Scanned-Probe Characterization of Charge Trapping and Fluctuations in Organic Semiconductors

技术概述：目前缺乏对有机半导体中电荷捕获、输运、注入和电荷产生机制的微观理解。如果对这些基本过程有更好的基本了解，有机电路和太阳能电池的发展可能会大大加快。提高我们对有机半导体器件基本工艺的基本理解是具有挑战性的。几乎所有的有机半导体器件都表现出显著的器件间差异，而最有前途的器件通常由复杂的多组分混合物组成。为了建立有机半导体中电荷捕获和输运的微观图像，我们将使用真空变温电显微镜原位研究有机器件。我们将使用光增强电磁力显微镜作为光谱识别杂质的工具，研究电荷的产生，并在广泛的有机半导体中探测捕获机制。在第二组实验中，高顺应性硅微悬臂将用于测量有机半导体表面附近的微小电场梯度波动。从这些电场波动中，我们建议推导（并成像）悬臂尖端下电荷的扩散常数。我们期望这些微观研究将为推进我们对有机半导体材料和器件中的电荷产生、传输、捕获和注入的理解开辟令人兴奋的可能性。该项目将培养高级扫描探针显微镜和纳米制造方面的研究生。这些学生将通过与学术、联邦和工业实验室的科学家进行合作项目来扩大他们的训练。这项工作是由固态和材料化学项目资助的。为了使我们的国家获得能源独立，我们必须能够制造出能将太阳光有效地转化为电能的太阳能电池。许多材料正在被研究用于太阳能电池，但没有一种能达到我们所需要的效果。一类很有前途的材料是半导体聚合物，这种塑料具有既能吸收光又能导电的显著特性。为了让这些材料在太阳能电池中很好地工作，材料需要吸收光，吸收的光必须转换成电流，电流必须通过材料并提取成导线。最后两个过程——光到电流的转换和电荷的传输——在这些材料中还没有得到很好的理解。如果对这些过程没有更好的了解，就不清楚如何用半导体聚合物制造改进的太阳能电池。表征这些材料是具有挑战性的，因为它们的性质在距离上显示出巨大的变化，距离仅为100亿分之一到1000亿分之一米-数百到数千个原子的距离。为了提高我们对半导体聚合物的理解，我们将开发新型显微镜，可以在工作的太阳能电池中拍摄这种长度尺度的运动和静止电荷的照片。这项工作将通过培养博士和本科生从事与能源有关的材料和纳米技术的研究来促进一般福利。这项工作将涉及多个大学、政府实验室和工业实验室之间的合作和知识共享。这项工作是由美国国家科学基金会固态和材料化学项目资助的。

TECHNICAL SUMMARY:A microscopic understanding of the mechanisms of charge trapping, transport, injection, and charge generation in organic semiconductors is presently lacking. The development of organic circuits and solar cells could be greatly accelerated if a better basic understanding of these fundamental processes were available. Improving our basic understanding of fundamental processes in organic semiconductor devices is challenging. Nearly all organic semiconductor devices show significant device-to-device variation, and the most promising devices are often comprised of complex multicomponent blends. To build up a microscopic picture of charge trapping and transport in organic semiconductors, we will study organic devices in situ using vacuum, variable-temperature electric force microscopy. We will use light-enhanced electric force microscopy as a tool to spectroscopically identify impurities, study charge generation, and probe trapping mechanisms in a wide range of organic semiconductors. In a second set of experiments, a high-compliance silicon microcantilever will be used to measure minute electric field gradient fluctuations near the surface of an organic semiconductor. From these electric field fluctuations we propose to deduce (and image) the diffusion constant of charges beneath the cantilever tip. We expect these microscopic studies will open up exciting possibilities for advancing our understanding of charge generation, transport, trapping, and injection in organic semiconductor materials and devices. This project will train graduate students in the arts of advanced scanned probe microscopy and nanofabrication. These students will broaden their training by working on collaborative projects with scientists at academic, federal, and industrial laboratories. This work is funded by the Solid State and Materials Chemistry program.NON-TECHNICAL SUMMARY:In order for our nation to obtain energy independence, we must be able to manufacture solar cells that can convert sunlight efficiently into electricity. Many materials are being examined for use in solar cells, and none work as well as we need. One promising class of materials is semiconducting polymers, plastics that have the remarkable property of being able to both absorb light and conduct electricity. In order to get these materials to work well in solar cells, the materials need to absorb light, the absorbed light must be converted into an electrical current, and the current must be carried through the material and extracted into a wire. These last two processes - the conversion of light to current and the transport of charge - are not well understood in these materials. Without a better understanding of these processes, it is not clear how to manufacture improved solar cells from semiconducting polymers. Characterizing these materials is challenging, because their properties show large variations across distances separated by only 10 billionths to 100 billionths of a meter - distances hundreds to thousands of atoms across. To advance our understanding of semiconducting polymers, we will develop new kinds of microscopes that can take pictures of both moving and stationary charges at this length scale in working solar cells. This work will promote the general welfare by training PhD and undergraduate students to do research in energy-related materials and nanotechnology. This work will involve collaboration and knowledge sharing among multiple universities, government laboratories, and industrial laboratories. This work is funded by the Solid State and Materials Chemistry program of the U.S. National Science Foundation.