Dye-sensitized solar cells based on electrolytes containing cobalt complexes as redox shuttles typically suffer a major limitation in terms of slow diffusion of those couples through the mesoporous TiO2 film. This results in a drop of the photocurrent density, particularly at high incident light intensities, reducing the overall cell performance. This work illustrates how tuning the four characteristic parameters of the mesoporous TiO2 layer, namely film thickness, particle size, pore size and porosity, by simply optimizing the TiCl4 post-treatment, completely eliminates diffusion problems of cobalt(III/II) tris(2,2'-bipyridine) and at the same time maximizes the short-circuit photocurrent density. As a result, a power conversion efficiency of 10.0?% at AM 1.5 G 100 mW?cm-2 was reached in conjunction with an organic sensitizer.