Template-free self-assembly of a nanoporous TiO2 thin film

We report a nanoporous TiO2 thin film prepared using a supersaturated aqueous solution containing peroxotitanium complex ions. The film morphology can be regulated by chemical kinetics, which was partially controlled by solution conditions such as the concentrations of starting materials, pH values, and the temperatures of the solutions. Porous films with various morphologies from particulate to curved sheet shaped were prepared on different substrates including Si, polymers, and glass. Porous microstructures of films permitted us to prepare a crack-free film 2-3 mu m in thickness. These films were still amorphous under the present treatment conditions. Dye-sensitized solar cells using annealed (anatase) films of different morphologies as electrodes yielded conversion efficiency ranging from 1.3% to 3.1%. Improvement in performance may be achieved by either increasing the film thickness or inducing crystallization in solutions.