CAREER: Mitigating Detrimental Vibrational Effects in Organic Semiconductors

有机半导体是一类很有前途的材料，有可能彻底改变先进的电子设备，从柔性显示器到高效太阳能电池。它们的广泛应用目前受到原子水平运动的限制，在许多情况下，这种运动降低了材料的有效性。在这个项目中，这些运动——特别是那些发生在太赫兹频率上的运动——将使用实验和计算相结合的方法进行研究。PI将以原子级精度调查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，将获得前所未有的洞察力，这转化为合理设计抑制有害现象的新材料的能力。这项研究与年轻科学家的培训和教育密切相关，从本科生到研究生的所有职业阶段的受训者都直接参与研究。此外，PI将开发一门大学水平的课程，纳入这项研究的成果，以进一步加强对年轻科学家的培训。参与研究的受训者与PI一起，也直接参与向更广泛的社区传播这一前沿研究的努力。通过与当地一家艺术博物馆的合作，PI正在努力扩大已开发方法的范围，以帮助鉴定、鉴定和保存其收藏的艺术品。通过与当地学区的合作，这一计划扩展到K-12教育，在当地学区提供研讨会和培训机会，将前沿研究与下一代STEM专业人员的发展结合起来。低频（太赫兹）动力学在有机半导体中各种体现象中所起的作用近年来得到了阐明。具体来说，在太赫兹频率下发生的大振幅振动运动已被证明是使这些材料的载流子动力学合理化的关键。在许多情况下，来自单太赫兹振动的有害电子-声子耦合足以显著降低载流子迁移率，这是实现先进电子技术的关键参数。本研究利用实验太赫兹时域光谱与量子力学模拟来探索太赫兹声子对有机半导体固体性质的关键作用。该项目涉及设计和实施新的实验和理论方法，这些方法也适用于一般的固态材料。具体来说，光泵浦-太赫兹探针光谱用于直接采样电荷载流子动力学以及电子-声子耦合，而非谐波密度泛函理论模拟用于预测温度和压力相关特性。利用实验有机合成方法和计算晶体结构设计，将这些实验结果用于合理设计新材料。这项研究还整合了多种教育活动，这些活动对社会的各个领域都有好处，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，太赫兹成像方法被应用于揭示艺术品中隐藏的特征，例如被层层油漆掩盖的签名。以这项研究为基础的展览计划在博物馆展出，同时为普通社区和K-12学生举办讲习班。此外，一门针对高级本科生和研究生的新课程正在基于该项目开发，这将转化为材料科学这一重要领域的专业知识。该奖项反映了美国国家科学基金会的法定使命，并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，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.