High‐Performance Thermoelectric Material and Module Driven by Medium‐Entropy Engineering in SnTe.

The emerged strategy of entropy engineering provides new ideas for realizing high‐performance thermoelectric materials, but it is still much unresolved how to achieve delicate trade‐off between the carrier mobility mH and the lattice thermal conductivity κph in taking advantage of configurational entropy ΔS. Herein, the significant advances of ultralow κph yet decent mH in a new medium‐entropy system of well‐designed (Pb, Ge, Sb, Cd) co‐alloyed SnTe is reported. Moreover, the co‐alloying also optimizes the carrier concentration nH and promotes the valence band convergence, thereby yielding an excellent Seebeck coefficient and compensating for decreased electrical conductivity. Consequently, a high peak ZT of 1.5 at 800 K, a record average ZT of 0.84 (300−800 K), and a remarkable Vickers hardness of 134 HV are concurrently attained in Cd0.02(Sn0.59Pb0.15Ge0.2Sb0.06)0.98Te. Benefiting from the synergistically increased ZT and mechanical strength, the fabricated 17‐couple SnTe‐based thermoelectric module exhibits a competitive conversion efficiency of 6.3% at ΔT = 350 °C. This study not only provides a paradigm of the medium‐entropy design for thermoelectric materials but also puts forward an innovative scheme for low‐grade heat harvest by SnTe‐based TE module. [ABSTRACT FROM AUTHOR]