Regensburg 2013 – scientific programme

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BP: Fachverband Biologische Physik

BP 4: Symposium Charge Transfer Effects in Molecular Materials (SYCT, joint with CPP, HL and DS)

BP 4.3: Invited Talk

Monday, March 11, 2013, 10:30–11:00, H1

Quantifying the energy of charge transfer states: From molecular crystals to donor-acceptor blends — •Reinhard Scholz — Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr Str. 1, 01069 Dresden, Germany

In molecular crystals, exciton models accounting for neutral molecular excitations and charge transfer (CT) allow to deduce their energy alignment from measured spectra.¹ Donor-acceptor blends may reveal weak CT absorption and photoluminescence spectra below the main absorption bands, and for polymer-fullerene solar cells, the respective energies correlate with the open circuit voltage.² Calculations of CT energies in these materials require computational methods with the correct asymptotics of the mutual Coulomb interaction between pairs of ionized donor and acceptor molecules like constrained DFT schemes.³ Moreover, the solvation energy arising from the embedding polarizable medium and the screening of the Coulomb interaction result in substantial deviations from the interaction between oppositely charged donor and acceptor molecules in vacuum. Based on a constrained DFT scheme and an embedding scheme accounting for the polarizable medium, calculated CT energies for selected donor-acceptor pairs are compared to available spectroscopic data and the open circuit voltage of photovoltaic devices.
[1] L. Gisslén and R. Scholz, Phys. Rev. B 80, 115309 (2009).
[2] K. Vandewal et al., Adv. Funct. Mater. 18 2064 (2008).
[3] M. Rapacioli, F. Spiegelman, A. Scemama, and A. Mirtschink, J. Chem. Theory Comput. 7, 44 (2011).