The ever-increasing world-wide energy consumption and crisis of environmental pollution have aroused enthusiasm on developing high-efficiency and green-clean energy conversion technology. Thermoelectric materials enable an environmentally friendly conversion between heat and electricity, and therefore serve as an optimum candidate for solving the current dilemma and contribute to the carbon-neutral target. Among the thermoelectric family, layered materials have shared a great portion with impressive thermoelectric performance originating from their (quasi-)two-dimensional crystal structure with hierarchical bonding, i.e., strong intralayer and weak interlayer bonds. This structure and bonding feature is believed to be propitious to low lattice thermal conductivity, low-dimensional electrical features, and anisotropic electron and phonon transport behaviors, which offer great opportunity to disentangle the inter-coupled thermoelectric parameters. For those benefits, layered materials emerge endlessly in the field of thermoelectricity and have achieved extensive attention. In this review, we highlight the recent progress in the field of layered thermoelectric materials. The structure and bonding peculiarities of layered thermoelectric materials are outlined. Then, following the classification of single-unit, quasi-double-unit, and double-unit layered thermoelectric materials, the crystal and bonding features in some typical layered thermoelectric materials are discussed, with focus on their current research interest and progresses. The possible mechanisms behind the performance optimization will be analyzed. Finally, some personal views on the prospect of this field, including chemical bond perspective and interlayer electronic transport enhancement are also presented.

中文翻译：

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层状热电材料：结构、粘合和性能机制

世界范围内能源消耗的不断增长和环境污染的危机，激发了开发高效、绿色清洁能源转换技术的热情。热电材料能够实现热电之间的环保转换，因此可作为解决当前困境的最佳候选材料，并有助于实现碳中和目标。在热电家族中，层状材料有很大一部分具有令人印象深刻的热电性能，这源于它们具有分级键合的（准）二维晶体结构，即强层内键和弱层间键。这种结构和键合特征被认为有利于低晶格热导率、低维电学特征、和各向异性的电子和声子传输行为，这为解开相互耦合的热电参数提供了很好的机会。为此，层状材料在热电领域层出不穷，受到广泛关注。在这篇综述中，我们重点介绍了层状热电材料领域的最新进展。概述了层状热电材料的结构和键合特性。然后，按照单单元、准双单元和双单元层状热电材料的分类，讨论了一些典型层状热电材料中的晶体和键合特征，重点介绍了它们目前的研究兴趣和进展。将分析性能优化背后的可能机制。最后，