Ferroelasticity Mediated Energy Conversion in Strained Perovskite Films

Metal halide perovskites (MHPs) have been shown to be key materials for next‐generation photovoltaic energy harvesting, electro‐optic detection, and all‐optical conversion. Room‐temperature tetragonal MAPbI3 has been reported to possess two space groups: polar I4cm and non‐polar I4/mcm. Although the space group of MAPbI3 is still under debate, significant effort has been expended to prove that I4cm MHPs are ferroelectric and I4/mcm MHPs are antiferroelectric. Both structures belong to the ferroelastic point group, and there has been debate regarding whether the domain structures observed on MHPs are ferroelectric or ferroelastic. The relationship between the ferroelectricity and ferroelasticity of MHPs has been discussed, whereas these two properties sometimes are regarded as mutually exclusive in MHPs. In this work, the ferroelectricity and ferroelasticity of MHPs originating from structural symmetry have been reviewed, and the interrelationship between the ferroelectricity and ferroelasticity of MHPs are discussed. Schematic illustration of the relationship between the ferroelectricity and ferroelasticity of metal halide perovskites.