Zhibin Xie

Supramolecular-Templated Thick Mesoporous Titania Films for Dye-Sensitized Solar Cells: Effect of Morphology on Performance

Highly crystallized mesoporous titania films of varying thicknesses and different morphologies, namely ordered body-centered orthorhombic and disordered wormlike mesostructure, have been successfully synthesized via a supramolecular-templated route and subsequent layer-by-layer deposition. The performance of these mesoporous films in dye-sensitized solar cells was investigated, achieving a maximum efficiency of 6-7% at the film thickness of 5-6 mum. The ordered mesoporous titania films outperformed the disordered counterpart of the same thickness in both short circuit current and efficiency. This behavior is elaborated with the dye-loading, optical, and charge-transport behavior as affected by the variation in mesoporous film morphology. The improved cell performance of the ordered mesoporous film is ascribed to the enhanced electron transport in the regularly packed titania network because of the enhanced crystalline grain connectivity. Nevertheless, the dependence of cell performance on the film morphology is weakened when the film thickness was above approximately 3.5 mum, because of the serious film cracks.

Highly efficient dye-sensitized solar cells of thick mesoporous titania films derived from supramolecular templating

Thick titania films of highly ordered orthorhombic pore organization and sufficient thickness up to a few micrometers have been synthesized via a supramolecular templated route and layer-by-layer deposition. An appropriate pre-heat treatment was applied to improve the mesopore accessibility. The mesoporous films were highly crystallized with the crystallite size of approximately 12 nm regardless of the film thickness, due to the spatial confinement of mesopores. A high optical transparency was demonstrated for the mesoporous films, which is ascribed to the high mesoporosity and uniformity of the ordered film structure. Both the mesopore accessibility and optical transparency have contributed to the high performance of these films as photoanodes in the dye-sensitized solar cells, showing a maximum solar energy conversion efficiency of 6.02% for a film of 5.08 microm in thickness.

Fast charge transport of titania nanotube arrays in dye-sensitized solar cells

Abstract Vertically oriented nanotubular titania arrays with a length of ca. 12 μm were fabricated by anodisation of titanium foils. Rietveld refinements of grazing incidence and wide angle XRD patterns for the annealed nanotube titania array showed that they consist of anatase crystals with a pronounced size anisotropy and a moderate preferred orientation. The energy conversion efficiency of dye sensitized solar cells based on the annealed nanotubular anatase array exceeds 6% under standard AM1.5 100 mW/cm2 irradiance and thus outperforms solar cells based on anatase nanoparticles when comparing analogous back illumination cell designs. Electrochemical impedance spectroscopy was employed to clarify the origin of the improved short circuit current and conversion efficiency. It was found that the effective diffusion length in the nanotube cells reaches >100 μm and no longer limits the onversion efficiency. The faster electron transport can be traced back to the larger crystallite size and the reduced intergrain orientation mismatch in the titania nanotubes.