Dresden 2014 – scientific programme
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O: Fachverband Oberflächenphysik
O 101: Molecular Films: Electronics, Photovoltaics and Structure
O 101.4: Talk
Friday, April 4, 2014, 11:15–11:30, WIL A317
Electric Potential Distributions in Space Charge Regions of Molecular Organic Adsorbates: The Distributed States Model — •Eric Mankel1,2, Corinna Hein3, Maybritt Kühn1,2, Thomas Mayer1,2, and Wolfram Jaegermann1,2 — 1TU Darmstadt, Surface Science Div., Darmstadt — 2InnovationLab GmbH, Heidelberg — 3TU Darmstadt, Electronic Materials Div., Darmstadt
We study the evolution of the electric surface potential for organic semiconductor adsorbates on different high work function substrates using photoelectron spectroscopy. Usually, the surface potential of these materials shows a typical progression in dependence of the adsorbate layer thickness indicating the formation of a space charge region around the contact. We found that these curve shapes cannot be fully explained by the Schottky model which is usually the standard to describe potential distributions in contact space charge regions. Therefore, the Schottky model has been extended assuming a continuous density of states distribution (DOS) in energy. The differences between the Schottky model and the distributed states model (DSM) will be discussed. Finally, both models are applied to measured values of the surface potential evolution of some exemplary organic molecules on varying substrates. We find that the surface potential evolution of the DSM describes the measured potential much more accurately than the surface potential evolution of the Schottky model. Although if this does not prove unequivocally the presence of a DOS in organic semiconductors their amount is estimated in the framework of the new model being between 1018 cm-3eV-1 and 1019 cm-3eV-1.