Improved anatase phase stability in small diameter TiO2 nanotube arrays for high performance dye-sensitized solar cells

•A simple preparation to synthesize pure anatase phase small diameter TiO2 nanotubes.•Reliable method to obtain TiO2 nanotube membranes with pure anatase phase.•This kind of TiO2 nanotubes were incorporated into DSSCs with higher efficiencies.

Anatase is the preferred phase of TiO2 in dye-sensitized solar cells (DSSCs) because of its lower charge recombination than other phases. However, for small diameter nanotubes before detached from the Ti foil, rutile rather than anatase appears upon a pre-treatment annealing at 400 °C or above. Here we have fabricated highly ordered free-standing small diameter (50 nm) TiO2 nanotube membranes which were pre-treated at 300 °C to maintain pure anatase phase. The free-standing nanotube membranes were used to fabricate the photoanodes and were further calcined at 500 °C to achieve full crystallization of the nanotubes. It was shown that the electron lifetime is much longer in the 300 °C-pre-treated nanotubes than those pre-treated at 400 or 500 °C, leading to a significantly improved power conversion efficiency of 4.59% (enhanced by ∼50%).

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