<br/>Domain features and domain walls in halide perovskites have attracted broad interest due to their possible impact on optoelectronic properties of this promising class of solution-processable semiconductors. Advanced scanning probe and optical imaging techniques have been developed to reveal the ferroic nature of the domains and to resolve the ongoing debate about their optoelectronic impact. Here, using non-polarized light and common simple imaging configurations, we directly visualize ferroelastic twin domains and their switchings through consecutive phase transitions. The optical contrast under non-polarized light originates from the finite reflection at the twin domain wall between the differently oriented anisotropic medium inside the material bulk. We show the direct optical contrast at twin domain walls strongly depends on the electronic band structure and illumination wavelength. This wavelength dependence optical contrast impacts multiple imaging modalities employed in domain structure and property investigations. We observe all the low symmetry phases that could in principle show ferroelasticity indeed display coherent twinning and reversible switching, in both hybrid and inorganic lead halide perovskites. First-principles calculations reveal a modest domain wall switching energy barrier, explaining their stable presence and facile switching. The generality of ferroelasticity in lead-halide perovskites results from their polarizable and soft bonding characteristics.

Direct visualization of universal ferroelasticity in lead halide perovskites

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ACS Fall 2022

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