Pseudo‐Nanostructuring and Grain Refinement Enhance the Near‐Room‐Temperature Thermoelectric Performance in n‐type PbSe

PbSe, a promising Te-free thermoelectric material for medium-temperature applications, has garnered considerable attention due to its substantial thermoelectric potential and relatively low cost. However, the vast majority of research on polycrystalline PbSe thermoelectrics has focused primarily on improving its medium-temperature performance, often neglecting the enhancement of near-room-temperature performance and effective module design. Here, an n-type polycrystalline PbSe material (Cu_0.01Pb_0.85Ge_0.15Se) is presented that exhibits a room-temperature zT of ≈0.6 and an average zT of 0.86 from 303 to 523 K. This superior performance is realized through the incorporation of a high-concentration Ge into n-type Cu_0.01PbSe, which induces a novel pseudo-nanostructure and grain refinement, promoting electron-phonon decoupling. Based on this, seven-pair module devices are fabricated, achieving a record-high conversion efficiency of up to 5.1% at a temperature difference of only 228 K, and an unprecedented maximum cooling temperature difference of 47.2 K when the hot-side temperature is 350 K. The findings provide a strong foundation for advancing Te-free polycrystalline PbSe-based materials for thermoelectric cooling and low-temperature power generation.