Dresden 2017 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 29: Organic Thin Films I
DS 29.7: Vortrag
Mittwoch, 22. März 2017, 11:00–11:15, CHE 91
How molecular quadrupole moments affect the energetics in organic thin films — •Martin Schwarze1, Christopher Gaul2, Katrin Ortstein1, Frank Ortmann2, and Karl Leo1 — 1Dresden Integrated Center for Applied Physics and Photonic Materials, TU Dresden, 01069 Dresden, Germany — 2Institute for Materials Science and Dresden Center for Computational Materials Science, TU Dresden, 01069 Dresden, Germany
The efficiency of organic semiconductor devices crucially depends on the precise energy level alignment of different organic layers. In most organic semiconductors, the ionization energy (IE) and the electron affinity (EA) of single molecules determine the electronic levels in organic devices and, therefore, their optimization is usually based on the IE and the EA of neat materials. However, these values can change substantially with the film morphology, at interfaces or in blends of different molecules.
By photoelectron spectroscopy, we obtain the IE of neat films at different molecular orientations and of blends with varying mixing ratios for a variety of small molecule materials. The changes of the IE, as a function of molecular orientation and mixing ratio, scale directly with the magnitude of the molecular quadrupole moments, as obtained by density functional theory simulations. By adjusting the mixing ratio of two different donor molecules, namely ZnPc and F4ZnPc, such electrostatic effects can be exploited in organic solar cells to tune the open-circuit voltage [1].
[1] Schwarze et al., Science 352, 1446 (2016)