# Polaronic Mass Enhancement and Polaronic Excitons in Metal Halide Perovskites

## TL;DR

The study explores how electron-phonon interactions in metal halide perovskites affect optical properties and carrier behavior.

## Contribution

The paper introduces a new understanding of excitonic properties and carrier mass enhancement due to polaronic effects in perovskites.

## Key findings

- Excitons in metal halide perovskites exhibit non-hydrogenic behavior due to strong Fröhlich coupling.
- Carrier-phonon interactions lead to an increase in the effective mass of charge carriers.
- The effective mass of carriers shows a strong temperature dependence due to phonon mode population.

## Abstract

In metal halide perovskites, the complex dielectric screening
together
with low energy of phonon modes leads to non-negligible Fröhlich
coupling. While this feature of perovskites has already been used
to explain some of the puzzling aspects of carrier transport in these
materials, the possible impact of polaronic effects on the optical
response, especially excitonic properties, is much less explored.
Here, with the use of magneto-optical spectroscopy, we revealed the
non-hydrogenic character of the excitons in metal halide perovskites,
resulting from the pronounced Fröhlich coupling. Our results
can be well described by the polaronic-exciton picture where electron
and hole interactions are no longer described by a Coulomb potential.
Furthermore, we show experimental evidence that the carrier-phonon
interaction leads to the enhancement of the carrier’s effective
mass. Notably, our measurements reveal a pronounced temperature dependence
of the carrier’s effective mass, which we attribute to a band
structure renormalization induced by the population of low-energy
phonon modes. This interpretation finds support in our first-principles
calculations.