Facile fabrication of vertically aligned TiO₂ nanorods with high density and rutile/anatase phases on transparent conducting glasses: High efficiency dye-sensitized solar cells

We present a facile and effective method to prepare vertically aligned TiO₂ nanorods (NRs) with a high density and rutile/anatase mixture phases on transparent conducting oxide (TCO) glasses. The anatase TiO ₂ nanoparticles grafted with hydrophilic poly(oxyethylene) methacrylate (POEM), which can coordinate with a TiO₂ precursor such as Ti(BuO₄), were introduced in the presence of glycine. Following application of a hydrothermal process and calcination at 450 °C, vertically well-aligned TiO₂ NRs with diameters of 70 nm and lengths of 3 μm were generated, as confirmed by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The larger wavenumber shift observed with TiO₂-POEM in FT-IR spectra suggests more favorable and stronger interactions that facilitate the nucleation and growth of NRs on the transparent conductive fluorine-doped tin oxide (FTO) substrates, resulting in increased NRs density. Dye-sensitized solar cells (DSSCs) fabricated using TiO₂ NRs with a high density and rutile/anatase mixture phases exhibited improved energy conversion efficiency, irrespective of the type of electrolyte. When liquid electrolyte was used, the DSSCs exhibited an efficiency of 5.7% at 100 mW cm^-2, which is the highest value for DSSCs fabricated with NRs directly grown on TCO substrates. High cell efficiencies of 4.5 and 3.7% were also obtained with quasi-solid-state and solid-state electrolytes, respectively, due to the reduced interfacial resistance of electrolyte/electrode and improved electron transport.