Synthesis of micrometer-sized hierarchical rutile TiO2 flowers and their application in dye sensitized solar cells

Abstract

Cactus-like hierarchical rutile TiO₂ flowers and three dimensional (3D) highly branched rutile TiO₂ nanorods with sizes measuring up to 5 microns were synthesized on conductive substrates by a facile hydrothermal route without the presence of a surfactant or template. These samples with different morphologies and microstructures were studied by X-ray powder diffraction (XRD), field emission-scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). We also studied the photovoltaic performances of these samples by using them as photoanodes in dye-sensitized solar cells (DSSCs). The highly branched TiO₂ nanorod based photoanode in DSSCs showed a power conversion efficiency of 3.07% which was significantly higher than that of the cactus TiO₂ flower based (2.66%) photoanode. The electrochemical impedance spectroscopy (EIS) analysis of the interfacial charge transfer kinetics in these photoanodes in DSSCs showed higher recombination resistance (R₂) and longer electron lifetime in highly branched nanorods. The enhancement of the efficiency of the highly branched TiO₂ nanorod photoanode based DSSC compared to that of cactus TiO₂ flower DSSC is mainly attributed to the superior light scattering capability, fast electron transfer and longer electron lifetime with suppressed recombination.