Alloying Small‐Cation into Low‐Dimensional Perovskite Motif Gives Multiaxial Ferroelectrics with Enhanced Photo‐Pyroelectricity

Abstract

Abstract Photoactive ferroelectrics have shown huge potentials for assembling high‐performance optoelectronic devices. Bismuth‐based halides are emerging as a vigor ferroelectric subclass due to unique structural diversity and flexibility, while studies on their photo‐ferroelectricity coupling remain extremely scarce. Here, we have alloyed organic mixed‐cations into Bismuth‐based prototype to design a series of new multiaxial ferroelectrics with strong photo‐pyroelectricity, as notably exemplified by (BZA) 2 (DMA)BiBr 6 ( 1 , where BZA is benzylammonium; DMA is dimethylammonium). The dynamic motions of small DMA + cation afford the driving force to trigger symmetry breaking of , thus giving its multiaxial ferroelectricity with 6 equivalent polarization directions. Strikingly, 1 exhibits photo‐pyroelectricity in a broad ultraviolet‐to‐NIR spectral range (266–980 nm), which couples with ferroelectric bulk photovoltaics to create giant photocurrent enhancement ratio of ∼4800%. This merit far surpasses those of known ferroelectric materials. These results shed light on the design of new photoactive ferroelectric candidates for smart photoelectronic device applications.