Scanned-probe Characterization of Charge Generation, Recombination, and Motion in Organic Semiconductors

摘要：阳光是一种无限的清洁能源。我们如何为每个人提供一种廉价的方式来捕获和利用太阳能来运行他们的电器和车辆？屋顶硅基光伏电池已经存在，可以将阳光转化为电能；然而，这些电池的制造和安装都很昂贵。该项目的目标是研究由塑料和有机分子制成的太阳能电池，这可以使太阳能电池像一层油漆一样薄而便宜。塑料/有机太阳能电池材料已经研究了很长时间，但是这些材料如何在分子水平上将光转化为电仍然知之甚少。为了更好地了解这些材料，我们正在开发一种显微镜，能够在一纳秒（十亿分之一秒）或更快的时间尺度上观察电荷在分子水平上的运动。这种显微镜将给我们提供一种新的方法来研究分子水平的过程，从光合作用到发生在金属表面的工业上重要的化学反应。该项目资助的研究人员正在利用他们在科学仪器和计算机编程方面的知识开发实验，向初高中学生介绍从音乐物理学到电化学原理的各种主题。技术摘要：该项目的目标是测试分子设计规则，该规则被认为是控制如何在由电子接受和电子提供分子（所谓的供体-受体混合物）制成的薄膜太阳能电池中将光转化为电。电荷重组动力学和电荷迁移率的局部测量在供体-受体共混物上进行，这些共混物由具有系统变化的能级和背景电荷密度的分子制备，以支持或反驳描述这些共混物中如何从阳光产生电荷的理论。为了实现这些研究，扫描探针显微镜测量技术得以发展，能够以纳秒级的时间分辨率和纳米级的空间分辨率，在纳秒级持续光脉冲的作用下，确定供体-受体混合薄膜中的自由电荷产率和随后的重组动力学。开发了一套单独的扫描探针测量，用于从近表面电场波动的测量推断局部电荷迁移率。在这个项目中创建的工具有望最终在研究工业上重要的过程，如光催化和电催化，以及在自然中重要的过程，如光合作用方面有广泛的应用。这项研究资助的研究人员正在利用他们在科学仪器和计算机编程方面的知识开发实验，向初高中学生介绍从音乐物理学到电化学原理的各种主题。

Nontechnical Abstract:Sunlight represents a limitless source of clean energy. How can we provide everyone with a cheap way to capture and use the sun's energy to run their appliances and vehicles? Rooftop silicon-based photovoltaic cells already exist for converting sunlight into electricity; however, these cells are expensive to manufacture and install. This project's goal is to study solar cells made from plastics and organic molecules, which could allow solar cells to be as thin and inexpensive as a coat of paint. Plastic/organic solar-cell materials have been studied for a long time, but how these materials convert light into electricity at the molecular level remains poorly understood. To better understand these materials we are developing a microscope capable of watching charge move at the molecular level on the timescale of one nanosecond (one billionth of a second) or faster. Such a microscope would give us a new way to study molecular-level processes ranging from photosynthesis to industrially important chemical reactions taking place at a metal surface. The researchers funded by this project are using their knowledge of scientific instrumentation and computer programming to develop experiments introducing middle and high school students to topics ranging from the physics of music to the principles of electrochemistry.Technical Abstract:The goal of this project is to test molecular design rules thought to govern how light is converted into electricity in thin-film solar cells made from electron-accepting and electron-donating molecules, so-called donor-acceptor blends. Localized measurements of charge recombination dynamics and charge mobility are carried out on donor-acceptor blends prepared from molecules with systematically varied energy levels and background charge density to support or refute theories describing how charge is generated from sunlight in these blends. To enable these studies, scanned-probe-microscope measurements are developed capable of determining, with nanosecond temporal resolution and nanometer spatial resolution, the free charge yield and subsequent recombination dynamics in a thin film of a donor-acceptor blend following the application of a nanosecond-duration pulse of light. A separate set of scanned-probe measurements are developed for inferring the local charge mobility from measurements of near-surface electric field fluctuations. The tools created during this project are expected to ultimately have broad applications in studying industrially important processes like photocatalysis and electrocatalysis and in naturally important processes like photosynthesis. The researchers funded by this research are using their knowledge of scientific instrumentation and computer programming to develop experiments introducing middle and high school students to topics ranging from the physics of music to the principles of electrochemistry.