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

Abstract

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)]Cl₂1 (bpy = bipyridine). Surface coverage was shown to increase with the film thickness, from 0.7 × 10⁻⁹ mol cm⁻² (one layer, 45 nm) to 3.5 × 10⁻⁹ mol cm⁻² (ten layers, 470 nm), the latter value being ∼100 times larger than that for commercially available planar ITO. In the presence of an electron mediator, photocurrents up to 50 μA 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.