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Study and Fabrication of Dye Sensitized Solar Cells Based on Nitrogen and Neodymium Doped Titanium Dioxide Photoelectrodes

Shogh, Shiva | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48006 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Iraji Zad, Azam; Mohammadpour, Raheleh; Taghavinia, Nima
  7. Abstract:
  8. In this thesis, we focus on studying and fabrication of doped titanium dioxide electrodes and their application in nanostructured dye sensitized solar cells (DSSCs). For this purpose, non-metallic nitrogen (N) and metallic neodymium (Nd) elements were selected. N-doped titanium dioxide nanoparticles were synthesized via solvothermal method and their structural and optoelectrical properties were investigated in comparison to undoped titanium dioxide synthesized by the same method. Based on the obtained results, doping of titanium dioxide by nitrogen resulted in shifting the Fermi level up-ward, increase in charge carriers density, shift of optical absorbance to higher wavelength, and decrease in surface trap levels as compared to pure anatase titanium dioxide. In addition, a comprehensive study on photovoltaic characteristics of these samples showed that employing sub-micron size N-doped TiO2 with 2.88% doping level as the active medium, scattering layer as well as in a composite structure with DSSCs photoelectrode nanoparticles, makes performance of the cells based on standard iodide electrolyte enhanced up to 21%, 13% and 17%, respectively compared to pure one. The improvement was due to charge collection efficiency improvement and shallow traps density reduction. Nd-doped TiO2 pastes were also synthesized by the hydrothermal method with various doping level of 0, 0.4, 0.8, 1.2, 2.4 and 4 mol percent. The investigation on the structural, optical and electrical features of these samples exhibited that Nd doping prevents crystalline phase transition of titanium dioxide to rutile, and reduced band gap energy and enhanced charge carriers in the semiconductor due to formation of 4f levels below the conduction band. Also, photovoltaic characterizations of the specimens revealed that using Nd-doped TiO2 with 0.4% doping level as the photoelectrode of DSSCs based on ionic liquid electrolyte, enhanced cell performance up to 26% as compared the undoped sample and reaches the overall conversion efficiency to 9.08%. It seems that the improvement is due to increase of the charge carriers’ mobility because of crystalline phase transition, and enhancement of the charge carriers and the electron injection efficiency because of band gap tailoring. By a complete investigation using carriers transport, electron lifetime and charges extraction measurements, it was found that for the optimum (0.4 mol%) doping level, the charge collection efficiency improved and high value of voltage was obtained with lower charge density. Therefore, nitrogen and neodymium were introduced as the effective dopant in titanium dioxide photoelectrode to improve the DSSCs performance
  9. Keywords:
  10. Titanium Dioxide ; Nitrogen ; Dye Sensitized Solar Cells ; Doping ; Light Scattering Layer ; Neodymium 123 Compound

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