Fabrication of Titanium Dioxide Nanotubes and their Photovoltaic Performance for Dye-sensitized Solar Cells

Abstract

TiO2 nanotubes (TNTs) were prepared by the electrochemical anodization method using titanium thin films deposited on indium tin oxide (ITO) substrates by the DC magnetron sputtering technique. The effect of voltage (20-40 V) and amount of ammonium fluoride (NH4F) (0.4-1.4 wt%) were investigated. The fabricated TNTs were characterized by field emission scanning electron microscopy (FE-SEM), X-Ray Diffraction (XRD), X-ray Photoemission spectroscopy (XPS), and Fourier-Transformed Infrared Spectrophotometry (FT-IR) techniques. XRD pattern data exhibited anatase phase when TNTs were annealed at 400 o C for 3 h. The XPS results revealed complement of Ti, O, F, Sn, In and C. The FT-IR spectrum exhibited the characteristic bands of the TiO2 which indicate the Ti-O stretching mode. The average diameter and length of TNTs depend on ammonium fluoride, water and voltage and the optimal conditions were found to be 0.8 wt% ammonium fluoride, and voltage at 30 V. The obtained TNTs have an averaged diameter of 38 nm and length of 763 nm. For dye-sensitized solar cells (DSSCs) application, ruthenium complex (N719) was used as a sensitizer in this work. The energy conversion efficiency (η) of TNTs was also evaluated.

The Anodization of Thin Titania Layers as a Facile Process towards Semitransparent and Ordered Electrode Material

“…This allows the further annealing of the anodized material at 360 °C to obtain TNTs anatase phase. Vomiero et al [ 69 ] anodized Ti deposited on Kapton HN polyimide sheet in glycerol (GI) bath containing 0.5 wt% NH 4 F and 2 M H 2 O and the prepared photoanode without calcination exhibited a conversion efficiency of 0.5% which is higher than those obtained by Aiempanakit et al [ 30 ] (0.4%) and Elsanousi et al [ 70 ] (0.43%) by using calcined TNTs grown on TCO. The performance of the prepared material was further improved by annealing the anodized material at 350 °C for 5 h. A crack-free TNTs layer was obtained over the Kapton substrate with an average length of 6 µm.…”

“…Magnetron sputtering technique including direct current, radio frequency, and high-power impulse magnetron sputtering has been largely used for the deposition of Ti:X onto TCO such as ITO [ 16 , 30 ], and FTO [ 9 , 31 ]. As mentioned earlier, the morphological features of the deposited titanium film including surface roughness, the shape of grains and their size distribution can be also controlled by adjusting the substrate temperature.…”

“…Photoactive materials consisting of TNTs grown on TCO have been investigated to address global challenges such as organic pollutant degradation [ 58 ], solar-to-electricity conversion [ 30 ], and solar-to-hydrogen conversion [ 59 ]. The large band gap of TiO 2 , i.e., 3 eV for rutile and 3.2 eV for anatase phase, is the fundamental drawback of TNTs-based materials.…”

“…Additionally, TCO substrates exhibit high light transmission capacity and good mechanical stability [ 66 ]. Aiempanakit et al [ 30 ] optimized the anodization process of Ti film sputtered on ITO by adjusting both the applied voltage (20–40 V) and the amount of NH 4 F (0.4–1.4 wt%), and investigated the dependency of the performance of dye-sensitized solar cells on the anodization conditions. Figure 13 shows the SEM top view and cross sectional images of the closed-packed architecture of as-fabricated TNTs, and Table 2 summarizes the geometrical features i.e., the average length and diameter of TNTs obtained for each anodization conditions and their photo-electron conversion efficiencies.…”

“… SEM images of as-prepared TNTs grown onto ITO. ( a – d ) Top view images for: ( a ) 0.4 wt% NH 4 F; ( b ) 0.8 wt% NH 4 F; ( c ) 1.2 wt% NH 4 F; ( d ) 1.4 wt% NH 4 F. ( e – h ) Cross-section images for: ( e ) 0.4 wt% NH 4 F; ( f ) 0.8 wt% NH 4 F; ( g ) 1.2 wt% NH 4 F; ( h ) 1.4 wt% NH 4 F. Reprinted from reference [ 30 ] under license CC BY 4.0. …”