Dresden 2009 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 33: Organic Photovoltaics II
CPP 33.4: Talk
Thursday, March 26, 2009, 14:45–15:00, ZEU 222
Ultrahigh time resolution nonlinear spectroscopy of polymer/fullerene blends — •Sarah Maria Falke1, Daniele Brida2, Giulio Cerullo2, and Christoph Lienau1 — 1Insitut für Physik, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany — 2Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy
Blends of polymers and fullerene derivatives are important prototype structures for efficient photoinduced charge generation and transport in organic photovoltaic devices. It is well established that photoexcitation of polymer/fullerene blends can result in an efficient ultrafast charge transfer from the excited polymer to the electron accepting fullerene moiety. It is generally believed that this charge transfer occurs within 50-100 fs [1]. Here we study ultrafast nonlinear spectra of pristine polymers (poly(3-hexylthiophene-2,5-diyl, P3HT) and polymer/fullerene ([6,6]-phenyl-C61 butyric acid methyl ester, PCBM) blends with a high time resolution of only 5 fs using a novel two-color pump-probe setup with broadband detection range. By comparing transient spectra of polymers and the polymer blend we observe an extremely rapid buildup of a band between 450 nm and 525 nm in the blend, occuring on a sub-10-fs time scale. Since the band is generally assigned to the stimulated emission from the indirectly excited fullerene moiety, our results indicate excitation transfer from the photoexcited polymer to the fullerene moiety on a sub-10-fs time scale, much faster than previously thought. The implications of these results for the microscopic charge generation processes in polymer/fullerene blends are discussed. [1] C.J. Brabec, Chem. Phys. Lett. 340, 232 (2001).