Singlet Fission for Highly Efficient Organic Photovoltaics

美国国家科学基金会化学部的化学结构、动力学和机制项目支持科罗拉多大学博尔德分校的Charles Musgrave教授领导两项密切相关的研究工作，即有机光伏（PV）材料中的单线态裂变（SF）和自旋控制激子扩散（SCED）。这项工作的重点是使用计算量子化学来探索这两个研究重点所涉及的基本原理，以发现和理解可能在未来技术应用中被利用的现象。本研究计划旨在了解经济发展和经济及经济发展局的运作机制，以及这些过程所遵循的原则。SF包括吸收太阳光子产生单线态激子，或束缚电子-空穴对，然后将这个激子分裂成两个低能量的耦合三重态激子。SF的动机是能够吸收高能光子并将其能量向下转换而几乎没有损失，而高能光子的多余能量通常会通过转换为热量而消散。因此，如果成功，SF可能会带来更高效的太阳能电池。这个过程的关键是一个光学暗多激子态在激子裂变过程中的可能作用。该项目的主要目的是探索各种有机光伏材料中这种暗态的本质，并确定其在控制SF过程中的作用。SCED是一种被提出的现象，它可能会影响激子的速率，从而在有机PV中传输能量。在有机PV中，激子从分子到分子的传输速率受到局部磁场的影响，通过自旋-轨道耦合产生激子，激子不再是玻恩-奥本海默纯自旋态，但可以在激子经历非辐射衰变以耗散能量之前快速传输以获取能量。如果传输速率可以加快，就有可能产生更厚的光伏薄膜，从而捕获更多的太阳辐射能量。该项目的目标是阐明这些过程的支配原则，以预测，发现和理解新的SF和SCED材料，这些材料可以导致新的，更高效的太阳能电池。这些相同的现象也可能被用来获得更高效和环保的LED照明。这项工作还旨在将研究与教育和推广结合起来，传播通过这项研究获得的新知识，并教育未来的技术工作者和非专家关于将太阳能转化为光伏发电的电能的性质。最终，这个项目的目的是准备多样化的本科生和研究生创新和生产的学术，工业，政府实验室的职业生涯。

The Chemical Structure, Dynamics, and Mechanism program in the Chemistry Division of the National Science Foundation supports Professor Charles Musgrave of the University of Colorado Boulder to lead two closely related research efforts on singlet fission (SF) and spin controlled exciton diffusion (SCED) in organic photovoltaic (PV) materials. This effort focuses on using computational quantum chemistry to explore the fundamental principles involved in these two research thrusts to discover and understand phenomena that might be exploited in future technological applications. The project aims to understand the mechanisms of SF and SCED and the principles that govern these processes. SF involves absorbing a solar photon to create a singlet exciton, or bound electron-hole pair and then splitting this exciton into two coupled triplet excitons of lower energy. The motivation for SF is the ability to absorb high-energy photons and down convert their energy with little loss whereas the excess energy of the high-energy photon would usually be dissipated through conversion into heat. Thus, if successful, SF could lead to more efficient solar cells. A key to this process is the possible role of an optically dark multiexcitonic state in the exciton fission process. A major thrust of this project is to explore the nature of this dark state in various organic PV materials and to determine its role in governing the SF process. SCED is a proposed phenomena that may affect the rate at which excitons, and thus energy is transported in organic PV where the exciton transfer rate from molecule to molecule is affected by a local magnetic field through spin-orbit coupling to create excitons that are no longer Born-Oppenheimer pure spin states, but which can be quickly transported to harvest their energy before they undergo non-radiative decay to dissipate their energy. If the transport rate can be accelerated, it offers the potential to create significantly thicker PV films that could capture a larger fraction of the energy contained in solar radiation. The goal of this project is to elucidate the governing principals of these processes to predict, discover and understand new SF and SCED materials that can lead to new, more efficient solar cells. These same phenomena might also be exploited to obtain more efficient and environmentally friendly LED lighting. The work also aims to integrate research with education and outreach to disseminate the new knowledge obtained through this research and to educate future technology workers and non-experts about the nature of interconverting solar energy into electrical energy for PVs. Ultimately, this project aims to prepare diverse undergraduate and graduate students for innovative and productive academic, industrial, government laboratory careers.