Title: Mechanism of the double heterostructure TiO2/ZnO/TiO2 for photocatalytic and photovoltaic applications: A theoretical study,
Abstract: Understanding the mechanism of the heterojunction is an important step
towards controllable and tunable interfaces for photocatalytic and photovoltaic
based devices. To this aim, we propose a thorough study of a double
heterostructure system consisting of two semiconductors with large band gap,
namely, wurtzite ZnO and anatase TiO2. We demonstrate via first-principle
calculations two stable configurations of ZnO/TiO2 interfaces. Our structural
analysis provides a key information on the nature of the complex interface and
lattice distortions occurring when combining these materials. The study of the
electronic properties of the sandwich nanostructure TiO2/ZnO/TiO2 reveals that
conduction band arises mainly from Ti3d orbitals, while valence band is
maintained by O2p of ZnO, and that the trapped states within the gap region
frequent in single heterostructure are substantially reduced in the double
interface system. Moreover, our work explains the origin of certain optical
transitions observed in the experimental studies. Unexpectedly, as a
consequence of different bond distortions, the results on the band alignments
show electron accumulation in the left shell of TiO2 rather than the right one.
Such behavior provides more choice for the sensitization and functionalization
of TiO2 surfaces.