Methylphosphonium Tin Bromide: A 3D Perovskite Molecular Ferroelectric Semiconductor

Abstract 3D ABX 3 organic–inorganic halide perovskite (OIHP) semiconductors like [CH 3 NH 3 ]PbI 3 have received great attention because of their various properties for wide applications. However, although a number of low‐dimensional lead‐based OIHP ferroelectric semiconductors have been documented, obtaining 3D ABX 3 OIHP ferroelectric semiconductors is challenging. Herein, an A‐site cation [CH 3 PH 3 ] + (methylphosphonium, MP) is employed to successfully obtain a lead‐free 3D ABX 3 OIHP ferroelectric semiconductor MPSnBr 3 , which shows clear above‐room‐temperature ferroelectricity and a direct bandgap of 2.62 eV. It is emphasized that MPSnBr 3 is a multiaxial molecular ferroelectric with the number of ferroelectric polar axes being as many as 12, which is far more than those of the other OIHP ferroelectric semiconductors and even the classical inorganic perovskite ferroelectric semiconductors BiFeO 3 (4 polar axes) and BaTiO 3 (3 polar axes). MPSnBr 3 is the first MP‐based 3D ABX 3 OIHP ferroelectric semiconductor. This finding throws light on the exploration of other excellent 3D ABX 3 OIHP ferroelectric semiconductors with great application prospects.