# Perspective: Exciton polarons in two-dimensional hybrid metal-halide perovskites

## TL;DR

This paper explores how polaronic effects influence excitons in two-dimensional hybrid metal-halide perovskites, revealing their spectral signatures and impact on excitonic properties, which is crucial for understanding these materials' quantum dynamics.

## Contribution

It demonstrates that polaronic effects are intrinsically present in 2D-HIOPs excitons, affecting their spectral structure and dynamics, and highlights the need for a rigorous theoretical framework.

## Key findings

- Exciton spectral structure shows multiple non-degenerate resonances with constant inter-peak spacing.
- Population and dephasing dynamics indicate the significant role of polaronic effects.
- Long-range and short-range exciton-lattice couplings give rise to exciton polarons affecting effective mass and radius.

## Abstract

While polarons --- charges bound to a lattice deformation induced by electron-phonon coupling --- are primary photoexcitations at room temperature in bulk metal-halide hybrid organic-inorganic perovskites (HOIP), excitons --- Coulomb-bound el\-ectron-hole pairs --- are the stable quasi-particles in their two-dimensional (2D) analogues. Here we address the fundamental question: are polaronic effects consequential for excitons in 2D-HIOPs? Based on our recent work, we argue that polaronic effects are manifested intrinsically in the exciton spectral structure, which is comprised of multiple non-degenerate resonances with constant inter-peak energy spacing. We highlight our own measurements of population and dephasing dynamics that point to the apparently deterministic role of polaronic effects in excitonic properties. We contend that an interplay of long-range and short-range exciton-lattice couplings give rise to exciton polarons, a character that fundamentally establishes their effective mass and radius, and consequently, their quantum dynamics. Finally, we highlight opportunities for the community to develop the rigorous description of exciton polarons in 2D-HIOPs to advance their fundamental understanding as model systems for condensed-phase materials in which lattice-mediated correlations are fundamental to their physical properties.