Microsphere assembly of TiO2 with tube-in-tube nanostructures: anisotropic etching and photovoltaic enhancement

Abstract

We report an anisotropic etching route to prepare rutile TiO2 microspheres with a tube-in-tube nanostructure from their rod-like precursor. The crystalline structures and morphologies of both the precursor and the final product were examined by X-ray powder diffraction (XRD), field emission-scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). We also examined the photovoltaic performances of our samples by assembling them in photoanodes in dye-sensitized solar cells (DSSCs). The TiO2 microspheres sample with the tube-in-tube nanostructure shows a 213% and 269% increase in short current and conversion efficiency compared to that of TiO2 nanorods microspheres. The most interesting result in this study is that, even under the conditions with less dye adsorption (ca. 20% less), an optimized photoanode containing our TiO2 sample showed an energy-conversion efficiency of 7.57%, higher than the value (6.50%) of the photoanode containing solely anatase TiO2 nanoparticles. We concluded that the unique micro and nanostructure helps to increase the light harvesting and, thus, improve the photovoltaic performance of DSSCs.