Investigating the manufacturability of flexible thin-film device (TEG) using roll-to-roll

This thesis investigates how to large-scale manufacture flexible thin-film electronics using high-throughput/cost-effective roll-to-roll processing. In this case, a flexible/wearable thermoelectric generator is explored which can locally provide a continuous low-power source for a variety of wearable technologies, to be a competitive alternative to the portable (Li-ion) battery-based system (with typical issues of recharging, short lifetime, energy storage limit and replacement cost, etc.). One of the best conventional thermoelectric materials for wearable thermoelectric generators, bismuth telluride, is studied for scale-up in an industrial-scale roll-to-roll web coater. Magnetron sputtering is employed as a promising technique for scale-up because it is stable, controllable, continuous, already widely used in industrial manufacturing, scalable for fabricating high-quality films at moderate throughput speed, easily incorporated into the roll-to-roll process, compatible with fabrication lines (patternable). Four key challenges are explored to achieve the goal of advanced roll-to-roll manufacture of flexible thermoelectric generators: (1) exploration of using very thin films to balance the fast roll-to-roll web speed and low vacuum-deposition rate; (2) post-deposition radiation treatments to improve thermoelectric performance and use of interlayers to improve mechanical resilience; (3) replacing a solid shadow mask by other approaches (compatible with roll-to-roll), to make in-line patterns; (4) exploring the preferred architecture of flexible thermoelectric generators suitable for both wearable applications and roll-to-roll. Correspondingly, (1) a thinner bismuth telluride film is found to possess a greater thermoelectric performance which also satisfies a high deposition throughput; (2) two feasible post-deposition annealing means to be compatible with high-throughput roll-to-roll processes are studied, besides, two types of substrate-to-coating interlayers are proposed to improve the mechanical resilience of flexible thermoelectric films; (3) a selective metallisation technique is explored to pattern flexible thermoelectric generators; (4) the dimension of the thermoelectric strip and cheap/high-performance contact materials are studied, most interestingly a novel stacked design is invented for flexible thermoelectric generators. These studies give a significant boost to the commercialisation of flexible thin-film electronics, to fulfil the increasing demand for flexible electronics in the upcoming era of the Internet of Things and Artificial Intelligence.