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

PI：光永LiProposal编号：1132819智能优点基于聚合物材料的太阳能电池制造简单，成本可能较低，但与基于无机半导体的太阳能光伏器件相比，太阳能转换效率较低。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(施主)与富勒烯分子(受体)混合形成纳米结构的体相异质结(BHJ)有源层而制成的。共混物的纳米级形态决定了电荷的产生和传输特性，从而决定了器件的性能。然而，由于缺乏原位表征工具，很难准确地将形貌与器件性能相关联，也很难理解工艺条件如何控制所需形貌的形成。扫描探针显微镜(SPM)是表征环境状态下有机光伏电池的一种潜在的通用工具。然而，目前的扫描隧道显微镜方法不能在纳米尺度上区分施主和受主结构域，也不能在体异质结形成过程中原位观察到形态变化，特别是在退火过程中。这项拟议的研究的目的是通过使用开尔文探针力显微镜(KPFM)来发展纳米级形貌、OPV设备性能和形成BJH的工艺条件之间的关系。开尔文探针力显微镜具有区分相分离的施主和受主结构域的潜力，能够实时观察材料加工过程中体相异质结的形态演变，具有高灵敏度和纳米级的分辨率。具体地说，体异质结的横截面将暴露在扫描探针上，并用KPFM进行表征。横截面的表面预计将提供更能代表实际BJH精细结构的原位形态细节。通过使用具有超尖尖端和定制形状的悬臂梁的扫描探头，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的拟议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工艺条件，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将太阳能主题纳入研究生和本科生课程，以及当地高中。基于这项研究的课程材料将为扫描探针显微镜和光伏领域的研究生开发。本科生将参与高级设计项目，包括太阳能电池装置表征和扫描探针显微镜的动手学习。PI将与匹兹堡大学机器人俱乐部合作开发一款太阳能驱动的移动机器人，用于一年一度的高中生机器人展，并将访问当地的高中，就柔性有机太阳能电池进行演示。

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.