Hydrothermal Growth of ZnO Nanorods for Use in Dye-Sensitized Solar Cells

Zinc oxide nanorods were grown hydrothermally and used as a photoanodic material in dye-sensitized solar cells (DSSCs). The influence of hydrothermal growth time on the synthesis of ZnO nanorods was expounded by various characterizations, viz., FESEM, EDXS, XRD, FTIR, XPS, and UV-visible spectroscopy. The FESEM imaging ascertained the rod-shape morphology of ZnO. The XRD and FTIR measurements confirmed the formation of the defect-free and crystalline hexagonal wurtzite ZnO nanorod-like structure. The XRD calculations also demonstrated the increase in lattice strain and thereby the length of ZnO nanorods as a result of an increase in the hydrothermal growth time. The purity and surface properties of ZnO nanorods were confirmed by EDXS and XPS. The UV-visible spectroscopy revealed an electronic transition in bandgap energy due to quantum confinement effect, resulting in a decrease in the bandgap energy. The consequences of reaction time were also observed on the photovoltaic parameters of the DSSCs. The DSSC fabricated with the 9-ZNR sample exhibited a maximum efficiency of 1.62%, and hence the optimal time for the growth of ZnO nanorods was confirmed as 9 h. A passivating layer of TiO2 on ZnO nanorods boosted the efficiency by almost 2-fold, which was ascribed to factors like a decrease in the interfacial charge recombination, a reduction in the dissolution of ZnO, and a reduction in interfacial traps.