(Invited) 3D Conformal Printing of High-Performance and Flexible Thermoelectric Devices Using Colloidal Nanocrystals

Abstract

The flexible thermoelectric generator (f-TEG) is a very promising technology for energy harvesting to enable self-powered wireless sensors and wearable devices, an area of exponential growth. Here, we present a scalable and cost-effective additive manufacturing process to fabricate f-TEGs using colloidal nanocrystals, and an innovative and highly efficient photonic sintering method to sinter large areas of printed films using pulsed light. Flexible TE films and devices were printed using screen printing and aerosol jet printing, followed by pulsed photonic sintering process. The pulsed sintering confines the delivered thermal energy within the printed film region without over heating the substrate, enabling TE film sintering on flexible polymer based substrates with relatively low melting point. In addition, the pulsed sintering limits grain size growth due to an ultrafast heating and cooling process, and lower thermal conductivity can be achieved than films sintered by conventional thermal processing. The p-type and n-type printed films demonstrate peak ZTs of 1 and 0.43 near room temperature along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density above 19 mW/cm2 with 80 ºC temperature difference between the hot side and cold side. The additive printing and photonic sintering can enable a highly scalable and low-cost roll-to-roll manufacturing process to transform high-efficiency colloidal nanocrystals into high-performance and flexible TEG devices for widespread applications.