A solution has been presented for improving the properties and commercializing thermoelectric power plants that produce electricity by recycling waste heat generated in various industrial and transportation fields, and it is expected that this will provide a breakthrough in the research on n-type thermoelectric semiconductors that has been stagnant for the next several decades.

The Korea Institute of Materials Science (KIMS, President Choi Chul-jin) announced on the 7th that the research team led by Dr. Kim Kyung-tae of the Nanomaterials Research Division developed a bismuth telluride (Bi-Te) thermoelectric semiconductor material with artificially formed atomic-scale defects and presented a solution to improve the properties of materials for utilizing waste heat energy.

This technology is a semiconductor technology applied to thermoelectric power plants that produce electricity by recycling waste heat below 200℃ generated in industrial and transportation fields such as factories, automobiles, and ship engines.

Thermoelectric generators are made of a combination of p-type and n-type semiconductors that reversibly convert temperature differences into electrical energy.

Until now, research has focused on improving the properties of p-type thermoelectric materials composed of bismuth (Bi) and tellurium (Te).

On the other hand, n-type thermoelectric semiconductors containing selenium (Se) have been pointed out as an obstacle to the commercialization of thermoelectric power plants because the improvement of physical properties is slow due to the difficulty in controlling the composition and microstructure.

The research team focused on the study of n-type thermoelectric semiconductors, which determine the performance of thermoelectric power plants, and broke the barrier to improving material properties that had been stagnant for decades.The breakthrough lies in the doping material and manufacturing process.

Doping materials are elements added to improve the electrical conductivity of semiconductors. The research team took note of the fact that p-type bismuth telluride thermoelectric semiconductors containing antimony (Sb) as a doping material are more likely to achieve optimal performance, and developed a material that exhibits n-type characteristics by adding antimony (Sb) instead of selenium (Se), a common doping material, to n-type thermoelectric semiconductors.

In addition, the research team developed a method to increase electrical conductivity and decrease thermal conductivity by artificially inducing 'atomic defects' that promote electron formation and 'atomic layer distortion' that slows down the transfer of lattice phonons, which are heat transfer mediators, during the manufacturing process of n-type thermoelectric semiconductors. Since the technology uses a method of putting powdered materials into a mold, heating them, and then stamping them out, it has the advantage of being easy to manufacture thermoelectric semiconductors in a designed shape and size.

The n-type thermoelectric semiconductor developed through this technology clearly exhibited the thermoelectric properties required for thermoelectric elements, such as improving electrical conductivity by more than two times while reducing thermal conductivity. In particular, the application of the research team's thermoelectric semiconductor technology, which has energy conversion performance and easy material combination, is expected when recycling heat at around 200℃ at room temperature that is wasted around us, including human body heat.

The thermoelectric power plant market is growing at a compound annual growth rate of 8.2% and is expected to reach $1.018 billion worldwide by 2029, drawing much attention. The research team is currently developing thermoelectric power plants in collaboration with Living Care Co., Ltd. In addition, we are conducting a pilot study to build a power generation system to recover waste heat generated from casting molds through cooperation with Hyundai Motor Company’s Ulsan plant.

Kim Kyung-tae, the principal researcher and the head of the research, said, “This study has laid a stepping stone to solving the property control of n-type thermoelectric semiconductor materials, which had been an obstacle to the recycling of various types of exhaust and waste heat below 200℃.” He added, “It is significant in that we have developed nanostructured thermoelectric semiconductor material technology with controlled atomic-level defects using traditional powder metallurgy technology.”

This research was conducted with the support of the Basic Project of the Korea Institute of Materials Science and the Bridge Convergence Project (Waste Heat Recovery Thermoelectric Convergence Research Group) of the National Research Foundation of Korea. In addition, the research results were published on July 31st in the world-renowned academic journal, American Chemical Society'Applied Materials & Interfaces (IF: 11.1/ First author, Senior Researcher Jeong Su-ho), and were also selected as the cover paper.