Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 60: Organic Electronics and Photovoltaics: OPV II (jointly with CPP, HL)
TT 60.1: Vortrag
Mittwoch, 18. März 2015, 09:30–09:45, C 130
Impact of Mesoscale Order on Energetics in Organic Semiconductors — •Carl Poelking1, Max Tietze2, Chris Elschner2, Selina Olthof3, Dirk Hertel3, Björn Baumeier1, Frank Würthner4, Klaus Meerholz3, Karl Leo2, and Denis Andrienko1 — 1Max Planck Institute for Polymer Research, Mainz, Germany — 2Institut für Angewandte Photophysik, Dresden, Germany — 3Physikalische Chemie, Universität zu Köln, Germany — 4Institut für Organische Chemie, Universität Würzburg, Germany
The interaction of charged excitations with the molecular surrounding in organic semiconductors is strictly long-ranged, due to their quadrupolar building blocks and preferential or absolute structural order. We show how atomistic simulations access the resulting energetics of charges and charge pairs and derived quantities, notably the charge-density-dependent open-circuit voltage across organic heterojunctions, with excellent accuracy. We compute level diagrams for a variety of donor-fullerene interfaces, with direct experimental validation. The underlying simulation approach takes into account long-range electrostatic effects that persist up to the mesoscale. The resulting mesoscale fields not only produce flat level profiles, but provide orientation-dependent push-out forces across a donor-acceptor interphase that can drive the charge-separation process. Correct polarity of these push-out forces is a requirement for functional solar cells, with operation closely above an isopolar point as the optimum tradeoff between magnitude of these push-out forces and the photovoltaic gap.