First-principles theoretical study of organic/metal interfaces: Vacuum level shifts and interface dipoles

In this article, we discuss recent progress in theoretical studies on the electronic properties of organic/metal interfaces, especially on the origin of the interface dipoles. We first discuss the effect of the interface dipole on the charge injection barriers at organic/metal interfaces. Then, we observe the importance of the interface structure, especially of the organic-metal distances in physisorption systems. The experimentally observed substrate dependence of the interface dipole can be attributed mainly to the difference in the organic-metal distance. In the case of chemisorption systems, the induced density of interface states tends to pin the Fermi level relative to the HOMO and LUMO levels of molecules. We also point out an important role of van der Waals (vdW) interaction between organic molecules and metal substrates. Density functional theory (DFT) within a generalised gradient approximation (GGA) plus a recently proposed semi-empirical vdW correction can describe atomic geometries of organic/metal interfaces reasonably well. (c) 2012 Elsevier B.V. All rights reserved.