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.