Te-free Bi₂S₃-based thermoelectric materials show great potential for eco-friendly and industrial scale-up applications because of their high-abundance, low-cost, low-toxicity, and low-thermal-conductivity features. However, their low figure of merit, ZT limits their further applications. In this work, we report a high ZT of ~0.8 at ~760 K in n-type polycrystalline Bi₂S₃ by a combination of hierarchical structure manipulation and carrier density optimization. A step-by-step fabrication by using mechanical alloying, high-pressure and high-temperature treatment, spark plasma sintering, and annealing leads to unique micro/nanostructures in polycrystalline Bi₂S₃ including refined grains, high-density Bi-rich nanoprecipitates, significant lattice distortions, and nanopores that confirmed by comprehensive characterizations, which contribute to significantly suppressed lattice thermal conductivity of 0.41 W m⁻¹ K⁻¹ at ~760 K. A further 0.5 mol% CuCl₂-doping triggers impurity band in the electronic structure of Bi₂S₃ and narrows the bandgap for optimizing the carrier concentration at ~1 × 10²⁰ cm⁻³, confirmed by both experimental results and first-principles density functional theory calculations. The optimized carrier concentration and maintained low lattice thermal conductivity give rise to a high power factor of ~5.3 μW cm⁻¹ K⁻² and high ZT that ranks as a top value. This work provides a new route to achieve high thermoelectric performance in n-type polycrystalline Bi₂S₃.

不含Te的Bi ₂ S ₃基热电材料具有高丰度，低成本，低毒性和低导热性的特点，因此在生态友好型和工业规模化应用中显示出巨大潜力。但是，由于ZT的低品质因数，限制了它们的进一步应用。在这项工作中，我们通过结合分层结构操作和载流子密度优化，在n型多晶Bi ₂ S _3中报告了在〜760 K时〜0.8的高ZT。通过机械合金化，高压和高温处理，火花等离子体烧结和退火的分步制造，可以在多晶Bi ₂ S中产生独特的微观/纳米结构_3个样品，包括精炼晶粒，高密度的富含Bi的纳米沉淀，明显的晶格畸变和通过综合表征证实的纳米孔，这有助于在〜760 K时显着抑制0.41 W m ^-1 K ^-1的晶格导热率。进一步0.5 mol％CuCl ₂掺杂会触发Bi ₂ S ₃电子结构中的杂质带，并缩小能带隙，以优化〜1×10 ²⁰ cm ^-3的载流子浓度由实验结果和第一性原理密度泛函理论计算所证实。优化的载流子浓度和保持的低晶格导热率导致〜5.3μWcm ^-1 K ^-2的高功率因数和最高ZT成为最高值。这项工作为在n型多晶Bi ₂ S _3中实现高热电性能提供了一条新途径。