Polar twin walls identified in CsPbI3 perovskite films using low-dose STEM

Using low-dose scanning transmission electron microscopy, researchers identified ferroelastic twin walls in vapor-deposited CsPbI3 thin films, as reported in the Proceedings of the National Academy of Sciences doi.orgProceedings of the National Academy of Sciencesdoi.orgOpen source ↗. The observed twin walls form parallel to {110} and {112} crystallographic planes inside the halide perovskite semiconductor.

Despite CsPbI3 being a centrosymmetric and nonpolar material, the authors directly observed that lead atoms shift at {110} twin walls, driving a local ferroelectric-like polarization doi.orgProceedings of the National Academy of Sciencesdoi.orgOpen source ↗. These polar twin walls form an intrinsic array of nanoscale interfaces, spaced approximately 30 to 50 nm apart, embedded directly within the nonpolar perovskite lattice.

In contrast, {112} twin walls do not exhibit polar displacements of lead atoms doi.orgProceedings of the National Academy of Sciencesdoi.orgOpen source ↗. Instead, they strongly suppress octahedral tilting and off-center cesium atom displacements, revealing an untapped structural degree of freedom. According to the study, this nanoscale polarization and domain wall engineering present opportunities for enhancing conductivity and photovoltaic behavior in halide perovskites used for solar cells, laser sources, and X-ray detectors.