Regensburg 2013 – scientific programme
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O: Fachverband Oberflächenphysik
O 27: Organic Electronics and Photovoltaics II (jointly with CPP, DS, HL)
O 27.9: Talk
Tuesday, March 12, 2013, 11:45–12:00, H32
Molecular orientation at heterojunctions for organic photovoltaics studied by NEXAFS — •Andreas Opitz1, Norbert Koch1, Ulrich Hörmann2, Wolfgang Brütting2, Christopher Lorch3, Alexander Hinderhofer3, Frank Schreiber3, and Ellen Moons4 — 1Inst. f. Physik, Humboldt-Universität zu Berlin, Germany — 2Inst. of Physics, University of Augsburg, Germany — 3Inst. of Applied Physics, University of Tübingen, Germany — 4Dept. of Physics and Electrical Engineering, Karlstad University, Sweden
Organic/organic heterojunctions are widely used in organic photovoltaic cells. The morphology at the interface, where the charge carrier separation takes place, plays an important role. In this contribution the interfaces between sexithiophene (6T) as donor and the acceptor materials fullerene (C60) and diindenoperylene (DIP) [1] were analysed by angle resolved near-edge X-ray absorption fine structure spectroscopy and the results were compared to X-ray scattering data.
Different orientations are observed for molecules in the bulk, at free surfaces and at buried interfaces. Here, the orientation at the free surfaces depends on the substrate temperature during deposition for 6T but not for DIP. Furthermore, the acceptor molecules influence the orientation of the underlying 6T molecules. An improved crystallization and pronounced upright standing of the molecules in the underlying 6T film was observed upon deposition of C60. In contrast the deposition of DIP on top of 6T leads to an orientational relaxation of the 6T molecules to the bulk inclination angle.
[1] U. Hörmann et al., phys. stat. sol. RRL 5 (2011) 241.