Formation of mesoporous TiO₂ with large surface areas, interconnectivity and hierarchical pores for dye-sensitized solar cells

TiO₂ nanoparticles with anatase/rutile mixed phase and <100 nm in size were surface-modified using hydroxyethyl methacrylate (HEMA) and sulfosuccinic acid (SA), which can coordinate to the TiO₂ precursor, titanium(iv) isopropoxide (TTIP). The HEMA in TiO₂-HEMA nanoparticles underwent a graft/crosslink polymerization to poly(hydroxyethyl methacrylate) (PHEMA), i.e. TiO₂-PHEMA. Following the application of a sol-gel process with TTIP, 3-dimensional (3D) nanostructured TiO₂ photoelectrodes with interconnectivity, large surface area and bimodal pores were successfully obtained. The energy conversion efficiency of a polymer electrolyte dye-sensitized solar cell (DSSC) fabricated with TiO ₂-PHEMA/TTIP photoelectrode reached 3.5% at 100 mW cm^-2, which was much higher than those of pristine TiO₂ (1.4%), TiO ₂/TTIP (1.6%) and TiO₂-HEMA/TTIP (2.0%) photoelectrodes. The higher cell performance of TiO₂-PHEMA/TTIP is due to enhanced light harvesting, reduced charge recombination and excellent penetration of polymer electrolytes into the TiO₂ pores.