Revealing nanomechanical domains and their transient behavior in mixed-halide perovskite films

TL;DR

This study uncovers nanoscale mechanical domains in mixed-halide perovskite films, showing how light-induced ion migration affects their mechanical and optoelectronic properties, with implications for advanced optoelectronic devices.

Contribution

It introduces a combined microscopy approach to reveal mechanical domains and their transient behavior in halide perovskite films, linking mechanical, chemical, and optical properties.

Findings

Mechanical domains are enclosed by boundaries with higher Young's Modulus.

Light soaking homogenizes mechanical properties via ion migration.

Mechanical boundaries correlate with bromide-rich clusters.

Abstract

Halide perovskites are a versatile class of semiconductors employed for high performance emerging optoelectronic devices, including flexoelectric systems, yet the influence of their ionic nature on their mechanical behaviour is still to be understood. Here, a combination of atomic-force, optical and compositional X-ray microscopy techniques is employed to shed light on the mechanical properties of halide perovskite films at the nanoscale. We reveal mechanical domains within and between morphological grains, enclosed by mechanical boundaries of higher Young's Modulus than the bulk parent material. These mechanical boundaries are associated with the presence of bromide-rich clusters as visualized by nano-X-ray fluorescence mapping. Stiffer regions are specifically selectively modified upon light soaking the sample, resulting in an overall homogenization of the mechanical properties towards the bulk Young's Modulus. We attribute this behaviour to light-induced ion migration processes that homogenize the local chemical distribution, which is accompanied by photobrightening of the photoluminescence within the same region. Our work highlights critical links between mechanical, chemical and optoelectronic characteristics in this family of perovskites, and demonstrates the potential of combinational imaging studies to understand and design halide perovskite films for emerging applications such as photoflexoelectricity.