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 1,2-dimethyl-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.