Layer Number Dependent Ferroelasticity in 2D Ruddlesden-Popper Organic-inorganic Hybrid Perovskites

Abstract Ferroelasticity represents material domains possessing spontaneous strain that can be switched by external stress. Three-dimensional (3D) perovskites like methylammonium lead iodide (MAPI), which have demonstrated efficient solar cells and photodetectors, are determined to be ferroelastic. Apart from 3D perovskites, Ruddlesden-popper layered perovskites have been applied in optoelectronic devices with outstanding performance. However, the understanding of lattice strain as well as ferroelasticity in 2D layered perovskites is still lacking. Here，using the in-situ observation of switching domains in layered perovskite single crystals under external strain, we discover the existence of ferroelasticity in layered perovskites with layer number more than one, while the 2D perovskites with single octahedra layer do not show ferroelasticity. Density functional theory calculation shows that ferroelasticity in 2D perovskites originates from the distortion of inorganic octahedra resulting from the rotation of aspherical methylammonium cations. Additionally, the absence of methylammonium cations in single layer perovskite is consistent with the lack of ferroelasticity. These ferroelastic domains do not induce non-radiative recombination or reduce the photoluminescence quantum yield appreciably, indicating the glissile ferroelastic twin boundaries are benign defects. Our findings provide scientific insights in understanding strain-dependent material properties in 2D perovskites and lead to new potential flexible electronics controlled by strain engineering.