Phthalocyanine-sensitized nanostructured TiO2 electrodes prepared by a novel anchoring method

A novel method for anchoring phthalocyanines substituted with ester groups onto nanostructured TiO2 films is described. Such phthalocyanines did not a dsorb on nanostructured TiO2 film by the ordinary methods. In our new metho d, the TiO2 film is pretreated with (CH3)(3)COLi to change the surface hydr oxyl groups (-OH) into oxygen anions (-O-), thus making the surface more re active toward the ester functionalities of the dye. The dye can then be anc hored onto the semiconductor surface through the produced carboxylate group (s). The amount of anchored dye on the semiconductor shows a dependence on both the time of base treatment and the time of dye treatment. Electrodes t reated with the free base phthalocyanine and zinc phthalocyanine were chara cterized by absorption spectroscopy, photocurrent action spectroscopy, and photocurrent-photovoltage measurements. The homogeneous blue-green color an d the absorption bands in the far-red region are indicative of an attachmen t of the dye on TiO2 film. A monochromatic incident photo-to-current conver sion efficiency of 4.3 % was achieved at 690 nm for a cell where the base-t reated electrode was treated with ZnPcBu.