Sol–gel approach for the growth of vertically aligned 3D-TiO2 nanorod arrays as an efficient photoanode for high-performance dye-sensitized solar cells

Abstract

In this study, a facile, low cost, and scalable sol–gel method has been proposed for the coating of ultra-thin layer of TiO2 on FTO substrate as a seed layer for the growth of 3D-TiO2 nanorod (3D-TiO2-NR) arrays on FTO. Then, the two-step hydrothermal process including nanorod growth and the chemical etching treatment was proceeded for the fabrication of FTO/3D-TiO2-NR photoanodes. The thickness of the deposited TiO2 in FTO/TiO2-sg samples was measured with small-angle X-ray scattering technique, and it was obtained to be 21.3 nm. FE-SEM and TEM techniques were used for the morphological characterization of 3D-TiO2-NR, and it was obtained that the tightly adhered film of vertically aligned 3D-TiO2-NR with two-layer nanostructuring is formed with a cubic base and a nanorods head. Finally, DSSCs with iodine-based and cobalt(II/III) tris(2,2′-bipyridine) complex-based electrolytes with two different photoanodes including 3D-TiO2-NR and TiO2-NP were assembled and their photovoltaic characteristics were investigated. For [Co(bpy)3]2+/3+ shuttle-based DSSC, the obtained power conversion efficiency (η) was about 3.5% with Jsc of 9.36 mA cm−2 in 3D-TiO2-NR-based DSSC, while η of TiO2-NP-based DSSC was about 1.4%. The results showed that employing 3D-TiO2-NR-based photoanode in DSSCs with bulky electron shuttles remarkably improves the photovoltaic characteristics of DSSCs. Electrochemical impedance spectroscopic studies also showed the lower charge transfer resistances for DSSCs with nanorod-based photoanode building blocks.