First-Principles Investigation of Energy Transport within Highly Ordered Organic Molecular Arrays

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NONTECHNICAL SUMMARYThe CMMT Program of the Division of Materials Research, and the CTMC Program of Division of Chemistry jointly fund this award on research and education in energy transport in organic molecular arrays based on first-principles calculations. Solar energy conversion, i.e. harnessing solar energy and converting it to electricity or chemical energy, is a promising technology for addressing the challenges associated with the projected future growth in energy needs. This technology requires new materials, designed specifically to create more efficient and inexpensive devices for solar energy conversion. This project focuses on organic materials, composed of assemblies of carbon-based molecules, a particularly promising class of materials for such applications. In contrast to the traditional inorganic materials used in solar energy conversion devices, organic materials are low in cost, abundant, and extensively tunable by virtue of the mature field of synthetic organic chemistry. To utilize and improve these materials for solar energy conversion, it is necessary to understand their fundamental properties; however, this understanding is hindered by the challenges in characterizing the behavior of electrons, both experimentally and theoretically, at nanometer length scales. By utilizing and developing state-of-the-art simulation methods, the PI and her research team will investigate the fundamental properties that govern the interaction of light with assemblies of organic molecules, and elucidate the factors critical to the design of advanced solar energy conversion materials. This project will disseminate the knowledge gained through numerous channels: i) The developments made to the simulation methods will be made publicly available through the computational tool BerkeleyGW on nanoHub.org. Nanohub is a website created by the National Science Foundation Network for Computational Nanotechnology, that allows experts in nanotechnology-related fields to share knowledge and simulation tools. ii) In collaboration with the Boston University (BU) Technology Innovation Scholars Program, where undergraduate students interested in becoming teachers will contribute to teaching at diverse high schools throughout the Boston area, lesson plans will be developed that incorporate the applicability of the research to solar energy conversion. iii) In collaboration with the BU Outreach and Diversity Program, an animated tutorial aimed at younger students will be developed and broadcast on the BU YouTube channel. TECHNICAL SUMMARYThe CMMT Program of the Division of Materials Research, and the CTMC Program of the Division of Chemistry jointly fund this award on research and education in energy transport in organic molecular arrays based on first-principles calculations. The intent of this research is to aid in the design of new organic molecular assemblies for solar energy conversion. Organic materials are a highly tunable class of optically active materials that are promising for photovoltaics and artificial photosynthesis. To make organic materials in such applications feasible requires an intuitive understanding of how to improve the efficiency and lifetime of the component materials. Moreover, the vast space of realizable organic molecular systems afforded by the maturity of the field of organic synthesis provides a great opportunity to both explore new physical phenomena and design novel materials. Theoretical approaches are necessary to develop deeper physical intuition about the optoelectronic properties of these materials in order to advance the technology. This project focuses on the role of long-range order on the optical and electronic properties of recently synthesized perylene diimide molecular arrays. The PI and research team will employ first-principles electronic structure theory to better understand how optically excited states within ordered organic assemblies can be controlled to deliver improved photovoltaic and photocatalytic efficiency. This project addresses a key, unanswered question related to energy transport within molecular assemblies: what is the role of inter-molecular interactions on the evolution of the excited-state? The determination of structure-property relationships is critical for design of new molecules; this study will quantify aspects of inter-molecular interactions and electronic structure, such as the interplay between electron-phonon and electron-electron interactions, enabling their application to molecular design. This approach is unique in that the first-principles calculations focus on extended systems, where long-range interactions play a significant role on the nature of excitations. Additionally, this work will develop new computational methodology for probing the role of electron-phonon interactions, which are very difficult to characterize for extended systems. Experimental collaborators will test the predications using their unique synthetic technologies, validating and improving upon the computational approach, and thereby increasing the impact of this research. The ultimate aim of this research to provide new design rules to efficiently direct optical excitations along molecular nanowires that will be synthesized.This project will disseminate the knowledge gained through numerous channels: i) The developments made to the simulation methods will be made publicly available through the computational tool BerkeleyGW on nanoHub.org. Nanohub is a website created by the National Science Foundation Network for Computational Nanotechnology, that allows experts in nanotechnology-related fields to share knowledge and simulation tools. ii) In collaboration with the Boston University (BU) Technology Innovation Scholars Program, where undergraduate students interested in becoming teachers will contribute to teaching at diverse high schools throughout the Boston area, lesson plans will be developed that incorporate the applicability of the research to solar energy conversion. iii) In collaboration with the BU Outreach and Diversity Program, an animated tutorial aimed at younger students will be developed and broadcast on the BU YouTube channel.