Chlorinating the π-extended central core of nonfullerene acceptor enables high-performance polymer solar cells

The rational design of non-fullerene acceptors (NFAs) with high crystallinity is of crucial importance for achieving high-efficiency organic solar cells (OSCs). Here, the crystallinity of NFA is modulated by chlorinating the π-extended central unit of NFA. Two phenazine (Pz)-based acceptors (P2Br, P2Cl) with varying halogen substitution in the central acceptor core are designed and synthesized to investigate their impact on OSCs performance. Notably, OSCs incorporating the chlorinated NFA demonstrate a significantly higher power conversion efficiency (PCE = 13.62%) than those with brominated NFA (5.97%) in binary OSCs. Theoretical and experimental analyses reveal that chlorination enhances electrostatic interactions, donor-acceptor miscibility, and crystallinity versus the brominated NFA, thereby promoting exciton dissociation, more balanced hole/electron mobility, and reduced exciton recombination rates in the corresponding OSCs. Finally, ternary solar cells incorporating the chlorinated NFA as the third component achieve an impressive PCE of 19.68% due to improved crystallinity, suppressed charge recombination, and enhanced charge mobilities of the blend film. These findings provide valuable insights into the molecular design of future high-performance NFAs for OSCs applications. © 2025 Elsevier B.V.