title: Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells.
abstract: In photovoltaic devices, the photo-generated charge carriers are typically assumed to be in thermal equilibrium with the lattice. In conventional materials, this assumption is experimentally justified as carrier thermalization completes before any significant carrier transport has occurred. Here, we demonstrate by unifying time-resolved optical and electrical experiments and Monte Carlo simulations over an exceptionally wide dynamic range that in the case of organic photovoltaic devices, this assumption is invalid. As the photo-generated carriers are transported to the electrodes, a substantial amount of their energy is lost by continuous thermalization in the disorder broadened density of states. Since thermalization occurs downward in energy, carrier motion is boosted by this process, leading to a time-dependent carrier mobility as confirmed by direct experiments. We identify the time and distance scales relevant for carrier extraction and show that the photo-generated carriers are extracted from the operating device before reaching thermal equilibrium.
authors.affiliation: Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden.
authors.forename: Armantas
authors.initials: A
authors.lastname: Melianas
authors.affiliation: Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Etzold
authors.affiliation: Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, 2628 BL Delft, The Netherlands.
authors.forename: Tom J
authors.initials: TJ
authors.lastname: Savenije
authors.affiliation: Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany.|Physical Sciences and Engineering Division, Material Science and Engineering, Solar and Photovoltaics Engineering Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Laquai
authors.affiliation: Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden.
authors.forename: Olle
authors.initials: O
authors.lastname: Inganäs
authors.affiliation: Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden.|Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Martijn
authors.identifier: http://orcid.org/0000-0002-7104-7127
authors.initials: M
authors.lastname: Kemerink