CAREER: Mitigating Detrimental Vibrational Effects in Organic Semiconductors

有机半导体是一类很有前途的材料，有可能给从柔性显示器到高效太阳能电池的先进电子设备带来革命性的变化。它们的广泛使用目前受到原子级运动的限制，在许多情况下，这会降低材料的有效性。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将以原子级的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。这项研究与青年科学家的培训和教育密切相关，从本科生到研究生，所有职业阶段的受训人员都直接参与了这项研究。此外，为进一步加强对青年科学家的培训，该研究所还将开发一门大学级课程，纳入这项研究的成果。参与这项研究的受训人员还与PI一起，直接参与向更广泛的社区传播这一尖端研究的努力。通过与当地一家美术馆的合作，PI正在努力扩大开发的方法的覆盖范围，以帮助对其收藏中的艺术品进行表征、鉴定和保存。这一点通过与当地学区的合作扩展到K-12教育，在那里提供研讨会和培训机会，提供尖端研究与下一代STEM专业人员发展的汇聚。近年来，低频(太赫兹)动力学在有机半导体中的各种块状现象中所起的作用已被阐明。具体地说，在太赫兹频率下发生的大幅度振动运动已被证明是使这些材料的电荷-载流子动力学合理化的关键。在许多情况下，单太赫兹振动产生的有害电子-声子耦合足以显著降低电荷-载流子迁移率，这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--这些方法一般也适用于固态材料。具体地说，光泵太赫兹探测光谱被用来直接采样电荷-载流子动力学和电子-声子耦合，而非简谐密度泛函理论被用来预测与温度和压力有关的性质。这些实验的结果被用来合理地设计新材料，使用实验有机合成方法以及计算晶体结构设计。这项研究还整合了多种有益于社会各阶层的教育活动，包括未来的STEM领导人和非科学界。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，例如被油漆层遮挡的签名。基于这项研究的展览计划在博物馆展出，同时还将为普通社区和K-12学生举办研讨会。此外，基于这个项目，正在为高级本科生和研究生开发一门新的课程，这将转化为材料科学这一重要领域的专业知识的增长。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。

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.