Photovoltaic properties of TiO₂-ZnO composite electrodes for dye-sensitized solar cells

Photovoltaic properties of wet-type dye-sensitized solar cells were investigated with emphasis on the structures of two types of TiO₂-ZnO composites as photoelectrodes. One was the mixed electrode of TiO₂ and ZnO powders. Another was the TiO₂-coated ZnO nanorod array prepared by a sol-gel process. The composite films were loaded on a transparent electrode and clacined at 450-500°C, on which dye molecules were adsorbed. The currentvoltage characteristics were measured in iodide electrolyte solution under a simulated solar light. The mixed electrode exhibited a significant decrease in current density and photovoltaic efficiency compared to TiO ₂ electrode. Although the photovoltaic efficiency of ZnO was lower than that of TiO₂, TiO₂coating of ZnO nanorod array improved the photovoltaic properties. The addition of triblockcopolymer as pore former in TiO₂ coating was effective to increase the photovoltaic efficiency. The control of the concentration of TiO₂ slurry was also important for homogeneous penetration into ZnO nanorod array.