Avoiding diffusion limitations in cobalt(III/II)-tris(2,2'-bipyridine)-based dye-sensitized solar cells by tuning the mesoporous TiO2 film properties.

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 TiO(2) 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 TiO(2) layer, namely film thickness, particle size, pore size and porosity, by simply optimizing the TiCl(4) 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.