Controlled synthesis and photoelectrochemical properties of highly ordered TiO ₂ nanorods

Highly ordered TiO ₂ nanorods (NRs) were grown directly on fluorine doped tin oxide (FTO) substrate by a single step hydrothermal synthesis at 150°C. The morphology of TiO ₂ was significantly altered by changing the solvents of ethanol/deionized (DI) water as the precursor solutions. With ethanol/DI water (80:20 v/v) as solvent, the highly ordered tetragonal TiO ₂ NRs were achieved on FTO substrates with the average lengths of ∼2-4 μm and diameters ∼50-70 nm respectively. While, the round headed and distorted hexagonal TiO ₂ NRs were formed with ethanol/DI water ratios of 50:50 v/v and 0:100 v/v as the precursor solutions respectively. The grown TiO ₂ NRs possessed the anatase phase with typical tetragonal crystal structures. XPS studies evidenced that the grown TiO ₂ NRs exhibited the O:Ti stoichiometric ratio of 2:1 with lower impurities of the carbon species. The grown TiO ₂ NRs thin film substrates were applied as photoanodes for efficient dye-sensitized solar cells (DSSCs). A solar-to-electricity conversion efficiency of ∼3.2% was achieved by DSSC, fabricated with highly ordered tetragonal TiO ₂ NRs photoanode, whereas DSSC with the distorted hexagonal TiO ₂ NRs photoanode showed inferior overall conversion efficiency (∼1.08%). The improved photovoltaic performance was credited to the highly ordered morphology of the TiO ₂ NRs, which executed the high charge collection and the transfer of electrons at the interfaces of the TiO ₂ NRs photoanode and the electrolyte layer.