Metal Oxide Thin Film Growth by Laser Ablation and Its Applications in High Surface Area Photoanodes Public Deposited

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  • March 22, 2019
Creator
  • Ghosh, Rudresh
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
Abstract
  • Thin films are widely used in various applications, including but not limited to simple reflective coatings for mirrors, electrodes for lithium batteries, conducting substrates for electronic circuits, gas sensors and solar cells. As the scope of their applications has widened over the years so has the need to obtain different structural motifs for thin films. A large variety of fabrication techniques are commonly employed to obtain these structures. Pulsed laser deposition (PLD) can be used to obtain films varying from extremely compact and only a few angstroms thick to micron thick porous structures. In this dissertation I introduce a model for predicting different structures as a function of laser parameters and deposition environments in a pulsed laser deposition system. This is followed by a comparison of simulated and experimentally obtained structures. I then use this model to obtain tailored structures suited for individual applications. One of the unique structures obtained using the PLD consists of vertically-aligned structures with nanoparticles as their building blocks. I investigate the superiority of this unique structure over random nanoparticle networks as photoanodes for titanium dioxide (TiO2)-based dye-sensitized solar cells (DSSC). UV-Vis studies show that there is a 1.4 x enhancement of surface area for PLD-TiO2 photoanodes compared to the best sol-gel films. PLD-TiO2 incident photon to current efficiency (IPCE) values are comparable to 3 x thicker sol-gel films and nearly 92% absorbed photon to current efficiency (APCE) values have been observed for optimized structures. I also examine the suitability of PLD-synthesized niobium oxide (Nb2O5) and tantalum-doped titanium oxide (Ta: TiO2) as photoanode materials. For optimized PLD-Nb2O5-based DSSCs IPCE values up to 40%, APCE values around 90% and power conversion efficiency of 2.41% were obtained. DSSCs made of PLD-Ta:TiO2 show enhanced photocurrents as well photo efficiency over those based on PLD-TiO2. I show that this improvement is due to the slower recombination rates because of the presence of Ta5+. I also show the applicability of other structures obtained using the PLD. I use very compact thin films for obtaining the band edges of different potential candidates suitable for photoanodes of dye sensitized photoelectrochemical cells (DSPEC). This is done by a combination of x-ray and ultraviolet photoemission spectroscopy (XPS-UPS) and inverse photoemission spectroscopy (IPS). I also use porous tungsten oxide (WO3) PLD films as H2 sensors. I determine the optical constants for WO3 in the colored and bleached states and use them to correlate the gasochromic and electrochromic behavior of WO3. I also introduce polymer encapsulation of WO3 thin films to protect them from aging.
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  • In Copyright
Advisor
  • López Noriega, René
Degree
  • Doctor of Philosophy
Graduation year
  • 2012
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