Improved short-circuit photocurrent densities in dye-sensitized solar cells based on ordered arrays of titania nanotubule electrodes

We report on the synthesis of highly ordered arrays of titania nanotubules and their applications in enhanced photoelectrochemical cells. Ordered arrays of titania nanotubules of ∼120 nm external diameter, ∼100 nm internal diameter, and ∼5 μm length were fabricated on transparent conductive oxide (TCO) glass substrates by sol–gel processes using in-house prepared anodic alumina templates. After thermal bonding and template removal, the resultant nanotubule structures were applied in dye-sensitized solar cells (DSCs). Overall photoconversion efficiency of nearly 4.8% was achieved with Ru-bipyridine dye, N719, and iodolyte liquid electrolyte. This remarkable performance, for electrodes only ∼5 μm thick, is attributed to an unexpectedly high short-circuit photocurrent density of 16 mA/cm² for masked cells and up to 17 mA/cm² for unmasked cells. The enhanced short-circuit photocurrent (J_sc) is attributed to the high surface area (roughness factor ca. 1207) of the nanotubules and thus improved dye adsorption to the electrodes. The improved J_sc is also attributed to the parallel and vertical orientation of the nanostructures and thus to a well-defined electron diffusion path.