Regensburg 2007 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 6: Organic Photovoltaics (SYOE 2)
DS 6.3: Vortrag
Montag, 26. März 2007, 16:30–16:45, H32
Efficient thin film organic solar cells containing low band gap oligothiophenes with tailored heterojunction level alignment — •R. Schüppel1, K. Schmidt2, C. Uhrich1, K. Schulze1, D. Wynands1, J. L. Brédas2, B. Männig1, M. Pfeiffer3, K. Leo1, E. Brier4, E. Reinold4, and P. Bäuerle4 — 1Institut für Angewandte Photophysik, Technische Universität Dresden, Germany — 2Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, Georgia, USA — 3Heliatek GmbH Dresden, Germany — 4Institut für Organische Chemie II und Neue Materialien, Universität Ulm, Germany
The recently demonstrated power conversion efficiency of 3.4% in a thin film solar cell (OSC), which utilized C60 as acceptor (A) and a new acceptor-substituted oligothiophene (OT) as donor (D) [1], stimulated us to study the energy (ET) and electron transfer (CT) taking place at this D/A heterojunction along a homologous series of these OT. The HOMO is tuned using different OT chain lengths, while the LUMO is essentially fixed by the acceptor-type end-groups (dicyano-vinylene). We study electron transfer at the heterojunction to C60 using photoinduced absorption. The observed transitions were unambiguously identified by TD-DFT calculations. With increasing the effective energy gap of the D/A pair, CT is eventually replaced by ET, which alters the OSC operation. Therefore, the optimum open circuit voltage between 1.0V-1.1V in our OSC has to be considered as a trade-off between an efficient charge separation and a maximized effective gap. [1] K. Schulze et al., Adv. Mater. 18, 2872 (2006)