Femtosekundenlasersystem (TIERUS)
Final Report Abstract
The Time, energy and polarization resolved ultrafast spectroscopy (TIERUS) instrument has successfully been installed and commissioned in 2015. Since then a number of experimental studies have been performed. The instrument has been used to investigate the relation between molecular order and charge/exciton transport in blends of small conjugated molecules and C 60 derivatives. In particular using TIERUS we have shown that molecular aggregation suppresses the formation of interfacial charge transfer states which is beneficial for the functionality of organic solar cells. We have also investigated the charge and exciton dynamics in so-called hybrid perovskite materials which show a solar cell efficiency exceeding 20% and are therefore very promising for future optoelectronic applications. Local variations of the stoichiometry of this material lead to the existence of inefficient regions in the material. We have shown that an efficient exciton transport exists between these inefficient regions and efficient regions thereby harvesting excitations which otherwise would be lost. The thermoelectric material PbTe has a very high ZT (thermoelectric efficiency). This is partially due to the incipient ferroelectric nature of the material leading to strong phonon scattering and a low thermal conductivity. The material also has a relatively high charge (hole) mobility adding to the high ZT. Through an experimental study using TIERUS we have shown that the high mobility is due to a suppressed scattering of holes near the sigma point in the Brillouin zone. Follow up time resolved ARPES experiments have confirmed this picture. The magnetization dynamics in the chiral magnet Cu2OSeO3 is driven by spin-lattice coupling. Using TIERUS we have determined the transient lattice temperature after pumping the Cu d-d transition. Together with time resolved Raman data obtained using the TiReRa instrument this led to a consistent picture of the spin-dynamics in Cu2OSeO3 suggesting a surprisingly weak coupling between low and high energy spin excitations.
