  Three driving forces control the energy level alignment between
transition-metal oxides and organic materials: the chemical interaction between
the two materials, the organic electronegativity and the possible space charge
layer formed in the oxide. This is illustrated in this letter by analyzing
experimentally and theoretically a paradigmatic case, the TiO2(110) / TCNQ
interface: due to the chemical interaction between the two materials, the
organic electron affinity level is located below the Fermi energy of the
n-doped TiO2. Then, one electron is transferred from the oxide to this level
and a space charge layer is developed in the oxide inducing an important
increase in the interface dipole and in the oxide work function.
