On Refining Exciton Dissociation and Charge Transport of Nonfullerene Organic Photovoltaics: from Star-Shaped Acceptors to Molecular Doping.

Nonfullerene acceptor-based organic solar cells have recently taken a milestone leap with power conversion efficiencies approaching 20%. A key to further boost the efficiencies up to the Shockley-Queisser limit rests upon attaining a delicate balance between exciton dissociation and charge transport. This perspective presents two seminal and reciprocal strategies developed by our group and others to reconcile the intricacy of charge carrier dynamics, spanning from intrinsic molecular structure design to extrinsic dopant exploitation. Emerging star-shaped nonfullerene structures are highlighted by their favorable impacts of 3D molecular characteristics, aggregation-state attributes, and donor:acceptor miscibility on exciton dissociation. Complementarily, n-type molecular doping is implemented on the nonfullerene photoactive layers by finely optimizing energy landscape to facilitate charge transport and manipulating the blend film morphology, especially in donor-dilute semitransparent organic solar cells. The remaining challenges to these two modular approaches are elucidated, and further deployments are envisioned with insightful viewpoints on leveraging exciton and charge dynamics.