Thickness effect of single crystalline TiO2 nanorods for dye-sensitized solar cells

A hydrothermal method was explored to synthesize single-crystalline (sc) rutile TiO2 nanorods (NRs) with a thickness ranging from 2.4 μm to 6.4 μm on a transparent conductive fluorine-doped tin oxide (FTO) substrate. The variation of precursor ratios in the synthesis solution modulates the length of sc-TiO2 NRs. That is, as the amount of the precursor (titanium butoxide) is decreased in the synthesis bath, the growth length of sc-TiO2 NRs is reduced steadily; the rod diameter is also decreased in the circumstance where all experimental conditions are identical. These samples were applied to dye-sensitized solar cells (DSSCs), the efficiency of which was increased with the thickness of the rods. However, the efficiency of 6.4 μm-thick TiO2 NRs is inversely decreased, resulting from the blocking of pores between NRs from unfavourable electrolyte penetration. These results were confirmed by the incident photon to current efficiency (IPCE).