Exceeding the Limit in Solar Energy Conversion with Exciton Fission

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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.