Structure modification of anatase TiO₂ nanomaterials-based photoanodes for efficient dye-sensitized solar cells

Different structures of anatase TiO₂ from nanoparticles-based spheres to aggregated nanoparticles have been successfully fabricated by a simple refluxing method using a prepared titanium glycolate precursor. Variations in crystal phase, morphology, and size of TiO₂ nanostructures were investigated by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman spectroscopy, and the Brunauer-Emmett-Teller method. It was found that the size of the prepared titanium glycolate precursor plays an important role in the formation of different anatase TiO₂ aggregated spheres with high specific surface area (≈260 m² g^-1). Different TiO₂ structures show a significant effect on the photovoltaic performance of dye-sensitized solar cells (DSSCs). The aggregated anatase TiO₂ nanoparticles photoanode-based DSSC presents an overall light-to-electricity conversion efficiency of 4.2% accompanying a short-circuit current density of 13.63 mA cm^-2, which is higher than those of closely packed TiO ₂ sphere (3.4%) and loosely packed TiO₂ sphere (3.7%) photoanodes. The higher short-circuit current density and conversion efficiency for the aggregated nanoparticles-based DSSCs may be attributed to the high surface areas, which lead to larger dye loading and less resistance to electron transfer, and the high charge transfer at the interface of photoanode (TiO ₂/dye) and electrolyte layer.