The First 2D Homochiral Lead Iodide Perovskite Ferroelectrics: [<i>R</i>‐ and <i>S</i>‐1‐(4‐Chlorophenyl)ethylammonium]₂PbI₄

Abstract

Abstract 2D organic–inorganic lead iodide perovskites have recently received tremendous attention as promising light absorbers for solar cells, due to their excellent optoelectronic properties, structural tunability, and environmental stability. However, although great efforts have been made, no 2D lead iodide perovskites have been discovered as ferroelectrics, in which the ferroelectricity may improve the photovoltaic performance. Here, by incorporating homochiral cations, 2D lead iodide perovskite ferroelectrics [ R ‐1‐(4‐chlorophenyl)ethylammonium] 2 PbI 4 and [ S ‐1‐(4‐chlorophenyl)ethylammonium] 2 PbI 4 are successfully obtained. The vibrational circular dichroism spectra and crystal structural analysis reveal their homochirality. They both crystalize in a polar space group P 1 at room temperature, and undergo a 422 F 1 type ferroelectric phase transition with transition temperature as high as 483 and 473.2 K, respectively, showing a multiaxial ferroelectric nature. They also possess semiconductor characteristics with a direct bandgap of 2.34 eV. Nevertheless, their racemic analogue adopts a centrosymmetric space group P 2 1 / c at room temperature, exhibiting no high‐temperature phase transition. The homochirality in 2D lead iodide perovskites facilitates crystallization in polar space groups. This finding indicates an effective way to design high‐performance 2D lead iodide perovskite ferroelectrics with great application prospects.