Photoexcited Charge Transport and Accumulation in Anatase TiO₂

Photogenerated charge separation and redox reactions on photoexcited semiconductors are of great significance in many photon excited systems, such as photocatalytic water splitting systems, photocatalytic pollutant removal systems, photovoltaic devices, etc. It is highly desirable if we know the charge separation directions inside the semiconductor crystals, the preferred crystal facets the charge accumulate after separation, and the preferred facets where redox reactions occur, so we can grow the semiconductor crystals accordingly with the desired facets exposed on the surface to have large numbers of the photoaccumulated electrons and holes on the facets in order to realize a high photocatalytic efficiency for both oxidation and reduction on the surface or to achieve a large photovoltaic efficiency. Here, we attempt to convert the information from the electronic band structure calculations in the k space into the real space in bulk crystals and combine the surface electronic band structures of various facets to gain a comprehensive understanding of the charge transport inside the crystal and the preferred accumulations of electrons and holes on the surface facets, along with comparison with experimental observations. Anatase titanium dioxide (TiO2) is tried as an example with this strategy to elucidate such an effort.