Thermopower in Organic Molecular Solids

有机半导体是碳基材料，类似于染料，可以导电。它们可以溶解在溶剂中，并使用喷墨打印在柔性基板上印刷，用于显示器和传感器等低成本电子产品。基于有机半导体的发光二极管已经在移动电话中商业化。在材料研究部固态和材料化学项目的支持下，该研究项目通过研究它们的基本物理性质（如导电性）来扩展它们的应用，并探索将多余热能转化为电能的可能性。该项目对未来的科研队伍产生了重大影响，因为从事该研究的研究生研究人员在多学科材料科学与工程方面获得了重要的培训。研究小组还通过当地K-12学校的教育活动向公众宣传。分子有机电子材料的关键挑战是通过固态有序控制其电子性能。有机半导体的电掺杂对于有机发光二极管和太阳能电池的电极层以及新兴的热电应用具有重要意义。本项目的研究考察了在溶液中处理有机半导体的晶体顺序，无论是在整齐的薄膜中还是在与受体混合的情况下，如何影响它们的导电性和电子结构。比较了分子受体掺杂的样品在模型双层结构和体中导电的内在特性。热功率测量和先进的x射线结构表征进行确定如何微观结构和电子结构的有机分子固体的演变在电掺杂。门控热功率测量用于确定未掺杂材料的电子结构，以深入了解其电子结构。本研究提供了控制有机半导体电导率的新方法，以确定这些重要材料系统的电性能极限。

Non-Technical AbstractOrganic semiconductors are carbon-based materials, similar to dyes, that conduct electricity. They can be dissolved in solvents and printed using inkjet-printing on flexible substrates for use in low-cost electronics such as displays and sensors. Light emitting diodes based on organic semiconductors are already commercially available in mobile phones. With support from the Solid State and Materials Chemistry Program in the Division of Materials Research, this research project expands their use through the study of their fundamental physical properties such as their electrical conductivity, and explores possibilities for converting excess thermal energy to electrical power. The project has significant impact on the future scientific workforce because graduate student researchers carrying out the research gain significant training in multidisciplinary materials science and engineering. The research team also performs outreach to the public through educational activities in local K-12 schools.Technical AbstractA key challenge in molecular organic electronic materials is the control of their electronic properties through solid state ordering. Electrical doping of organic semiconductors is important for electrode layers in organic light emitting diodes and solar cells and in emerging thermoelectric applications. The research in this project examines how the crystalline order in solution processed organic semiconductors, both in neat films and in blends with acceptors, affects their electrical conductivity and electronic structure. The intrinsic properties of electrical conduction are compared in samples doped by molecular acceptors in model bilayer structures and in the bulk. Thermopower measurements and advanced x-ray structural characterization are carried out to determine how the microstructure and electronic structure of organic molecular solids evolve upon electrical doping. Gated thermopower measurements are used to determine the electronic structure of undoped materials to gain insight into their electronic structure. This research provides insight into new means to control the electrical conductivity of organic semiconductors in order to determine the limits of the electrical properties of these important materials systems.