Rapid Dye Adsorption via Surface Modification of TiO₂ Photoanodes for Dye-Sensitized Solar Cells

A facile method for increasing the reaction rate of dye adsorption, which is the most time-consuming step in the production of dye-sensitized solar cells (DSSCs), was developed. Treatment of a TiO₂ photoanode with aqueous nitric acid solution (pH 1) remarkably reduced the reaction time required to anchor a carboxylate anion of the dye onto the TiO₂ nanoparticle surface. After optimization of the reaction conditions, the dye adsorption process became 18 times faster than that of the conventional adsorption method. We studied the influence of the nitric acid treatment on the properties of TiO₂ nanostructures, binding modes of the dye, and adsorption kinetics, and found that the reaction rate improved via the synergistic effects of the following: (1) electrostatic attraction between the positively charged TiO₂ surface and ruthenium anion increases the collision frequency between the adsorbent and the anchoring group of the dye; (2) the weak anchoring affinity of NO₃^– in nitric acid with metal oxides enables the rapid coordination of an anionic dye with the metal oxide; and (3) sufficient acidity of the nitric acid solution effectively increases the positive charge density on the TiO₂ surface without degrading or transforming the TiO₂ nanostructure. These results demonstrate the developed method is effective for reducing the overall fabrication time without sacrificing the performance and long-term stability of DSSCs