Dye Sensitized solar cells based on nanowire sculptured thin film titanium dioxide photoanodes
Open Access
- Author:
- Pursel, Sean M.
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 10, 2011
- Committee Members:
- Mark William Horn, Dissertation Advisor/Co-Advisor
Mark William Horn, Committee Chair/Co-Chair
Jian Xu, Committee Member
Barbara Shaw, Committee Member
Joan Marie Redwing, Committee Member - Keywords:
- sculptured thin film
dye sensitized solar cell
nanowire
photoanode - Abstract:
- Energy harvested from the sun using photovoltaics (PVs) is a renewable resource in high demand. Photovoltaics convert photons into electron-hole pairs which are then separated and used for electrical power. 75 TW of energy arrives from the sun every year onto US soil. Harvesting it all would provide enough energy to power the entire world for more than five years. It is this abundance of energy that makes PVs an attractive alternative to fossil fuels. PVs currently produce 0.15% of the energy consumed in the US. Production needs to grow as the worldwide demand for energy is projected to almost double by 2050. Fundamental and device based PV research have made steady efficiency gains in silicon based devices and thin film devices have started to become commercially viable. However, less expensive devices with suitable efficiency have not been fully developed. Dye sensitized solar cells (DSSCs) are one such device which has been optimized using standard components. However, device efficiency has not increased significantly since DSSCs were first conceived in 1991. Interestingly, none of the standard components are optimized, but act in a synergistic way in the most efficient devices. This research, along with other parallel research, attempts to optimize a single component of DSSCs with the goal of combining efforts to produce a device with increased efficiency. This research attempts to optimize the TiO2 photoanode used in DSSCs in terms of electron collection, dye coverage, light harvesting, and novel electrolyte infiltration by replacing the standard colloidal structure with nanowires deposited using physical vapor deposition at an oblique angle to form sculptured thin films. The results are quantified through standard photovoltaic testing, electrochemical impedance spectroscopy, UV-Vis-NIR spectroscopy, and general materials characterization techniques. The nanowire photoanodes are engineered during deposition using reactive evaporation, substrate heating, substrate positioning/movement, and co-deposition. The influence of substrate roughness, source material, and post deposition processing in device performance is also quantified. The novel nanowire sculptured thin film photoanodes are shown to have the ability to advantageously modulate dye coverage, electron lifetime, light scattering, and pore spacing more than the standard colloidal photoanode. Device performance using standard dye and electrolyte is shown to be closely matched to that of colloidal based devices constructed as control samples. Along with optimized dye and electrolytes these nanowire based photoanodes should be considered for the research and development of a fully optimized DSSC which would operate more efficiently than the current state of the art.