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 degrees 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%) congruent to 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 mm thick nanocrystalline TiO2 film. As a result, the order of energy conversion efficiency was 15TNW (5.0%) congruent to 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.