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-电能转换效率由约31%的肖克利-奎瑟极限决定，这是由于吸收能量高于半导体带隙的光子而产生的热电子和空穴中多余能量的损失。一个可行的方法来超过这个限制是创建两个电子空穴对从一个光子的吸收过程中称为激子裂变。激子裂变吸引了新的兴趣，因为设计分子的最佳裂变产额的巨大潜力。为了成功地实现激子裂变用于太阳能转换，PI和他的学生正在解决三个基本问题：1）控制最佳激子裂变产率的物理原理是什么？2)如何有效的能量转移发生在有机半导体界面的单重态和三重态激子？3)从单线态裂变中收获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解决相干电子耦合与热激活的作用，并探测激子裂变中电子离域的影响。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。所有这些实验都有助于建立激子裂变实现高效太阳能转换的基本原理。非技术描述：除了新的科学发现和发展，将形成未来太阳能转换技术的基础，大大提高效率，该项目还提供了一个很好的教育机会，培养未来的高科技劳动力。教育和推广活动包括三个主要部分：1）在韦尔奇基金会夏季奖学金计划内监督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）与新兴太阳能产业合作，特别是与Konarka Technologies，Inc.，是聚合物基光化学的先驱和领导者; 3）开发新的太阳能本科课程，为学生在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.