Berlin 2012 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 34: Organic thin films II: Interface spectroscopy
DS 34.3: Vortrag
Donnerstag, 29. März 2012, 15:30–15:45, H 2032
Tuning the work function of ZnO with a molecular electron acceptor — •Raphael Schlesinger1, Yong Xu3, Stefanie Winkler2, Antje Vollmer2, Patrick Rinke3, Matthias Scheffler3, Sylke Blumstengel1, Fritz Henneberger1, and Norbert Koch1,2 — 1Humboldt-Universität zu Berlin — 2Helmholtz-zentrum Berlin, BESSY II — 3Fritz-Haber-Institut Berlin
Combining conjugated organic with inorganic semiconductors opens up new possibilities for tailoring the properties and efficiency of optoelectronic devices by utilizing the advantages of each material class. Being able to tune the alignment of the frontier energy levels of hybrid inorganic/organic systems is essential to control their function. Employing molecular acceptor interlayers to tune the work function (φ) of a metal and thus the energy level alignment between the metal and an organic semiconductor was demonstrated previously.
We now extend this concept to the polar surfaces of ZnO by using the strong molecular acceptor F4TCNQ. φ of bare ZnO surfaces was strongly increased by up to 3eV upon adsorption of a monolayer of the acceptor, as evidenced by photoelectron spectroscopy. In contrast to the strong inorganic-to-organic electron transfer found for F4TCNQ on metal surfaces, no peak associated with the LUMO below EF, that would be expected for electron transfer from ZnO, is found in our experiments. DFT calculations suggest strong intramolecular charge rearrangement of F4TCNQ as mechanism for the φ increase on ZnO. The energy level alignment of sexiphenyl (6P) adsorbed on top of acceptor interlayers on ZnO is shown to be controlled via the φ changes.