Methylphosphonium Tin Bromide: A 3D Perovskite Molecular Ferroelectric Semiconductor

3D ABX3 organic-inorganic halide perovskite (OIHP) semiconductors like [CH3 NH3 ]PbI3 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 ABX3 OIHP ferroelectric semiconductors is challenging. Herein, an A-site cation [CH3 PH3 ]+ (methylphosphonium, MP) is employed to successfully obtain a lead-free 3D ABX3 OIHP ferroelectric semiconductor MPSnBr3 , which shows clear above-room-temperature ferroelectricity and a direct bandgap of 2.62 eV. It is emphasized that MPSnBr3 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 BiFeO3 (4 polar axes) and BaTiO3 (3 polar axes). MPSnBr3 is the first MP-based 3D ABX3 OIHP ferroelectric semiconductor. This finding throws light on the exploration of other excellent 3D ABX3 OIHP ferroelectric semiconductors with great application prospects.