Phase Transition Induced Carrier Mass Enhancement in 2D Ruddlesden-Popper Perovskites

TL;DR

This study reveals that a phase transition in 2D Ruddlesden-Popper perovskites causes a significant increase in exciton effective mass, which can be tuned via temperature and organic spacer variation, impacting optoelectronic applications.

Contribution

It demonstrates the phase transition-induced carrier mass enhancement in 2D perovskites and links optical properties to structural changes supported by DFT calculations.

Findings

Exciton reduced mass increases by ~30% in low temperature phase.

Diamagnetic coefficient decreases 2-3 fold with phase transition.

Absorption features in spectra are phonon-related side bands.

Abstract

There is a variety of possible ways to tune the optical properties of 2D perovskites, though the mutual dependence between different tuning parameters hinders our fundamental understanding of their properties. In this work we attempt to address this issue for (C$_n$H$_{2n+1}$NH$_3$)$_2$PbI$_4$ (with n=4,6,8,10,12) using optical spectroscopy in high magnetic fields up to 67T. Our experimental results, supported by DFT calculations, clearly demonstrate that the exciton reduced mass increases by around 30% in the low temperature phase. This is reflected by a 2-3 fold decrease of the diamagnetic coefficient. Our studies show that the effective mass, which is an essential parameter for optoelectronic device operation, can be tuned by the variation of organic spacers and/or moderate cooling achievable using Peltier coolers. Moreover, we show that the complex absorption features visible in absorption/transmission spectra track each other in magnetic field providing strong evidence for the phonon related nature of the observed side bands.