Advances in Soft and Wearable Energy Harvesters Using Stretchable Thermoelectrics

To improve operational lifetimes of wearable electronics, energy harvesting solutions must be introduced to offset the limitations of current battery technologies. These solutions must both have energy harvesting performance metrics that can meaningfully extend the operational lifetime of wearable health monitoring systems, along with being biocompatible. Soft and deformable materials must be introduced to replace the rigid components of these systems to allow for these energy harvesters to not impede movement. Currently, various wearable energy harvesting solutions have been introduced including piezoelectric, triboelectric, dielectric elastomer, and thermoelectric generators. While these systems have been developed to be deformable and stretchable, the energy densities still must be improved to meaningfully increase power output while not sacrificing mechanical performance. Thermoelectrics, in particular, have the advantage of operating off of temperature differentials and not requiring biomechanical movement. When a temperature difference is applied across oppositely doped thermoelectric semiconductor junctions, a voltage is generated through the Seebeck effect. Conversely, when a current is driven across the semiconductor junctions, a temperature potential can be generated through the Peltier effect.<br/><br/>In this talk I will discuss recent work on the creation of soft and stretchable thermoelectric generators along with their introduction as a power source for wearable electronic devices. To replace rigid materials such as ceramic thermal interfaces and copper interconnects, we introduce 3D printed elastomers and eutectic gallium indium liquid metals as material replacements for the device substrate and conductive traces. Device packaging and fabrication is discussed for multiple generations of these devices. Seebeck and Peltier characterization along with electromechanical characterization is reported, highlighting performance metrics under strain. Wearable integration is also reported with on-body testing conducted to better understand the relative performance changes during wear. Separately, recent integration of these TEGs into soft robotics is discussed through their combination with liquid crystal elastomer shape memory polymers. These TEGs are introduced as both the heating and cooling element along with energy harvesting capabilities.