal bioinspired devices.