Exciton Propagation in Two-Dimensional Hybrid Perovskites

Layered hybrid perovskites are a highly interesting class of materials with intriguing fundamental properties and emerging potential for optoelectronic applications. Conceptually, they represent natural quantum well systems composed of nanometer-thin sheets of inorganics separated by organic spacer molecules. Due to enhanced Coulomb interaction 2D perovskites host tightly-bound electron-hole pairs, known as excitons, dominating their optical response. While the properties of these quasiparticles have been broadly studied, their spatial behavior remains barely explored so far. Here, we report the results of our study of exciton diffusion in hBN-encapsulated 2D perovskites, monitored from liquid helium up to room temperature conditions [1]. We find efficient propagation of long-lived excitons at all temperatures above 50 K with characteristic features of free-particle transport. At lower temperatures we observe a non-trivial behavior of a rapidly expanding exciton population followed by a slow and even negative effective diffusion. We discuss our results in the context of efficient exciton-phonon coupling in a simplified framework of a semi-classical model and outline general considerations of exciton transport in these systems.
[1] J.D. Ziegler et al: 10.1021/acs.nanolett.0c02472