Research into renewable energy sources is crucially increasing to counteract the ever more concerning impact of non-renewable sources. Theoretically, Quantum Dot Solar Cells (QDSCs) can achieve much greater efficiencies than current, commercial solar cells, but its expansion is still in its very early stages of scientific study and development. In this project TiO2, one of the most efficient and cost-effective photocatalysts, is coupled with Cadmium Selenide (CdSe) Quantum Dots (QD) in a study of interfacial charge transfers. Thus far, in other studies, CdSe QDs have shown some of the most promising results of QDSCs. EPR spectroscopy has been used here to study charge transfer processes in CdSe quantum dot (QD) sensitised titania. Visible light excitation of QDs directly adsorbed onto titania surfaces causes electron transfer to the titania, producing characteristic EPR signals of trapped electrons in the titania. Under ultraviolet excitation the trapped electron signals seen in titania alone are suppressed in the presence of directly adsorbed quantum dots, as is the formation of superoxide in the presence of oxygen. These observations suggest that reverse electron transfer from the titania to the QDs can also occur. No visible light excited electron transfer occurs in the case of QDs attached to the titania surface via bi-linker molecules, but under ultraviolet excitation a similar suppression of electron trapping in the titania phase is seen. These results show that the nature of the interface between the QDs and the titania phase is crucially important in the electron transfer processes in both directions. The study also looks at the pitfalls of synthesis techniques used for making the CdSe QDs as well as the method of attaching it to the TiO2. Ionic deposition, which generally resulted in the best photocurrents in other studies, was discovered early on this project produced very impure samples. Direct Adsorption produces low titania surface coverage, which can potentially be improved. Whereas the lack of discussion in literature of clear purification methods in synthesis techniques for attaching QDs via a bi-linker molecule, through ligand exchange, causes a significant drawback in the study of such systems.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:720579 |
| Date | January 2016 |
| Creators | Beukes Stewart, Eva-Panduleni |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232399 |
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