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

Abstract

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 triplet and triplet-pair excitons have hindered the development of efficient SF-sensitized devices. In this Perspective, we summarize recent progress in understanding the excitonic processes contributing to inefficiencies in SF-sensitized PV devices. We discuss how inconsistent classification of triplet and triplet-pair excitons can result in misleading quantification of SF yields, and identify emerging design principles for improving the separability of triplet-pair excitons. We then demonstrate the importance of accounting for anisotropic 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.