Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 13: Focus Session: Structural Ordering and Electronic Transport II (jointly with CPP)

HL 13.4: Talk

Monday, March 26, 2012, 16:00–16:15, ER 270

Probing Exciton and Charge Dynamics in Low-Bandgap Polymer:Fullerene Blends by NIR Transient Absorption Spectroscopy — Ian Howard, Fabian Etzold, Clare Dyer-Smith, Hannah Mangold, Ralf Mauer, Michael Meister, and •Frédéric Laquai — Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research Mainz, Germany

Low-bandgap polymers are among the most promising donor materials for bulk heterojunction organic solar cells with efficiencies now exceeding 7 %. However, the photophysics of the pristine polymers and the mechanisms of charge generation and recombination in low-bandgap polymer:fullerene blends are still not entirely understood. In this contribution we compare the exciton and charge carrier dynamics of relevant low-bandgap polymers including PCDTBT, PCPDTBT and PTB-type polymers and their photovoltaic blends, which we study by broadband transient absorption (TA) spectroscopy covering a dynamic range from femto- to milliseconds. We present the previously unobserved near-infrared (NIR) spectral range up to 2000 nm, which we observe with our recently developed broadband NIR-TA setup. We show that by detecting the NIR spectral range we are able to distinguish between the spectral features of singlet and triplet excitons as well as charge-transfer states and mobile polarons and that we can study their generation and decay dynamics, which is difficult, if not impossible, by conventional broadband visible transient absorption spectroscopy.