Correlating Structural and Electronic Disorder in Organic Semiconductor Single Crystals

有机半导体单晶中结构和电子无序的关联

• 批准号: 1806419
• 负责人: Daniel Frisbie
• 金额: $ 52.27万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1806419&HistoricalAwards=false
• 关键词: Correlating; Structural; Electronic; Disorder; Organic

Non-Technical Abstract:Organic semiconductors are the advanced materials enabling bright displays commonly found in smart phones and televisions. OLEDs(organic light-emitting diodes) employ thin films of organic semiconductors to convert electricity to red, green, and blue lights necessary for displays. In this project, principal investigator Daniel Frisbie is seeking to understand the properties of single crystals of organic semiconductors that have applications in other types of devices such as organic field effect transistors (OFETs). For OFETs, charge velocity is critically important, but structural defects in crystals can trap electrical charges, lowering their average speed. Professor Frisbie aims to determine what types of defects exist in organic semiconductor single crystals using a powerful high resolution microscopy technique called scanning Kelvin probe microscopy (SKPM). SKPM images electric potential and many types of defects in crystals have a "voltage signature" that can be detected. Frisbie will use SKPM and a combination of other characterization techniques such as X-ray diffraction and electron microscopy to locate defects, to determine the structural nature of defects and to characterize their electrical properties. The work should lead to a better understanding of structure-property relationships in organic semiconductors and thus enable expanded real-life applications. An important broader impact will be the training of graduate students in organic semiconductor materials science and device physics.Technical Abstract:The goal of this project is to advance the materials science of organic semiconductors by elucidating relationships between mechanical strains, defects, surface potential, and electrical transport in single crystals of pi-conjugated molecules. The experimental plan builds on prior work in the Principal Investigator's (PI's) laboratories that demonstrated surface potential imaging by scanning Kelvin probe microscopy (SKPM) is surprisingly sensitive to defects and inhomogeneous strains in crystalline organic semiconductors. The PI seeks (1) to understand the causes of the strain/defect-surface potential relationship, (2) to demonstrate its relevance to broad classes of crystalline organic semiconductors, and (3) to establish the relationship between surface potential variations and electrical transport. The research focuses on organic single crystals as their low levels of disorder facilitate identification and analysis of precise structure-property relationships. Single crystals of benchmark organic semiconductors are grown by vapor transport and characterized with a spectrum of methods including SKPM, ultraviolet photoelectron spectroscopy (UPS), and X-ray diffraction (XRD). The PI employs a robust platform to apply strains to crystals inside operating SKPM, UPS and XRD instrumentation. Strains ranging from 0.01-0.5% are applied this way, which allows for precise quantitation of the mechanical strain-surface potential relationship. In a second direction, the PI is uncovering the causes of step edge potentials so far observed in a handful of organic semiconductor single crystals and correlates the potentials with field effect (FET) transport. In a third vein, he examines the impact of planar defects induced by solid-solid phase transitions on the surface potential of organic crystals and correlates the results with FET performance. The work is leading to a deeper understanding of structure-property relationships in organic semiconductors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术摘要：有机半导体是一种先进材料，可实现智能手机和电视中常见的明亮显示屏。OLED（有机发光二极管）采用有机半导体薄膜将电转换为显示器所需的红光、绿色和蓝光。在这个项目中，首席研究员丹尼尔弗里斯比正在寻求了解有机半导体单晶的性质，这些单晶在其他类型的器件中有应用，如有机场效应晶体管（OFFET）。对于OFFEX，电荷速度至关重要，但晶体中的结构缺陷可以捕获电荷，降低其平均速度。Frisbie教授的目标是确定有机半导体单晶中存在什么类型的缺陷，使用一种强大的高分辨率显微镜技术，称为扫描开尔文探针显微镜（SKPM）。SKPM图像电势和晶体中的许多类型的缺陷具有可以检测到的“电压特征”。Frisbie将使用SKPM和其他表征技术（如X射线衍射和电子显微镜）的组合来定位缺陷，确定缺陷的结构性质并表征其电气特性。这项工作将有助于更好地理解有机半导体的结构-性质关系，从而扩大实际应用。一个重要的更广泛的影响将是在有机半导体材料科学和器件physics.Technical摘要：本项目的目标是通过阐明机械应变，缺陷，表面电位和电输运π共轭分子的单晶之间的关系，以推进有机半导体材料科学的研究生的培训。该实验计划建立在主要研究者（PI）实验室先前的工作基础上，该实验室证明了通过扫描开尔文探针显微镜（SKPM）进行的表面电位成像对晶体有机半导体中的缺陷和不均匀应变非常敏感。PI旨在（1）理解应变/缺陷-表面电位关系的原因，（2）证明其与广泛类别的晶体有机半导体的相关性，以及（3）建立表面电位变化与电输运之间的关系。研究重点是有机单晶，因为它们的低无序水平有助于识别和分析精确的结构-性质关系。基准有机半导体的单晶体通过气相传输生长，并且用包括SKPM、紫外光电子能谱（UPS）和X射线衍射（XRD）的一系列方法来表征。PI采用了一个强大的平台，在SKPM、UPS和XRD仪器内对晶体施加应变。以这种方式施加0.01-0.5%的应变，这允许精确定量机械应变-表面电位关系。在第二个方向上，PI正在揭示迄今为止在少数有机半导体单晶中观察到的阶跃边缘电位的原因，并将这些电位与场效应（FET）输运关联起来。在第三种情况下，他研究了固体-固体相变引起的平面缺陷对有机晶体表面电位的影响，并将结果与FET性能相关联。该奖项反映了NSF的法定使命，通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。