Singlet Fission Materials for Photovoltaics: From Small Molecules to Macromolecules

Singlet fission (SF) is a spin-allowed process in which a singlet state splits into two triplet states. Materials that enable SF have attracted great attention in the last decade, mainly stemming from the potential of overcoming the Shockley-Queisser (SQ) limit in photoenergy conversion. In the past decade, a large number of new molecules exhibiting SF are explored and many devices based on SF materials are studied, though the mechanistic understanding is still obscure. This review focuses on the recent developments of SF materials, including small molecules, oligomers, and polymers. The molecular design strategies and related mechanisms of SF are discussed. Then the dynamics of charge transfer and energy transfer between SF materials and other materials are introduced. Further, the progresses of implementing SF in photovoltaics are discussed. It is hoped that a comprehensive understanding to the SF materials, devices, and mechanism may pave a new way for the design of next generation photovoltaics.