Insights into the Charge Carrier Terahertz Mobility in Polyfluorenes from Large-Scale Atomistic Simulations and Time-Resolved Terahertz Spectroscopy

Abstract

Multiscale atomistic simulations were used to understand the factors that determine the charge carrier mobility spectrum obtained from time-resolved terahertz (THz) spectroscopy in conjugated polymers. The simulation approach combines classical molecular dynamics simulations of atomic structure, large-scale electronic structure calculations, and the evaluation of the THz mobility using Kubo’s linear response formula. We found that THz radiation probes a single carrier hop at low temperatures and high frequencies, while the transport over somewhat longer distances is probed in the opposite cases. Our results indicate that charge carrier transport at THz frequencies is thermally activated but with a much smaller activation energy compared to the dc case. The shape of the real and imaginary part of the mobility spectral curve reveals the presence of above THz hopping rates that are relevant for charge carrier transport. Strong differences of the mobilities in the polymer and the corresponding monomer material are largely caused by stronger energetic disorder of the monomer material.