Sub-band-gap photoresponse ofTiO2−xthin-film—electrolyte interface

When a $\mathrm{Ti}{\mathrm{O}}_{2-x}$ thin-film—electrolyte interface is illuminated by the monochromatic light in the sub-band-gap region, broad photocurrent peaks are observed at 462, 515, 1050, and 1258 nm. The energies of these peaks are in good agreement with the energies of defect levels of the Ti${\mathrm{O}}_2$ single crystal due to oxygen vacancies. From these experimental results, the photoresponse of the $\mathrm{Ti}{\mathrm{O}}_{2-x}$ thin-film—electrolyte interface in the sub-band-gap region is interpreted as arising from electronic excitations between the trap levels which originate from the defects of the $\mathrm{Ti}{\mathrm{O}}_{2-x}$ thin film and the conduction band.