Berlin 2018 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 13: Organic Electronics and Photovoltaics - Hybrid and Organic Layer Systems
CPP 13.2: Vortrag
Montag, 12. März 2018, 15:15–15:30, C 243
Bias dependency of hybrid charge transfer emission at planar ZnO/small molecule interfaces — •Stefan Zeiske1, Ulrich Hörmann1, Fortunato Piersimoni1, Lukas Hoffmann2, Thomas Riedl2, Denis Andrienko3, and Dieter Neher1 — 1Universität Potsdam, Germany — 2Bergische Universität Wuppertal, Germany — 3MPI Mainz, Germany
Recent studies propose that the electroluminescence from hybrid charge transfer excitons (HCTX) depends not only on the interfacial energy gap but also on the applied bias. The models to explain these observation base either on filling of trap states, or on the assumption of delocalized HCT state confined in a triangular quantum well created by the electric field. Here, we investigate the origin of the bias dependent HCTX emission at planar interfaces between the ZnO and different small molecules. We find a nearly linear dependency of the EL peak position on the applied electric field. The independency of the slope on the organic layer thickness confirms that the shift is caused by a field and reminds of the linear Stark effect. Simple 1D quantum mechanical models confirm this interpretation and predict a moderate hole delocalization in the organic of the order of the typical size of a small molecule. Electrostatic treatment of the interaction of the charged molecule with its image potential, however, reveals that the observed field dependence is considerably influenced by the polarizability of the organic cation. As a direct consequence the field-induced shift of the EL peak is expected to be strongly dependent on the molecular orientation at the hybrid interface.