title: Charge-transfer crystallites as molecular electrical dopants.
abstract: Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi-Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites-rather than individual acceptor molecules-should be regarded as the dopants in such systems.
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.|Departamento de Física, Pontificia Universidad Javeriana, Carrera 7, No. 43-82 Ed. 52 Of. 606, Bogotá, Colombia.
authors.forename: Henry
authors.initials: H
authors.lastname: Méndez
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Heimel
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.|Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Bereich Solarenergieforschung, Albert-Einstein-Straße 15, 12489 Berlin, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Winkler
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.|Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Bereich Solarenergieforschung, Albert-Einstein-Straße 15, 12489 Berlin, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Frisch
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Opitz
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.
authors.forename: Katrein
authors.initials: K
authors.lastname: Sauer
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.
authors.forename: Berthold
authors.initials: B
authors.lastname: Wegner
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.|Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Bereich Solarenergieforschung, Albert-Einstein-Straße 15, 12489 Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Oehzelt
authors.affiliation: Institut für Festkörperphysik, Graz University of Technology, Petersgasse 16, Graz 8010, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Röthel
authors.affiliation: Jiangsu Key Laboratory for Carbon Based Functional Materials and Devices and Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, 199 Ren-Ai Road, Suzhou 215123, China.|Soochow University-Western University Joint Centre for Synchrotron Radiation Research (SWC) and Collaborative Innovation Center of Suzhou Nano Science &Technology (NANO-CIC), Soochow University, 199 Ren-Ai Road, Suzhou 215123, China.
authors.forename: Steffen
authors.initials: S
authors.lastname: Duhm
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie GmbH-BESSY II, Abteilung Kristallographie, Albert-Einstein-Straße 15, 12489 Berlin, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Többens
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.|Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Bereich Solarenergieforschung, Albert-Einstein-Straße 15, 12489 Berlin, Germany.|Jiangsu Key Laboratory for Carbon Based Functional Materials and Devices and Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, 199 Ren-Ai Road, Suzhou 215123, China.
authors.forename: Norbert
authors.initials: N
authors.lastname: Koch
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik and IRIS Adlershof, AG Supramolekulare Systeme, Brook-Taylor Straße 6, 12489 Berlin, Germany.
authors.forename: Ingo
authors.identifier: http://orcid.org/0000-0001-9977-3422
authors.initials: I
authors.lastname: Salzmann