Engineering of the energy level alignment at organic semiconductor interfaces by intramolecular degrees of freedom: Transition metal phthalocyanines

We have determined the energy level alignment at interfaces between various transition metal phthalocyanines (MnPc, FePc, CoPc, NiPc, CuPc, ZnPc) and gold using photoemission spectroscopy. We demonstrate that the energy level alignment at these interfaces depends upon the type of transition metal. This offers a route to adjust the hole injection barrier via the choice of otherwise equivalent molecular organic semiconductors. In particular, the interfaces MnPc/Au and CoPc/Au are characterized by a small hole injection barrier, which would be advantageous for applications. © 2009 American Chemical Society.