title: How intermolecular geometrical disorder affects the molecular doping of donor-acceptor copolymers.
abstract: Molecular doping of conjugated polymers represents an important strategy for improving organic electronic devices. However, the widely reported low efficiency of doping remains a crucial limitation to obtain high performance. Here we investigate how charge transfer between dopant and donor-acceptor copolymers is affected by the spatial arrangement of the dopant molecule with respect to the copolymer repeat unit. We p-dope a donor-acceptor copolymer and probe its charge-sensitive molecular vibrations in films by infrared spectroscopy. We find that, compared with a related homopolymer, a four times higher dopant/polymer molar ratio is needed to observe signatures of charges. By DFT methods, we simulate the vibrational spectra, moving the dopant along the copolymer backbone and finding that efficient charge transfer occurs only when the dopant is close to the donor moiety. Our results show that the donor-acceptor structure poses an obstacle to efficient doping, with the acceptor moiety being inactive for p-type doping.
authors.affiliation: Department of Physics, University of Bath, Bath BA2 7AY, UK.
authors.forename: Daniele
authors.identifier: 0000000244629068
authors.initials: D
authors.lastname: Di Nuzzo
authors.affiliation: 1] Department of Physics, University of Bath, Bath BA2 7AY, UK [2] Dipartimento di Scienze Chimiche e Geologiche, Universita' di Modena e Reggio Emilia, Modena 41125, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Fontanesi
authors.affiliation: Department of Physics, University of Bath, Bath BA2 7AY, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Jones
authors.affiliation: Macromolecular Chemistry Group and Institute for Polymer Technology, Bergische Universität Wuppertal, Wuppertal 42119, Germany.
authors.forename: Sybille
authors.initials: S
authors.lastname: Allard
authors.affiliation: Macromolecular Chemistry Group and Institute for Polymer Technology, Bergische Universität Wuppertal, Wuppertal 42119, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Dumsch
authors.affiliation: Macromolecular Chemistry Group and Institute for Polymer Technology, Bergische Universität Wuppertal, Wuppertal 42119, Germany.
authors.forename: Ullrich
authors.initials: U
authors.lastname: Scherf
authors.affiliation: Department of Physics and Astronomy, Physics of Energy, VU University Amsterdam, Amsterdam 1081 HV, The Netherlands.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: von Hauff
authors.affiliation: 1] Physics Department and Center for Optoelectronics and Photonics Paderborn (CeOPP), Universität Paderborn, Paderborn 33098, Germany [2] College of Optical Sciences, University of Arizona, Tucson, Arizona AZ85721, USA.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schumacher
authors.affiliation: Department of Physics, University of Bath, Bath BA2 7AY, UK.
authors.forename: Enrico
authors.initials: E
authors.lastname: Da Como