Abstract
The global energy use is predicted to grow by up to 50% in the coming decades, placing both pressure on resources and heavy demands on the energy efficiency of technologies around us. The majority of primary energy consumption is wasted as heat, which is ubiquitous in a difficult-to-use low-grade form. At the same time, the number of electronic devices in both everyday life and industry is increasing rapidly. Thermoelectric materials enable converting heat into electricity, but their large-scale use is hindered by a low power per cost figure. The use of nanostructuring has enabled improving the thermoelectric performance by careful engineering of both electronic and thermal properties of these materials. Concurrently, also other material properties, such as optical transparency or mechanical flexibility, can be improved. The emergence of thermoelectric materials with functional properties could promote the widespread adoption of thermoelectric devices by providing novel uses and application domains. This thesis presents ways to engineer thermoelectric materials for functional applications using nanostructuring as well as demonstrates a few proof-of-concept devices based on these materials. The thesis first studies the thermal properties of core-shell GaAs-AlAs nanowire arrays, a material system important for a variety of optoelectronic devices. Characterization by the transient thermoreflectance technique indicates that the thickness of the introduced epitaxial AlAs shell can be exploited in controlling the thermal properties of the heterostructure. Second, widely studied transparent thermoelectric material, ZnO, is grown using atomic layer deposition (ALD). Sandwiching of Zr in between ZnO layers grown by ALD is found to improve the room-temperature thermoelectric performance of ZnO at a 2% nominal concentration of Zr. Further, nanoporous grass-like alumina (GLA) surface is used as a template for ALD of Al-doped ZnO (AZO), showing increased carrier concentration and subsequently improved electrical conductivity and thermoelectric power factor. In addition, the transparency of the AZO film grown on GLA is enhanced due to the antireflective behaviour partly inherited from GLA. Finally, nanostructured materials are used in two instances to realize flexible thermoelectric devices. First, a thermoelectric generator based on InAs nanowire networks grown directly on flexible plastic is demonstrated. Second, a thermal distribution sensor based on spray-deposited multilayer graphene is presented. The results obtained in this thesis demonstrate various ways for engineering the properties of thermoelectric materials for functional applications. Further, approaches enabling the scalable and cost-efficient fabrication of these materials are presented, drafting routes for practical utilization of functional thermoelectric devices.
Translated title of the contribution | Nanorakenteiset lämpösähköiset materiaalit läpinäkyviin ja taipuisiin sovelluksiin |
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Original language | English |
Qualification | Doctor's degree |
Awarding Institution |
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Supervisors/Advisors |
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Publisher | |
Print ISBNs | 978-952-64-1374-7 |
Electronic ISBNs | 978-952-64-1375-4 |
Publication status | Published - 2023 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- thermoelectricity
- nanostructures
- thin films
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Seitsonen, J. (Manager) & Rissanen, A. (Other)
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