Role of interfacial dipole layer for energy-level alignment at organic/metal interfaces

The energy-level alignment at Cu-phthalocyanine/metal interfaces has been studied using the Kelvin probe method. The organic layer on a metal surface plays two important roles in the energy-level alignment: the formation of the interfacial dipole (ID) and the passivation of the metal surface. The ID layer determines the injection barrier between the metal and the organic semiconductor. In cases where the lowest unoccupied molecular orbital level of the organic layer on the ID layer is below the Fermi level of the passivated metal substrate, the spontaneous charge transfer from the passivated metal substrate to several organic layers leads to the Fermi-level pinning.