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Fabrication and Photoelectrochemical Characterization of Ordered Nanotube Arrays of TiO2 for Solar Cell Application

Mohammadpour, Raheleh | 2010

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40762 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Iraji zad, Aazam; Dolati, Abolghasem; Taghavinia, Neima
  7. Abstract:
  8. In this research we focus on study and fabrication of ordered nanotube arrays of titanium oxide and their applications in photoelectrochemical cell. Nanotubular films of titanium oxide have been fabricated using anodization method. Short-length nanotubes, less than one micrometer, have been synthesized in aqueous electrolyte containing deionized water, hydrofluoric acid and phosphoric acid. To get Micron-length nanotubes, we have employed organic electrolyte containing ethylene glycol, deionized water and fluoride ammonium. After fabrication, the photo-catalytic activity of nanotubular structures was evaluated by measuring the rate of degradation of in methylene blue aqueous solution. The photo-electro-catalytic activity oxidation behavior of methanol over nanotubular film, under UV irradiation has been investigated by measuring photocurrent and employing electrochemical impedance spectroscopy. By evaluating the effect of size and crystallinity of nanotubes on their photo-catalytic photo-electro-catalytic activity, their performance have been optimized and also compared to non-ordered multi-porous samples. It was found that the photo-catalytic and photo-electro-catalytic activity of nanotubular structure reached maximum for nanotubes anodized at 20 V and calcined at 550 oC. Moreover, based on the results, it was found that the ordered nanotubular TiO2 electrodes have considerably better performance in comparison with non-ordered multi-porous samples in photo-catalytic and photo-electro-catalytic performance. In this project, photoelectrochemical dye sensitized solar cell based on nanoparticular and nanotubular electrodes on titanium substrates have been fabricated. By optimizing the size and crystallinity of nanotubes, maximum conversion efficiency of 2.13% with short circuit current of 5.22 mA/cm2 and open circuit voltage of 710 mV has been achieved, using nanotubular electrodes with thickness of 30 m and annealed at 520 oC. Employing wide range of photoelectrochemical characterization, we have done comprehensive investigation on the performance of dye sensitized solar cells based on nanotubular and nanoparticular electrodes, we have found that the electron life time is much more longer, the effective diffusion coefficient is comparable, the diffusion length is much larger and the diffusion coefficient of conduction band electrons is much bigger in nanotubes in comparison to nanoparticles. Taking advantages of nanotubes and nanoparticles, novel dye sensitized solar cell based on nanotube/nanoparticle electrodes on transparent substrate have been fabricated, maximum conversion efficiency of 5.6% with short circuit current of 12.6 mA/cm2 and open circuit voltage of 780 mV has been obtained.
  9. Keywords:
  10. Anode Oxidation ; Titanium Dioxide ; Photocatalytic Activity ; Dye Sensitized Solar Cells ; Ordered Nanotubular Arrays ; photoelectrocatalytic Activity

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