Mesoporous ZnO/TiO2 Nanowire Heterojunction Photo-anodes for Quantum-Dot Sensitised Solar Cells
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Date
2025
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University of the Western Cape
Abstract
Research into quantum dot-sensitised solar cells (QDSSCs) is crucial for advancing sustainable energy solutions due to their unique advantages over conventional solar technologies. QDSSCs offer the potential for high power conversion efficiencies by leveraging the tunable bandgaps of quantum dots (QDs), which allow for broad spectral absorption and efficient light harvesting across the solar spectrum. Their low-cost fabrication such as solution processing and printing techniques, make them economically attractive for large-scale production and flexible applications. QDSSCs can also operate effectively under low-light conditions and offer design versatility, opening pathways for integration into diverse environments and products. This ongoing research is vital for developing next-generation solar cells that are not only more efficient and affordable but also more adaptable to various energy demands, contributing significantly to global efforts in renewable energy. Zinc oxide nanowires (ZnO2 NWs) offer an interesting alternative to traditional titanium dioxide (TiO2) as an electron transport layer in QDSSCs primarily due to their superior electron mobility and direct growth capabilities. Their one-dimensional nanostructure provides a direct pathway for electron transport, significantly reducing recombination losses and enhancing charge collection efficiency. ZnO NWs may be grown at lower temperatures and offer greater flexibility in morphology control, allowing for tailored architectures that optimise light harvesting and QD dot loading. This combination of excellent charge transport properties, tunable morphology and cost-effective synthesis makes ZnO NWs a highly promising material for developing more efficient and scalable QDSSCs. As such, this thesis presents a comprehensive study on the optimisation and characterisation of ZnO NWs for their integration into QDSSCs. The research systematically explores how the morphology and thickness of ZnO seed layers, controlled through spin-coating parameters, affect the growth, alignment and optical properties of ZnO nanowires. Optimal conditions were identified for producing vertically aligned, hightransparency NWs, which are crucial for efficient light absorption. The study further establishes the ideal configuration for the TiO2 mesoporous layer and demonstrates successful sensitisation with CdS QDs. Device-level testing confirms that the structural quality of each component significantly impacts overall solar cell performance, with the best device achieving a power conversion efficiency of 1.9%. Despite these advances, the research highlights ongoing challenges related to interface engineering and device stability. The thesis concludes by outlining future directions, including advanced surface passivation, alternative quantum dot and electrode materials, and strategies for improving device durability and scalability, thereby providing a robust framework for further development of ZnO NW-based QDSSCs.
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Photovoltaics, Renewable energy, Nanoscience and nanotechnology, Quantum dot sensitised solar cells, Zinc oxide nanowires