CAREER: Mitigating Detrimental Vibrational Effects in Organic Semiconductors

有机半导体是一类很有前途的材料，有可能彻底改变从柔性显示器到高效太阳能电池的先进电子设备。目前它们的广泛使用受到原子级运动的限制，在许多情况下，原子级运动会降低材料的有效性。在这个项目中，这些运动——特别是那些在太赫兹频率下发生的运动——将使用实验和计算相结合的方法进行研究。 PI将以原子级精度研究和量化影响有机半导体材料性能的精确动力学。通过这项研究，我们将获得前所未有的洞察力，这意味着能够合理地设计新材料来抑制有害现象。这项研究与年轻科学家的培训和教育密切相关，受训者从本科生到研究生的各个职业阶段都直接参与研究。此外，PI还将开发一门包含这项研究成果的大学课程，以进一步加强对年轻科学家的培训。参与研究的学员与 PI 一起，也直接参与向更广泛的社区传播这项前沿研究的工作。通过与当地艺术博物馆合作，PI 正在努力扩大所开发方法的范围，以帮助表征、识别和保存其藏品中的艺术品。通过与当地学区的合作，这一举措扩展到了 K-12 教育，提供研讨会和培训机会，将前沿研究与下一代 STEM 专业人员的发展融为一体。近年来，低频（太赫兹）动力学在有机半导体的各种块体现象中所发挥的作用已得到阐明。具体而言，太赫兹频率下发生的大幅振动运动已被证明对于合理化这些材料的载流子动力学至关重要。在许多情况下，单太赫兹振动产生的有害电子声子耦合足以显着降低电荷载流子迁移率，而电荷载流子迁移率是实现先进电子学的关键参数。这项研究利用实验太赫兹时域光谱和量子力学模拟来探索太赫兹声子对有机半导体固体特性的关键作用。该项目涉及新的实验和理论方法的设计和实施——这些方法通常也适用于固态材料。具体来说，光泵太赫兹探针光谱用于直接对电荷载流子动力学以及电子声子耦合进行采样，同时进行非简谐密度泛函理论模拟来预测温度和压力相关的特性。这些实验的结果用于利用实验有机合成方法以及计算晶体结构设计来合理设计新材料。这项研究还整合了多种教育活动，使社会各阶层受益，包括未来的 STEM 领导者和非科学界。通过与弗莱明艺术博物馆的合作，太赫兹成像方法被用来揭示艺术品中隐藏的特征，例如被油漆层遮盖的签名。计划在博物馆展出基于这项研究的展览，并为普通社区和 K-12 学生举办研讨会。此外，基于该项目正在为高年级本科生和研究生开发一门新课程，这将转化为材料科学这一重要领域不断增长的专业知识。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Organic semiconductors are a promising class of materials with the potential to revolutionize advanced electronic devices, from flexible displays to high-efficiency solar cells. Their widespread use is currently limited by atomic-level motions that, in many cases, reduce the effectiveness of the material. In this project, these motions – specifically those that occur at terahertz frequencies – will be investigated using a combined experimental and computational approach. The PI will investigate and quantify the precise dynamics that influence the performance of organic semiconducting materials with atomic-level precision. Through this research an unprecedented level of insight will be gained, which translates to the ability to rationally engineer new materials that suppress detrimental phenomena. This research is strongly connected to the training and education of young scientists, with trainees directly involved in the research from all career stages, from undergraduates to postgraduates. In addition, the PI will develop a university-level course that incorporates the results of this research in order to further enhance the training of young scientists. The trainees involved in the research, in conjunction with the PI, are also directly involved in efforts to communicate this cutting-edge research to the wider community. Through a collaboration with a local art museum, the PI is working to expand the reach of the developed methods to aid in the characterization, identification, and preservation of artwork in their collections. This is extended to K-12 education through a partnership with a local school district, where workshops and training opportunities are offered, providing a convergence of cutting-edge research with the development of the next generation of STEM professionals.The role that low-frequency (terahertz) dynamics play in a wide-variety of bulk phenomena in organic semiconductors has been elucidated in recent years. Specifically, large-amplitude vibrational motions occurring at terahertz frequencies have been shown to be pivotal to rationalizing the charge-carrier dynamics of these materials. In many cases, detrimental electron-phonon coupling from a single-terahertz vibration is sufficient to significantly reduce charge-carrier mobility, a critical parameter for realizing advanced electronics. This research leverages experimental terahertz time-domain spectroscopy with quantum mechanical simulations to explore the crucial role that terahertz phonons play on the properties of organic semiconducting solids. This project involves the design and implementation of new experimental and theoretical methods – methods that are also applicable to solid-state materials in general. Specifically, optical pump-terahertz probe spectroscopy is used to directly sample both charge-carrier dynamics, as well as electron-phonon coupling, while anharmonic density functional theory simulations are performed to predict temperature- and pressure-dependent properties. The results of these experiments are used to rationally design new materials, using experimental organic synthetic methods as well as computational crystal structure design. This research also integrates multiple educational activities that are a benefit to a wide cross-section of society, including future STEM leaders and the non-scientific community. Through a collaboration with the Fleming Museum of Art, terahertz imaging methods are applied to reveal hidden features in artwork, such as a signature obscured by layers of paint. An exhibit based on this research is planned to be put on display at the museum, along with workshops for the general community and K-12 students. Additionally, a new course for advanced undergraduates and graduate students is being developed based on this project, which will translate to growing expertise in this important area of the materials sciences.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.