CAREER: Understanding the Role of Quantum Coherence in Exciton Transport and Separation in Molecular Aggregates

技术：这个职业奖的研究部分探索了量子相干在有机半导体中激子传输和电荷分离中的作用。有机光伏器件通常由复杂的纳米结构制成。需要一种策略来将激子定向到施主/受主界面并有效地将它们分开。最近在光合作用复合体中证明，相干耦合和非相干激子捕获之间的相互作用可以为激子的传输和分离提供一种有效的途径。对于分子晶体和PI共轭聚合物，激子通过相干耦合离域是众所周知的，但一些重要问题的答案仍然不清楚。例如，激子离域将如何夸大激子的输运范围？在光激发后的超快(1皮秒)时间尺度上，离域尺寸是如何变化的？激子离域在电荷分离中的作用是什么？知识差距的部分原因是缺乏能够以所需的空间(纳米)和时间分辨率(飞秒)测量激子运动的实验工具。为了克服这一障碍，PI同时使用飞秒时间分辨光电子能谱和荧光上转换光谱来测量激子的传输范围、离域大小和界面上的电荷转移动力学。非技术性：该项目解决了与有机半导体相关的基本材料问题。大规模实施低成本的可再生能源是21世纪的主要挑战之一。该项目通过探索可以提高下一代太阳能电池效率的机制来帮助应对这一挑战。该项目的教育活动与研究活动相结合。例如，最新的研究主题被纳入本科课程。为本科生、高中生和教师提供研究机会。PI和他的学生参观了当地的学校，并通过讲座和实验演示向K-12学生介绍了与可再生能源相关的基础科学。旨在提高公众对可再生能源的认识的公开讲座是通过堪萨斯大学的成人教育项目进行的。

Technical: The research component of this CAREER award explores the role of quantum coherence in exciton transport and charge separation in organic semiconductors. Organic photovoltaic devices are often made from complex nanostructures. A strategy is needed to direct excitons to and separate them effectively at the donor/acceptor interfaces. As recently demonstrated in photosynthetic complex, the interplay between the coherent coupling and incoherent exciton trapping could provide an effective way for exciton transport and separation. For molecular crystals and pi-conjugated polymers, it is well known that excitons delocalize through coherent coupling, but answers to several important questions remain unclear. For example, how will the exciton delocalization boast the exciton transport range? How does delocalization size change in an ultrafast ( 1 picosecond) timescale after photoexcitation? What are the roles of exciton delocalization in charge separation? The knowledge gap is partially due to the lack of experimental tools that can measure exciton motion with the required spatial (nanometer) and temporal resolution (femtosecond). To overcome this barrier, the PI uses both femtosecond time-resolved photoemission spectroscopy and fluorescence up-conversion spectroscopy to measure the exciton transport range, delocalization size, and charge transfer dynamics at interfaces.Non-technical: The project addresses fundamental materials issues related to organic semiconductors. The large-scale implementation of low cost renewable energy is one of the major challenges in the 21st century. The project helps to address the challenge through exploring the mechanisms that could improve the efficiency of next generation solar cells. The education activities in this project are integrated with the research activities. For example, up-to-date research topics are incorporated into undergraduate courses. Research opportunities are provided to undergraduates as well as high school students and teachers. The PI and his students visit local schools and introduce basic science related to renewable energy to K-12 students through lectures and experimental demonstrations. Public lectures designed to increase the public awareness of renewable energy are given through adult education programs at the University of Kansas.