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 the influence of Li+ and 1,2dimethyl-3-hexyl imidazolium ions in the electrolyte on the photovoltaic properties was compared. The electrolyte containing 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 toward more positive potentials. At the same time, both the short-circuit photocurrent and the maximum value of the incident-photon-current conversion efficiency (IPCE) of the electrolyte containing Li+ ions were relatively higher. Data analysis suggests that presence of adsorbed Li+ ions improves via the phenomenon of band-edge movement the charge-injection efficiency by altering both the energy and number of excited state levels of the dye that participate in electron injection.