title: Absorption Tails of Donor:C60Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation.
abstract: In disordered organic semiconductors, the transfer of a rather localized charge carrier from one site to another triggers a deformation of the molecular structure quantified by the intramolecular relaxation energy. A similar structural relaxation occurs upon population of intermolecular charge-transfer (CT) states formed at organic electron donor (D)-acceptor (A) interfaces. Weak CT absorption bands for D-A complexes occur at photon energies below the optical gaps of both the donors and the C60acceptor as a result of optical transitions from the neutral ground state to the ionic CT state. In this work, we show that temperature-activated intramolecular vibrations of the ground state play a major role in determining the line shape of such CT absorption bands. This allows us to extract values for the relaxation energy related to the geometry change from neutral to ionic CT complexes. Experimental values for the relaxation energies of 20 D:C60CT complexes correlate with values calculated within density functional theory. These results provide an experimental method for determining the polaron relaxation energy in solid-state organic D-A blends and show the importance of a reduced relaxation energy, which we introduce to characterize thermally activated CT processes.
authors.forename: Koen
authors.initials: K
authors.lastname: Vandewal
authors.forename: Johannes
authors.initials: J
authors.lastname: Benduhn
authors.forename: Karl Sebastian
authors.initials: KS
authors.lastname: Schellhammer
authors.affiliation: Material Physics Division, Institute for Materials Research (IMO-IMOMEC), Hasselt University , Universitaire Campus, Wetenschapspark 1, B-3590 Diepenbeek, Belgium.
authors.forename: Tim
authors.identifier: 0000-0003-1936-9521
authors.initials: T
authors.lastname: Vangerven
authors.forename: Janna E
authors.initials: JE
authors.lastname: Rückert
authors.affiliation: Institute of Physics and Astronomy, University of Potsdam , Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany.
authors.forename: Fortunato
authors.initials: F
authors.lastname: Piersimoni
authors.forename: Reinhard
authors.initials: R
authors.lastname: Scholz
authors.forename: Olaf
authors.initials: O
authors.lastname: Zeika
authors.affiliation: Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States.
authors.forename: Yeli
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States.
authors.forename: Stephen
authors.initials: S
authors.lastname: Barlow
authors.affiliation: Institute of Physics and Astronomy, University of Potsdam , Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Neher
authors.affiliation: Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States.
authors.forename: Seth R
authors.initials: SR
authors.lastname: Marder
authors.affiliation: X-LaB, Hasselt University , Universitaire Campus, Agoralaan 1, B-3590 Diepenbeek, Belgium.
authors.forename: Jean
authors.initials: J
authors.lastname: Manca
authors.forename: Donato
authors.initials: D
authors.lastname: Spoltore
authors.forename: Gianaurelio
authors.identifier: 0000-0002-6574-7848
authors.initials: G
authors.lastname: Cuniberti
authors.forename: Frank
authors.initials: F
authors.lastname: Ortmann