Seminars

2D metal halide perovskites (MHPs) are emerging family of low-cost, high-performance semiconductor materials for numerous energy and electronics applications. Mechanical stress is ubiquitously found in their applications and causes stability issues, which calls for a thorough understanding of the mechanical behaviors of 2D MHPs in both pristine form and under service environments. This talk will overview the research effort in my lab in the past 6 years on understanding the mechanical behavior of 2D MHPs. We will first establish a structure-property relationship regarding the in-plane elastic properties of 2D MHPs and compare the results to those from the out-of-plane directions. An interesting in-plane vs. out-of-plane mechanical anisotropy is uncovered, which can be tuned over a wide range by controlling the chemistry of the materials. We further employ the angle-resolved Brillouin Spectroscopy to directly measure the in-plane stiffness matrix and shed light on the in-plane elastic anisotropy of these materials. We will then show an anomalous thermo-mechanical behavior of 2D MHPs compared to other low-dimensional systems. Our results suggest that this thermo-mechanical anomaly is likely arising from the order-to-disorder transition of the organic spacer molecules inside the crystal structure. Finally, we report the creep and fatigue behavior of 2D MHPs under subcritical, time-dependent loading conditions. 2D MHPs exhibit better fatigue resilience compared to typical polymer materials, and can survive over one billion cycles when the mean stress is about 40% of their fracture strength. Failure morphology suggests the presence of an unexpected plastic deformation in these ionic crystals at low mean stress, which might be responsible for the long fatigue lifetime, but is significantly suppressed at high mean stress. Our results will provide invaluable insights to improve the mechanical reliability of 2D MHPs and pave the way for commercializing devices based on these materials.