Singlet Fission: Mechanisms and Molecular Design

Exciton multiplication processes provide a means of overcoming thermalization losses in photovoltaic devices. In this chapter we will introduce one promising exciton multiplication process, termed singlet fission, which occurs in carbon-based semiconductors. After introducing the photophysics of organic semiconductors, we discuss the mechanism of singlet fission and the role of spin and electronic structure in the singlet fission process. Based on this mechanistic discussion we will introduce design rules for singlet fission materials related to their energy level alignment, molecular structure and crystal packing.