A Hybrid Zinc Phthalocyanine / Zinc Oxide System for Photovoltaic devices: a DFT and TD-DFPT Theoretical Investigation

By combining ab initio density functional theory (DFT) and time-dependent density functional perturbation theory (TDDFPT) methods, we investigate the structural, electronic and optical properties of a zinc phthalocyanine (ZnPc) molecule interacting with the zinc oxide (ZnO) wurtzite (10-10) surface. Our results reveal the existence of a strong molecule-surface coupling whose major effect is the appearance of a new unoccupied electronic level, deriving from an intimate mixing of ZnPc and ZnO electronic states and strategically located within the ZnO conduction band and below the ZnPc LUMO. This level induces appreciable changes in the ZnPc absorption spectrum and is expected to significantly favor a molecule-to-surface transfer of photo-excited electrons, a key process in the functioning of hybrid photovoltaic devices. The molecule-surface interactions are also characterized by significant van der Waals forces and by the formation of molecule-surface chemical bonds, thus resulting in appreciable molecular adhesion to the surface.