Engineered Grain Boundaries and their Properties in Crystalline Organic Semiconductors

技术说明：该研究项目的目标是揭示晶体有机半导体晶界的结构-性能关系。这种基本的理解，预计将导致材料或加工技术，减轻晶界的影响。为了研究晶界，工程微结构制造使用剪切涂布或毛细力光刻。这些技术允许形成晶粒边界，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所述晶粒边界上的分子取向差。使用场效应晶体管研究了这些特征良好的晶界之间的电荷传输。此外，使用超灵敏的子带隙光谱的半导体的带隙中的陷阱状态的存在下进行评估。传输数据和子间隙吸收数据的相关性有助于阐明跨晶界传输瓶颈的性质。除了运输，晶粒边界结构的半导体的电子稳定性和从大气中吸附的极性分子的作用，在调整晶粒边界的电子性质的影响进行了研究。通过对晶界结构的函数进行这些研究，可以全面了解结构在控制晶界电子性质方面的作用。非技术性描述：有机半导体已经在显示器行业中作为发光体得到应用。这一系列电子材料的多功能性，可以合成和功能化，以表现出广泛的性能，有望实现整个电子电路与有机半导体以及太阳能电池和化学传感器。然而，由于这些材料通过弱的分子间力保持在一起，因此它们存在缺陷或缺陷。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。该项目特别关注薄膜中形成的晶体之间的边界，这通常会限制电子材料的性能。通过制造模型系统，这些边界得到很好的控制，这些边界的结构对电子性质的影响被揭示。研究的社会影响通过外联活动得到扩大。例如，远程光学和电子显微镜，高中学生从事研究材料的微观和纳米级，提供了结构（如在显微镜中观察到的）和属性之间的直接联系。

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.