Electrospray Preparation of Hierarchically-structured Mesoporous TiO2 Spheres for Use in Highly Efficient Dye-Sensitized Solar Cells

We report a simple method to prepare hierarchically structured TiO2 spheres (HS-TiO2), using an electrostatic spray technique, that are utilized for photoelectrodes of highly efficient dye-sensitized solar cells (DSSCs). This method has an advantage to remove the synthesis steps in conventional sol-gel method to form nano-sized spheres of TiO2 nanoclusters. The fine dispersion of commercially available nanocrystalline TiO2 particles (P25, Degussa) in EtOH without surfactants and additives is electro-sprayed directly onto a fluorine-dopoed tin-oxide (PTO) substrate for DSSC photoelectrodes. The DSSCs of HS-TiO2 photoelectrodes show high energy conversion efficiency over 10% under illumination of light at 100 mW cm(-2), AM1.5 global. It is concluded from frequency-dependent measurements that the faster electron diffusion coefficient and longer lifetime of HS-TiO2 than those in nonstructured TiO2 contribute to the enhanced efficiency in DSSCs.