Dye-Sensitized Core−Shell Nanocrystals:  Improved Efficiency of Mesoporous Tin Oxide Electrodes Coated with a Thin Layer of an Insulating Oxide

Coating nanocrystalline SnO2 electrodes for dye-sensitized solar cell applications with a thin layer of ZnO, TiO2, ZrO2, MgO, Al2O3, Y2O3, or other insulating oxides was found to improve dye adsorption and increase the sensitized photocurrent. The surface of the oxide coating is more basic than SnO2, which renders dye attachment by its carboxyl groups more favorable. At the same time, the photovoltage and fill factor are strongly enhanced, resulting in much better energy conversion efficiencies. This change is ascribed to inhibition of electron back transfer from SnO2 to the redox electrolyte (I3-) by the insulating oxide. The optimum coating thickness is only a few angstroms, suggesting that electron transfer…