Thermoelectric energy converters are attractive for application in waste heat utilization technologies. Peltier coolers are a vital part of modern thermal management systems. However, a comparatively low efficiency of the state of the art thermoelectric materials hinders a wide scale expansion of high performance thermoelectric devices. To increase the efficiency of thermoelectric materials, a deep understanding of the interlinked electron and phonon transport properties in nanostructured materials is a prerequisite for a tailored engineering of thermoelectric materials. Challenges remain on how to increase the stability of the thermoelectric material and the compatibility with environmental requirements. The fabrication of thermoelectric devices includes further technological challenges arising from the electrical and thermal contacting.
In this research topic we cover aspects from fundamental research to the applied engineering of lab-scale devices. We investigate the transport properties and develop processing techniques for nanocrystalline thermoelectric materials, bulk as well as films, and work on concepts for device integration.
Ran He, Taishan Zhu, Yumei Wang, Ulrike Wolff, Jean-Christophe Jaud, Andrei Sotnikov, Pavel Potapov, Daniel Wolf, Pingjun Ying, Max Wood, Zhenhui Liu, Le Feng, Nicolás Pérez, G. Jeffrey Snyder, Jeffrey C. Grossman, Kornelius Nielsch and Gabi Schierning
Energy & Environmental Science (2020)
Half-Heusler (HH) compounds are among the most promising thermoelectric (TE) materials for large-scale applications due to their superior applicability such as high power factor, excellent mechanical and thermal reliability, and non-toxicity. Their only drawback is the remaining-high lattice thermal conductivity. Various mechanisms were reported with claimed effectiveness to enhance the phonon scattering of HH compounds including grain-boundary scattering, phase separation, and electron-phonon interaction. In this work, however, we show that point-defect scattering has been the dominant mechanism for phonon scattering other than the intrinsic phonon-phonon interaction for ZrCoSb and possibly many other HH compounds. Induced by the charge-compensation effect, the formation of Co/4d Frenkel point defect is responsible for the drastic reduction of lattice thermal conductivity in ZrCoSb1-xSnx. Our work systematically depicts the phonon scattering profile of HH compounds and illuminates subsequent material optimizations.
Guodong Li, Javier Garcia Fernandez, David Alberto Lara Ramos, Vida Barati, Nicolás Pérez, Ivan Soldatov, Heiko Reith, Gabi Schierning & Kornelius Nielsch
Nature Electronics 1, 555-561 (2018)
Microthermoelectric modules are of potential use in fields such as energy harvesting, thermal management, thermal imaging and high-spatial-resolution temperature sensing. In particular, microthermoelectric coolers (µ-TECs)—in which the application of an electric current cools the device—can be used to manage heat locally in microelectronic circuits. However, a cost-effective µ-TEC device that is compatible with the modern semiconductor fabrication industry has not yet been developed. Furthermore, the device performance of µ-TECs in terms of transient responses, cycling reliability and cooling stability has not been adequately assessed. Here we report the fabrication of µ-TECs that offer a rapid response time of 1 ms, reliability of up to 10 million cycles and a cooling stability of more than 1 month at constant electric current. The high cooling reliability and stability of our µ-TEC module can be attributed to a design of free-standing top contacts between the thermoelectric legs and metallic bridges, which reduces the thermomechanical stress in the devices.
Johannes Gooth, Gabi Schierning, Claudia Felser, and Kornelius Nielsch
MRS BULLETIN Vol. 43, Issue 3 (Materials for Energy Harvesting) March 2018, pp. 187-192
Research in thermoelectric (TE) quantum structures was greatly propelled by the prediction in the early 1990s of a significant boost in TE efficiency by quantum size effects. Recently, research interest has shifted from quantum size effects in conventional semiconductors toward new types of quantum materials (e.g., topological insulators [TIs], Weyl and Dirac semimetals) characterized by their nontrivial electronic topology. Bi2Te3, Sb2Te3, and Bi2Se3, established TE materials, are also TIs exhibiting a bulk bandgap and highly conductive and robust gapless surface states. The signature of the nontrivial electronic band structure on TE transport properties can be best verified in transport experiments using nanowires and thin films. However, even in nanograined bulk, the typical peculiarities in the transport properties of TIs can be seen. Finally, the remarkable transport properties of Dirac and Weyl semimetals are discussed.
Nature Energy | VOL 3 | FEBRUARY 2018 | 92–93 | (DOI: 10.1038/s41560-018-0093-4)
One third of industrial processes occur at high temperatures above 1300 K, but current methods of waste heat recovery at these temperatures are limited. Now, reduced graphene oxide is shown to be a highly efficient and reliable thermoelectric material up to 3000 K.
Ran He, Gabi Schierning, and Kornelius Nielsch
Adv. Mater. Technol. 2018, 1700256 (DOI: 10.1002/admt.201700256)
In recent years, the substantially improved performance of thermoelectric (TE) materials has attracted considerable interest in studying the potential applications of the TE technique. Serving as the bridge between TE materials and applicable TE products, TE devices must be properly designed, engineered, and assembled to meet the required performance of TE products for cooling (thermoelectric cooler) and power generation (thermoelectric generator). The principle feasibility of the TE technique has been demonstrated using a variety of different materials and processing technologies, and many different architectures of TE devices have been successfully realized. This review discusses the architectures of TE devices, including bulk and thin-film TE devices, TE devices with flexible designs, pn-junction-based TE devices that provide robust solutions for high operation temperatures, and the meta-material-based transverse TE devices. In addition, the assembly of TE devices involves contact layers on which the reliability of TE devices depends. Thus solutions to contact issues, including bonding strength, contact resistance, and thermomechanical stress, are also reviewed.