Effect of cations on the open-circuit photovoltage and the charge-injection efficiency of dye-sensitized nanocrystalline rutile TiO2 films

Dye-sensitized nanocrystalline rutile TiO2 solar cells were prepared, and t he influence of Li+ and 1,2dimethyl-3-hexyl imidazolium ions in the electro lyte on the photovoltaic properties was compared. The electrolyte containin g Li+ ions produced a lower open-circuit photovoltage than the electrolyte with 1,2-dimethyl-3-hexyl imidazolium ions, suggesting that the adsorption of Li+ ions to the rutile TiO2 surface causes a shift in the band edges tow ard more positive potentials. At the same time, both the short-circuit phot ocurrent and the maximum value of the incident-photon-current conversion ef ficiency (IPCE) of the electrolyte containing Li+ ions were relatively high er. Data analysis suggests that presence of adsorbed Li+ ions improves via the phenomenon of band-edge movement the charge-injection efficiency by alt ering both the energy and number of excited state levels of the dye that pa rticipate in electron injection.