Single crystal tin selenide (SnSe) has a recorded high thermoelectric figure of merit (ZT) value of 2.6 at 923 K, but it is easy to form mechanical cracks and difficult to apply in thermoelectric conversion devices. Polycrystalline SnSe has better mechanical properties but inferior ZT values, which needs further optimization for applications. This work aims at enhancing the thermoelectric performance of polycrystalline SnSe through synergistic optimization of sliver (Ag) and aluminum (Al) co-doping with the hydrogen reduction. The effects of Ag and Al doping on electronic transport properties are systematically investigated by density functional theory calculation and experimental measurement. Compared with pristine SnSe, Ag doping can effectively increase the hole concentration to 1.58 × 10¹⁹ cm⁻³ and improve the conductivity. Results also indicate that using Al dopant may slightly decrease the hole concentration but reduce the thermal excitation temperature, and introduce point defects reducing the lattice thermal conductivity through scattering phonons. In addition, the hydrogen reduction of sample powders before synthesis can effectively remove Sn oxides and reduce lattice thermal conductivity. At last, a state-of-the-art maximum ZT value of 1.69 at 823 K is obtained in Ag_0.01Al_0.01Sn_0.98Se. This study provides a theoretical basis and technical guidance for designing high-performance polycrystalline SnSe.

中文翻译：

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通过能带结构修饰和氢还原实现Ag/Al共掺杂多晶SnSe的高热电性能

单晶硒化锡 (SnSe) 在 923 K 时具有 2.6 的高热电品质因数 (ZT) 值，但容易形成机械裂纹，难以应用于热电转换器件。多晶 SnSe 具有较好的力学性能，但ZT值较差，需要进一步优化应用。这项工作旨在通过协同优化银 (Ag) 和铝 (Al) 与氢还原共掺杂来提高多晶 SnSe 的热电性能。通过密度泛函理论计算和实验测量，系统地研究了Ag和Al掺杂对电子传输特性的影响。与原始 SnSe 相比，Ag 掺杂可以有效地将空穴浓度提高到 1.58 × 10 ¹⁹cm ^-3并提高电导率。结果还表明，使用Al掺杂剂可能会略微降低空穴浓度，但会降低热激发温度，并通过散射声子引入降低晶格热导率的点缺陷。此外，合成前样品粉末的氢还原可以有效去除Sn氧化物，降低晶格热导率。_{最后，在 Ag 0.01} Al _0.01 Sn _0.98 Se中获得了 823 K 时的最新最大ZT值为 1.69 。该研究为设计高性能多晶SnSe提供了理论依据和技术指导。