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

University Of Kansas Center For Research Inc, Lawrence KS

Investigators

Abstract

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.