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 liqs. (diethylmethylsulfonium iodide, dibutylmethylsulfonium iodide or 3-hexyl-1-methylimidazolium iodide) or an org. 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 coeff. for the triiodide that transports pos. 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 satn. It is proposed that this is caused by recombination processes. The electron lifetime is depending on the type of cation used in the ionic liq., where bulky, less absorptive cations seem to give longer lifetimes.