High thermoelectric performance of α-MgAgSb for power generation

Solid-state thermoelectric devices enable the conversion of waste heat and solar energy into electricity, providing an alternative route for energy harvesting to tackle the challenges of energy sustainability. α-MgAgSb-based materials have recently gained popular attention as a new promising p-type candidate for low-temperature (between room temperature and 550 K) applications. A high figure of merit (ZT) of 1.2-1.4 at 550 K was achieved, along with experimental demonstration of a record high conversion efficiency of ∼8.5% under a cold- and hot-side temperature difference of 225 K, which holds the realistic prospect for power generation. In this review, we summarize the recent progress in both material-level understanding and device-level measurement of the α-MgAgSb system. First, the phase transitions and common fabrication methods are briefly introduced. Then, the origin of the "phonon glass electron crystal" behavior of α-MgAgSb is thoroughly elucidated with regard to some critical factors, such as the crystal structure, lattice dynamic properties, defect chemistry, microstructure, and band structure. Afterwards, the effective strategies to further enhance the ZT are illustrated, including optimizing the carrier concentration and intrinsic defect engineering. In addition, other feasible methods in theory are also presented. Finally, the conversion efficiency on a single-leg device is presented. In the outlook section, the currently unsolved questions as well as future directions and challenges for this material system are discussed.