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<img alt="Symbol support vote.svg" src="https://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Symbol_support_vote.svg/15px-Symbol_support_vote.svg.png" decoding="async" width="15" height="15" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Symbol_support_vote.svg/23px-Symbol_support_vote.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Symbol_support_vote.svg/30px-Symbol_support_vote.svg.png 2x" data-file-width="180" data-file-height="185"> <b><bdi>–1</bdi></b> K<img alt="Symbol support vote.svg" src="https://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Symbol_support_vote.svg/15px-Symbol_support_vote.svg.png" decoding="async" width="15" height="15" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Symbol_support_vote.svg/23px-Symbol_support_vote.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Symbol_support_vote.svg/30px-Symbol_support_vote.svg.png 2x" data-file-width="180" data-file-height="185"> <b><bdi>–1</bdi></b> 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.
Chongjian Zhou  ORCID: orcid.org/0000-0002-2245-30571 na1, Yong Kyu Lee1 na1, Yuan Yu  ORCID: orcid.org/0000-0002-3148-66002 na1, Sejin Byun1,3, Zhong-Zhen Luo4, Hyungseok Lee  ORCID: orcid.org/0000-0001-6432-56701,3, Bangzhi Ge1, Yea-Lee Lee5, Xinqi Chen6, Ji Yeong Lee7, Oana Cojocaru-Mirédin  ORCID: orcid.org/0000-0001-6543-203X2, Hyunju Chang  ORCID: orcid.org/0000-0001-7241-53425, Jino Im  ORCID: orcid.org/0000-0001-6594-87735, Sung-Pyo Cho8, Matthias Wuttig  ORCID: orcid.org/0000-0003-1498-10252, Vinayak P. Dravid  ORCID: orcid.org/0000-0002-6007-30639, Mercouri G. Kanatzidis4,9 &amp; In Chung  ORCID: orcid.org/0000-0001-6274-33691,3
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