High-Throughput Printing of High-Performance and Flexible Thermoelectric Devices for Energy Harvesting and Energy Autonomous Sensors

Thermoelectric devices offer tremendous opportunities in direct conversion of waste heat into electricity and solid-state refrigeration with no moving parts or environmental emission from refrigerants. To realize its broad applications in energy harvesting and thermal management, significant advances are required to not only increase thermoelectric figure of merit zT but also improve the mechanical flexibility and reduce the manufacturing time and cost. Here, we present novel and scalable ink based printing methods that enable high-throughput development and low-cost manufacturing of thermoelectric materials and devices.<br/>An aerosol based high-throughput combinatorial printing (HTCP) method is developed to accelerate the discovery and optimization of high-efficiency thermoelectric materials. The HTCP was employed to print thermoelectric materials with gradient doping, and<br/>investigate the role of sulfur doping level in bismuth telluride based materials. This leads to rapid discovery of the optimal doping level, yielding a printed n-type material with high room-temperature power factor of 1774 µW/mK².<br/>Sintering is a very critical process in controlling the microstructures and properties of printed thermoelectric materials. We demonstrate a machine learning assisted high-throughput printing and ultrafast (&lt; 1 second) photonic flash processing method that produces silver selenide based flexible films with room temperature zT &gt; 1, which is among the highest in flexible materials. The films show excellent flexibility with 92% retention of the power factor (PF) after 1000 bending cycles with a 5 mm bending radius.<br/>Highly scalable and low-cost extrusion printing and screen printing processes were applied to transform high-efficiency thermoelectric particles into high-performance devices. The thermoelectric power factor in our printed p-type materials reaches 3500 µW/mK², which is among the highest in the best reported values in printed TE materials in the last decade. This results in highly competitive room temperature ZT of 1.3. The scalable printing methods can enable film-based devices manufactured with the optimum thicknesses and form factors to realize very competitive performance/cost ratio compared with commercial bulk devices. Moreover, the film-based devices offer mechanical flexibility and adaptability to curved surfaces, making it advantageous for a much broader range of applications than the rigid bulk devices. A fully printed wearable thermoelectric generator generates an electrical power density of 0.5 mW/cm² and 26.6 mW/cm² at temperature difference of 10 K and 70 K, respectively.<br/>The highly scalable and cost-effective printing technology is poised to become a game changer to unlock the immense potential for thermoelectric devices to play an important role in energy harvesting and enable energy-autonomous sensing systems.