C-doped TiO2 nanotubes with pulsed laser deposited Bi2O3 films for photovoltaic application.

Anodization was used to obtain a nanotubular TiO 2 photoanode on F–SnO 2 glass. Subsequent annealing in the CH 4 atmosphere promoted the C-doping and improved the crystallinity of the TiO 2 nanotubes. The pulsed laser deposition was applied to cover the nanotubes with Bi 2 O 3 , serving as a hole transport material. X-ray photoelectron spectroscopy analyses of the doped samples reveal a shift in the valence band's maximum position towards lower binding energy as compared to those observed for the undoped samples (annealed in the air). The doping positively affects the absorption by shifting the absorption edge to 567 nm. I – V measurements under illumination show that the C-doping of TiO 2 increases the current density following the absorbance results. The highest open circuit voltage was reached for the samples with the 300 °C-deposited Bi 2 O 3 layer, pointing to better quality of the p-n junction, hence of the contact between Bi 2 O 3 and TiO 2. This in situ annealing provided the formation of close contact between Bi 2 O 3 and TiO 2 , which enabled a faster charge transport as compared to the contact obtained with no annealing or even with post annealing. [Display omitted] • C-doping of anodized TiO 2 NTs supported on FTO by annealing in CH 4. • PLD to cover TiO 2 NTs with Bi 2 O 3 film, serving as a hole transport material. • XPS: Shift of VBM to lower BE for the doped vs. the undoped NTs (annealed in air). • DRS: Absorption red shift from 430 nm (undoped NTs) to 567 nm (doped NTs). • Best PV performances: C-doped TiO 2 with Bi 2 O 3 deposited at 300 °C in situ. [ABSTRACT FROM AUTHOR]