Exceeding the Limit in Solar Energy Conversion with Exciton Fission

技术说明：传统太阳能电池的最大太阳能-电力转换效率由大约31%的Shockley-Queisser极限决定，该极限来自热电子和空穴中多余能量的损失，这些能量是在吸收能量高于半导体带隙的光子时产生的。超过这一极限的一个可行方法是，在一个称为激子裂变的过程中，从一个光子的吸收中产生两个电子-空穴对。激子裂变重新引起了人们的兴趣，因为设计分子以获得最佳裂变产额的巨大潜力。为了成功地将激子裂变转化为太阳能，Pi和他的学生们正在解决三个基本问题：1)控制最佳激子裂变产额的物理原理是什么？2)如何在有机半导体界面上有效地传递单态和三态激子的能量？3)从单态裂变中获取多个载流子的最佳策略是什么？研究小组使用具有不同能量或不同结晶度的模型有机半导体来研究相干电子耦合与热激活的作用，并探索电子离域在激子裂变中的作用。该团队还使用模型有机半导体界面来探测能量转移和电荷转移。所有这些实验都为实现激子裂变以实现高效的太阳能转换奠定了基本原理。非技术描述：除了将为未来效率大大提高的太阳能转换技术奠定基础的新的科学发现和发展外，该项目还为培养未来的高科技劳动力提供了一个极好的教育机会。教育和外展活动包括三个主要部分：1)在韦尔奇基金会暑期奖学金计划范围内指导K-12学生进行太阳能研究，并作为西湖高中独立学习导师计划的成员；2)与新兴太阳能行业合作，特别是与聚合物光伏领域的先驱和领先者Konarka Technologies，Inc.合作；以及3)开发新的太阳能本科课程，帮助学生为太阳能经济中新兴的就业市场做好准备。

Technical Description: The maximum solar-to-electric power conversion efficiency of a conventional solar cell is determined by the Shockley-Queisser limit of about 31%, which comes from the loss of excess energies in hot electrons and holes created from the absorption of photons with energies above the semiconductor bandgap. A viable approach to exceed this limit is to create two electron-hole pairs from the absorption of one photon in a process called exciton fission. Exciton fission has attracted renewed interest because of the great potential of designing molecules for optimal fission yields. To successfully implement exciton fission for solar energy conversion, the PI and his students are addressing three fundamental questions: 1) What are the physical principles that govern optimal exciton fission yield? 2) How does efficient energy transfer occur at organic semiconductor interfaces for singlet and triplet excitons? 3) What is the best strategy to harvest multiple carriers from singlet fission? The research team uses model organic semiconductors with varying energetics or with different degrees of crystallinity to address the roles of coherent electronic coupling vs. thermal activation and to probe the effect of electronic delocalization in exciton fission. The team also uses model organic semiconductor interfaces to probe energy transfer and charge transfer. All these experiments serve to establish fundamental principles in the implementation of exciton fission for efficient solar energy conversion.Non-technical Description: In addition to new scientific discoveries and developments that will form the foundation of future solar energy conversion technologies with much improved efficiency, this project also provides an excellent educational opportunity for the training of the future high-tech workforce. The educational and outreach activities consist of three major parts: 1) supervising K-12 students in solar energy research within the Welch Foundation Summer Scholar program and as a member of the West Lake High school's Independent Study Mentorship program; 2) collaboration with emerging solar industries, in particular, with Konarka Technologies, Inc., a pioneer and leader in polymer based photovoltaics; and 3) developing new undergraduate curriculum on solar energy, which serves to prepare students for the emerging job market in the solar energy economy.