Dresden 2017 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 22: Organic Electronics and Photovoltaics II: Doping
HL 22.3: Talk
Monday, March 20, 2017, 15:45–16:00, ZEU 260
Frontier orbital energy levels and exciton binding energies in organic charge transfer complexes — •Paul Beyer1, Stefan Krause2, Timo Florian1, Eduard Meister3, Lutz Grubert4, Wolfgang Brütting3, Norbert Koch1,2, and Andreas Opitz1 — 1Dep. of Physics, Humboldt-Universität zu Berlin — 2Helmholtz-Zentrum Berlin — 3Institute of Physics, University of Augsburg — 4Dep. of Chemistry, Humboldt-Universität zu Berlin
The frontier π-orbitals of planar molecules tend to overlap upon contact and hybridization takes place resulting in charge transfer complexes (CTC) with modified energy levels [1]. We characterize the energy levels for the materials diindenoperylene (DIP) and hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ) in solution by cyclic voltammetry as well as in thin films and in planar heterojunction geometry by photoelectron spectroscopy. Optical transitions were measured by UV/Vis/NIR absorption and X-ray transitions by near edge X-ray absorption fine structure spectroscopy.
At the planar DIP/F6TCNNQ interface CTC formation occurs. Due to the energy level alignment at the interface, which will be shown in detail for standing and lying molecular orientations, and the lower gap of the CTC in contrast to the semiconductor DIP, doping is present and DIP field-effect transistors with F6TCNNQ deposited on top are showing a strongly reduced threshold voltage. Furthermore, the exciton binding energies, which are much larger for X-ray than for optical excitations, will be discussed together with the energy levels.
[1] H. Méndez et al., Nat. Commun. 6 (2015) 8560.