Achieving Enhanced Thermoelectric Performance in Multiphase Materials

ConspectusThermoelectric (TE) devices enable direct solid-state energy conversion from heat to electricity and vice versa, thereby showing great potential in warranting the supply of sustainable energy and mitigating the potentially catastrophic effects of climate change. Therefore, as a clean-energy-generation technology, TE materials have received tremendous research efforts in both industrial and academic communities for applications in the recovery of ubiquitous low-grade waste heat. Achieving high efficiency in TE materials is an ongoing pursuit of the TE research community, considering approximately 90% of all waste heat in the USA comes from medium-temperature (e.g., from 573 to 873 K) heat sources. Hence, synergistic enhancements in the figures-of-merit (ZT) are still highly desired and remain a key task for improving commercial applications of TE materials.Over the past decades, by navigating the interplay between heat and electronic transport, different advanced paradigms in current state-of-the-art TE materials, as well as emerging TE materials, have been adopted to obtain high ZT values, especially for the average ZT (ZT_avg), as the power conversion efficiency (PCE) of a TE device depends on the ZT_avgover a wide temperature range. Yet, now there are few reviews or perspective reports on methods to synergistically boost both the peak ZT (ZT_peak) and ZT_avg, Herein, our recently developed strategies for optimizing and designing high-performance TE materials through advanced multiphase nanocomposite paradigms and material design are presented. Multiphase composites with distributed nanostructures (e.g., nanoplates and/or nanoparticles) provide effective phonon scattering through the nanoscale secondary phases. On the basis of the physical mechanism (the charge carrier transfer, phonon transfer/scattering, phonon-charge carrier interaction, and interface phenomenon), one can derive the optimum direction for the improvement of ZT_peakand ZT_avgof TE semiconductors.In this Account, we summarize and discuss the recent advances and insights from our work in designing TE materials with both high ZT_peakand ZT_avgby combining precisely engineered doping and nanostructuring. This Account is organized as follows: First, we summarize the advances of representative state-of-the-art TE materials in chronological order, including the advancement of performance-improving mechanisms. Second, we highlight the application of our effective multiphase material design strategies to leading Pb-based (PbTe, PbSe, and PbS) TE materials, with an emphasis on ZT_avgand SnSe-based TE materials. Third, we introduce Sb₂Si₂Te₆, which possesses an ultralow thermal lattice conductivity, as a promising new TE material, which was enhanced through a cellular nanostructure strategy. Finally, we outline an entropy-driven paradigm to optimize current SnSe-based and MnTe-based materials, thereby improving their TE performances.