Regensburg 2013 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 24: Organic Semiconductors
CPP 24.4: Vortrag
Mittwoch, 13. März 2013, 10:30–10:45, H40
A comprehensive picture of p-doping P3HT with the molecular acceptor F4TCNQ — •Patrick Pingel and Dieter Neher — Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam
Molecularly doped semiconducting polymers can exhibit exceptionally high electrical conductivity, making them suitable for use in solution-processed organic circuitries. It has, however, been shown that the density of the created free charges is well below the density of applied dopant molecules, which has been attributed to aggregation of the dopants and/or insufficient charge carrier dissociation. We used optical absorption spectroscopy, surface potential and conductivity measurements to unravel the mechanism leading to reduced doping efficiency in blends of poly(3-hexylthiophene), P3HT, doped with tetrafluorotetracyanoquinodimethane, F4TCNQ. Within the broad range of doping ratios investigated, we find that almost every F4TCNQ dopant undergoes full charge transfer with a P3HT donor site. The majority of these charge pairs remains, however, strongly bound and only ca. 5% of the doping-induced holes on P3HT are mobile and contribute to electrical conduction. The conductivity turns from a sublinear increase (i.e., a decrease of mobility) at low-to-moderate doping ratios towards a superlinear increase at high doping ratios. This dependency is quantitatively reproduced applying a numerical mobility model of Arkhipov et al. [Phys. Rev. B 72, 235202 (2005)], which considers the broadening of the energetic landscape for charge transport upon doping by the Coulomb potential of the left-behind F4TCNQ anions.