Hybrid energy harvesting towards a sustainable energy system

Thesis

Soaring energy demands are inevitable because of the continual increase in the global population as well as the greater reliance on electronic technologies. Current energy generation systems are highly dependent upon fossil fuels, for which the imminent risks and limitations are well known. First of all, we are confronting an energy crisis due to the depletion of these fossil fuels. However, current sustainable and renewable energy sources are not in a position to fully replace them as of yet. In fact, less than 10% of energy that is generated is from renewable energy sources, such as from hydroelectric power and solar power. Secondly, the emission of carbon dioxide (CO₂) and greenhouse gases (GhGs) from fossil fuels is currently at a serious level. As a result, today we are facing and experiencing abnormal climate changes.

In order to mitigate and potentially resolve the energy crisis, energy generation systems are now shifting from fossil fuels to sustainable and renewable energy sources. Developments in energy harvesting technologies are considered to be a practical and promising way to deal with this crisis. Energy harvesting is a process that involves the generation of electrical energy by harnessing ambient environmental energy that is otherwise wasted. Generally, energy harvesting refers to a small amount of power for technologies such as portable electronic devices and wireless sensor networks. However, going forward, energy harvesting technologies beyond these would enable a bottom-up approach from ‘the cell’ scale to ‘a large farm’ scale.

My DPhil thesis deals with energy harvesting technologies that involve harnessing different environmental energy sources, such as solar and mechanical energy, using quantum dots for solar cells and polyvinylidene fluoride (PVDF)-based polymers for mechanical energy harvesting applications. Via novel approaches, such as the fabrication of a multi-junction quantum dot solar cell (QDSC) and the development of a room temperature polymer crystallisation method (solvent annealing), a significant enhancement in energy harvesting performance has been achieved. In addition, I have demonstrated more advanced energy harvesting devices by combining two alternative technologies together. Initially, a high efficiency QDSC is presented using the ferroelectric and piezoelectric coupling effect in PVDF-based polymer. Secondly, the integration of a QDSC with a mechanical energy harvester is demonstrated, which showed a combined enhancement by generating higher power beyond that observed from the individual components. Lastly, the thesis concludes with a demonstration of an application of these hybrid devices to self-powered electronics, which shows promise for future sustainable energy systems using energy harvesting technology.

Authors: Cho, Y

• DOI: 10.5287/ora-e2eajxvav
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English