Spectroscopic Investigations of Electron Transfer Processes at Semiconductor Interfaces Public Deposited

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Last Modified
  • March 20, 2019
Creator
  • Knauf, Robin
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Clean and renewable energy sources are essential to meet the worlds growing energy demands. Consequently, there has been a large scientific focus on designing inexpensive and efficient solar energy devices. Dye-sensitized solar cells, which couple light absorbing molecules to low cost metal oxides, show promise as cost effective alternatives to traditional silicon solar cells; furthermore, dye-sensitized photoelectrosynthesis cells provide a means for storing solar energy in the form of chemical bonds. The rates of the electron transfer process that occur in these devices ultimately dictate their efficiencies. Understanding the factors that govern these electron transfer processes will guide rational device design. This dissertation aims to answer the following questions: What are the mechanisms by which these interfacial electron transfer processes occur, and does the rate or mechanism change with metal oxide used? Can new emerging materials, specifically semiconductor quantum dots, be incorporated as efficient chromophores in these devices? By comparing the electron transfer rates in SnO2-chromophore and TiO2-chromophore systems, it was determined that the rates of back electron transfer in these systems are influenced by the identity of localized trap states within the metal oxide, how these states are populated, and the specific pathways by which back electron transfer can proceed. Recombination mechanisms were also examined for SnO2/TiO2 core shell systems,as these architectures have shown increased performance in solar energy devices. It was determined that electron recombination in these systems occurs via two mechanisms, tunneling and direct recombination from localized shell trap states. The contribution from each mechanism is dependent on the TiO2 shell thickness. Semiconductor quantum dots were also investigated as possible chromophores for solar energy devices. Common methods of incorporating quantum dots into device architectures require exchanging native ligands for functionalized ligands that couple the quantum dots to the desired substrate. However the mechanisms of these ligand exchange processes are not well understood. These ligand exchange reactions were studied using NMR, absorbance, and photoluminescence spectroscopies. Carboxylic acid exchanges were found to occur in equilibrium, with a Keq=0.83. Phosphonic acid and thiol ligand exchanges were found to be irreversible, and alter the inorganic core of the quantum dots.
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Rights statement
  • In Copyright
Advisor
  • Meyer, Gerald
  • Papanikolas, John
  • Moran, Andrew
  • Schauer, Cynthia
  • Dempsey, Jillian
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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