Materials science

High entropy alloys

Optoelectronics

Engineering

Composite material

Thermoelectric effect

Physics

Nanotechnology

Vickers hardness test

Entropy (arrow of time)

Seebeck coefficient

Band gap

Thermal conductivity

Condensed matter physics

Engineering physics

Thermoelectric materials

Microstructure

Thermodynamics

Advanced Functional Materials

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 m H and the lattice thermal conductivity κ ph in taking advantage of configurational entropy Δ S . Herein, the significant advances of ultralow κ ph yet decent m H 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 n H 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 H V are concurrently attained in Cd 0.02 (Sn 0.59 Pb 0.15 Ge 0.2 Sb 0.06 ) 0.98 Te. 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 Δ T = 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.

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