Berlin 2012 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 34: Organic thin films II: Interface spectroscopy
DS 34.7: Vortrag
Donnerstag, 29. März 2012, 16:30–16:45, H 2032
Orientation of Non–Planar Molecules in thin Polycrystalline Layers from Infrared Ellipsometry Spectra – OFET and OPV materials — •Jens Trollmann, Robert Lovrinčić, Carl Pöl-king, and Annemarie Pucci — Kirchhoff–Institut für Physik der Universität Heidelberg
The determination and control of molecular ordering in organic thin films is of particular interest for designing and improving production processes for organic field effect transistors (OFET) and organic photovoltaic (OPV) devices. By enhancing the molecular ordering in the conducting film performance of OFETs can be significantly improved. Furthermore the fill factor in organic solar cells can be increased by reorienting molecules. In this talk we show how to reliably conclude on the predominant molecular orientation in a thin film by a computation based comparison of infrared (IR) ellipsometric measurements with density functional theory calculations of vibrational eigenvalues and eigenvectors for a single molecule. To proof this concept we determined the anisotropic dielectric functions of two organic semiconductor thin films, ID583 and NDI-F, in the spectral range of 350 to 5000cm−1. The approach is especially advantageous if applied to molecules with an anisotropic and non-planar structure forming X-ray amorphous layers with a preferred molecular orientation but an insufficient degree of long-range order for diffraction based methods. In such cases our analysis yields more accurate and significant results than achievable by only comparing ordinary and extraordinary refractive indices in the visible range. Funding by BMBF (Polytos) is gratefully acknowledged.