This article highlights a novel strategy for designing molecules with high thermoelectric performance, which are resilient to fluctuations. In laboratory measurements of thermoelectric properties of single-molecule junctions and self-assembled monolayers, fluctuations in frontier orbital energies relative to the Fermi energy E_F of electrodes are an important factor, which determine average values of transport coefficients, such as the average Seebeck coefficient 〈S〉. In a worst-case scenario, where the relative value of E_F fluctuates uniformly over the HOMO–LUMO gap, a “worst-case scenario theorem” tells us that the average Seebeck coefficient will vanish unless the transmission coefficient at the LUMO and HOMO resonances take different values. This implies that junction asymmetry is a necessary condition for obtaining non-zero values of 〈S〉 in the presence of large fluctuations. This conclusion that asymmetry can drive high thermoelectric performance is supported by detailed simulations on 17 molecules using density functional theory. Importantly, junction asymmetry does not imply that the molecules themselves should be asymmetric. We demonstrate that symmetric molecules possessing a localised frontier orbital can achieve even higher thermoelectric performance than asymmetric molecules, because under laboratory conditions of slight symmetry breaking, such orbitals are ‘silent’ and do not contribute to transport. Consequently, transport is biased towards the nearest “non-silent” frontier orbital and leads to a high ensemble averaged Seebeck coefficient. This effect is demonstrated for a spatially-symmetric 1,2,3-triazole-based molecule, a rotaxane-hexayne macrocycle and a phthalocyanine.

中文翻译：

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分子级热电：最坏的情况。

本文重点介绍了设计具有高热电性能且可抵抗波动的分子的新颖策略。在实验室测量单分子结和自组装单分子层的热电特性时，相对于电极费米能量E _F的前沿轨道能量的波动是重要的因素，它决定了传输系数的平均值，例如平均塞贝克系数〈S〉。在最坏的情况下，E _F的相对值在HOMO-LUMO间隙上均匀波动，一个“最坏情况假设定理”告诉我们，除非LUMO和HOMO共振处的透射系数取不同值，否则平均塞贝克系数将消失。这意味着结点不对称是获得< S的非零值的必要条件〉波动较大时。使用密度泛函理论对17个分子进行的详细模拟，支持了不对称性可以驱动高热电性能的结论。重要的是，连接不对称并不意味着分子本身应该是不对称的。我们证明，拥有局部前沿轨道的对称分子比非对称分子可以获得更高的热电性能，因为在轻微对称性破坏的实验室条件下，此类轨道“沉默”且无助于运输。因此，运输偏向最近的“非沉默”边界轨道，并导致较高的集合平均塞贝克系数。对于基于空间对称的1,2,3-三唑的分子，可以证明这种效果，