Mechanism of the double heterostructure TiO2/ZnO/TiO2 for photocatalytic and photovoltaic applications: A theoretical study

TL;DR

This theoretical study investigates the TiO2/ZnO/TiO2 double heterostructure, revealing stable configurations, electronic properties, and optical transition explanations, advancing understanding for photocatalytic and photovoltaic device design.

Contribution

It provides a detailed first-principles analysis of the interface structures, electronic behavior, and optical properties of the TiO2/ZnO/TiO2 heterostructure, which was not previously characterized.

Findings

Two stable interface configurations identified.

Reduced trap states within the band gap compared to single heterostructures.

Electron accumulation occurs in TiO2's left shell, affecting surface functionalization.

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.