AN EXPLORATION OF P-TYPE METAL OXIDE SEMICONDUCTORS FOR USE AS A HOLE TRANSPORT LAYER IN SOLAR ENERGY CONVERSION DEVICES

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  • March 22, 2019
Creator
  • McCullough, Shannon
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • As the global economy continues to develop, the demand for sustainable non-polluting fuel source continues to grow. Different solar energy conversion device architectures provide a variety of advantages and disadvantages. Specifically, moving to a photoelectrochemical cell would synthesize solar fuels obviating the need for a battery. Photoelectrochemical cells employ two photoactive electrodes which motivates the study and improvement of p-type metal oxide photocathode material. Here, several candidates are identified and their viability explored via characterization in a dye-sensitized solar cells (DSSCs). Nickel oxide, the current champion p-DSSCs, is the first candidate explored. NiO is modified by introducing a shell of CuxO on the surface of the NiO electrode to introduce a staggered valence band alignment with the purpose of decreasing recombination. Further investigation on NiO extended into exploration of the various cations used in the electrolyte of the DSSC. Four different cations were tested: Li+, Mg2+, TBA+, and Al3+. Compared to the most commonly used cation, Li+, the use of Mg2+ featured several device improvements with a 60 mV increase in VOC.Moving to a novel photocathode material for p-DSSCs, zinc cobalt oxide is next explored. A mechanochemical nanoparticle synthesis is developed with a tunable Zn:Co stoichiometry. The tunable stoichiometry manipulates several significant parameters including bandgap, doping level, and mobility. All stoichiometries of zinc cobalt oxide were tested in p-DSSCs. Another alternative material for photocathodes that was tested was CuO decorated TiO2 nanoparticles. By introducing ultrasmall nanoparticles of CuO on the surface of TiO2 nanoparticles, we can use the electronic properties of CuO while maintaining optical transparency. CuO is also deposited on Al2O3 which functions similarly to TiO2 as a transparent scaffold that supports the CuO ultrananoparticles. The CuO decorated transparent nanoparticles are tested as materials via several physical and chemical techniques including characterization in a p-DSSC. Throughout the work presented here, several tactics were employed to further understanding and improve performance of p-type metal oxide semiconductors. All the approaches successfully created a hole transport layer within a p-DSSC. Their performances varied with some aspects leaving room for future improvement and some aspects exceeding the benchmark NiO devices.
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Advisor
  • Meyer, Gerald
  • Moran, Andrew
  • Warren, Scott
  • Cahoon, James
  • Dempsey, Jillian
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2018
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