The Photoresponse of Iron- and Carbon-Doped TiO2 (Anatase) Photoelectrodes

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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 hν > Eg is significantly larger than for undoped TiO2. At the same time, the donor density of oxidized C-doped TiO2 is > 1.9× 1019 cm−3, compared to 3.2× 1017 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.

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