Electronic properties of hybrid Zinc Oxide - Oligothiophene nanostructures

Using density functional theory in combination with model potential molecular dynamics, we study hybrid systems consisting of oligothiophene molecules with increasing chain length (two, four, and six rings) adsorbed onto a ZnO nanoparticle model. We investigate the energetics of adhesion and the morphological features at the curved interface. We compute the energy-level alignment taking many body effects into account within the ΔSCF approach. Our results show that, as a consequence of the local curvature of the interface, the electronic coupling between the organic and inorganic component affects the energy-level alignment in all systems, making it less favorable for charge separation. In particular, the energy-level alignment for sexithiophene on the ZnO curved nanoparticle does not lead to a type-II junction with staggered band gaps, contrary to what was recently found for sexithiophene on a flat (101̅0) ZnO surface. Although the limited size (and hence the large curvature) of the nanoparticle does not allow us to make a general statement, this indicates a trend that is valid for systems in which quantum confinement effects are important. As a side result of our study, we propose a simple practical model to predict the energy-level alignment in hybrid systems, which gives consistent results compared to ΔSCF.