Enhancing charge collection in dye-sensitized solar cells by trimming sidewall of the TiO ₂ nanotubes

The morphological properties of TiO ₂ nanotube heavily influence the performance of dye-sensitized solar cell using TiO ₂ nanotube-array as the photoanode. We report an efficient trimming method of fabricating 18.8 μm TiO ₂ nanotube-arrays with sidewall thicknesses ranged from 23 nm to 12 nm. With the photoanode of thin-wall nanotube-array, the photocurrent density of the dye-sensitized solar cell increased from 13.0 mAcm ²⁺ to 16.2 mAcm ²⁺ when the thickness of the sidewall was thinned down from 23 nm to 14 nm. Electrical impedance spectroscopy showed a significant difference of internal electrical characteristics between the solar cells with the as-prepared and with thin-wall nanotube-arrays. The thinning of the sidewall of the nanotubes had little influence on the diffusion of the electrons; the improvements in photocurrent density are the result of the more efficient infiltration of electrolyte into wider voids between neighboring thin-wall nanotubes.