Effects of the Morphology of the Electrode Nanostructures on the Performance of Dye-Sensitized Solar Cells

This article reports the performances of dye-sensitized solar cells based on different working electrode structures, namely (1) highly ordered arrays of TiO(2) nanorods, (2) highly ordered arrays of TiO(2) nanotubules of different wall thicknesses, and (3) sintered TiO(2) nanoparticles. Even though highest short-circuit current density was achieved with systems based on TiO(2) nanotubules, the most efficient cells were those based on ordered arrays of TiO(2) nanorods. This is probably due to the higher open-circuit photovoltage values attained with TiO(2) nanorods compared with TiO(2) nanotubules. The nanorods are thicker than the nanotubules and therefore the injected electrons, stored in the trap states of the inner TiO(2) particles, are shielded from recombination with holes in the redox electrolyte at open-circuit. The high short-circuit photocurrent densities seen in the ordered TiO(2) systems can be explained by the fact that, in contrast to the sintered nanoparticles, the parallel and vertical orientation of the ordered nanostructures provide well defined electron percolation paths and thus significantly reduce the diffusion distance and time constant.