Screening the Local Structural Space in Lead Halide Perovskites with Diffuse Scattering and Brillouin Spectroscopy

Recent investigations have revealed that halide perovskites are best described at equilibrium as containing short-lived (picosecond), nanoscale (a few unit cells) domains of lower symmetry than the bulk average structure, where the corner-sharing lead halide octahedra are tilted relative to each other. In this study, we employ Brillouin spectroscopy and X-ray diffuse scattering to systematically screen the local structural space across various perovskite compositions. We demonstrate that, in selected compositions, finite polarisation vector fields are generated in the vicinity of these nanodomains. Furthermore, by controlling the temperature, we modulate both the size and the dynamics of the nanodomains, a change that is directly observable as a softening of the elastic stiffness tensor upon cooling. Our precise determination of the symmetry and shape of these nanodomains across different average phases highlights the tunability achieved through A-site cation and halide anion substitutions. Given the strong correlation between these local structures and the macroscopic performance of these materials, our findings pave the way for the future tuning of optoelectronic properties in lead halide perovskite devices.