Effect of synthesis temperature on structure, optical and photovoltaic properties of TiO2 nanorod thin films

We report a facile hydrothermal method for epitaxial growth of TiO2 nanorods directly on fluorine doped tin oxide substrates without any seed layer. The diameter, density, length and the phase of the nanorods depended on synthesis temperature. We observed a systematic increase in the width of the nanorod with increase in growth temperature. Single crystalline nanorods having tetragonal rutile structure were deposited at 150 °C whereas the nanorod film deposited at higher temperatures had polycrystalline nature. The absorption spectra of a typical nanorod film showed direct and indirect optical transitions at 3.28 eV and 2.66 eV, respectively. The Raman spectra contained two characteristic bands at 447.68 cm−1 and 613.98 cm−1 corresponding to rutile tetragonal TiO2. A light to electricity conversion efficiency of 3.7% could be achieved with a 2 μm-thick TiO2 nanorod film photoanode dye sensitized solar cell. The electrochemical impedance spectroscopy result suggested that the internal resistances of the solar cells changed remarkably with variation in the growth temperatures of the photoanodes. The cell with minimum internal resistance and maximum carrier life time had maximum power conversion efficiency.

► Nanorods of TiO2 have been synthesized by a single step hydrothermal technique.
► The nanorods have tetragonal rutile structure.
► The Raman bands at 447.68 cm−1 and 613.98 cm−1 are Eg and A1g modes of rutile TiO2.
► Maximum light to electricity conversion efficiency for nanorod DSSC was 3.7%.
► The electron life time in the dye sensitized solar cell is as high as 0.19 s.