Compositional design toward universal band convergence for high-performance Zintl thermoelectrics

Band convergence can impact the thermoelectric performance of materials in a positive manner, but seeking the composition that shows such a feature in a series of alloys remains a time-consuming task. Here we propose, for the first time, a novel and effective method to design a series of compositions at one time, with Zintl materials as a case to study, where valence band convergence is presumably realized in all these compositions. Validity of this presuming design is subsequently testified from both experimental and theoretical standpoints. In addition, we define a new parameter to Zintl compounds, termed “number of aligned pairs”, and its effect on electrical properties of the materials is investigated. Finally, benefiting from such a design, good thermoelectric performance is universally achieved in these compositions, the best among which, furthermore, exhibits a peak zT that turns out to be one of the highest in all reported p-type Zintls to date. By pairing it with an outstanding n-type material, a thermoelectric module for power generation is assembled, and has demonstrated its potential for enabling heat-to-electricity energy conversion with high efficiency.