Fermi level pinning at interfaces with tetrafluorotetracyanoquinodimethane (F4-TCNQ): The role of integer charge transfer states

We have shown that the energy level alignment at the interfaces of tetrafluorotetracyanoquinodimethane (F4-TCNQ) and the substrates that span work function range from 3.45 to 5.8 eV corresponds to the Fermi level pinning regime. The Fermi level is pinned at 5.55 ± 0.1 eV as measured versus vacuum level. Within the range of ϕs studied, the magnitude of the observed interfacial dipole Δ scales linearly with substrate work function.