Van der Waals Grain Boundary and Entropy Engineering Realize Broad‐Temperature High Thermoelectric Performance in SnTe

Achieving high conversion efficiency in thermoelectric materials requires excellent performance over a broad temperature range. In this work, the high thermoelectric performance of SnTe‐based materials is extended from a single temperature point to a wide temperature range of approximately 200 K. Elemental doping and Sn vacancy engineering modulate the electronic structure and promote band convergence, thereby enhancing electrical transport properties. Meanwhile, abundant Sn vacancies aggregate at grain boundaries to form ordered van der Waals gaps, which enhance phonon scattering while maintaining favorable electrical transport. Additionally, multi‐element doping induces lattice softening and increases configurational entropy, resulting in strong lattice distortion that further intensifies phonon scattering. These effects collectively enable the synergistic optimization of electrical and thermal performance. The lattice thermal conductivity is substantially reduced, and a peak ZT value of 1.4 (823 K) and a high average ZT of ∼1.3 (623–823 K) is achieved in Sn 0.61 Sb 0.10 Pb 0.15 Mn 0.09 Te. The single‐stage module based on optimized SnTe achieves a conversion efficiency of 8%. This synergistic approach to modifying the lattice and grain boundaries provides a new perspective for optimizing the thermoelectric performance of materials in the medium‐ to high‐temperature range.