In-situ and Operando Studies of Metastable and Transient States of Organic Semiconductor Thin Films

非技术描述：有机半导体是在分子水平上设计的，以展示有用的特性，它们有望实现新一代电子电路和太阳能电池。这项研究活动利用高度可控的方法，从含有小有机分子的液体溶液中沉积有序的晶体薄膜。人们正在进行实验，以了解分子如何从无序的溶液状态组织成高度有序的结晶固体。这些分子排列也可以通过拉伸或压缩薄膜来灵敏地调整，这可能会极大地影响它们的性质。实验利用偏振光学显微镜和x射线散射技术，这两种技术可以帮助确定薄膜中的分子顺序。电子测量被用来确定电子在这些材料中移动的容易程度。计算也在进行，以测试分子排列和电子运动之间联系的理论预测。创新的社区外展活动扩大了研究的社会影响，包括讲座和演示，旨在让公众参与讨论能源、光和纳米材料的科学和应用。该项目在一个高度跨学科的领域培养研究生，并向本科生介绍x射线科学和薄膜沉积技术。技术描述：矩形空心笔头法可以生产出晶粒尺寸可控的高取向薄膜，可超过1厘米，而气相沉积薄膜通常具有随机取向的纳米级晶粒。该项目涉及研究工艺参数与薄膜性能之间的关系，如晶粒尺寸和取向、应变和缺陷密度。最近的研究表明，许多小分子材料在溶液结晶过程中会经历前体阶段，这种状态可以通过光学和x射线研究的结合来明确地观察到。偏振光学视频显微镜对颗粒结构的成核和发育非常敏感，而实时光谱学对局部有序（如聚集和分子堆积几何）非常敏感。实时同步加速器x射线衍射具有很强的互补性，因为它对长程顺序很敏感，可以进行毫秒级分辨率的时间分辨研究。有机场效应晶体管中的载流子输运也将作为薄膜和衬底的弹性拉伸施加应变的函数进行研究。结果将与应变对电子能带结构和载流子输运性质影响的从头算研究有关。这项研究可能会导致基于卷对卷工艺的新的环保制造方法。这些方法将为低成本、柔性电子产品和太阳能电池的新技术奠定基础。

Nontechnical Description: Organic semiconductors are designed at the molecular level to exhibit useful properties, and they promise the realization of a new generation of electronic circuits and solar cells. This research activity utilizes highly controllable methods of depositing ordered crystalline thin films from liquid solutions bearing small organic molecules. Experiments are being performed to understand ways that molecules organize from a disordered solution state into highly ordered crystalline solids. These molecular arrangements can also be sensitively tuned by stretching or compressing thin films, which may dramatically affect their properties. The experiments utilize polarized optical microscopy and X-ray scattering - two techniques which can help determine molecular ordering in the films. Electronic measurements are used to determine how easily electrons move in these materials. Calculations are also being performed to test theoretical predictions of the link between the molecular arrangement and electron motion. The societal impact of the research is amplified by innovative community outreach activities, including lectures and demonstrations designed to engage the public in a discussion of science and applications of energy, light, and nano-materials. This project provides graduate student training in a highly interdisciplinary area, and it introduces undergraduate students to X-ray science and thin film deposition technology.Technical Description: The rectangular hollow pen writer method can produce highly oriented films with controllable grain size that can exceed one centimeter, while in comparison, vapor deposited films typically have randomly oriented nanometer-scale grains. This project involves studies of the relationships between process parameters and film properties, such as grain size and orientation, strain, and defect density. Recent work suggests that many small molecule materials pass through a precursor stage during crystallization from solution, and this state can be unambiguously observed through a combination of optical and X-ray studies. Polarized optical video microscopy is sensitive to the nucleation and development of grain structure, while real-time optical spectroscopy is highly sensitive to local ordering, such as aggregation and molecular packing geometries. Real-time synchrotron X-ray diffraction is highly complementary because it is sensitive to long-range order, allowing time-resolved studies with millisecond resolution. Carrier transport in organic field effect transistors will also be studied as a function of applied strain by elastic stretching of thin films and substrates. The results will be related to ab-initio studies of the effect of strain on the electronic band structure and carrier transport properties. This research may lead to new environmentally responsible manufacturing methods based on roll-to-roll processes. These methods will underpin new technologies for low-cost, flexible electronics and solar cells.