The high-entropy concept provides extended, optimized space of a composition, resulting in unusual transport phenomena and excellent thermoelectric performance. By tuning electron and phonon localization, we enhanced the figure-of-merit value to 2.7 at 750 kelvin in germanium telluride–based high-entropy materials and realized a high experimental conversion efficiency of 13.3% at a temperature difference of 506 kelvin with the fabricated segmented module. By increasing the entropy, the increased crystal symmetry delocalized the distribution of electrons in the distorted rhombohedral structure, resulting in band convergence and improved electrical properties. By contrast, the localized phonons from the entropy-induced disorder dampened the propagation of transverse phonons, which was the origin of the increased anharmonicity and largely depressed lattice thermal conductivity. We provide a paradigm for tuning electron and phonon localization by entropy manipulation, but we have also demonstrated a route for improving the performance of high-entropy thermoelectric materials. Description Disordered but efficient Thermoelectric materials, many having relative simple compositions, convert heat into electricity. However, Jiang et al. found that adding more cations into a germanium tellurium–based material stabilized a phase with excellent thermoelectric properties. This high-entropy material has low thermal conductivity due to the cation disordering but improved symmetry that helps maintain good electrical properties. The material was used in several devices that showed a high thermoelectric efficiency. —BG A high-entropy material is an outstanding thermoelectric with a combination of delocalized electrons and localized phonons.

High figure-of-merit and power generation in high-entropy GeTe-based thermoelectrics

Thermoelectric materials can be potentially employed in solid-state devices that harvest waste heat and convert it to electrical power, thereby improving the efficiency of fuel utilization. The spectacular increases in the efficiencies of these materials achieved over the past decade have raised expectations regarding the use of thermoelectric generators in various energy saving and energy management applications, especially at mid to high temperature (400–900 °C). However, several important issues that prevent successful thermoelectric generator commercialization remain unresolved, in good part because of the lack of a research roadmap. Thermoelectric materials can generate energy from a heat differential. This Review provides an overview of mid- to high-temperature thermoelectrics, their application in modules, and the issues that need to be addressed to enable commercial implementation of state-of-the-art materials.

High-performance thermoelectrics and challenges for practical devices.

Thermoelectric materials allow for direct conversion between heat and electricity, offering the potential for power generation. The average dimensionless figure of merit ZTave determines device efficiency. N-type tin selenide crystals exhibit outstanding three-dimensional charge and two-dimensional phonon transport along the out-of-plane direction, contributing to a high maximum figure of merit Zmax of ~3.6 × 10−3 per kelvin but a moderate ZTave of ~1.1. We found an attractive high Zmax of ~4.1 × 10−3 per kelvin at 748 kelvin and a ZTave of ~1.7 at 300 to 773 kelvin in chlorine-doped and lead-alloyed tin selenide crystals by phonon-electron decoupling. The chlorine-induced low deformation potential improved the carrier mobility. The lead-induced mass and strain fluctuations reduced the lattice thermal conductivity. Phonon-electron decoupling plays a critical role to achieve high-performance thermoelectrics. Description A material with high potential Thermoelectic materials convert heat to electricity and are attractive for energy generation or solid-state cooling. Su et al. found that doping tin selenide with chlorine and lead substantially improved the thermoelectric figure of merit over a wide temperature range. This effect was mostly due to an improvement in the material’s deformation potential related to mass and strain fluctuations introduced into the n-type material. Improving the figure of merit in this way is challenging because properties are often intertwined and trying to improve one will often degrade others. —BG Doping tin selenide with lead and chlorine results in a material with high thermoelectric efficiency over a broad temperature range.

High thermoelectric performance realized through manipulating layered phonon-electron decoupling

Bulk nanostructuring has been one of the leading strategies employed in the past decade for the optimization of thermoelectric properties by introducing strong grain boundary scattering of low-frequency phonons. However,...

Carrier Grain Boundary Scattering in Thermoelectric Materials

Compared with traditional active cooling methods, thermoelectric coolers are more accessible to be integrated with electronics as an effective thermal management solution due to their reliability, silence, compatibility, and controllability. Considering the rapid development of processors and chips in electronics, this work comprehensively reviews the progress of state-of-the-art on-chip thermoelectric coolers and summarizes the related fundamentals, materials, designs, and system logic. Particularly, we highlight on-chip thermoelectric coolers with self-cooling design and on-demand requirement. In the end, we point out current challenges and opportunities for future improvement of designs, performance, and applications of on-chip thermoelectric coolers. 

Thermoelectric coolers for on-chip thermal management: Materials, design, and optimization

Thermoelectric materials transfer heat and electrical energy, being useful for power generation or cooling applications. Many of these materials have narrow bandgaps, especially for cooling applications where this property has been seen as particularly important for enhancing the thermoelectric properties. We developed SnSe crystals with a wide bandgap Eg ~ 33 kBT with attractive thermoelectric properties through Pb alloying. The momentum and energy multiband alignment promoted by Pb alloying resulted in an ultra-high power factor ~75 μWcm–1K–2 at 300 K, and a ZTave ~ 1.90. We show that a 31-pair thermoelectric device can produce a power generation efficiency ~4.4% and a cooling ΔTmax ~ 45.7 K. These results demonstrate that wide bandgap compounds can be used for thermoelectric cooling applications.

Xixi Liu

Papers

Power generation and thermoelectric cooling enabled by momentum and energy multiband alignments.