Electron transport and recombination in dye-sensitized solar cells with ionic liquid electrolytes

The electron transport and recombination in dye-sensitized TiO2 solar cells with different electrolytes have been investigated. The electrolytes were based on iodine-doped ionic liquids (diethylmethylsulphonium, dibutylmethylsulphonium or 3-hexyl-1-methylimidazolium iodide) or an organic solvent (3-methoxypropionitrile with LiI, I2 and 1-methylbenzimidazole). The most viscous electrolytes showed a clear limitation in photocurrent, which can be attributed to a low diffusion coefficient for the triiodide that transports positive charge to the counter electrode. No essential difference was found in the electron transport properties of the solar cells, which appear to be dominated by the properties of the nanostructured TiO2 film. The intensity-modulated photocurrent response was strongly affected by current saturation. This is proposed being caused by recombination processes. The electron lifetime is depending on the type of cation used in the ionic liquid, where bulky, less absorptive cations seem to give longer lifetimes.