Structural and Electrical Properties of Nb-Doped Anatase TiO2 Nanowires by Electrospinning

One-dimensional nanostructures of niobium-doped anatase TiO2 (Nb:TiO2) up to 5 at.% Nb were synthesized by electrospinning a polymeric solution containing titanium and niobium precursors and subsequent annealing. Thus obtained fibers had diameter similar to 150 nm. The undoped TiO2 fibers were constituted by larger single crystalline grains of size similar to 50 nm, whereas the doped ones had decreased grain sizes (similar to 30 nm) under similar processing conditions. The Nb doping decreased the BET surface area of TiO2. A strain-induced lattice contraction was observed in Nb:TiO2. The continuous nanofibers were shortened to nanowires (NW) of aspect ratio 10:1 by ultrasonically dispersing them in acetic acid, which were developed as films of thickness similar to 8-13 mu m onto conducting glass substrates. The TiO2 and Nb:TiO2 nanowire films were further sensitized by a dye; the amount of dye anchored was found to decrease with increase in the dopant concentration. The dye-sensitized solar cells fabricated using the doped fibers, although with a nominally increased current density (J(SC)), have reduced efficiency due to lower fill factor and open circuit voltage (V-OC). The electron diffusion coefficient (D-n) and mobility (mu(n)) of the TiO2 and Nb:TiO2 NW in the presence of iodide/triiodide ions were an order of magnitude higher compared with the undoped samples.