Reduction of phonon mediated thermal transport properties, i.e., lattice thermal conductivity (κL), of semiconductors can strongly affect the performance of thermoelectrics and optoelectronics. Although extrinsic routes to reduce κL have been achieved through selective scattering of phonons via doping, alloying, and hierarchical nano-structuring, semiconductors with intrinsically low κL have recently gained widespread attention due to their ability to decouple electronic and phonon transports. While innate low κL in crystalline semiconductors is a desired requirement to achieve high performance thermoelectrics, the solar upconversion efficiency of photovoltaics based on metal halide perovskites (MHPs) have been shown to increase due to their ultralow κL through the hot-phonon bottleneck effect. Therefore, understanding the microscopic mechanisms underlying ultralow κL in crystalline semiconductors is extremely important. Several structural factors that are intrinsic to a material have been shown to strongly influence the reduction of κL. Among them, the presence of rattling atoms, lone-pair electrons, and large lattice anharmonicity have been widely studied. Here, we bring out yet another largely unexplored intrinsic characteristic of materials related to the filled antibonding valence states (AVS) near the Fermi level, which are shown to induce low κL in crystalline compounds. We focus our review on an emerging class of compounds–metal halide semiconductors including MHPs and investigate the interplay between structures, chemical bonding and κL, carefully curating from literature a list of 33 compounds having different structure dimensionality with known κL. We established a universal connection between the elastic moduli, speeds of sound, and κL with the presence of AVS just below the Fermi level. We found that large peak in the AVS correlates positively with lower values of elastic moduli, speeds of sound, and κL, providing antibonding states based design criteria of low-κL compounds. Furthermore, we discuss different synthesis strategies, which are crucial for experimental realization of ultralow κL through structure manipulation. Additionally, we outline how chemical bonding data can be utilized in machine learning models for predictive modeling of κL. We hope that our approach of understanding low-κL through the viewpoint of chemical bonding theory would encourage exploration of phonon transport properties in other families of materials having filled AVS that can provide further insights on the structure-bonding-property relationships aiding novel materials design approaches.

中文翻译：

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反键合价态在金属卤化物半导体中诱导低晶格热导率


声子介导的半导体热传输特性（即晶格热导率 （κL））的降低会强烈影响热电和光电子学的性能。尽管通过掺杂、合金化和分层纳米结构对声子进行选择性散射已经实现了降低 κL 的外源途径，但具有本质低 κL 的半导体最近因其能够解耦电子和声子传输而受到广泛关注。虽然晶体半导体中固有的低 κL 是实现高性能热电的理想要求，但基于金属卤化物钙钛矿 （MHP） 的光伏的太阳能上转换效率已被证明是提高的，因为它们通过热声子瓶颈效应实现了超低的 κL。因此，了解晶体半导体中超低 κL 的微观机制极为重要。材料固有的几个结构因素已被证明会强烈影响 κL 的降低。其中，嘎嘎作响的原子、孤对电子和大晶格不谐性的存在已被广泛研究。在这里，我们揭示了与费米能级附近的填充反键合价态 （AVS） 相关的另一个基本未开发的材料的本征特性，这些特性被证明可以在晶体化合物中诱导低 κL。我们将综述重点放在一类新兴化合物——包括 MHP 的金属卤化物半导体上，并研究结构、化学键和 κL 之间的相互作用，从文献中仔细整理了 33 种具有不同结构维度且已知 κL 的化合物。 我们在弹性模量、声速和 κL 之间建立了一个普遍的联系，AVS 的存在略低于费米能级。我们发现 AVS 中的大峰与较低的弹性模量、声速和 κL 值呈正相关，为低 κL 化合物提供了基于反键状态的设计标准。此外，我们讨论了不同的合成策略，这些策略对于通过结构操纵实验实现超低 κL 至关重要。此外，我们还概述了如何在机器学习模型中利用化学键数据进行 κL 的预测建模。我们希望我们从化学键理论的角度理解低 κL 的方法能够鼓励探索其他填充 AVS 的材料家族的声子传输特性，从而为有助于新型材料设计方法的结构-键合-性能关系提供进一步的见解。