Cooling materials — Out of the 3D printer

Thermoelectric coolers, also called solid-state refrigerators, can induce localized cooling by using an electric current to transfer heat from one side of the device to another. Their long lifetimes, invulnerability to leaks, size and shape tunability, and the lack of moving parts (such as circulating liquids) make these devices ideal for diverse cooling applications, such as electronics. However, manufacturing them out of ingots is associated with high costs and generates lots of material waste. In addition, the devices’ performance remains limited.

Now, a team at the Institute of Science and Technology Austria (ISTA), led by Verbund Professor for Energy Sciences and Head of the Werner Siemens Thermoelectric Laboratory Maria Ibáñez, with first author and ISTA postdoc Shengduo Xu, developed high-performance thermoelectric materials out of the 3D printer and used them to build a thermoelectric cooler. “Our innovative integration of 3D printing into thermoelectric cooler fabrication greatly improves manufacturing efficiency and reduces costs,” says Xu. Also, in contrast to previous attempts at 3D printing thermoelectric materials, the present method yields materials with considerably higher performance. ISTA Professor Ibáñez adds, “With commercial-level performance, our work has the potential to extend beyond academia, holding practical relevance and attracting interest from industries seeking real-world applications.”

Pushing the boundaries of thermoelectric technologies

While all materials demonstrate some thermoelectric effect, it is often too negligible to be useful. Materials exhibiting a high enough thermoelectric effect are usually so-called “degenerate semiconductors,” i.e., “doped” semiconductors, to which impurities are introduced intentionally so they behave like conductors. Current state-of-the-art thermoelectric coolers are produced using ingot-based manufacturing techniques — expensive and power-hungry procedures requiring extensive machining processes after production, where a lot of material is wasted. “With our present work, we can 3D print exactly the needed shape of thermoelectric materials. In addition, the resulting devices exhibit a net cooling effect of 50 degrees in the air. This means that our 3D-printed materials perform similarly to ones that are significantly more expensive to manufacture,” says Xu. Thus, the team of ISTA material scientists proposes a scalable and cost-effective production method for thermoelectric materials, circumventing energy-intensive and time-consuming steps.

Printed materials with optimized particle bonding

Beyond applying 3D printing techniques to produce thermoelectric materials, the team designed the inks so that, as the carrier solvent evaporates, effective and robust atomic bonds are formed between grains, creating an atomically connected material network. As a result, the interfacial chemical bonds improve the charge transfer between grains. This explains how the team managed to enhance the thermoelectric performance of their 3D-printed materials while also shedding new light on the transport properties of porous materials. “We employed an extrusion-based 3D printing technique and designed the ink formulation to ensure the integrity of the printed structure and boost particle bonding. This allowed us to produce the first thermoelectric coolers from printed materials with comparable performance to ingot-based devices while saving material and energy,” says Ibáñez.

Medical applications, energy harvesting, and sustainability

Beyond rapid heat management in electronics and wearable devices, thermoelectric coolers could have medical applications, including burn treatment and muscle strain relief. In addition, the ink formulation method developed by the team of ISTA scientists can be adapted for other materials to be used in high-temperature thermoelectric generators — devices that can generate electrical voltage from a temperature difference. According to the team, such an approach could broaden the applicability of thermoelectric generators across various waste energy harvesting systems.

“We successfully executed a full-cycle approach, from optimizing the raw materials’ thermoelectric performance to fabricating a stable, high-performance end-product,” says Ibáñez. Xu adds, “Our work offers a transformative solution for thermoelectric device production and heralds a new era of efficient and sustainable thermoelectric technologies.”