Effect of Rare-Earth Metal Oxide Nanoparticles on the Conductivity of Nanocrystalline Titanium Dioxide: An Electrical and Electrochemical Approach

Doping of rare-earth metal oxides into nanocrystalline titanium dioxide (NTD) films is known to improve performance for photovoltaic and photocatalytic applications; however, the reasons for this improvement are not well understood. To explore the enhancement mechanism, an electrical and electrochemical study of rare-earth oxide-doped NTD films was performed. Doped films were found to be 40–50 times more conductive than undoped films, with linear current–voltage characteristics and decreased light sensitivity. Cyclic voltammograms of doped samples show an enhanced scan rate dependence in the deep trap regime due to a slower charge trapping rate. Finally, electrochemical impedance measurements reveal a decrease in space charge density and a shift in the flat-band potential. Taken together, these results suggest that charge transfer from the rare earth oxide neutralizes the deep trap states in the NTD film, decreasing charge scattering, and improving the NTD performance as an electron acceptor and electron transport material.