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Fabrication and Optimisation of Solid State Dye Sensitized Solar Cells Based on Nanostructured TiO2 and SnO2 Photoelectrodes

Sadoughi, Golnaz | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 43828 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Iraji Zad, Azam; Taghavinia, Nima
  7. Abstract:
  8. Dye-sensitized solar cells were introduced by M. Gratzel in 1991. These solar cells have a power conversion efficiency of about 12% over the AM1.5 full sun. Traditionally, a liquid electrolyte redox system is used to regenerate the dye. Due to stability issues, a solid hole transport material has been employed to replace the liquid electrolyte as an attempt to create solid-state Dye-sensitized solar cell (ssDSC). Over past few years power conversion efficiency of ssDSCs has improved considerably and reached over 7%.
    Here, ss-DSCs based on TiO2 nanoparticles as photoelctrode and P3HT as hole transport material were fabricated and characterized. We used three different methods; dip coating, spin coating and spray pyrolysis to make compact layer of ssDSCs. The best results were obtained with spray pyrolysis method. The spray pyrolysed compact layers were optimized. Finally ssDSCs exhibited efficiencies of 2.36% based on P3HT as hole transporter and 3.75% based on spiroOMeTAD as hole transporter.
    Then we investigated the role of a new TiO2 structure as ssDSC’s photoelectrode. The photoanodes of ssDSCs embedded with different contents of TiO2 hollow spheres (HSs) were prepared and characterized. TiO2 hollow spheres were synthesized by a facile sacrificial templating method and added in different ratios to TiO2 nanoparticle (NP) paste, from which composite HS/NP electrodes were fabricated. The composite photoanodes include hollow spheres of 300-700 nm with enhanced light scattering in visible range which leads to improved light absorption in thin film electrodes of ssDSC. By optimizing the amount of HSs, 40% improvement in efficiency was obtained in comparison to pure NP electrodes. By increasing the fraction of HSs in the electrode the current density increased by 56% (from 2.5 to 3.9 mA cm-2). The improved photovoltaic performance of ssDSC is primarily due to different morphology and altered charged trap distribution in HSs in comparison to NP which leads to significant enhancement in electron transport time and electron lifetime as well as charge collection efficiency and light absorption properties.
    Nano-crystalline TiO2 exhibits low electron-mobility and consequently slow transport which is less competitive with recombination processes. On the other hand, SnO2 exhibits high electron-mobility. P3HT’s hole-mobility is rather high too. So, SnO2 and P3HT have been established as promising “high mobility” alternatives to conventional ssDSC components.
    We present an investigation on the optimization of ssDSCs comprising mesoporous SnO2 photoanodes infiltrated with P3HT and sensitized with an organic dye. High conductivites of SnO2 and P3HT, preclude conventional device configurations because of high leakage current and low shunt-resistance. To minimize the “hole leakage current” through the FTO anode, we employed a double compact layer structure, and to minimize “electron leakage current” at the silver cathode, we developed a protocol for depositing an optimal P3HT “capping layer”. After optimization of cell fabrication, the electron lifetime is increased considerably and the solar cells exhibited simulated AM1.5 full sun solar power conversion efficiencies in excess of 1%. Then we investigate ssDSC based on SnO2 one dimentional structures. Oriented SnO2 nanowires on titanium foil were synthesised and optimised as photoelectrodes of ssDSCs. Electron transport times improved by a factor of 4 to6 and electron lifetimes improved 4 to 40 times in comparison to SnO2 nanoparticle ssDSCs
  9. Keywords:
  10. Squeeze Film ; Nanowire ; Titanium Dioxide ; Solidstate Dye Sensitized Solar Cell ; Tin Dioxide

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