title: Electronic structure dynamics in a low bandgap polymer studied by time-resolved photoelectron spectroscopy.
abstract: Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials.
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Ute B
authors.initials: UB
authors.lastname: Cappel
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Stefan
authors.initials: S
authors.lastname: Plogmaker
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Joachim A
authors.initials: JA
authors.lastname: Terschlüsen
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se and Uppsala-Berlin Joint Laboratory on Next Generation Photoelectron Spectroscopy, Albert-Einstein-Str. 15, 12489 Berlin, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Leitner
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, 751 20 Uppsala, Sweden.
authors.forename: Erik M J
authors.initials: EM
authors.lastname: Johansson
authors.affiliation: Department of Engineering Sciences - Solid State Physics, Uppsala University, Box 534, 751 21 Uppsala, Sweden.
authors.forename: Tomas
authors.initials: T
authors.lastname: Edvinsson
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Sandell
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Olof
authors.initials: O
authors.lastname: Karis
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Hans
authors.initials: H
authors.lastname: Siegbahn
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se and Uppsala-Berlin Joint Laboratory on Next Generation Photoelectron Spectroscopy, Albert-Einstein-Str. 15, 12489 Berlin, Germany.
authors.forename: Svante
authors.initials: S
authors.lastname: Svensson
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se and Uppsala-Berlin Joint Laboratory on Next Generation Photoelectron Spectroscopy, Albert-Einstein-Str. 15, 12489 Berlin, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Mårtensson
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Håkan
authors.initials: H
authors.lastname: Rensmo
authors.affiliation: Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden. Ute.cappel@physics.uu.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Söderström