Soft-Matter Engineering for Thermoelectric Wearables with Unprecedented Power Generation

Stretchable thermoelectric generators (S-TEGs) have recently drawn attention since they can compliantly be attached to complex surfaces to induce temperature change or harvest electricity from waste heat. Unlike conventional thermoelectric modules that are rigid and brittle, flexible thermoelectric devices commonly comprise elastic polymers with encapsulated semiconductor pellets. This stretchable device architecture also provides conformal contact with curved surfaces such as the human body. We have designed multifunctional elastomer composites to enhance the heat management and deformability of these emerging TEGs. Our approach involves dispersing liquid metal droplets within elastomers to create liquid metal elastomer composites (LMECs). LMECs with microdroplets exhibit high thermal conductivity while remaining electrically insulating, serving as thermal interface materials in the devices. Additionally, we have embedded hollow thermoplastic microspheres in the base elastomer to synthesize soft matter with low thermal conductivity, which separates the top and bottom thermal interface layers and encapsulates the semiconductor pellets. The difference between the conductivity of the two elastomer composites facilitates a larger heat flux in thermoelectric semiconductors, leading to improved device performance.<br/>In this talk, we will begin with a brief overview of TEGs that utilize liquid metals and bismuth telluride semiconductors. Following this introduction, we will present our new findings on the design rationale of S-TEG, focusing on the improvement of energy harvesting performance at low-temperature gradients, along with enhancing mechanical resilience and stretchability. In particular, we will highlight the essential role of device structure in thermoelectric energy conversion, utilizing both numerical simulations and experimental analyses to illustrate our findings. The resulting S-TEG design is optimized for efficient thermal management, resulting in a notable power harvesting performance increase, exceeding baseline levels by more than sixfold. The electromechanical and energy harvesting characterization of this engineered S-TEG will be presented to showcase its full potential for a range of emerging applications. To conclude, we will explore the practical applications of these thermoelectric generators across various use cases.