Ultrafast THz probe of photo-induced polarons in lead-halide perovskites

TL;DR

This study uses ultrafast THz spectroscopy to investigate the polaronic behavior of photo-excited charge carriers in lead-halide perovskite nanocrystals, revealing coupling between charges and lattice vibrations.

Contribution

It provides direct ultrafast spectroscopic evidence of polaron formation and charge-lattice coupling in CsPbBr3 nanocrystals, supported by DFT calculations.

Findings

Observation of deviation from Drude response indicating polaronic carriers

Transient blueshift of phonon frequencies shows charge-lattice coupling

Confirmation of polaronic behavior through DFT calculations

Abstract

We study the nature of photo-excited charge carriers in CsPbBr3 nanocrystal thin films by ultrafast optical pump - THz probe spectroscopy. We observe a deviation from a pure Drude dispersion of the THz dielectric response that is ascribed to the polaronic nature of carriers; a transient blueshift of observed phonon frequencies is indicative of the coupling between photogenerated charges and stretching-bending modes of the deformed inorganic sublattice, as confirmed by DFT calculations.