Dye-sensitized solar cells based on a nanoparticle/nanotube bilayer structure and their equivalent circuit analysis

Dye-sensitized solar cells (DSSCs) were prepared by capitalizing on a TiO ₂ bilayer structure composed of P-25 nanoparticles and freestanding crystalline nanotube arrays as photoanodes. After being subjected to sequential TiCl ₄ treatment and O ₂ plasma exposure, the bilayer photoanode was sensitized with N719 dye. DSSCs based on a 20 μm TiO ₂ nanoparticle film solely and a bilayer of 13 μm TiO ₂ nanoparticles and 7 μm TiO ₂ nanotubes exhibited the highest power conversion efficiency, PCE, of 8.02% and 7.00%, respectively, compared to the devices made of different TiO ₂ thicknesses. On the basis of J-V parameter analysis acquired by equivalent circuit model simulation, in comparison to P-25 nanoparticles, charge transport in nanotubes was found to be facilitated due to the presence of advantageous nanotubular structures, while photocurrent was reduced owing to their small surface area, which in turn resulted in low dye loading, as well as the lack of cooperative effect of anatase and rutile phases.