Thermoelectric materials generate electric energy from waste heat, with conversion efficiency governed by the dimensionless figure of merit, ZT. Single-crystal tin selenide (SnSe) was discovered to exhibit a high ZT of roughly 2.2–2.6 at 913 K, but more practical and deployable polycrystal versions of the same compound suffer from much poorer overall ZT, thereby thwarting prospects for cost-effective lead-free thermoelectrics. The poor polycrystal bulk performance is attributed to traces of tin oxides covering the surface of SnSe powders, which increases thermal conductivity, reduces electrical conductivity and thereby reduces ZT. Here, we report that hole-doped SnSe polycrystalline samples with reagents carefully purified and tin oxides removed exhibit an ZT of roughly 3.1 at 783 K. Its lattice thermal conductivity is ultralow at roughly 0.07 W m^–1 K^–1 at 783 K, lower than the single crystals. The path to ultrahigh thermoelectric performance in polycrystalline samples is the proper removal of the deleterious thermally conductive oxides from the surface of SnSe grains. These results could open an era of high-performance practical thermoelectrics from this high-performance material.

热电材料从废热中产生电能，转换效率由无量纲品质因数 ZT 决定。发现单晶硒化锡 (SnSe) 在 913 K 时表现出大约 2.2-2.6 的高 ZT，但相同化合物的更实用和可部署的多晶版本的整体 ZT 差得多，从而阻碍了具有成本效益的铅的前景- 免费热电。多晶块体性能差的原因是有痕量的锡氧化物覆盖在 SnSe 粉末的表面，这增加了热导率，降低了电导率，从而降低了 ZT。在这里，我们报告了经过仔细纯化并去除氧化锡的空穴掺杂 SnSe 多晶样品在 783 K 时的 ZT 约为 3.1。其晶格热导率超低，约为 0.07 W m^–1  K ^–1在 783 K，低于单晶。在多晶样品中获得超高热电性能的途径是从 SnSe 晶粒表面适当去除有害的导热氧化物。这些结果可能会开启这种高性能材料的高性能实用热电时代。