Imaging charge recombination dynamics in organic semiconductor films

非技术总结：我们的经济需要能源来运行。太阳光是一种免费的、基本上无限的能量来源。为了利用这种能源，需要能够将阳光转换为电流和电压的经济型太阳能电池。现有的硅太阳能电池太昂贵，无法大规模制造、图案化和安装。另一方面，由塑料和小分子制成的太阳能电池可能像油漆一样便宜，并且像新闻纸一样容易在高速下形成图案。塑料/分子太阳能电池正在世界范围内进行深入研究，但这些复杂材料如何将光转化为电仍然是一个谜。通过这个项目，由材料研究部的固态和材料化学项目支持，康奈尔大学的John Marohn教授和他的研究小组将开发出观察薄膜中电荷如何被阳光激活的方法。研究小组将使用一种专用显微镜，可以在纳秒（十亿分之一秒）的时间尺度上观察纳米（十亿分之一米）的电荷移动距离。通过允许在分子水平上观察电荷运动，预计这些测量将大大促进我们对塑料/分子太阳能电池材料如何将光转化为电的理解。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虚拟高中科学实验的物理波适合在人和远程学习。技术摘要：在最好的有机光伏材料，光载流子复合时间是非常长的。如果这种异常行为可以被理解，那么它可以被利用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，将研究有机供体/受体（D/A）混合物中纳米级空间分辨率和纳秒级时间分辨率的电荷产生和复合。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;宽带局部介电谱，测量局部稳态电导率和能量紊乱;和“相位踢”电力显微镜（PK-EFM），测量瞬态电导率。通过同时测量器件电流和局部电场，将在单组分薄膜中研究电荷迁移率。在绝缘和金属衬底上制备的D/A共混物中的电荷复合瞬态将使用PK-EFM记录，并与批量时间分辨微波电导率测量进行比较。利用pk-EFM频闪观测了非均匀D/A共混物中光生电荷的漂移和扩散。将检查由具有富勒烯和非富勒烯受体的聚合物供体组成的膜。预计从这些测量中收集的微观材料参数将使电荷复合假说的严格测试成为可能。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

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.