One-dimensional hierarchical titania for fast reaction kinetics of photoanode materials of dye-sensitized solar cells

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Abstract
To overcome kinetic limitations of nanoparticles and one-dimensional nanostructures, and enhance fast reaction kinetics of photoanode materials for dye-sensitized solar cells, one-dimensional hierarchical titanate was prepared by coating protonated titanate nanoparticles on one-dimensional protonated titanate nanorods. The one-dimensional hierarchical titania was obtained subsequently after calcination at different temperatures, and was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET). The photoelectrochemical and electrochemical performance of the one-dimensional hierarchical titania was then carried out by photocurrent–voltage curves, electrochemical impedance spectroscopy (EIS), intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS). It is clear that titania nanoparticles grow uniformly on the surface of titania nanorods. The one-dimensional hierarchical titania obtained subsequently can not only provide a matrix similar to the hybrid structure matrix but also avoid forming a large amount of grain boundaries, since the hierarchical structure forms by growth of nanoparticles on nanorods. In particular, the titania with such hierarchical structures after calcination at 600 and 700 °C show optimized fast reaction kinetics: low charge-transfer resistance, fast electron transport and long electron lifetime. The knowledge acquired in this work is important for the design of efficient photoanode materials of dye-sensitized solar cells.