Unprecedented 2D Homochiral Hybrid Lead‐Iodide Perovskite Thermochromic Ferroelectrics with Ferroelastic Switching

Abstract Chiral perovskites have emerged as a significant class of materials showing promising optoelectronic and spintronic applications. Reports of chiral perovskite ferroelectrics, however, have been scarce. In this work, we have successfully synthesized homochiral lead–iodide perovskite ferroelectrics [( R )‐ N ‐(1‐phenylethyl)ethane‐1,2‐diaminium]PbI 4 and [( S )‐ N ‐(1‐phenylethyl)ethane‐1,2‐diaminium]PbI 4 by introducing a methyl group into the organic cation of the parent ( N ‐benzylethane‐1,2‐diaminium)PbI 4 . Vibrational circular dichroism spectra identify the chiral mirroring relationship. They both undergo 222 F 2‐type paraelectric–ferroelectric behavior at around 378 K coupled with clear ferroelastic domain “ON/OFF” switching. Besides, they exhibit an evident thermochromism with color change from orange–yellow to orange–red. To our knowledge, the discovery of integrated ferroelectricity, ferroelasticity, and reversible thermochromism in chiral perovskites is unprecedented.