Electronic Structure of Interfaces between Thiophene and TiO2 Nanostructures

We investigated the electronic properties of hybrid combinations of organic-inorganic interfaces relevant for photovoltaic applications, a thiophene (molecule or polymer) and a TiO2-anatase nanostructure, using ab initio density functional theory (DFT) and many-body perturbation theory calculations for model systems. The DFT results concerning electronic charge distribution show interface states coupling the polymer to the oxide substrate at the molecule's lowest unoccupied state, favoring electron transfer from the organic to the oxide through photoexcitation. Concerning the energy level structure, DFT predicts a virtually zero effective energy gap between polymer valence and oxide conduction bands. The GW-based results lead to proper band alignment, restoring the interface energy gap, and at the same time highlight the confinement effects to be expected for oxide nanostructures.