| Summary: | High ordered titanium dioxide (TiO2) nanotube arrays are an important alternative photoanodes for dye-sensitised solar cells (DSSCs) due to fast electron transport, while its lower specific area leads to a lower conversion efficiency compared to the conventional nanocrystalline DSSCs. High-aspect-ratio TiO2 nanotubes with small diameter can provide a greater surface area for the dye loading, thus resulting in higher conversion efficiency of DSSCs. There are many anodizing parameters to affect the geometry of the nanotubes, such as electrolyte composition, voltage duration etc. Among these factors, applied potential is one of the most important parameters to determine the tube diameter and length.
In this project, two low voltages (i.e. 15V and 25V) were applied for different anodizing times to produce TiO2 nanotubes with small diameter. In order to further increase tube growth rate (i.e. tube length), hybrid method (combined potentiostatic and galvanostatic anodization) with stirring at an initial voltage of 15V were investigated. The as-anodized TiO2 nanotubes were characterized by analysing its tube length and pore diameter. After which, the aspect-ratio of the nanotubes were calculated and compared to determine the best anodizing method which can produce the highest aspect ratio TiO2 nanotubes.
Results show that the potentiostatic method at low voltage of 15V produced the smallest diameter of 42.14 ± 4.66 nm with uniformity but with short tube length of only 3.1 ± 0.16 μm after 20 hours. In comparison, hybrid anodic method with stirring produced the longest tube length but at the expense of larger pore diameters which are less uniform in the same time. In conclusion, the hybrid anodic method with stirring with an initial voltage of 15V produced the highest aspect-ratio TiO2 nanotubes of 112.19 after 10 hours of anodization.
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