Date of Completion
Prabhakar Singh, Alexander Agrios
Field of Study
Materials Science and Engineering
Master of Science
The evolving generations of photovoltaics for a generally cheaper and environmentally-friendly, but equally efficient source of energy has led to the concept of dye-sensitized solar cells (DSSC). The cell architecture includes a sensitizing dye adsorbed onto a porous film of crystalline titanium dioxide (TiO2) nanoparticles and surrounded by a redox electrolyte, which is sandwiched between two fluorine-doped tin oxide (FTO) glass electrodes. The conversion from photons to an electronic current begins with the absorption of photons at the dye, followed by the excitation and injection of electrons into the conduction band of the TiO2 photoanode. Electrons are then transported to the FTO-coated glass substrate via diffusion and are extracted to an external load, while reduction of the dye and electrolyte are imposed by the reintroduction of electrons at the platinum-coated counter electrode. Since each process must work efficiently to contribute to the whole cell, it is first imperative to optimize them individually.
Particularly, the structural properties of TiO2 directly impact the electron transport in the photoanode and can be modified through the deposition technique and post-deposition treatment. In this study, TiO2 was deposited via pulsed-laser deposition (PLD) as an amorphous film and was later crystallized through post-deposition annealing. The latter was important since changes in the annealing temperature and time altered the crystallinity, crystal phase, size, and morphology of TiO2. Annealing temperatures were varied from 400 to 600 °C at 120 minutes and annealing times 1 to 120 minutes at 500 °C. The films were characterized with Raman, XRD, SEM and chromatographic analysis of roughness factor. Results showed larger particles, transition from anatase to rutile, as well as rod-like, hyperbranched structures with increasing annealing temperature and time. The decrease of roughness factor, the active surface area in which dye molecules can be adsorbed, was also exhibited at higher temperatures and times. Lastly, XRD peak intensity ratios for anatase  to  were found to be substantially higher in these samples than in powder: implying preferential growth for anatase . Further studies must be done to see how structural properties of TiO2 affect electron transport in the photoanode, and cell efficiency through the fabrication of cells.
Patel, Tulsi, "Structural Properties of Titanium Dioxide Films for Dye-Sensitized Solar Cells" (2014). Master's Theses. 649.