title: Structural correlations in the generation of polaron pairs in low-bandgap polymers for photovoltaics.
abstract: Polymeric semiconductors are materials where unique optical and electronic properties often originate from a tailored chemical structure. This allows for synthesizing conjugated macromolecules with ad hoc functionalities for organic electronics. In photovoltaics, donor-acceptor co-polymers, with moieties of different electron affinity alternating on the chain, have attracted considerable interest. The low bandgap offers optimal light-harvesting characteristics and has inspired work towards record power conversion efficiencies. Here we show for the first time how the chemical structure of donor and acceptor moieties controls the photogeneration of polaron pairs. We show that co-polymers with strong acceptors show large yields of polaron pair formation up to 24% of the initial photoexcitations as compared with a homopolymer (η=8%). π-conjugated spacers, separating the donor and acceptor centre of masses, have the beneficial role of increasing the recombination time. The results provide useful input into the understanding of polaron pair photogeneration in low-bandgap co-polymers for photovoltaics.
authors: Photonics and Optoelectronics Group, Department of Physics and CeNS Ludwig-Maximilians-Universität München,                 80799                 Munich, Germany.
authors: Raphael
authors: R
authors: Tautz
authors: Enrico
authors: E
authors: Da Como
authors: Thomas
authors: T
authors: Limmer
authors: Jochen
authors: J
authors: Feldmann
authors: Hans-Joachim
authors: HJ
authors: Egelhaaf
authors: Elizabeth
authors: E
authors: von Hauff
authors: Vincent
authors: V
authors: Lemaur
authors: David
authors: D
authors: Beljonne
authors: Seyfullah
authors: S
authors: Yilmaz
authors: Ines
authors: I
authors: Dumsch
authors: Sybille
authors: S
authors: Allard
authors: Ullrich
authors: U
authors: Scherf