Robust excitons across the phase transition of two-dimensional hybrid perovskites

TL;DR

This study investigates how structural phase transitions in two-dimensional hybrid perovskites affect exciton properties, revealing their robustness and challenging conventional understanding of exciton behavior in these materials.

Contribution

It provides the first detailed analysis showing exciton binding energy and diffusion remain stable across phase transitions in 2D perovskites, highlighting their unusual excitonic nature.

Findings

Exciton properties are robust across phase transitions.

Significant changes in free carrier masses do not affect excitons.

Challenging traditional effective mass and transport models.

Abstract

Two-dimensional halide perovskites are among intensely studied materials platforms profiting from solution based growth and chemical flexibility. They feature exceptionally strong interactions among electronic, optical as well as vibrational excitations and hold a great potential for future optoelectronic applications. A key feature for these materials is the occurrence of structural phase transitions that can impact their functional properties, including the electronic band gap and optical response dominated by excitons. However, to what extent the phase-transitions in two-dimensional perovskites alter the fundamental exciton properties remains barely explored so far. Here, we study the influence of the phase transition on both exciton binding energy and exciton diffusion, demonstrating their robust nature across the phase transition. These findings are unexpected in view of the associated substantial changes of the free carrier masses, strongly contrast broadly considered effective mass and drift-diffusion transport mechanisms, highlighting the unusual nature of excitons in two-dimensional perovskites.