Anisotropic mechanical behavior of cesium tin iodide perovskite subjected to uniaxial tension

Lead-based metal halide perovskites (MHPs) have wide-ranging applications as solar cells, field-effect transistors, diodes, and photodetectors. However, their poor stability and concerns about toxicity have enabled lead-free tin-based MHPs to emerge as a promising alternative. We utilize molecular dynamics (MD) simulations to investigate the anisotropic mechanical behavior of single-crystal cubic CsSnI3, a promising lead-free MHP, under uniaxial tension. Among the three investigated crystal orientations, [111] is found to be the strongest and to exhibit the highest ultimate strain while [100] is the weakest. While shear strain localization and amorphization precede fracture along [100], fracture directly follows strain localization along [110] and [111]. We also investigated the influence of a crystal defect, in the form of an embedded rectangular crack, on the anisotropic mechanical behavior of cubic CsSnI3. The presence of crystal defects is found to substantially reduce the anisotropy in mechanical properties, with very similar crack growth behavior and almost identical stress-strain response noted along starkly different crystal orientations of loading. Finally, the ultimate strengths and ultimate strains of cubic CsSnI3 determined here are comparable to or higher than those of cubic CsPbI3 and MAPbI3 determined in prior MD-based investigations. Thus, our study supports the applicability of cubic CsSnI3 as a lead-free alternative to commonly used cubic MHPs, while the sensitivity to crystal defects revealed here underlines the importance of defect control for obtaining robust devices with reliable properties.