Nonlinear Mechanical Properties of Polymorphic CsPbI3 Perovskite from Reactive Molecular Dynamics Simulations

All-inorganic cesium lead triiodide (CsPbI3) perovskite makes efficient solar cells, for which the nonlinear induced fracture properties are important for its mechanical stability, but these nonlinear mechanical behaviors under finite deformation remain unclear. Here, we perform reactive molecular dynamics simulations to investigate the mechanical properties of CsPbI3 of different phases under finite deformation. Our simulations reveal that Young's modulus and Poisson's ratio exhibit anisotropy in the linear elastic region. The orthorhombic phase exhibits a lower hardness and higher flexibility compared to the tetragonal and cubic phases, resulting in higher susceptibility to stress. The average atomic charge decreases with increasing strain and concentrates at the cracks during fracture progress. We also discover that negative Poisson's ratio occurs in the xz-direction during finite deformation of tetragonal and orthorhombic phases, which is well explained by the Pb–I–Pb angle perpendicular to the xy-plane. Our findings provide valuable insights into the mechanical behavior and fracture characteristics of CsPbI3 perovskite, which have important implications for designing perovskite-based devices for different applications.