title: Impact of morphology on polaron delocalization in a semicrystalline conjugated polymer.
abstract: We investigate the delocalization of holes in the semicrystalline conjugated polymer poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) by directly measuring the hyperfine coupling between photogenerated polarons and bound nuclear spins using electron nuclear double resonance spectroscopy. An extrapolation of the corresponding oligomer spectra reveals that charges tend to delocalize over 4.0-4.8 nm with delocalization strongly dependent on molecular order and crystallinity of the PBTTT polymer thin films. Density functional theory calculations of hyperfine couplings confirm that long-range corrected functionals appropriately describe the change in coupling strength with increasing oligomer size and agree well with the experimentally measured polymer limit. Our discussion presents general guidelines illustrating the various pitfalls and opportunities when deducing polaron localization lengths from hyperfine coupling spectra of conjugated polymers.
authors.affiliation: Freie Universität Berlin, Berlin Joint EPR Lab, Institut für Experimentalphysik, Berlin, Germany. robert.steyrleuthner@fu-berlin.de j.behrends@fu-berlin.de.
authors.forename: Robert
authors.identifier: http://orcid.org/0000-0002-8484-4037
authors.initials: R
authors.lastname: Steyrleuthner
authors.affiliation: King Abdullah University of Science & Technology, Solar & Photovoltaics Engineering Research Center, Thuwal 23955-6900, Saudi Arabia and Department of Chemistry, Hubei University, Wuhan 430062, China.
authors.forename: Yuexing
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Polymer Science and Engineering, Conte Research Center, University of Massachusetts, 120 Governors Drive, Amherst, MA 01003, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Freie Universität Berlin, Berlin Joint EPR Lab, Institut für Experimentalphysik, Berlin, Germany. robert.steyrleuthner@fu-berlin.de j.behrends@fu-berlin.de.
authors.forename: Felix
authors.initials: F
authors.lastname: Kraffert
authors.affiliation: Department of Polymer Science and Engineering, Conte Research Center, University of Massachusetts, 120 Governors Drive, Amherst, MA 01003, USA.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Cherniawski
authors.affiliation: Freie Universität Berlin, Berlin Joint EPR Lab, Institut für Experimentalphysik, Berlin, Germany. robert.steyrleuthner@fu-berlin.de j.behrends@fu-berlin.de.
authors.forename: Robert
authors.initials: R
authors.lastname: Bittl
authors.affiliation: Department of Polymer Science and Engineering, Conte Research Center, University of Massachusetts, 120 Governors Drive, Amherst, MA 01003, USA.
authors.forename: Alejandro L
authors.initials: AL
authors.lastname: Briseno
authors.affiliation: King Abdullah University of Science & Technology, Solar & Photovoltaics Engineering Research Center, Thuwal 23955-6900, Saudi Arabia.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Bredas
authors.affiliation: Freie Universität Berlin, Berlin Joint EPR Lab, Institut für Experimentalphysik, Berlin, Germany. robert.steyrleuthner@fu-berlin.de j.behrends@fu-berlin.de.
authors.forename: Jan
authors.identifier: http://orcid.org/0000-0003-1024-428X
authors.initials: J
authors.lastname: Behrends