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Fluorine, chlorine, and bromine were introduced into the central core of azaphenanthrene-fused acceptors. Increasing halogen size progressively improved crystallinity and packing order; CHNBr delivered a 78.84% fill factor and enabled binary organic solar cells with power conversion efficiency above 20%.
Credit: ©Science China Press
Organic solar cells are attractive as lightweight and flexible photovoltaic devices that can be fabricated from solution. Their performance, however, depends on simultaneously maintaining a high open-circuit voltage, short-circuit current density, and fill factor. Molecular core expansion can reduce energy loss and improve acceptor packing, but enlarging fused frameworks may also disturb molecular organization. Most existing core-expanded acceptors rely on quinoxaline-fused frameworks, and larger systems containing five or more fused rings remain comparatively rare.
A Nankai University team addressed this limitation with a heteroatom-guided molecular design. The researchers constructed a series of azaphenanthrene-fused non-fullerene acceptors and introduced fluorine, chlorine, or bromine into the central core. Comparison of the three halogenated acceptors revealed a clear size-dependent trend. As the halogen radius increased from fluorine to chlorine to bromine, the crystallinity and packing order of the acceptors were progressively enhanced. The results show how atom-level substitution within an expanded core can govern solid-state organization rather than merely extend the conjugated skeleton. As a result, PM6:CHNBr-based devices deliver an outstanding FF of 78.84% and a champion PCE of 20.18%, representing the highest efficiency reported for binary OSCs employing polycyclic fused-ring acceptors.
Taken together, the findings establish N/halogen engineering as a way to reconcile two objectives that can otherwise conflict in multi-ring acceptors: expanding the molecular core and preserving favorable molecular packing. The strategy provides a design direction for polycyclic acceptors that balance voltage, current, and fill factor, and may support further development of efficient organic photovoltaic materials.

See the article:
Azaphenanthrene-based polycyclic acceptors regulated by N/halogen engineering achieving over 20% efficiency in binary organic solar cells
https://doi.org/10.1007/s11426-026-3507-9
Science China Chemistry
10.1007/s11426-026-3507-9
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Science China Press
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Expert Contact
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Institute of Polymer Chemistry, College of Chemistry, Nankai University
xjwan@nankai.edu.cn

Science China Press


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Copyright © 2026 by the American Association for the Advancement of Science (AAAS)

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