Four-wave mixing in perovskite photovoltaic materials reveals long dephasing times and weaker many-body interactions than GaAs

TL;DR

This study uses four-wave mixing to compare the coherent optical responses of perovskite and GaAs, revealing that perovskites have longer dephasing times and weaker many-body interactions, indicating fundamental differences in their photophysical properties.

Contribution

It provides the first direct comparison of coherent optical responses between perovskite and inorganic semiconductors, highlighting weaker Coulomb interactions and longer dephasing times in perovskites.

Findings

Perovskites exhibit much weaker Coulomb interactions than GaAs.

Dephasing times in perovskites are approximately three times longer than in GaAs.

Weak exciton-carrier scattering in perovskites prevents the enhancement of FWM signals seen in GaAs.

Abstract

Perovksite semiconductors have shown promise for low-cost solar cells, lasers and photodetectors, yet their fundamental photophysical properties are not well understood. Recent observations of a low ($\sim$few meV) exciton binding energy and evidence of hot phonon effects in the room temperature phase suggest that perovskites are much closer to inorganic semiconductors than the absorber layers in traditional organic photovoltaics, signaling the need for experiments that shed light on the placement of perovskite materials within the spectrum of semiconductors used in optoelectronics and photovoltaics. Here we use four-wave mixing (FWM) to contrast the coherent optical response of CH$_3$NH$_3$PbI$_3$ thin films and crystalline GaAs. At carrier densities relevant for solar cell operation, our results show that carriers interact surprisingly weakly via the Coulomb interaction in perovskite, much weaker than in inorganic semiconductors. These weak many-body effects lead to a dephasing time in CH$_3$NH$_3$PbI$_3$ $\sim$3 times longer than in GaAs. Our results also show that the strong enhancement of the exciton FWM signal tied to excitation-induced dephasing in GaAs and other III-V semiconductors does not occur in perovskite due to weak exciton-carrier scattering interactions.