Effects of the nanostructure and the chemistry of various oxide electrodes on the overall performance of dye-sensitized solar cells
Chou, Tammy Ping-Chun
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With the need for alternative energy resources, solar cell research utilizing solar energy to produce electrical energy has emerged as an important area of research with great potential. In this dissertation, various oxide nanostructures are explored to improve the overall performance of dye-sensitized solar cells. This study examines the solar cell performance of: (1) TiO2 nanoparticle film with varying particle sizes, (2) TiO2-ITO nanocomposite films with various nanoparticle and nanorod structures, and (3) ZnO nanostructures consisting of nanoparticles and nanowires. Additional investigation in the dye loading of TiO2 and ZnO nanoparticle films are also reported. From this study, it was found that the TiO2 nanoparticle film with larger particles ∼18nm in diameter resulted in a higher efficiency ∼5.2%, possibly due to (1) better crystallinity, (2) larger contact points, and (3) better dye adsorption. The addition of ITO nanoparticles to the TiO2 nanoparticle film also improved the overall efficiency from ∼4.7% to ∼5.6%, possibly due to the increase in the overall electron mobility and reduced recombination losses in the TiO 2-ITO system. In addition, the ZnO nanoparticle film prepared by sol-gel processing had a higher overall efficiency of ∼3.5%, as compared to commercially-obtained ZnO nanoparticle film. This is most likely due to the hierarchical structure of sol-gel-derived ZnO consisting of primary nanoparticles ∼20nm in size and secondary colloidal spheres ∼300nm in size, giving rise to (1) a higher surface area and (2) a greater light scattering ability. It was also found that the manner of dye loading for both TiO2 and ZnO had two competing processes: (1) complete surface adsorption and (2) surface dissolution. A higher and lower concentration of dye required a shorter and longer amount of time, respectively, for adequate dye adsorption and complete surface coverage.