Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 19: Organic Interfaces (SYSA 6)
DS 19.9: Vortrag
Mittwoch, 27. Februar 2008, 16:45–17:00, H 2013
Molecular band offsets and Charge Neutrality Levels at organic interfaces — •Héctor Vázquez1, Mads Brandbyge1, Antti-Pekka Jauho1, and Fernando Flores2 — 1MIC-Department of Micro and Nanotechnology, Technical University of Denmark, DTU, DK-2800 Lyngby, Denmark. — 2Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Spain.
We present a theoretical method to calculate the energy level alignment at interfaces of organic semiconductors based on the Charge Neutrality Levels (CNLs). The CNLs act as the electronegativity or effective Fermi level of the organic material at the interface.
We calculate the CNL position from the isolated organic molecule, rather than at the interface. We perform a DFT calculation of the molecule and consider energy corrections associated with the addition or removal of an electron; these result in shifts of the molecular levels, increasing the molecular gap with respect to DFT. The CNL position is calculated from the branch point of the molecular Greens function. The screening parameters at the interface, which also affect molecular level offsets, can be estimated from the static dielectric functions of the organic materials.
We have performed this analysis for several organic molecules, including, bathocuproine, Alq3 and hexaazatrinaphthylene derivatives, comparing induced dipoles and interface properties with experiment. Our work suggests that, at interfaces where the details of the interaction are not important, the CNL picture represents a general and intuitive model for understanding organic semiconductor interfaces.