Electronic-Insulating Coating of CaCO₃ on TiO₂ Electrode in Dye-Sensitized Solar Cells:  Improvement of Electron Lifetime and Efficiency

Electronic-insulating coating of CaCO 3 on nanocrystalline TiO 2 electrode for dye-sensitized solar cells was found to increase both short-circuit photocurrent ( J sc ) and open-circuit photovoltage ( V oc ) remarkably. The significant increase in J sc is mainly attributed to the remarkably increased dye adsorption resulting from the more basic surface of CaCO 3 than TiO 2, while the increase in V oc originates from suppression of charge recombination owing to the surface covering of TiO 2 with an insulating coating of CaCO 3, revealed by intensity-modulated photovoltage spectroscopy. A 15 μm TiO 2 (23 nm) nanocrystalline electrode coated with 1 wt % CaCO 3, sensitized with N719, produced power conversion efficiency of 10.2%, where N719 is cis -di(thiocyanato)-bis(2,2‘-bipyridyl-4,4‘-dicarboxylate) ruthenium(II), using an antireflective film on the cell surface.