Carrier Lifetimes and Polaronic Mass Enhancement in the Hybrid Halide Perovskite CH$_3$NH$_3$PbI$_3$ from Multiphonon Fr\"ohlich Coupling

TL;DR

This study uses ab initio calculations to analyze electron-phonon interactions in CH$_3$NH$_3$PbI$_3$, revealing how specific phonons affect carrier relaxation and effective mass, thus clarifying carrier dynamics in hybrid perovskites.

Contribution

It identifies the dominant phonon modes influencing carriers and quantifies their effects on relaxation times and polaron mass, advancing understanding of electron-phonon coupling in perovskites.

Findings

Ultrafast carrier relaxation within 6-30 fs

Polaron effective masses 28% heavier than band masses

Identification of key phonon modes affecting carriers

Abstract

We elucidate the nature of the electron-phonon interaction in the archetypal hybrid perovskite CH$_3$NH$_3$PbI$_3$ using ab initio many-body calculations and an exactly solvable model. We demonstrate that electrons and holes near the band edges primarily interact with three distinct groups of longitudinal-optical vibrations, in order of importance: the stretching of the Pb-I bond, the bending of the Pb-I-Pb bonds, and the libration of the organic cations. These polar phonons induce ultrafast intraband carrier relaxation over timescales of 6-30 fs and yield polaron effective masses 28% heavier than the bare band masses. These findings allow us to rationalize previous experimental observations and provide a key to understanding carrier dynamics in halide perovskites.