Scanned-probe characterization of degradation and charge generation in organic semiconductors

John Marohn教授和他的研究团队通过使用电场力显微镜来获得表面电位和电容的时间分辨和波长分辨图像，从而检查了有机半导体中的两个性能决定过程。在第一项研究中，研究小组制造了有机薄膜晶体管(由一系列n沟道有机半导体分子使用不同材料作为晶体管的介质层)，并使用时间分辨、空间分辨和波长分辨的电荷陷阱形成和衰减速率测量来揭示电荷陷阱机制，并潜在地揭示电荷陷阱物种的内部电子能级。在第二项研究中，这些研究人员制备太阳能电池薄膜(通过旋转聚合物混合物和聚合物：分子混合物到具有不同且控制良好的功函数的图案化电极的衬底上)，并研究这些薄膜中的局部电荷产生动力学作为空间位置和照明波长的函数，以更好地从微观上了解有机太阳能电池薄膜中电荷产生效率与背景电荷密度的关系。能源在美国经济中发挥着核心作用。出于环境和安全原因，预计太阳能发电将成为美国未来能源组合中至关重要的组成部分。设计一种能够以合理的成本大量生产的太阳能电池仍然是一个挑战。既然塑料已经可以大量生产，了解如何用塑料制造更好的太阳能电池是有意义的。为了加速塑料太阳能电池的制造，本研究调查了两个关键工艺的细节-塑料太阳能电池材料在运行中如何降解以及它们如何将光转化为电能。在这项研究过程中指导的学生和博士后科学家是美国保持和提高其在基于纳米技术的能源发电和能源储存行业的领先地位所必需的。

Prof. John Marohn and his research team examine two performance-determining processes in organic semiconductors by using electric force microscopy to acquire time-resolved and wavelength-resolved images of surface potential and capacitance. In the first study, the research team fabricates organic thin-film transistors (from a series of n-channel organic semiconductor molecules using different materials for the transistor's dielectric layer) and uses time-resolved, spatially resolved, and wavelength-resolved measurements of the rate of charge trap formation and decay to reveal charge-trapping mechanisms and, potentially, the internal electronic energy levels of the charge-trapping species. In a second study, these researchers prepare solar-cell films (by spinning polymer blends and polymer:molecule blends onto substrates with patterned electrodes having varying, well controlled work functions) and study local charge generation kinetics in these films as a function of spatial position and illumination wavelength to obtain a better microscopic understanding of the dependence of charge generation efficiency on background charge density in organic solar cell films.Energy plays a central role in the U.S. economy. For environmental and security reasons, it is expected that solar power generation will become a crucially important component of the U.S. energy portfolio of the future. It remains a challenge to devise a solar cell that can be manufactured in sufficiently large quantities at reasonable cost. Since plastics can already be made in large quantities, it makes sense to understand how to make better solar cells from plastics. In order to accelerate the manufacturing of improved plastic solar cells, this research investigates the details of two key processes - how plastic solar-cell materials degrade under operation and how they turn light into electricity. The students and postdoctoral scientist mentored during the course of this research are needed for the U.S. to retain and improve its lead in the nanotechnology-based energy-generation and energy-storage industries.