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A new type of high surface area TiO(2) electrode for DSSCs is proposed. The new electrode consists of a transparent conductive nanoporous matrix that is coated with a thin layer of TiO(2). This design ensures a distance of several nanometers between the TiO(2)-electrolyte interface and the current collector throughout the nanoporous electrode, in contrast to several micrometers associated with the standard electrode. In addition the new electrode contains inherent screening capability due to the high doping level of the conducting core matrix. Theoretically, this electrode should overcome the collection and image field problems associated with solid-state DSSCs. Using a flat analogue of the new electrode we show that unless the TiO(2) coating is thicker than 6 nm, the electrode performance is very low due to fast recombination. Two mechanisms for the thickness effect on the recombination rate, that are proposed, provide new insight to the DSSC operation.

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The electron diffusion coefficient at varying porosity has been determined in a series of nanostructured TiO(2) films of different initial thicknesses. The porosity was changed by applying different pressures prior to sintering, thereby modifying the internal morphology of the films though not their chemical and surface conditions. A systematic increase of the effective diffusion coefficient was observed as the porosity was decreased, indicating the improvement of the internal connectivity of the network of nanoparticles. The experimental results have been rationalized using percolation theory. First of all, applying a power law dependence, the diffusion coefficient as a function of porosity from different films collapsed in a single master curve. In addition, application of the models of effective medium approximation (EMA) allows us to compare the experimental results with previous data from Monte Carlo simulation. The different data show a similar dependence in agreement with the EMA predictions, indicating that the geometrical effect of electron transport due to variation of porous morphology in TiO(2) nanoparticulate networks is well described by the percolation concept.

Layers of porous TiO(2) fabricated by electrophoretic deposition at different temperatures with subsequent sintering in air were investigated by transient photocurrent measurements in aqueous electrolyte. The effective diffusion coefficient of excess electrons changed between 1.6 x 10(-5) and 1.4 x 10(-4) cm(2)/s depending strongly on the solution temperature during the TiO(2) layer deposition. Characterization, in terms of average degree of preferred orientation, shows that low deposition temperature results in orientation of the nanocrystals forming the porous film. Consequently, the increase of effective diffusion coefficient is attributed to a higher degree of ordering in the nanoporous TiO(2) layer.