Ferroelectricity and Interfacial Engineering in Low‐Bandgap Ag _0.9 K _0.1 NbO ₃ : Achieving Robust Coexistence of Piezo/Pyro/Photovoltaic Effects for Multimodal Tactile Sensing

Abstract Ferroelectric oxides inherently exhibit piezoelectric, pyroelectric, and photovoltaic properties, enabling multi‐sensing capabilities within a single material, a critical advantage for next‐generation smart sensing devices. However, the intrinsic trade‐off between maintaining robust ferroelectric polarization and achieving a narrow bandgap for effective photovoltaic conversion presents a significant challenge. Here, a breakthrough is reported in the ferroelectric oxide Ag 0.9 K 0.1 NbO 3 , which achieves a narrow bandgap of 2.58 eV while retaining robust ferroelectricity ( P r ≈ 25.6 µC cm − 2 ), along with an enhanced piezoelectric constant ( d 33 ≈78 pC/N), a high pyroelectric coefficient ( ρ ≈270 µC m − 2 K −1 ), and a remarkable photovoltaic responsivity of 25.5 µA/W at 450 nm. Atomic‐scale structural analysis reveals that this synergistic enhancement stems from the coexistence of orthorhombic and tetragonal polar nanoregions, coupled with significant atomic displacements. Furthermore, beyond the dominated depolarization field, strategic interfacial engineering boosts photocurrent 6.7‐fold via tailored Schottky barriers and controlled oxygen vacancies while preserving intrinsic piezoelectric and pyroelectric properties. The ITO/Ag 0.9 K 0.1 NbO 3 /ITO device exhibits outstanding multi‐sensing capabilities, enabling simultaneous detection of mechanical pressure, temperature fluctuations, and optical signals. This work not only introduces a pioneering ferroelectric material but also provides a promising strategy for advancing high‐performance multi‐sensing devices.