Energy level alignment

Fig.1 Schematic representation of the adjustment of equilibrium conditions at an (inorganic) semiconductor/metal interface. The charge transfer across the interface could cause the formation of a band bending in the semiconductor and/or localized interface dipoles.

Generally, dipoles at metal-organic interfaces were found for many systems, expressed by a shift of the vacuum level at the interface as probed by photoemission. But rules for inorganic semiconductor interfaces cannot be applied on organic semiconductors without limitations. For instance, correlation effects and the distinct lower charge carrier concentration in organic materials has to taken into consideration. Models for the electronic structure of organic semiconductor interfaces are still discussed controversy. Bringing two materials into contact, the thermodynamic equilibrium can be achieved via charge flow across the interface. But further effects such as the reduction of the substrate work function at the interface (in the case of metal/organic interfaces), polarization effects, or the redistribution of electrons in the organic material have to be considered.

Related publications:

Electronic properties of interfaces between model organic semiconductors and metals

M. Knupfer, H. Peisert phys. stat. sol.(a) (Special Issue on Organic Semiconductors), 201 (2004) 1055-1074.

Site-specific charge transfer screening at organic/metal interfaces

H. Peisert, D. Kolacyak, T. Chassé J. Phys. Chem. C, 113 (2009) 19244–19250.