Abstract Thermal-electricity conversion is one of the most promising routes to harvest heat and convert it as easily storable and deliverable electric energy. Significant progress has been made since the discovery of Seebeck effect in 1821, particularly, the figure of merit zT approached a record high value of 2.6 in 2014. However, for thermoelectric devices, high average zT values (zTave) over the operating temperature range is more important as it is directly related to the conversion efficiency ( η ). Approaching highly stable and repeatable ultra-high zTave for Te-free materials has been historically challenging over the past century though exciting progress with zTave well above 1.10 was made recently. Here, through synergistic band engineering strategy for single crystalline SnSe, we report a series of record high zTave over a wide temperature range, approaching ∼1.60 in the range from 300 K to 923 K in Na-doped SnSe0.9S0.1 solid solution single crystals, with the maximum zT of 2.3 at 773 K. These ultra-high thermoelectric performance derive from the new multiple valence band extrema near the band edges in SnSe0.9S0.1 and the shift of Fermi level towards the multi-valley bands through Na doping which introduce additional carrier pockets to attend electrical transport. These effects result in an optimized ultrahigh power factor exceeding 4.0 mW m−1 K−2 in Sn0.97Na0.03Se0.9S0.1 single crystals. Combined with the extremely lowered thermal conductivity attributed from the intrinsic anharmonicity and point defect phonon scattering, the series of ultra-high zTave and a record high calculated conversion efficiency of 21% over a wide temperature range are approached.

中文翻译：

---

协同带设计的 Sn x Na 1− x Se 0.9 S 0.1 单晶的超高平均品质因数

摘要 热电转换是收集热量并将其转换为易于储存和输送的电能的最有前途的途径之一。自 1821 年发现塞贝克效应以来取得了重大进展，特别是品质因数 zT 在 2014 年接近创纪录的 2.6。然而，对于热电器件，工作温度范围内的高平均 zT 值 (zTave) 是更重要的是它与转换效率 (η) 直接相关。在过去的一个世纪里，为无 Te 材料实现高度稳定和可重复的超高 zTave 一直是历史上的挑战，尽管最近 zTave 远高于 1.10 取得了令人兴奋的进展。在这里，通过单晶 SnSe 的协同能带工程策略，我们报告了一系列创纪录的高 zTave 在很宽的温度范围内，在 Na 掺杂的 SnSe0.9S0.1 固溶体单晶中在 300 K 到 923 K 的范围内接近~1.60，在 773 K 时最大 zT 为 2.3。这些超高的热电性能源于 SnSe0.9S0.1 中带边缘附近的新多价带极值，以及费米能级通过 Na 掺杂向多价带移动，Na 掺杂引入了额外的载流子袋以参与电传输。这些效应导致在 Sn0.97Na0.03Se0.9S0.1 单晶中优化的超高功率因数超过 4.0 mW m-1 K-2。结合由于固有非谐性和点缺陷声子散射而导致的极低的热导率，