Imaging charge recombination dynamics in organic semiconductor films

非技术性综述：我们的经济需要能源才能运行。阳光是一种免费的、本质上是无限的能源。为了开发这种能源，需要能够将太阳光转化为电流和电压的经济型太阳能电池。现有的硅太阳能电池过于昂贵，无法大规模制造、构图和安装。另一方面，由塑料和小分子制成的太阳能电池可能像涂料一样便宜，像新闻纸一样容易高速打印。塑料/分子太阳能电池正在全球范围内得到深入研究，但这些复合材料如何将光转化为电能仍然是一个谜。在材料研究部固态和材料化学计划的支持下，康奈尔大学的约翰·马罗恩教授和他的研究小组将开发出观察薄膜中的电荷如何在阳光下运动和松弛的方法。研究小组将使用一种特殊的显微镜，能够在纳秒(十亿分之一秒)的时间尺度上观察电荷移动纳米(十亿分之一米)的距离。通过在分子水平上观察电荷运动，预计这些测量将极大地促进我们对塑料/分子太阳能电池材料如何将光转化为电能的理解。这项研究将为研究半导体芯片和电池开辟新的途径，这两项增长技术对我们的经济至关重要。由该项目资助的研究人员将开发适用于现场和远程学习的虚拟高中波物理科学实验。技术摘要：在最好的有机光伏材料中，光载体复合时间异常长。如果这种反常行为能够被理解，那么就可以利用它来改善有机太阳能电池的开路电压和电流。该项目由材料研究部的固态和材料化学计划支持，将在纳米尺度的空间分辨率和纳秒的时间分辨率下研究有机给体/受体(D/A)共混物中电荷的产生和复合。拟议的实验包括扫描开尔文探针力显微镜，测量局部静电势和电场；宽带局部介电光谱，测量局部稳态电导率和能量无序；以及“相位踢”电力显微镜(PK-EFM)，测量瞬时电导率。通过同时测量器件电流和局域电场来研究单组分薄膜中的电荷迁移率。在绝缘和金属衬底上制备的D/A混合物中的电荷复合瞬变将使用PK-EFM记录下来，并与整体时间分辨微波电导率测量进行比较。利用PK-EFM对非均匀D/A共混物中光生电荷的漂移和扩散进行了频闪观测。由富勒烯和非富勒烯受体的聚合物给体组成的薄膜将被检查。预计从这些测量中收集的微观材料参数将能够对电荷复合假说进行严格测试。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY: Our economy requires energy to run. Sunlight is a free and essentially limitless source of energy. To exploit this energy source, economical solar cells that can convert sunlight into electrical current and voltage are needed. Existing silicon solar cells are too expensive to create, pattern, and install on a massive scale. Solar cells made from plastics and small molecules, on the other hand, can potentially be as inexpensive as paint to create and as easy as newsprint to pattern at high speed. Plastic/molecular solar cells are being intensely studied worldwide, but how these complex materials convert light to electricity remains a puzzle. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Professor John Marohn and his research group at Cornell University will develop methods for watching how electrical charges in a film activated by sunlight move and relax. The research team will utlizie a specialized microscope which enables the observation of charges moving distances of nanometers (one billionth of a meter) on the timescale of nanoseconds (one billionth of a second). By allowing the observation of charge motion at the molecular level, it is expected that these measurements will significantly advance our understanding of how plastic/molecular solar cell materials convert light into electricity. This research will open new ways to study semiconductor chips and batteries, two growth technologies central to our economy. Researchers funded by this project will develop virtual high-school science experiments on the physics of waves suitable for both in-person and remote learning.TECHNICAL SUMMARY: In the best organic photovoltaic materials, the photocarrier recombination time is anomalously long. If this anomalous behavior could be understood then it could be exploited to improve the open-circuit voltage and current of organic solar cells. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, will study charge generation and recombination in organic donor/acceptor (D/A) blends at nanoscale spatial resolution and nanosecond temporal resolution. Proposed experiments include scanning Kelvin probe force microscopy, measuring local electrostatic potential and electric field; broadband local dielectric spectroscopy, measuring local steady-state conductivity and energetic disorder; and "phase-kick" electric force microscopy (pk-EFM), measuring transient conductivity. Charge mobility will be studied in single-component films by simultaneously measuring device current and local electric field. Charge recombination transients in D/A blends prepared on both insulating and metallic substrates will be recorded using pk-EFM and compared to bulk time-resolved microwave conductivity measurements. The drift and diffusion of photogenerated charges in inhomogeneous D/A blends will be observed stroboscopically via pk-EFM. Films comprised of polymer donors with both fullerene and non-fullerene acceptors will be examined. It is expected that the microscopic material parameters gleaned from these measurements will enable the rigorous testing of charge-recombination hypotheses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.