Ab initio study of electronic effects in the ZnO/TiO2 core/shell interface: application in dye sensitized solar cells

Abstract

Core/shell structure of ZnO nanowires coated with a monolayer of TiO₂ is investigated using Density Functional Theory (DFT). The electronic states of the semiconductor is calculated and compared before and after coating of the TiO₂ monolayer on a ZnO [10 0] surface. The effect of TiO₂ coating induce surface states changes and shifts the conduction and valence band edges to higher energies. Our results, in qualitative agreement with the experimental work of Matt Law et al. (J. Phys. Chem. B, 110, 22652), show an increase in open circuit voltage and a decrease in short circuit current in ZnO/TiO₂ core shell dye sensitized solar cells. Regarding the semiconductor density of states (DOS), TiO₂ coated ZnO have more conduction band acceptor states and lower electronic back recombination in agreement with experimental results. Surface dipoles are attributed to changes of the local density of states of the surface. This method can be used for more investigation of starting effects of semiconductor interface and helps the study of surface states and their physical origin in dye sensitized solar cells.