Chemical interaction, space-charge layer and molecule charging energy for metal oxide / organic interfaces

TL;DR

This paper investigates the energy level alignment at metal oxide/organic interfaces, focusing on chemical interactions, space-charge effects, and molecule charging energies through experimental and theoretical analysis of TiO2(110)/TCNQ.

Contribution

It provides a combined experimental and theoretical analysis of the factors influencing energy level alignment at metal oxide/organic interfaces, highlighting the role of chemical interaction and space charge layers.

Findings

Chemical interaction shifts organic electron affinity below the Fermi level.

Electron transfer from oxide to organic creates a space charge layer.

Interface dipole and work function increase due to charge transfer.

Abstract

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.