Recent Progress in Singlet Exciton Fission

Singlet exciton fission is the process by which a high-energy singlet exciton splits into two low-energy triplet excitons. Organic solar cells based on singlet fission have the potential to exceed the Shockley-Queisser limit and, in doing so, may improve their efficiency from 30% to 44.4%. Although progress in singlet fission materials and photovoltaic devices has accelerated with recent research, many challenges and debates remain with regard to clarifying the relationship between molecule structures and the rate and efficiency of singlet fission. This review addresses recent advances in singlet fission materials and summarizes the work of our own research group. We begin by introducing the background of singlet fission, following with the general concept, the requirements for singlet fission to proceed, and the applications of transient absorption spectroscopy. Two mechanisms have been proposed to explain singlet fission molecules, intermolecular and intramolecular singlet fission, and these two types of materials are summarized, focusing on dimers, which are novel structures that undergo efficient intramolecular singlet fission. Based on the latest developments in singlet fission, we discuss the possible future advances in, and prospects for the application of, singlet fission materials.