The Influence of Materials and Fabrication Techniques on Dye-sensitized Solar Cell Performance

Thesis (Master's)--University of Washington, 2012The performance of dye-sensitized solar cells (DSC) as reported in the literature varies even when the materials and/or methods cited are essentially the same. DSC performance even varies significantly within a single lab from researcher to researcher, as has been observed in our lab. To better constrain the sources of the variability and determine which materials and techniques yielded the best DSC performance, various materials and techniques for fabrication of dye-sensitized solar cells were evaluated for their effect on DSC performance. Materials investigated included two types of TiO₂ nanoparticles (Aeroxide ® P25 and a nanoparticle synthesized in our lab) as well as two different electrolytes (Dyesol's High Performance Electrolyte and an electrolyte synthesized in our lab). Results in the literature suggest that nanoparticle dispersion during screen printing paste fabrication is important for the dye loading and optical properties of DSCs, so dispersion techniques including mortar grinding, sonication, roller milling, and ball milling were investigated. DSC fabrication and assembly techniques were also suspected to be important. Comparisons were made between doctor bladed and screen printed films, dye loading of the TiO₂ films under ambient pressures and vacuum, and various sealed and unsealed cell testing configurations. Results from the material and assembly technique comparisons showed varying degrees of impact on DSC film quality and performance. Ball milling was found to be an effective method of disaggregating P25 TiO₂ nanoparticles for screen printing pastes, whereas mortar grinding left large TiO₂ clusters and yielded variable cluster size distributions from batch to batch. The presence of TiO₂ clusters increased film cracking, film peeling, and light scattering and consequently reduced DSC performance. Vacuum-assisted dye loading was not found to improve DSC performance. A comparison of gasket-sealed, epoxy-sealed, and unsealed DSCs did not show consistent differences in performance, though unsealed cells showed poor stability over short time periods. Both screen printing and doctor blading of TiO₂ films yielded films of uniform thickness and DSCs of comparable performance. Finally, a lab electrolyte was found to yield DSCs with a higher short circuit current compared to DSCs that used Dyesol's High Performance Electrolyte. The electrolyte performance difference is partially due to higher charge transfer resistance at the TiO₂-electrolyte interface