What Next for Singlet Fission in Photovoltaics? The Fate of Triplet and Triplet-Pair Excitons

Exciton multiplication through singlet fission (SF)has the potential to surpass the detailed-balance efficiency limit of single-junction photovoltaic (PV) devices. However, energy loss and exciton decay pathways arising from the complex dynamics of tripletand triplet-pair excitons have hindered the development of efficientSF-sensitized devices. In this Perspective, we summarize recentprogress in understanding the excitonic processes contributing toin efficiencies in SF-sensitized PV devices. We discuss howinconsistent classification of triplet and triplet-pair excitons canresult in misleading quantification of SF yields, and identify emergingdesign principles for improving the separability of triplet-pairexcitons. We then demonstrate the importance of accounting foranisotropic triplet-exciton diffusion in designing SF-sensitized device architectures. Finally, we examine recent advances in characterizing the processes of harvesting triplet-exciton energy and consider prospective future strategies for improving efficiencies in SF-sensitized PV devices