<p>The properties relevant for electron transfer processes between dye molecules and semiconductor substrates, titanium dioxide (TiO<sub>2</sub>) and zinc oxide (ZnO), have been studied by means of photoelectron spectroscopy, PES, near edge X-ray absorption spectroscopy, NEXAFS, and resonant photoemission, RPES.</p><p>For dye-sensitized solar cells, the currently used dyes are ruthenium polypyridine complexes adsorbed to the semiconductor via carboxyl linker groups. A series of such complexes has been investigated, and the most efficient dye so far, cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothiocyanato)ruthenium(II), RuL'<sub>2</sub>(NCS)<sub>2</sub>, was studied in more detail. The results revealed a high content of thiocyanate orbitals in the highest occupied molecular orbital, HOMO, of this complex, which partly explains its efficiency in the solar cell. The thiocyanate ligands were found to be highly influenced by the substrate when the dye is adsorbed onto ZnO, which is not the case for the corresponding TiO<sub>2</sub> system. </p><p>A bridge bonding between TiO<sub>2</sub> and the L' ligand was proposed, where the carboxyl groups are deprotonated and all oxygens interact with surface titanium ions. For ZnO, the results indicate a different bonding geometry, involving protonated carboxyl groups.</p><p>For the display system a dye molecule, which shifts color upon electrochemical treatment, was adsorbed on TiO<sub>2</sub> and studied in its reduced and oxidized states. The major electronic difference between the two states was shown to occur on the nitrogen atom. In addition, a reversible photoreduction process during the measurements was observed.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-685 |
| Date | January 2001 |
| Creators | Westermark, Karin |
| Publisher | Uppsala University, Department of Physics, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 639 |
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