Visible-Photo-Assisted Phase Switching of Antiferroelectric-to-Ferroelectric Orders in an I3--Intercalated 2D Perovskite.

ABSTRACT

Antiferroelectric (AFE) has emerged as a promising branch of electroactive materials, due to their intriguing physical attributes stemming from the electric field-induced antipolar-to-polar phase transformation. However, the requirement of an extremely high electric field strength to switch adjacent sublattice polarization poses great challenges for exploiting molecular AFE system. Although photoirradiation is striking as a noncontact and nondestructive manipulation tool to optimize physical properties, the optical control of antiferroelectricity is still unexplored. Here, by adopting light-sensitive triiodide I3- anion into the 2D perovskite family, we have designed the first I3--intercalated molecular AFE of (t-ACH)2EA2Pb3I10(I3)0.5·((H3O)(H2O))0.5 (1, t-ACH = trans-4-aminomethyl-1-cyclohexanecarboxylate, EA = ethylammonium). The I3--intercalating gives an ultra-narrow bandgap of 1.65 eV with strong absorption. In terms of AFE structure, the anti-parallel alignment of electric dipoles results in a spontaneous polarization of 4.3 µC/cm2. Strikingly, 1 merely shows AFE behaviour in the dark even under ultrahigh voltage, while the field-induced ferroelectric state can be facilely obtained upon visible illumination. Such unprecedented photo-assisted phase switching ascribes to the incorporation of photoactive I3- anions, which reduce the AFE-to-ferroelectric switching barrier for 1. This pioneering work on the photo-assisting transformation of ferroic orders paves a new way to develop future photoactive materials with significant potential applications.