Effect of electric field strength on the length of anodized titania nanotube arrays

For application in dye-sensitized solar cells, anodic titania nanotube arrays must have high-aspect-ratio configuration to load more dyes thus result in higher conversion efficiency. Although geometry of the nanotubes is reported to be affected by a variety of anodizing parameters, electric field strength is the essential factor in determining the tube features (length, pore diameter, wall thickness, etc.). In the present work, electric field strength was varied by changing applied potential and working distance. Effect of the field strength on tube length was studied under selected field strengths for prolonged anodizing durations. An Ion Flux Model, in consideration of F− and H+ concentration profiles within a single tube, is proposed to interpret the influence of the field strength on nanotube growth rate. The results indicate what essentially affects the tube length is the field strength which influences ion migration in electrolyte and ion transport in anodic barrier layer.