Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1264477 | Organic Electronics | 2007 | 7 Pages |
Ultraviolet photoelectron spectroscopy has been used to determine the energy level alignment at interfaces of molecular hole-transporting materials and various conductive substrates. Depending on the work function of the substrate, ϕs, a transition between two different energy level alignment regimes has been observed: namely vacuum level alignment and Fermi level pinning. The transition is associated with spontaneous positive charge transfer across the interface to the organic semiconductors above a certain material-specific threshold value of ϕs. The charge transfer results in formation of an interfacial dipole of a magnitude that scales with ϕs. In the vacuum level alignment regime, the hole-injection barriers scale linearly with ϕs, while in the Fermi level pinning regime, these barriers are constant and independent of ϕs.