Improper High-T c Perovskite Ferroelectric with Dielectric Bistability Enables Broadband Ultraviolet-to-Infrared Photopyroelectric Effects.

The photopyroelectric effect in ferroelectrics has shown great potential for application in infrared detection and imaging. One particular subclass is broadband with dielectric bistability, which allows for large pyroelectric figures-of-merit (FOMs). Herein, an improper high-T c perovskite ferroelectric, (IA) 2 (EA) 2 Pb 3 Cl 10 (1, where IA is isoamylammonium and EA is ethylammonium) is presented, in which spontaneous polarization (P s ) stems from the dynamic ordering of organic cations and the tilting of distorted PbCl 6 octahedra. Notably, 1 displays unusual dielectric bistability with small variations in the temperature-dependent dielectric constants near T c  = 392 K; this bistable attribute endows large pyroelectric FOMs with peak voltage efficiency (F V  = 1.7×10 -2  cm 2 µC -1 ) and sensitivity (F D  = 3.9×10 -4 Pa -1/2 ). These F V and F D parameters, beyond those of their proper counterparts, make 1 a promising candidate for infrared photodetection. As expected, the broadband photopyroelectric effects observed in 1 covered the ultraviolet to infrared-II spectral region (266-1950 nm). Such P s -directed photoactivities overcome the optical bandgap limitation and allow for wide-wave photodetection. As an innovative study on improper ferroelectricity, light is shaded here on the targeted engineering of new electrically ordered candidate materials for smart optoelectronic devices.