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Fabrication and Characterization of Dye-Sensitized Solar Cells based on the hybrids of Multi Wall Carbon Nanotube and Nanostructured TiO2

Mokarami Ghartavol, Hajar | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53371 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Afshar, Abdollah; Mohammadi, Mohammad Reza
  7. Abstract:
  8. This study presents a facile sol-gel template-assisted route to prepare CNT-TiO2 hybrid structures (CTH) for dye-sensitized solar cell (DSSC) applications. Non-covalent functionalized multi-walled carbon nanotubes (CNTs) with average diameter of 80 nm are used as the template for TiO2 deposition. The X-ray diffraction reveals that the hybrid structures are composed of primary anatase TiO2 nanoparticles with the average crystallite size of 12 nm, after heat treatment at 450°C in air atmosphere. TEM and FESEM images show that the shell thickness of the coated TiO2 on CNTs’ outmost walls varies between 60 to 120 nm, when the ratio of CNTs:TiO2 is 10wt. %. Photovoltaic measurements demonstrate that the introduction of CNT-TiO2 hybrid structures into nanocrystalline TiO2 photoanodes improves the power conversion efficiency (PCE) of DSSCs as a result of increasing conductivity and thus the short circuit current density (JSC). The DSSC containing 0.3 wt. % CNT-TiO2 shows the highest PCE of 7.94% compared with 5.81% for DSSCs made of pure TiO2 nanoparticles. Then, CNT template is removed by oxidation process at 600°C and carbon derived TiO2 nanotubes (TTs) are formed. FESEM and X-Ray diffraction analyses reveal that synthesized TTs are uniform with nanocrystallite size of 17 nm. The maximum JSC of 17.96 mA.cm-2 and the efficiency of 8.23% are achieved by adding 5 wt.% TTs to TiO2 nanoparticles in photoelectrodes. To further PCE enhancement, Nb-doped TiO2 photoelectrodes with different atomic ratios of 0-4 at. % Nb, as well as Zn-doped TiO2 photoanodes in the range of 0-1 at.% Zn, are decorated with TTs to investigate photovoltaic performance of DSSCs. XPS reveals that Nb+5 and Zn2+ ions are well doped in TiO2 lattice without any secondary phases. The maximum PCE of 7.87% and 7.52% are obtained for 3 at.% Nb and 0.75 at.% Zn, respectively. In addition, different percentages of TTs (0-20 wt. %) are added to the optimal Nb and Zn-doped TiO2 electrodes. The highest amount of cell efficiency of 9.02% and 8.47% are obtained for Nb and Zn doped electrodes through adding of 5 wt. % TTs, respectively. It is concluded that a mixture of 3 at. % Nb dopant with 5 wt. % TT has the highest PCE amongst the cells due to electron injection and transportation, and light scattering enhancement. The results indicate that the mixture of CNT-TiO2 hybrids and TTs in conventional TiO2 nanoparticle photoelectrodes can highly improve the energy conversion efficiency of DSSCs
  9. Keywords:
  10. Dye Sensitized Solar Cells ; Titanium Nanotube Arrays (TNA) ; Titanium Oxide-Carbon Nanotube (Tio2-CNT) ; Niobium Doping ; Zinc Doping ; Multi-Walled Carbon Nanotube

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