Centimeter‐Sized Single Crystals of Two‐Dimensional Hybrid Iodide Double Perovskite (4,4‐Difluoropiperidinium)4AgBiI8 for High‐Temperature Ferroelectricity and Efficient X‐Ray Detection

Abstract Ferroelectricity and X‐ray detection property have been recently implemented for the first time in hybrid bromide double perovskites. It sheds a light on achieving photosensitive and ferroelectric multifunctional materials based on 2D lead‐free hybrid halide double perovskites. However, the low T c , small P s , and relatively low X‐ray sensitivity in the reported bromide double perovskites hinder practical applications. Herein, the authors demonstrate a novel 2D lead‐free iodide double perovskite (4,4‐difluoropiperidinium) 4 AgBiI 8 (1) for high‐performance X‐ray sensitive ferroelectric devices. Centimeter‐sized single crystal of 1 is obtained and exhibits an excellent ferroelectricity including a high T c up to 422 K and a large P s of 10.5 μC cm −2 . Moreover, due to a large X‐ray attenuation and efficient charge carrier mobility (μ)–charge carrier lifetime (τ) product, the crystal 1 also exhibits promising X‐ray response with a high sensitivity up to 188 μC·Gy air −1 cm −2 and a detection limit below 3.13 μGy air ·s −1 . Therefore, this finding is a step further toward practical applications of lead‐free halide perovskite in high‐performance photoelectronic devices. It will afford a promising platform for exploring novel photosensitive ferroelectric multifunctional materials based on lead‐free double perovskites.