Photo‐Excited Switching and Enhancement of Dielectric Properties in Two‐Dimensional Double Perovskite Phase Transition Thin Films

Comprehensive Summary Optical controlling of solid‐sate electric properties is emerging as a non‐contact and nondestructive avenue to optimize the physical properties of electronic and optoelectronic devices. In term of strong light‐material coupling, two‐dimensional (2D) double perovskites hold great prospects to create photo‐dielectric activities for high‐performance device applications. Here, we have achieved the photo‐excited switching and enhancement of dielectric properties in the orientational thin films of a 2D double perovskite, (C 4 H 12 N) 4 AgBiI 8 ( 1 , where C 4 H 9 NH 3 + is isobutylammonium). It undergoes a structural phase transition at 384 K ( T c ), triggered by the dynamic ordering of organic cations and tilting motion of isometallic perovskite sheets. Most notably, the orientational thin films of 1 are extremely sensitive to light illumination, of which the dielectric constants can be facilely photo‐switched between the low‐ and high‐states. During this photo‐switching process, the dielectric constants are enhanced with a magnitude up to ~350% under 405 nm, far beyond most of the inorganic phase transition counterparts. In addition, this photo‐excited switching and enhancement of dielectric response exhibits an operational stability with superior anti‐fatigue characteristics. Our work opens up a potential avenue for assembling high‐performance optoelectronic devices with the controllable physical properties.