Nanoscale Thermal Strain Engineering-Driven Ferroelastic Domain Evolution in CH₃NH₃PbI₃ Perovskites

A local thermal strain engineering approach via an ac-heated thermal probe was incorporated into methylammonium lead triiodide (MAPbI₃) crystals and acts as a driving force for ferroic twin domain dynamics, local ion migration, and property tailoring. Periodically, striped ferroic twin domains and their dynamic evolutions were successfully induced by local thermal strain and high-resolution thermal imaging, giving decisive evidence of the ferroelastic nature in MAPbI₃ perovskites at room temperature. Local thermal ionic imaging and chemical mappings demonstrate that domain contrasts are from local methylammonium (MA⁺) redistribution into the stripes of chemical segregation in response to the local thermal strain fields. The present results reveal an inherent coupling among local thermal strains, ferroelastic twin domains, local chemical-ion segregations, and physical properties and offer a potential path to improve the functionality of metal halide perovskite-based solar cells.