Exciton-phonon Coupling Controls Exciton-polaron Formation and Hot Carrier Relaxation in Rigid Dion-Jacobson Type Two-Dimensional Perovskites

TL;DR

This study reveals how exciton-phonon interactions influence exciton-polaron formation and hot carrier dynamics in Dion-Jacobson 2D perovskites, highlighting ligand modification as a control strategy for optoelectronic properties.

Contribution

It demonstrates the role of ligand modification in tuning exciton-phonon coupling and hot carrier relaxation in Dion-Jacobson 2D perovskites, combining spectroscopy and calculations.

Findings

Polaronic excitons are confirmed at room temperature.

Ligand modification controls exciton-phonon coupling.

Stronger coupling extends hot carrier lifetime.

Abstract

The efficiency of two-dimensional Dion-Jacobson-type materials relies on the complex interplay between electronic and lattice dynamics; however, questions remain about the functional role of exciton-phonon interactions. This study establishes the robust polaronic nature of the excitons in these materials at room temperature by combining ultrafast spectroscopy and electronic structural calculations. We show that polaronic distortion is associated with low-frequency (30-60 cm-1) lead iodide octahedral lattice motions. More importantly, we discover how targeted ligand modification of this two-dimensional perovskite structure controls exciton-phonon coupling, exciton-polaron population, and carrier cooling. At high excitation density, stronger exciton-phonon coupling increases the hot carrier lifetime, forming a hot-phonon bottleneck. Our study provides detailed insight into the exciton-phonon coupling and its role in carrier cooling in two-dimensional perovskites relevant for developing emerging hybrid semiconductor materials with tailored properties.