Bilayer hollow/spindle-like anatase TiO₂ photoanode for high efficiency dye-sensitized solar cells

Derived from a hollow TiO₂ nanoparticle (HNP) as underlayer and a TiO₂ spindle (SP) as light scattering overlayer, a new bilayer single-crystalline photoanode (HNP/SP) is fabricated for dye-sensitized solar cell (DSSC) application. The prepared bilayer TiO₂ photoanode and two comparative HNP/HNP and SP/SP ones are fully characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy and N₂ adsorption-desorption isotherms. An overall photoelectric conversion efficiency of 8.65% has been achieved for HNP/SP DSSC, which is 25% higher than that of HNP/HNP DSSC, and also far superior to that of SP/SP or conventional P25 DSSC. The improved photovoltaic performance of HNP/SP DSSC is attributed to the synergic effects, i.e. the single-crystalline bilayer structure favoring for rapid interfacial electron transport, the relatively large specific surface area of HNP for effective dye adsorption, and the 1D geometry of single-crystalline TiO₂ spindles for direct electron transport pathway and strong light scattering effect.