Halogen-Atom Engineering on Aromatic-Core in Tethered Small Molecule Acceptors for High-Performance Polymer Solar Cells

Tethered small molecular acceptors (SMAs), where multiple SMA-subunits are connected to the aromatic core via flexible chains, are proposed to suppress thermodynamic relaxation when blended with polymer donors to construct stable polymer solar cells (PSCs). However, optimizing their chemical structure to further enhance device performance remains a challenge, requiring careful fine-tuning between molecular aggregation and photovoltaic efficiency. In this study, the photovoltaic properties of tethered dimers are effectively modulated simply through halogen-atom engineering on the aromatic core. Specifically, DY-Cl with a chlorine atom and DY-Br with a bromine atom are designed. The study revealed the chloride acceptor enhances the intermolecular interaction, promotes charge transport, and optimizes the morphology of the active layer compared with its bromide counterpart. Notably, DY-Cl based PSCs achieves a power conversion efficiency of 18.72%, maintaining over 80% of initial PCE after operating for 1000 h. These findings underscore the potential advantages of halogen-atom engineering on tethered acceptors as a straightforward yet effective method to achieve high efficiency and stable PSCs.