Bandgap Narrowing of Titanium Dioxides via Non-Compensated n-p Co-doping for Photocatalysis*

Titanium dioxide (TiO$_{2})$ is a promising photocatalyst for solar hydrogen production from water, yet its photocatalytic efficiency is limited by its intrinsic wide-bandgap nature. In this talk, we present a conceptually new and intuitive approach, termed non-compensated n-p co-doping, to narrow the bandgap of TiO$_{2}$. The validity of this approach has been demonstrated using first-principles calculations within density functional theory, showing that extra impurity bands are created in the gap region because of the non-compensated nature of the n-p co-doping, resulting in a narrowed bandgap around 2 eV. Moreover, the electrostatic attraction between the n and p dopants enhances their thermodynamic and kinetic solubility in the host semiconductors. Preliminary experimental results confirming the non-compensated n-p co-doping concept will also be presented, together with its applicability to other wide bandgap semiconductors.