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Exploring processes for industrial large-scale manufacture of low-cost electronics devices is timely for the upcoming era of the Internet of Things. In this study, a roll-to-roll process using selective metallisation (a combination of flexographic printing of an oil liquid-mask and physical vapour deposition: sputtering and evaporation) is explored for the large-scale manufacture of flexible electronics, with a wearable thermoelectric generator as an exemplar device. Two post-treatments (electron beam and infrared) are trialled to remove the residual oil after selective metallisation. Both are effective for the removal of oil, however, the oil used in selective metallisation degrades the functional thermoelectric material severely, causing a dramatic increase in the internal resistance of the device. This is attributable to (1) the doping and oxidation issues in the semiconductor film; (2) the existence of oil at the interface between the two coatings. The fabricated thermoelectric generator with post-treatments shows a good voltage output comparable to a standard device fabricated using shadow mask, providing an option for portable devices requiring a voltage source. This study reports an industrially compatible roll-to-roll manufacturing process for large-scale manufacture of flexible electronics. Further studies are under way to optimise the device performance.

Strain-induced failure is a major concern in wearable electronics. Herein, a ~ 90-nm thick bismuth telluride film is fabricated on 125-μm thick polyethylene terephthalate as the basis for a flexible thermoelectric generator. To simulate induced mechanical strains during wearable operation and roll-to-roll manufacture, both tensile and buckling strains are studied. To improve the mechanical resilience, two types of substrate-to-coating interlayers with varying thicknesses are investigated: 0.4–7.7 μm-thick Poly-tripropyleneglycol diacrylate (acrylate) and 2.5–16.8 μm-thick Poly-dimethyl siloxane (PDMS). The thermoelectric performance of the coating is influenced through the stress, applied on the polymer substrate, being transferred through to the coating. Samples exposed to tensile testing recover once the load is released, mitigating against change on the film morphology and thermoelectric performance, in contrast to those measured in-situ under buckling strain. Both interlayers are shown to assist in maintaining the film performance, as fewer cracks are formed in the semiconductor. A thicker interlayer is shown to better mitigate the impact of deformation of the substrate. Furthermore, in fatigue-bending tests, the film grown on a PDMS interlayer shows better cyclical fatigue performance.