2D/3D-Printed Bismuth Telluride-Based Flexible Thermoelectrics for Low-Scale Energy Harvesting

The swift development of the Internet of Things (IoT) and wearable electronics is urgently demanding innovative power solutions. Batteries alone can barely satisfy this demand for two main reasons: Firstly, battery replacement limits the implementation of some scenarios of the IoT in which nodes might be highly distributed in difficult access locations; Secondly, batteries are often too bulky and rigid to be seamlessly integrated on thin and soft wearable electronics, or small IoT nodes. Thermoelectric generators (TEGs) refer to renewable power sources able to assist -or even replace- batteries by generating electricity from the abundant waste heat in the environment. Conveniently, it has been suggested that for low-power applications, TEs can surpass other thermal engines in terms of efficiency.[1] Furthermore, TEs are also capable of on-demand cooling and heating. However, to meet the form factor required by the IoT and wearables (namely repeated bendability/stretchability, conformability to curved surfaces, and large areas), important advancements must be made on traditional TEGs, which are rigid, and hard to scale up to large-area devices.[2]<br/><br/>My group is working towards the development of high-performance thermoelectric materials that can be directly 2D- or 3D-printed on flexible substrates. In particular, I will describe our progress in the formulation of bismuth telluride powder as a printable paste/ink, and the process of selective laser sintering and the direct ink writing (DIW) to form in-plane and through-plane TEGs, respectively. Printing techniques can potentially reduce the material waste and cost of TEGs. Moreover, in combination with a flexible substrate, printing enables innovative device architectures, such as large-area and flexible devices that can be easily integrated on the skin/smart textiles to power wearables using the heat emitted by the human body, as well as adapt to hot curved surfaces, like hot pipes or engines, to power IoT nodes. Because we target energy harvesting around room temperature, bismuth telluride is used as a benchmark material to showcase our processes and device architectures. However, our technology is likewise compatible with emerging polymeric materials, which will be also presented for comparison. If successful, this line of research will holistically tackle the main bottlenecks of TEGs, paving the way to their broad implementation in wearables and other low-power energy harvesting applications.<br/><br/><i>Acknowledgments</i><br/>This work was supported by the European Research Council (ERC) un-der the European Union’s Horizon 2020 research and innovation pro-gramme: Grant Agreement No. 948922 – 3DALIGN; the Research Foundation - Flanders (project number 11E2621N); and the Internal Funds KU Leuven, C1 project C14/21/078.<br/><br/>[1] C. B. Vining, Nat. Mater. 2009, 8, 83.<br/>[2] F. Molina-Lopez, In 2020 IEEE Sensors, IEEE, Rotterdam, 2020, pp. 1–4.