Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 36: Organic Semiconductors (joined session with CPP, DS)

HL 36.1: Vortrag

Dienstag, 21. März 2017, 09:30–09:45, POT 251

Femtosecond time-resolved spectroscopy of an acceptor-donor-acceptor oligomer film — •Ephraim Sommer1, Antonietta De Sio1, Elena Mena-Osteritz2, Peter Bäuerle2, and Christoph Lienau11Institut für Physik, Carl-von-Ossietzky Universität Oldenburg — 2Institut für Organische Chemie II und Neue Materialien, Universität Ulm

Conjugated oligomers are gaining increasing popularity for application in organic solar cells as photoactive materials thanks to their high production reproducibility and device efficiencies [1]. However, a detailed understanding of the initial charge transfer in such systems is missing. Recently, in polymer based active materials it was found that coherent vibronic coupling plays an important role in this process [2]. This raises the question whether this also holds for oligomers. To answer this, we investigate a novel A-D-A-type oligomer by pump-probe and 2D electronic spectroscopy with femtosecond time resolution. Upon selective excitation of the donor unit, we observe strong peak-shifts of the exciton signals as a most dominant feature at early times. Moreover, the signal shows long lived vibrational oscillations. Such a peak shift cannot be explained within a vibronically coupled dimer model including only one dominant vibrational mode like in [2]. Our preliminary results suggest that the photoinduced charge transfer may occur via a conical intersection between the donor and acceptor potential energy surfaces. We will discuss theoretical modelling aimed at validating this idea.

[1] R. Fitzner et al., Adv. Funct. Mater., 12, (2015)

[2] A. De Sio et al., Nat. Commun., 7, (2016)

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