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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Organic Electronics and Photovoltaics: OPV II (joint session CPP, HL, TT)

CPP 36.1: Talk

Wednesday, March 18, 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.