Optimized Synthesis and Characterization of TiO2 Nanotubes via Electrochemical Anodization Method for Application in DSSCs

Abstract

Titania (TiO2) Nanotubes not only present a high surface area support for dye molecules but they would also enhance the efficiency of Dye Sensitized Solar Cells by increasing charge collection and light harvesting capability of the cell. These Nano tubular structures were produced in this study in an ethylene glycol electrolyte. Anodization technique was used for synthesis because of its simplicity and cost effectiveness. Pure Ti (>99.7%) foil was used as working electrode and lead (Pb) as counter electrode. Electrolyte solution contained Ammonium Fluoride (NH4F) dissolved in Ethylene Glycol (EG) and DI-water. The process of anodization produces a ‗thin layer‘ of oxide which covers the top surface of Titania nanotubes during synthesis in ethylene glycol solvent, various techniques were employed in this study to either remove the formed layer or avoid this ‗cover layer‘ from formation. Thereafter effect of different process parameters (fluoride ion concentrations and applied voltage) on the nanotube morphologies was investigated through a series of experiments. The anodization process was continuously monitored by online recording of changes in current during the process. The variation of current during the process has been related to mechanism of nanotube growth. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques were used to investigate the morphology and presence of crystalline phases of oxide nanotubes respectively. SEM results revealed formation of nanotubes with inner diameters ranging from 40-84nm and lengths in 14μm to 23μm. The duration of each process was kept constant at two hours. So a growth rate of 7μm/h to 10μm/h was obtained. XRD analysis of the oxide layer revealed that although the film formed after anodization was amorphous, annealing at high temperatures (400°C-550°C) for six hours desired crystalline (anatase) phase was obtained.