Effects of water on dye/TiO2 interfaces : A spectroscopic study for solar cell application

Abstract: The processes of light harvesting by a sensitiser as in a nanoporous dye-sensitised solar cell, DSC, is a promising device for solar to electric energy conversion. The DSC systems have already reached conversion efficiencies exceeding 11%. This thesis considers water effects on dye absorbed nanoporous TiO2 surfaces. They have been studied using FTIR, UV-vis and XPS spectroscopy. Photovoltaic properties and IPCE (incident photon-to-current conversion efficiency) were also measured. The work includes development of the IPCE apparatus and the techique which ultimately improved the results. Theoretical DFT calculations for the vibrational frequencies of the dye Ru(dcbpy)2(NCS)2 were used and verified the FTIR spectra. A few scenarios were considered to simulate the effects of water seen in the experimental spectra. All the spectroscopic measurements showed effects due to interactions with water. These effects were not only seen as a lowering of intensity due to losses of dye molecules to the water solution. The results gave information of how the dye N719 is bonded to the TiO2 surface and electronic structure as well as efficiency of the solar cell. Shifts in the spectra due to geometry changes, interaction with new ions bonded to the surface, effects of the pH level and losses of the TBA+ ions were discussed. Strategies to control the effects of water and thereby optimise the preformance are under consideration for the future.