Flexible Thermoelectric Energy Generators for E-textiles

Abstract

Thermoelectric generators are a solid-state energy harvesting technology that utilises thermal gradients to generate useable electricity. However, the applicable uses for thermoelectric generators remain in niche fields, due to their low efficiency as well as their bulky and rigid nature. To expand the applicable uses of thermoelectric generators it is vital to improve their flexibility as well as ensure the simplicity and scalability of their fabrication to incorporate them into future electronic textiles and internet of things applications. This thesis describes an investigation into the combination of polyol synthesis chemistry with screen printing to develop a procedure for the fabrication of scalable and flexible thermoelectric generators. Promising material candidates examined in this thesis are n-type nanowires of Bismuth telluride and Bismuth telluride selenide, as well as p-type Tellurium nanorods and Bismuth antimony telluride nanoplatelets. These nanomaterials were then screen-printed onto flexible substrates such as Kapton and a polyurethane-based interface layer on polyester-cotton. The paste used to print these nanomaterials was formulated using a solvent-binder system of N-Methyl-2-pyrrolidone as the solvent and polyvinylidene fluoride as the binder. For the first time, such a solvent-binder system was systematically studied, where the binder content was varied with respect to the amount of Bismuth telluride nanowires in the paste. This was done to optimise the binder content with respect to the thermoelectric material in post-annealed screen-printed films. The annealed Bismuth telluride films achieved a maximum Seebeck coefficient of -192 ± 10 µV K-1 with a Power factor of
36 ± 7 µW m-1 K-2 at 225 K. Additionally, a novel systematic study into the content of Tellurium nanorods in screen-printed Bismuth antimony telluride nanoplatelet films was carried out to identify an optimal concentration for improved thermoelectric performance. The ideal content of Tellurium nanorods in the p-type films was shown to be 12 % of the film's weight with a room temperature Seebeck coefficient of 210 ± 10 µV K-1 and a Power factor of 54 ± 6 µWm-1 K-2. Further testing in the form of bending studies was performed on the screen-printed films to observe their suitability for flexible applications. Finally, the screen-printed films were used to fabricate flexible thermoelectric generator devices where their power outputs were measured with respect to the
thermal gradient across the devices using a thermal camera. It was discovered that the p-type polyvinylidene fluoride-Tellurium nanorod composite films were compatible with electronic textile applications achieving a power output of 50 nW at a temperature gradient of 29.8 K. This was because the composite films could generate a power output after being printed onto a polyurethane-based interface layer on polyester-cotton without the composite films being annealed.

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Identifiers

ORCID for Iris Nandhakumar: orcid.org/0000-0002-9668-9126

ORCID for Stephen Beeby: orcid.org/0000-0002-0800-1759

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