Preparation of TiO₂ nanowires/nanotubes using polycarbonate membranes and their uses in dye-sensitized solar cells

Track-etched polycarbonate (PC) membranes were used as a soft template to synthesize mesoporous TiO₂ for use in dye-sensitized solar cells (DSSCs). The Ti precursor infiltrated into the cylindrical confined spaces of PC membranes. Upon calcination at 500 °C, TiO₂ nanowires (15TNW) were obtained from PC with a 15 nm pore diameter, whereas TiO₂ nanotubes (50TNT and 100TNT) were generated from PC with 50 and 100 nm diameter pores, respectively. TNW and TNT were used as photoelectrodes in DSSCs employing a polymer electrolyte. The ranking of the cell efficiencies of the 200 nm thick TiO₂ films was 50TNT (1.1%) > 15TNW (0.8%) ≅ 100TNT (0.7%), which was mostly attributed to different amounts of dye adsorption due to different surface areas. These TNW and TNT films were further coated with the graft copolymer-directed mesoporous TiO₂ and were used as interfacial layers between the FTO glass and the 4 μm thick nanocrystalline TiO ₂ film. As a result, the order of energy conversion efficiency was 15TNW (5.0%) ≅ 50TNT (4.8%) > 100TNT (4.1%). The improved performance of 15TNW was due to a higher transmittance through the electrode and a longer electron lifetime for recombination. The DSSC performance was systematically investigated in terms of interfacial resistance and charge recombination using electrochemical impedance spectroscopy.