Dresden 2017 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 50: Poster: Organic Electronics and Photovoltaics, Molecular Excitations
CPP 50.36: Poster
Wednesday, March 22, 2017, 18:30–21:00, P3
Absorption Tails of Donor:C60 Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation — •Johannes Benduhn1, Sebastian Schellhammer2, Fortunato Piersimoni3, Dieter Neher3, Donato Spoltore1, Frank Ortmann2, and Koen Vandewal1 — 1IAP, TU Dresden — 2Institute for Materials Science and cfaed, TU Dresden — 3University of Potsdam
In organic semiconductors, the transfer of a localized charge carrier causes a deformation of the molecular structure, quantified by the intra-molecular relaxation energy. Such structural relaxation occurs upon forming intermolecular charge-transfer (CT) states at organic electron donor (D)-acceptor (A) interfaces. D-A complexes show weak absorption at photon-energies below the optical gap of both the donor and the C60 acceptor, which is the result of an optical transition from the neutral ground state to the ionic CT state. We show that temperature-activated intra-molecular vibrations of the ground state play a major role in determining the line-shape of such CT absorption bands, allowing to extract values for the relaxation energy. Those experimental values for 20 donor:C60 CT complexes correlate with values calculated within density functional theory. These results provide an experimental method for determining the polaron relaxation energy in solid-state organic D-A blends and show the importance of a reduced relaxation energy for thermally activated CT processes.