Chemical interaction, space-charge layer, and molecule charging energy for a TiO₂/TCNQ interface

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 study 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.