Berlin 2015 – scientific programme

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DS: Fachverband Dünne Schichten

DS 39: Poster Session II

DS 39.20: Poster

Thursday, March 19, 2015, 16:00–18:30, Poster F

The Role of Chemical Defects for Charge Injection Barriers at Metal / Organic Semiconductor Interfaces — •Hermann Edlbauer, Shashank S. Harivyasi, Egbert Zojer, and Oliver T. Hofmann — Institute of Solid State Physics, NAWI Graz, Graz University of Technology, 8010 Graz, Austria

The efficiency of organic electronic devices is strongly determined by the contact resistance caused by the interface of the organic semiconductor and the metal electrode. One approach for its reduction is modifying the work function of the metal contact by adsorbing a monolayer of deliberately chosen molecules onto the metal surface. Our density functional theory (DFT) calculations for instance show that a monolayer of the electron acceptor tetrafluoro-benzoquinone adsorbed on Cu(111) causes a work function increase of about 0.5 eV. However, imperfections and chemical defects, e.g., through hydrogen adsorption, can mitigate this effect. Within this work, we investigate how sensitively the injection barrier depends on the formation of chemical defects. In particular, the corrugation of the electrostatic potential above the surface and the implications for the formation of ``hot spots" are discussed. This is studied by a gradual hydrogenation of parts of the molecules in a supercell. Using ab initio thermodynamics, further we show how the number of chemical defects and hence the work function change can be linked to the partial pressures of the participating molecules in a surrounding gas phase.