Backside illuminated dye-sensitized solar cells based on titania nanotube array electrodes

Backside illuminated solar cells based on 6 mu m long highly-ordered nanotube-array films sensitized by a self-assembled monolayer of bis(tetrabutylammonium)-cis-(dithiocyanato)-N,N'-bis(4-carboxylato-4'- carboxylic acid-2,2'-bipyridine)ruthenium(II) (commonly called 'N719') show a short-circuit current density of 8.79 mA cm(-2), 841 mV open circuit potential and a 0.57 fill factor yielding a power conversion efficiency of 4.24% under AM 1.5 sun. The solvent used to infiltrate the dye into the nanotube arrays, made by potentiostatic anodization of a titanium foil, was found to significantly influence the electrical characteristics of the resulting solar cell. A superior photoresponse was obtained with acetonitrile as the dye solvent. This is attributed to the improved wetting characteristics of the dye solution in acetonitrile enabling self-assembled monolayers with higher surface coverage to be formed inside the nanotubes. In comparison to nanocrystalline films, the nanotube-array films consistently exhibit larger open circuit photovoltage values; the origins of this enhancement are discussed.