Unraveling the Factors Affecting the Mechanical Properties of Halide Perovskites from First-Principles Calculations

In practical applications, the mechanical properties of halide perovskites (e.g., ABX₃; A = monovalent cation; B = divalent metal cation; X = halogen anion) are of fundamental importance in achieving the durability of perovskite-based devices. In contrast to the widely studied photovoltaic properties, the composition/structure-mechanical property relationship in halide perovskites remains largely unexplored. Here, taking cesium-based halide perovskite models as examples, we have investigated the effects of chemical composition, phase transition, structural dimensionality, octahedral layer thickness, and octahedral connectivity on their mechanical properties using first-principles calculations. Our calculations show that the geometric factors (i.e., ionic radius, bond length, and tolerance factor) can reasonably explain the elastic property trends when varying the X-site component. The electronic factors (i.e., electronegativity) also play an important role in determining the mechanical strength when varying the B-site component. The phase transition, the structural dimensionality, the thickness of the [BX₆] octahedral layer, and the [BX₆] octahedral connectivity have a crucial influence on the mechanical properties if the chemical composition remains unchanged. Our results provide valuable insights into the composition/structure-mechanical property relationship of halide perovskites, which can guide the material design and device optimization to achieve desired mechanical properties.