Alloying <i>n</i>‐Butylamine into CsPbBr₃ To Give a Two‐Dimensional Bilayered Perovskite Ferroelectric Material

Abstract

Cesium-lead halide perovskites (e.g. CsPbBr₃ ) have gained attention because of their rich physical properties, but their bulk ferroelectricity remains unexplored. Herein, by alloying flexible organic cations into the cubic CsPbBr₃ , we design the first cesium-based two-dimensional (2D) perovskite ferroelectric material with both inorganic alkali metal and organic cations, (C₄ H₉ NH₃ )₂ CsPb₂ Br₇ (1). Strikingly, 1 shows a high Curie temperature (T_c =412 K) above that of BaTiO₃ (ca. 393 K) and notable spontaneous polarization (ca. 4.2 μC cm^-2 ), triggered by not only the ordering of organic cations but also atomic displacement of inorganic Cs⁺ ions. To our knowledge, such a 2D bilayered Cs⁺ -based metal-halide perovskite ferroelectric material with inorganic and organic cations is unprecedented. 1 also shows photoelectric semiconducting behavior with large "on/off" ratios of photoconductivity (>10³ ).