Dresden 2017 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 36: Organic Semiconductors (joined session with CPP, DS)
HL 36.4: Vortrag
Dienstag, 21. März 2017, 10:15–10:30, POT 251
Investigating the doping efficiency of organic semiconductors by thermoelectric measurements — •Bernhard Nell1, Markus Krammer2, Karin Zojer2, and Koen Vandewal1 — 1Dresden Integrated Center for Applied Physics and Photonic Materials, Technische Universität Dresden, Dresden, Germany — 2Institute of Solid State Physics, Technische Universität Graz, Graz, Austria
We use thermovoltage (Seebeck effect) and temperature-dependent conductivity measurements on doped organic semiconductors to determine the dominating type of charge carriers introduced by the dopant and to gain insight into the position of the transport level with respect to the Fermi level. The investigation of fullerene dopants with a high degree of fluorination in various amorphous host materials allows us to tune the energy level offset between host and dopant and to study their influence on Fermi level position and overall doping efficiency systematically. Combining thermoelectric measurements with Kinetic Monte Carlo simulations gives further insight into the influence of Coulomb interactions on the trapping of mobile charge carriers in doped organic semiconductors. We find that at low doping concentrations a high amount of charge carriers is immobilized in trap states, leading to a reduced doping efficiency. Upon increasing the doping concentration, the trap states are subsequently passivated and an increased doping efficiency can be observed. Furthermore the doping efficiency is increased upon fluorination of the dopant molecules and we find a correlation between the energy level offset and the doping efficiency, at the same molar concentration.