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ZT values have been substantially improved by developing various strategies for increasing power factor (the product S 2 σ) or suppressing κ lat in the past decade. 2, 3, 4), where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and κ tot is the total thermal conductivity from the electrical ( κ ele) and lattice vibration contribution ( κ lat) 3.

The efficiency of thermoelectric semiconductors is assessed by the dimensionless figure of merit ZT = S 2 σT/ κ tot (refs.

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This conversion process is free of motion or moving parts, thus can be an eco-friendly solution to recovering and using enormous amounts of waste heat to create electricity. Thermoelectric power generators are semiconductor-based electronic devices that can turn such waste heat into electricity through the Seebeck effect 2.

More than 65% of the globally produced energy is lost as waste heat 1. These results could open an era of high-performance practical thermoelectrics from this high-performance material. 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. Its lattice thermal conductivity is ultralow at roughly 0.07 W m –1 K –1 at 783 K, lower than the single crystals. 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. 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. 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. Thermoelectric materials generate electric energy from waste heat, with conversion efficiency governed by the dimensionless figure of merit, ZT.

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