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 TiO2 nanorods, (2) highly ordered arrays of TiO2 nanotubules of different wall thicknesses, and (3) sintered TiO2 nanoparticles. Even though highest short-circuit current density was achieved with systems based on TiO2 nanotubules, the most efficient cells were those based on ordered arrays of TiO2 nanorods. This is probably due to the higher open-circuit photovoltage values attained with TiO2 nanorods compared with TiO2 nanotubules. The nanorods are thicker than the nanotubules and therefore the injected electrons, stored in the trap states of the inner TiO2 particles, are shielded from recombination with holes in the redox electrolyte at open-circuit. The high short-circuit photocurrent densities seen in the ordered TiO2 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.