Fast and anomalous exciton diffusion in two-dimensional hybrid perovskites

TL;DR

This study reveals ultrafast and anomalous exciton diffusion in 2D hybrid perovskites, with implications for optoelectronic applications and many-body physics, highlighting temperature-dependent behaviors and strong exciton-phonon interactions.

Contribution

It provides the first direct measurement of exciton diffusion in 2D hybrid perovskites across a wide temperature range, uncovering anomalous behaviors at cryogenic temperatures.

Findings

Fast exciton diffusion above 50 K consistent with free exciton propagation

Nonlinear, anomalous diffusion behavior at cryogenic temperatures

Strong exciton-phonon coupling influencing exciton dynamics

Abstract

Two-dimensional hybrid perovskites are currently in the spotlight of condensed matter and nanotechnology research due to their intriguing optoelectronic and vibrational properties with emerging potential for light-harvesting and -emitting applications. While it is known that these natural quantum wells host tightly bound excitons, the mobilities of these fundamental optical excitations at the heart of the optoelectronic applications are still largely unexplored. Here, we directly monitor the diffusion of excitons through ultrafast emission microscopy from liquid helium to room temperature in hBN-encapsulated two-dimensional hybrid perovskites. We find very fast diffusion with characteristic hallmarks of free exciton propagation for all temperatures above 50 K. In the cryogenic regime we observe nonlinear, anomalous behavior with an exceptionally rapid expansion of the exciton cloud followed by a very slow and even negative effective diffusion. We discuss our findings in view of efficient exciton-phonon coupling, highlighting two-dimensional hybrids as promising platforms for many-body physics research and optoelectronic applications on the nanoscale.