Visible Light Accelerates Ultralow Electric Field‐Induced Switching of Antipolar‐to‐Polar Orders in Photoactive Ferroelectric

ABSTRACT

Antiferroelectrics (AFEs) have emerged as intriguing electroactive materials due to their unique merits arising from electric field‐induced switching of antipolar‐to‐polar phases. For molecular AFEs, however, a high electric field strength is required to switch antipolar dipoles in adjacent sublattices because of complex intermolecular interactions. Herein, we propose visible‐light irradiation as a feasible strategy to accelerate electric field‐induced switching of antipolar‐to‐polar states in a photoactive AFE perovskite, (benzylammonium) ₂ (ethylammonium)BiI ₆ , with an ultralow coercive field. It is a multiaxial ferroelectric with large spontaneous polarization of 3.5 µC cm ⁻² . The cooperation of organic cation dynamics and inorganic octahedral distortion induces stepwise symmetry breaking in (benzylammonium) ₂ (ethylammonium)BiI ₆ , described by the point‐group sequence m ‐2/ m ‐3 m ‐ m . Strikingly, visible light accelerates its electric field‐induced AFE‐to‐ferroelectric switching; it shows near‐room‐temperature AFE behavior in the dark even under a high electric field, whereas visible‐light irradiation enables field‐induced ferroelectricity at an ultralow coercive field ( E _c = 0.8 kV cm ⁻¹ , merely 1/39 of that in the dark). Nanoscale piezoresponse force microscopy studies further confirm this light‐accelerated polarization modulation, resembling an optical writing/reading memory process. This work provides a new pathway to modulate ferroic orders toward electronic device applications.