Avoiding Diffusion Limitations in Cobalt(III/II)‐ Tris (2,2′‐Bipyridine)‐Based Dye‐Sensitized Solar Cells by Tuning the Mesoporous TiO 2 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.