Development of Highly Sensitive and High-Resolution Kelvin Probe Force Micorscopy for in situ Chacterization of Organic Photovoltaic Cells

主要研究者： 李广勇提案编号： 基于聚合物材料的太阳能电池提供了制造的便利性和潜在的低成本，但是相对于基于无机半导体的太阳能光伏器件具有低的太阳能转换效率。 迄今为止，最有效的有机光伏（OPV）太阳能电池是通过将共轭聚合物（供体）与富勒烯分子（受体）共混以形成纳米结构本体异质结（BHJ）活性层而制成的。 共混物的纳米级形态决定了电荷产生和传输特性，因此决定了器件性能。 然而，由于缺乏原位表征工具，很难准确地将形态与器件性能相关联，或者理解加工条件如何控制所需形态的形成。 扫描探针显微镜（SPM）是一种潜在的多功能工具，可用于表征环境状态下的有机光伏电池。 然而，目前的SPM方法不能区分纳米级的供体和受体域，也不能观察到本体异质结形成过程中，特别是退火过程中的原位形态变化。 这项研究的目的是开发纳米级形态，OPV器件性能，和用于形成BJH通过使用开尔文探针力显微镜（KPFM）的加工条件之间的关系。 开尔文探针力显微镜具有区分相分离的施主和受主畴的潜力，并且可以适于在材料加工过程中真实的时间内观察本体异质结的原位形态演变，具有高灵敏度和纳米尺度分辨率。 具体地，体异质结的横截面将暴露于扫描探针并通过KPFM表征。 横截面的表面预期提供更能代表实际BJH精细结构的原位形态细节。 通过使用具有超尖锐尖端和形状定制的悬臂梁的扫描探针，可以增强KPFM以在环境状态下实现高分辨率和高灵敏度。 与KPFM拟议的研究旨在更好地了解OPV器件的基本物理，并阐明产生有机体异质结的加工条件，从而提高太阳能转换效率。更广泛的影响拟议的教育和推广活动的重点是把太阳能专题纳入研究生和本科生课程，以及当地高中。 将为扫描探针显微镜和光化学领域的研究生开发基于该研究的课程材料。 本科生将参加高级设计项目，涉及动手学习太阳能电池器件表征和扫描探针显微镜。 PI将与匹兹堡大学机器人俱乐部合作开发一种由太阳能驱动的移动的机器人，用于每年一次的高中生机器人展览，并将访问当地高中，演示柔性有机太阳能电池。

PI: Guangyong LiProposal Number: 1132819Intellectual MeritSolar cells based on polymeric materials offer ease of fabrication and potentially low cost, but suffer from low solar energy conversion efficiency relative to inorganic semiconductor based solar photovoltaic devices. The most efficient organic photovoltaic (OPV) solar cells to date are made from blending conjugated polymers (donors) with fullerene molecules (acceptors) to form nanostructured bulk heterojunction (BHJ) active layers. The nanoscale morphology of the blend determines the charge generation and transport characteristics, and hence dictates the device performance. However, it is difficult to accurately correlate morphology to device performance, or to understand how processing conditions control the formation of desirable morphologies, due to the lack of in situ characterization tools. Scanning probe microscopy (SPM) is a potentially versatile tool for the characterization organic photovoltaic cells in the ambient state. However, current SPM approaches are not able to differentiate between the donor and acceptor domains at the nanoscale, and are also not able to observe in situ morphological changes during bulk heterojunction formation, particularly during annealing. The objective of this proposed research is to develop relationships between nanoscale morphology, OPV device performance, and processing conditions used to form the BJH through the use of Kelvin Probe Force Microscopy (KPFM). Kelvin probe force microscopy has the potential to differentiate between phase separated donor and acceptor domains, and can be adapted to observe the in situ morphological evolution of bulk heterojunctions in real time during material processing, with high sensitivity and nanometer scale resolution. Specifically, a cross-section of the bulk heterojunction will be exposed to the scanning probe and characterized by KPFM. The surface of the cross-section is expected to offer in situ morphological details that are more representative of the actual BJH fine structure. By using a scanning probe with an ultra-sharp tip and a shape-tailored cantilever, KPFM can be enhanced to achieve both high resolution and high sensitivity in the ambient state. The proposed studies with KPFM are designed to gain a better understanding of the fundamental physics of OPV devices, and to elucidate the processing conditions that create organic bulk heterojunctions which give rise to enhanced solar energy conversion efficiency. Broader ImpactsThe proposed education and outreach activities focus on bringing solar energy topics into graduate and undergraduate curricula, as well as to local high schools. Course materials based on the research will be developed for graduate students in the areas of scanning probe microscopy and photovoltaics. Undergraduate students will participate in senior design projects involving hands-on learning with solar cell device characterization and scanning probe microscopy. The PI will work with the University of Pittsburgh Robotics Club to develop a mobile robot driven by solar power for use at an annual robot show for high school students, and will visit local high schools to give demonstrations on flexible organic solar cells.