Engineered Grain Boundaries and their Properties in Crystalline Organic Semiconductors

技术描述：该研究项目的目标是解开晶态有机半导体晶界的结构-性质关系。这样的基本认识有望导致材料或加工技术，以减轻晶界的影响。为了研究晶界，工程微结构是用剪切涂层或毛细管力光刻来制造的。这些技术允许形成晶界，通过晶界可以使用基于同步加速器的X射线衍射精确地控制和表征分子的取向错误。我们使用场效应晶体管研究了这些表征良好的晶界上的电荷传输。此外，使用超灵敏的亚带隙光谱对半导体禁带中陷阱态的存在进行了评估。输运数据和子能隙吸收数据的关联有助于阐明跨越晶界的输运瓶颈的性质。除了输运外，还研究了晶界结构对半导体电子稳定性的影响，以及从大气中吸附的极性分子在调节晶界电子性质中的作用。通过将这些研究作为晶界结构的函数进行，对结构在控制晶界电子性质中的作用进行了完整的描述。非技术描述：有机半导体已经在显示器工业中作为光发射器得到了应用。这一电子材料家族的多功能性，可以合成和功能化，展示出广泛的性能，有望用有机半导体以及太阳能电池和化学传感器实现整个电子电路。然而，由于这些材料被微弱的分子间力结合在一起，它们会受到缺陷或缺陷的存在。本研究项目旨在阐明缺陷如何影响有机半导体的电子行为。特别是，这个项目关注的是薄膜中形成的晶体之间的边界，这往往会限制电子材料的性能。通过制作这些边界被很好地控制的模型系统，揭示了这些边界的结构对电子性质的影响。外展活动放大了这项研究的社会影响。例如，远程光学和电子显微镜，让高中生在微米和纳米尺度上学习材料，提供了结构(如显微镜中观察到的)和性能之间的直接联系。

Technical Description: The goal of this research project is to unravel structure-property relationships at the grain boundaries of crystalline organic semiconductors. Such fundamental understanding is expected to lead to materials or processing techniques that mitigate the effect of grain boundaries. In order to study grain boundaries, engineered microstructures are fabricated using shear-coating or capillary force lithography. These techniques allow to form grain boundaries across which the molecular misorientation can be controlled and characterized accurately using synchrotron-based X-ray diffraction. Charge transport across these well-characterized grain boundaries is studied using field-effect transistors. Furthermore, the presence of trap states in the bandgap of the semiconductor is assessed using ultra-sensitive sub-bandgap spectroscopies. The correlation of transport data and the sub-gap absorption data helps to elucidate the nature of transport bottlenecks across grain boundaries. In addition to transport, the effect of grain-boundary structure on the electronic stability of the semiconductor and the role of polar molecules adsorbed from the atmosphere in tuning the electronic properties of grain boundaries is studied. By conducting these studies as a function of grain-boundary structure, a complete picture of the role of structure in governing the electronic properties of grain boundaries is made to emerge.Non-technical Description: Organic semiconductors are already finding applications as light emitters in the display industry. The versatility of this family of electronic materials, which can be synthesized and functionalized to exhibit a broad range of properties, promises the realization of entire electronic circuits with organic semiconductors as well as solar cells and chemical sensors. Because these materials are held together by weak intermolecular forces however, they suffer from the presence of imperfections or defects. This research project aims at elucidating how defects affect the electronic behavior of organic semiconductors. In particular this project focuses on the boundaries between crystals that form in the film, which often limit the performance of the electronic material. By fabricating model systems, where these boundaries are well controlled, the effect of the structure of these boundaries on electronic properties is revealed. The societal impact of the research is amplified by outreach activities. For instance, remote optical and electronic microscopy, where high-school students are engaged to study materials at the micro and nanoscale, provide a direct link between structure (as observed in the microscope) and properties.