  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.
