Defects in Bismuth Vanadate: Insights from First Principles

Licentiatavhandling, 2022

Photoelectrochemical water splitting is an attractive technique for sustainable hydrogen production, but its efficiency is heavily dependent on the properties of the semiconducting photoelectrodes used in the process. These properties are intimately connected to the presence of point defects in the materials, and understanding this relationship is a key step towards the development of better photoabsorbers. The effects of single impurities are challenging to probe using experimental techniques, but the use of computer modelling makes it possible to study modifications on the level of individual atoms. This thesis investigates native point defects in bismuth vanadate using hybrid density functional theory. The fundamentals of water splitting and the properties of the material are reviewed. Additionally, the theoretical foundations of the applied computational methods are described. The calculations performed within the thesis highlight the structural complexity of native point defects in bismuth vanadate and the important role that charge localization plays in its defect chemistry. In addition, it is found that oxygen vacancies induce significant lattice distortions at realistic concentrations. Simulated powder X-ray diffraction patterns reveal that this makes phase identification difficult.