Elastic (acrylate/polydimethylsiloxane) substrate-to-coating interlayers for improving the mechanical resilience of thermoelectric films on poly(ethylene terephthalate) during roll-to-roll manufacture and in service operation

Abstract

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.