Development of Cu₂Se/Ag₂(S,Se)-Based Monolithic Thermoelectric Generators for Low-Grade Waste Heat Energy Harvesting

With the ongoing climate and energy crises, thermoelectric conversion has slowly emerged as a clean and reliable alternative energy source for small Internet of Things (IoT) devices. Commercially available thermoelectric generators (TEGs) are typically composed of expensive and toxic Bi₂Te₃-based thermoelectric materials and require complicated and energy-intensive device assembly processes. As an alternative solution, we have developed a Ag- and Cu-chalcogenide-based monolithic TEG using simple, quick, and low-energy-cost device fabrication processes for low-grade waste heat recovery for energy harvesting. We used ductile Ag₂S_0.55Se_0.45 and overstoichiometric Cu_2.075Se, both possessing excellent transport properties around room temperature, with a zT value of ∼0.5 at 300 K. By optimizing the device fabrication process, we were successfully able to assemble the monolithic TEGs without any significant Ag- or Cu-ion migration and obtained a dense and robust device. Strategic optimization of the device structure was able to reduce the electrical contact resistance of the device, which resulted in increased power output. A maximum power density of 0.68 mW/cm² at a ΔT = 30 K was obtained, which is comparable to a similar Bi₂Te₃-based monolithic TEG. These results show the potential of chalcogenide-based monolithic TEG as a simple and low-cost alternative to Bi₂Te₃-based TEGs for energy harvesting applications.