Tuning substrate roughness to improve uniform growth and photocurrent response in anodic TiO2 nanotube arrays

Here we report on the effect of Ti substrate surface roughness on the morphology of anodized TiO₂ nanotube arrays (TNAs), as well as their crystal structure and photocurrent response measured in the backside illuminated dye-sensitized solar cells (DSSCs). TNAs grown on Ti substrates with higher roughness exhibited a non-uniform morphology, which encompassed both thick and thin-walled nanotubes. Reduction of the substrate roughness by different polishing methods causes the morphology of all of nanotubes to become uniform with thin wall thickness. Moreover, the compressive strain was reduced by decreasing the roughness according to the X-ray diffraction patterns. DSSCs fabricated using TNAs grown on the smoothest substrate showed a significantly higher conversion efficiency than that of the TNAs grown on the roughest substrate by a factor of 100%. Furthermore, TNAs grown on the smoothest substrate showed higher electron lifetime and lower recombination. Therefore, it has an enhancing effect on the photocurrent response of the anodized TNAs in backside illuminated DSSCs.