UPS and Schottky barrier study of TiO₂ electrochemical anodes

The current-voltage, conductance-voltage and capacitance-voltage characteristics of metal-rutile and electrolyte-rutile barriers have been studied. The results show that the charge transfer rate limits the current through the electrolyte-rutile barriers. It is also found that there is an insulating rutile layer between the surface and the semiconducting (reduced) rutile which plays an important role in the charge transfer during the action of the barrier as an electrochemical solar cell. By combining these results and a UPS study of the rutile surface it is found that the states in the forbidden gap of semiconducting rutile help the charge transfer process. The open circuit voltage of the corresponding solar cells is found to increase with increasing redox potential of the ions in the electrolyte as well as with Cr doping of the rutile.