Soft lithographic patterned architectures in dye sensitized solar cells Public Deposited

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Last Modified
  • March 21, 2019
Creator
  • Ok, Myoung-Ryul
    • Affiliation: College of Arts and Sciences, Department of Applied Physical Sciences
Abstract
  • Arrays of periodic surface features were patterned on mesoporous Nb2O5 and TiO2 films by soft-lithographic techniques to construct photonic crystal (PC) structures on the back side of the oxide. The patterned oxide films were integrated into dye-sensitized solar cells (DSSCs) and their performance was evaluated relative to flat (unpatterned) counterparts. The PC structure on niobium oxide surfaces caused large changes in optical characteristics, particularly in the blue wavelength regime. The incident photon-to-current conversion efficiency (IPCE) of patterned niobium oxide anodes exhibited a relative enhancement over the entire wavelength range corresponding to the higher absorption in optical measurements. However, the effect of surface PC structures on the optical response of the TiO2 is different from that of the Nb2O5 photoanode. The enhancement of light harvesting efficiency (LHE) is not obviously due to the higher thickness and larger dye loading than Nb2O5 films. However, patterned TiO2 samples exhibited higher global efficiency than the flat reference, although there was no notable change in LHE. It was hypothesized that surface PC structures changed the de-trapping rate from trap states based on the simulated reflection behavior near the surface of the PC structure, and that in turn, enhances charge collection efficiency. A cubic array of rectangular ITO posts (5´5´6.5μm, 10μm period) were fabricated on FTO coated glass in order to reduce the distance between charge generation points in the mesoporous TiO2 film and the transparent conductive oxide (TCO) layer in an effort to enhance charge collection in the DSSCs. In spite of the decrease in optical transmission due to the tall ITO structures, DSSCs with patterned ITO exhibited increased photocurrent by 12~18% to the reference DSSCs with identical volume of sensitized TiO2. However, DSSCs with patterned ITO substructures showed deterioration in the open circuit voltage (Voc), fill factor, and global efficiency. Electrochemical impedance spectroscopy (EIS) showed that DSSCs with patterned ITO exhibited faster recombination rates leading to the decline in Voc,, fill factor, and global efficiency. We conclude that a barrier coating to suppress back electron transfer to the electrolyte should be conformally applied in order to take full advantage of the patterned ITO substructure.
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  • In Copyright
Advisor
  • Samulski, Edward T.
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2013
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