Visualization of Dynamic Polaronic Strain Fields in Hybrid Lead Halide Perovskites

TL;DR

This study visualizes and quantifies nanoscale strain fields caused by polarons in lead halide perovskites using femtosecond x-ray scattering, revealing their role in the material's optoelectronic properties.

Contribution

It introduces real-time visualization and quantitative analysis of polaronic strain fields in hybrid lead halide perovskites, advancing understanding of their dynamic structural distortions.

Findings

Radially-expanding nanometer-scale elastic strain fields observed

Polaronic distortions transiently modify carrier effective mass

Direct insights into dynamic structural distortions in perovskites

Abstract

Excitation localization involving dynamic nanoscale distortions is a central aspect of photocatalysis, quantum materials and molecular optoelectronics. Experimental characterization of such distortions requires techniques sensitive to the formation of point-defect-like local structural rearrangements in real time. Here, we visualize excitation-induced strain fields in a prototypical member of the lead halide perovskites via femtosecond resolution diffuse x-ray scattering measurements. This enables momentum-resolved phonon spectroscopy of the locally-distorted structure and reveals radially-expanding nanometer-scale elastic strain fields associated with the formation and relaxation of polarons in photoexcited perovskites. Quantitative estimates of the magnitude and the shape of this polaronic distortion are obtained, providing direct insights into the debated dynamic structural distortions in these materials. Optical pump-probe reflection spectroscopy corroborates these results and shows how these large polaronic distortions transiently modify the carrier effective mass, providing a unified picture of the coupled structural and electronic dynamics that underlie the unique optoelectronic functionality of the hybrid perovskites.