Dye-sensitized nanostructured crystalline mesoporous tin-doped indium oxide films with tunable thickness for photoelectrochemical applications

A simple route towards synthesis of nanostructured mesoporous Indium-Tin Oxide (templated nano-ITO) electrodes exhibiting both high conductivities and optimized bicontinuous pore-solid network is reported. The ITO films are first produced as an X-ray-amorphous, high surface area material, by adapting recently established template-directed sol-gel methods using Sn(IV) and In(III) salts. Carefully controlled temperature/atmosphere treatments convert the as-synthesized ITO films into nano-crystalline coatings with the cubic bixbyite structure. In particular, a multi-layered synthesis was successfully undertaken for tuning the film thickness. In order to evaluate the performances of templated nano-ITO as an electrode substrate for photoelectrochemical applications, photoelectrodes were prepared by covalent grafting of a redox-active dye, the complex [Ru(bpy)(2)(4,4'-(CH2PO3H2)(2)-bpy)]Cl-2 1 (bpy = bipyridine). Surface coverage was shown to increase with the film thickness, from 0.7 x 10(-9) mol cm(-2) (one layer, 45 nm) to 3.5 x 10(-9) mol cm(-2) (ten layers, 470 nm), the latter value being similar to 100 times larger than that for commercially available planar ITO. In the presence of an electron mediator, photocurrents up to 50 mu A cm(-2) have been measured under visible light irradiation, demonstrating the potential of this new templated nano-ITO preparation for the construction of efficient photoelectrochemical devices.