AgBi₃S₅ is a new n-type thermoelectric material that is environmentally friendly and composed of elements of earth-abundant, non-toxic and high performance-cost ratio. This compound features an intrinsically low thermal conductivity derived from its complex monoclinic structure. However, the terrible electrical transport properties greatly limited the improvement of thermoelectric performance. Most previous studies considered that carrier concentration is the main reason for low electrical conductivity and focused on improving carrier concentration by aliovalent ion doping. In this work, we found that the critical parameter that restricts the electric transport performance of AgBi₃S₅ was the extremely low carrier mobility instead of the carrier concentration. According to the Pisarenko relationships and density functional theory calculations, Nb doping can sharpen the conduction band of AgBi₃S₅, which contributes to reducing the effective mass and improving the carrier mobility. With a further increase of the Nb doping content, the conduction band convergence can enlarge the effective mass and preserve the carrier mobility. Combined with the decrease in lattice thermal conductivity due to the intensive phone scattering, a maximum ZT value of ∼0.50 at 773 K was achieved in Ag_0.97Nb_0.03Bi₃S₅, which was ∼109.6% higher than that of pure AgBi₃S₅. This work will stimulate the new exploration of high-performance thermoelectric materials in ternary metal sulfides.

AgBi ₃ S ₅是一种由地球丰富、无毒、性价比高的环保元素组成的新型n型热电材料。该化合物由于其复杂的单斜晶结构而具有本质上低的导热率。然而，糟糕的电传输性能极大地限制了热电性能的提高。以往的研究大多认为载流子浓度是导致电导率低的主要原因，并侧重于通过异价离子掺杂来提高载流子浓度。_{在这项工作中，我们发现限制AgBi 3} S ₅电传输性能的关键参数是极低的载流子迁移率而不是载流子浓度。_{根据Pisarenko关系式和密度泛函理论计算，Nb掺杂可以锐化AgBi 3} S ₅的导带，有助于降低有效质量，提高载流子迁移率。随着Nb掺杂含量的进一步增加，导带收敛可以扩大有效质量并保持载流子迁移率。结合由于强烈的电话散射而引起的晶格热导率的降低， Ag _0.97 Nb _0.03 Bi ₃ S ₅在 773 K 时实现了~0.50 的最大ZT值，比纯AgBi ₃ S ₅高约109.6% 。该工作将激发三元金属硫化物高性能热电材料的新探索。