The photoresponse of iron- and carbon-doped TiO2 (anatase) photoelectrodes

Fe-doped and C-doped anatase TiO2 films were made by spray pyrolysis. For Fe:TiO2, a small sub-bandgap photoresponse is observed which is attributed to the presence of additional states located just above the valence band. Although no visible-light photoresponse is observed for carbon-doped TiO2 due to the low carbon content, the photocurrent at hnu > E-g is significantly larger than for undoped TiO2. At the same time, the donor density of oxidized C-doped TiO2 is > 1.9 x 10(19) cm(-3), compared to 3.2 x 10(17) cm(-3) for undoped TiO2. Assuming that only light absorbed in the depletion layer contributes to the photocurrent, the photoresponse of C-doped anatase (at 330 nm) is 16 times larger than that predicted for undoped TiO2 under similar conditions. The strong enhancement of the absorption is most likely caused by a change in the electronic structure of the material due to the presence of carbon and/or related defects. Photoluminescence measurements suggest that the defects present in oxidized carbon-doped anatase resemble those present in undoped, reduced TiO2.