[论文解读] Ultralow lattice thermal conductivity and high thermoelectric performance near room temperature of Janus monolayer HfSSe

Jayanta Bera, Atanu Betal+1 more|arXiv (Cornell University)|Mar 5, 2020

Advanced Thermoelectric Materials and Devices被引用 8

一句话总结

本研究提出了一种高性能热电材料——Janus单层HfSSe，其晶格热导率极低（300 K时为0.36 W/mK），这是由于声子群速度降低和寿命缩短所致。基于密度泛函理论和玻尔兹曼输运理论的从头算计算表明，该材料在室温附近具有较高的热电优值（ZT ≈ 1），因此在从体热中收集能量的可穿戴设备中具有广阔前景。

ABSTRACT

Two-dimensional transition metal di-chalcogenides (TMDCs) have shown great potential as good quality thermoelectric materials at high temperature since past few years due to their suitable band gap tunabilty, low dimensionality and fantastic combination of electrical conductivity and lattice thermal conductivity. Here, a first principles calculations of electronic and thermoelectric performance of two dimensional monolayer HfS 2 , HfSe 2 and their Janus monolayer HfSSe has been performed with the help of density functional theory and Boltzmann transport equation. Thermodynamical stability of all three structures has been confirmed from phonon dispersion curves. The thermoelectric parameters such as Seebeck coefficient, power factor and electrical conductivity have been calculated at 300K, 400K and 500K. The lattice thermal conductivity at room temperature has been found very low in monolayer HfS 2 , HfSe 2 and HfSSe Janus monolayer as compared to very popular TMDCs such as MoS 2 and WS 2 . An ultralow value of lattice thermal conductivity of the value of 0.36 W/mK at room temperature in Janus monolayer HfSSe has been found which is lower than that of monolayer HfS 2 and HfSe 2 because of the very low group velocity and short phonon lifetime in HfSSe. This ultralow lattice thermal conductivity in Janus monolayer HfSSe results a very high thermoelectric figure of merit close to the value of 1 at room temperature. By constructing the Janus monolayer of HfS 2 and HfSe 2 the thermoelectric performances significantly enhanced. Our theoretical investigation predicts that Janus monolayer HfSSe can be a revolutionary candidate for the fabrication of next generation wearable thermoelectric power generator to convert human body heat into electricity.

研究动机与目标

• 研究单层HfS2、HfSe2及其Janus结构对应物HfSSe的热电性能。
• 评估HfSSe中结构非对称性对晶格热导率和热电性能的影响。
• 确定HfSSe是否能在室温附近实现高热电效率。
• 探索HfSSe作为下一代可穿戴热电发电机材料的潜力。
• 将HfSSe的热电性能与传统过渡金属二硫属化物（如MoS2和WS2）进行比较。

提出的方法

• 采用密度泛函理论（DFT）计算电子结构和通过声子色散曲线评估热力学稳定性。
• 在恒定弛豫时间近似下，利用玻尔兹曼输运方程计算热电输运性能。
• 在300 K、400 K和500 K下计算赛贝克系数、电导率和功率因子。
• 基于DFT计算得到的声子群速度和寿命，评估晶格热导率。
• 将HfSSe与对称单层HfS2和HfSe2的热电性能进行比较。
• 通过热电优值（ZT）评估热电效率，尤其关注室温条件下的表现。

实验结果

研究问题

• RQ1 与HfS2和HfSe2相比，Janus单层HfSSe在室温下的晶格热导率如何？
• RQ2 HfSSe中的结构非对称性如何影响声子输运和热导率？
• RQ3 HfSSe在接近300 K时的热电优值（ZT）是多少？与其他二维TMDC材料相比如何？
• RQ4 Janus HfSSe能否实现适用于可穿戴能量收集应用的高性能热电性能？
• RQ5 声子群速度和寿命在HfSSe中降低热导率的过程中起什么作用？

主要发现

• Janus单层HfSSe在300 K时表现出极低的晶格热导率（0.36 W/mK），显著低于HfS2和HfSe2。
• HfSSe中晶格热导率的降低源于结构非对称性导致的声子群速度抑制和声子寿命缩短。
• HfSSe的热电优值（ZT）在室温下可达到约1，表明其具有高热电效率。
• 由于电子结构调制能力增强，HfSSe的功率因子和塞贝克系数均高于对称的HfS2和HfSe2。
• 声子色散谱中无虚频模式，证实了HfSSe的热力学稳定性。
• 本研究预测，HfSSe是下一代可穿戴热电发电机的理想候选材料，可用于从体热中收集能量。