Thermoelectric properties of organic thin films enhanced by p-p stacking
Thermoelectric properties of organic thin films enhanced by p-p stacking
复制标题
p-p堆叠增强有机薄膜的热电性能
作者：
Wang X
由合成坚固的可伸缩分子组成的薄膜已被证明具有热电能量收集的主要潜力。先前对分子薄膜的研究倾向于集中在大量平行排列的离散但相同的共轭分子线上，这些分子线组装成垂直于电极表面的单层，并通过共价键固定，称为自组装单层。在这些研究中，为了优化薄膜的热电性能，需要在分子成分的合成复杂性和薄膜性能之间进行权衡，这限制了材料集成到实际热电器件中的机会。在这项工作中，我们展示了一种提高分子薄膜热电性能的替代策略。我们已经建立了一系列厚度可控的薄膜，其中基本单元——这里是四苯基卟啉锌——与电极平行，并通过π -π堆叠连接在一起。我们比较了三种常用的制造路线，并利用扫描探针和计算技术对所得薄膜进行了表征。利用Langmuir-Blodgett制备技术，我们成功地将垂直于ZnTPP多层膜平面的热功率提高了10倍，获得了−65 μV K−1的塞贝克系数。此外，垂直于薄膜平面的系统的电子输运遵循多层薄膜的隧穿机制，输运效率与大多数共轭系统相当。此外，扫描热显微镜表征显示，随着薄膜厚度从单层到多层的增加，热导率降低了7倍，这表明π -π堆叠结的热电性能得到增强。
Thin films comprising synthetically robust, scalable molecules have been shown to have major potential for thermoelectric energy harvesting. Previous studies of molecular thin-films have tended to focus on massively parallel arrays of discrete but identical conjugated molecular wires assembled as a monolayer perpendicular to the electrode surface and anchored via a covalent bond, know as self-assembled monolayers. In these studies, to optimise the thermoelectric properties of the thin-film there has been a trade-off between synthetic complexity of the molecular components and the film performance, limiting the opportunities for materials integration into practical thermoelectric devices. In this work, we demonstrate an alternative strategy for enhancing the thermoelectric performance of molecular thin-films. We have built up a series of films, of controlled thickness, where the basic units—here zinc tetraphenylporphyrin—lie parallel to the electrodes and are linked via π–π stacking. We have compared three commonly used fabrications routes and characterised the resulting films with scanning probe and computational techniques. Using a Langmuir-Blodgett fabrication technique, we successfully enhanced the thermopower perpendicular to the plane of the ZnTPP multilayer film by a factor of 10, relative to the monolayer, achieving a Seebeck coefficient of− 65 μV K− 1. Furthermore, the electronic transport of the system, perpendicular to the plane of the films, was observed to follow the tunnelling regime for multi-layered films, and the transport efficiency was comparable with most conjugated systems. Furthermore, scanning thermal microscopy characterisation shows a factor of 7 decrease in thermal conductance with increasing film thickness from monolayer to multilayer, indicating enhanced thermoelectric performance in a π–π stacked junction.