Surface modification of TiO₂ photoanodes with In³⁺ using a simple soaking technique for enhancing the efficiency of dye-sensitized solar cells

Indium-doped TiO₂ photoanode for dye-sensitized solar cells are prepared using a simple surface-doping technique by soaking the TiO₂ film in acidic In³⁺ solution at 70 °C for 30, 45 and 60 min followed by sintering at 450 °C. Structural characterization of In-doped TiO₂ films by SEM, TEM, EDX, XRD and Raman spectroscopy revealed the successful attachment of Indium to the surface of TiO₂ and that the amount of In dopant is proportional to the soaking time. The PCE of the devices fabricated from In-doped TiO₂ with a soaking time of 30 min produced an increase of 18.0 % compared to the undoped cells. Charge extraction analysis at open-circuit revealed that surface-doping with indium shifts TiO₂ band edge downward. However, the increase in V_OC was found as the net effect of negative movement of CB and retarded recombination caused by TiO₂ surface passivation via the In dopant.