High aspect-ratio transparent highly ordered titanium dioxide nanotube arrays and their performance in dye sensitized solar cells

High aspect-ratio transparent titanium dioxide (TiO2) nanotube arrays (TNAs) have been fabricated via anodizing titanium (Ti) thin films deposited by direct current magnetic sputtering at 400 °C. Anodization was conducted in glycol electrolyte containing 0.3 wt.% NH4F and 2 vol.% deionized (DI) water, and the anodizing voltage was 60 V. High aspect-ratio TNAs with thickness of 12 μm were achieved after the Ti films were anodized for 5 h. The as-formed TNAs were amorphous and had been transferred into anatase after heat treatment at 500 °C for 2 h. The annealed transparent TNAs present an excellent transmittance property. The solar cells constructed by our transparent TNAs show excellent performance in dye sensitized solar cells and yield power conversion efficiency of 4.38% under AM 1.5.

The present work provided a facile method to fabricate high aspect-ratio TiO2 nanotube arrays (TNAs) on transparent substrate (FTO). Compared with reported results, we optimized the process as follows: 1) improving the substrate's temperature to 400 °C during sputtering, which increases the adhesion between FTO and Ti film; 2) adopting higher anodic voltage during anodization, which accelerates the TNAs' growth rate. Therefore, high-aspect ratio TNAs (~ 120 nm in diameter, ~ 24 nm in wall thickness, ~ 12 μm in length) have been easily formed on the transparent substrate.Figure optionsDownload as PowerPoint slideHighlights
► High-aspect ratio TNAs were formed on the transparent substrate.
► The substrate's temperature was improved to 400 °C during sputtering.
► Higher anodic voltage of 60 V was adopted during anodization.
► The efficiency was improved to 4 times by extending TNAs' length to 12 μm from 1 μm.