Doubly open-ended TiO₂ nanotube arrays decorated with a few nm-sized TiO₂ nanoparticles for highly efficient dye-sensitized solar cells

Doubly open-ended TiO₂ nanotube (NT) arrays decorated with a few nm-sized TiO₂ nanoparticles (sNP@NT hybrid structure) were prepared and used as charge-collecting photoelectrodes in dye-sensitized solar cells (DSCs). The TiO₂ nanoparticles (NPs) on the NT array surfaces increased the dye loading on the sNP@NT-based DSCs by 9% compared to the undecorated NT-based DSCs, thereby enhancing the light harvesting capabilities. The power conversion efficiency (PCE) of the sNP@NT-based DSC prepared with 11 μm thick NT arrays was 10.0%, which constituted a 47% improvement over the corresponding NT-based DSCs (which displayed a 6.8% PCE). Despite having a dye loading level that was 22% lower than the dye loading level in the conventional TiO₂ NP-based DSCs, due to the limited internal surface area, the PCE of the sNP@NT-based DSC was 28% greater than that of the conventional TiO ₂ NP-based DSC (8.1% PCE) prepared with a light scattering layer. The high charge collection efficiency of the NT array and the good photovoltaic performance set a new record for efficiency among NT-based DSCs.