Defect engineering of photosensitive oxide materials. Example of TiO2 solid solutions

The imperative to protect the environment from increasingly apparent climate change imposes the urgent need to reduce the emissions of greenhouse gases to the atmosphere. This, consequently, results in intensification of research in the development of new materials and devices for the generation of energy that is environmentally clean. This work considers photosensitive oxide semiconductors for solar energy conversion by light-induced water oxidation. It has been documented that the performance of oxide semiconductors for solar-to-chemical energy conversion is determined by a range of defect-related properties, including the concentration of surface active sites, Fermi level, charge transport, electronic structure, and alignment of band edges with the energy level of the redox couple. The present work considers the research strategy in processing TiO2-based semiconductors, which are the promising candidates for a new generation of solar materials. It is shown that the performance-related properties of TiO2 and its solid solutions are determined by surface versus bulk defect disorder and the associated semiconducting properties. Therefore, the development of TiO2-based materials with enhanced performance could be based on using defect engineering for imposing optimized bulk versus surface properties. In this work, we discuss a range of defect-related properties of TiO2 and its solid solutions, such as electrical and optical properties and the related photocatalytic performance. We show that the phenomenon of segregation may be used as the technology for imposition of controlled surface versus bulk defect disorder that is required for processing the systems with optimized properties.