Modulating Surface Potential and Electron/Hole Overlap of Singlet Excited State in Asymmetry End‐Capped Dimeric Acceptors for Efficient and Stretchable Organic Solar Cells

Abstract

ABSTRACT Back‐to‐back dimeric acceptors have attracted widespread attention for organic solar cells (OSCs) due to their exceptional stability and unique three‐dimensional (3D) charge transport channels. However, these dimers suffer from inferior intermolecular interactions and molecular packing, limiting the development of OSCs. Here, we first employed an asymmetry end‐group strategy to develop a novel asymmetry back‐to‐back dimer DQx‐FCl. Breaking structural symmetry in DQx‐FCl alters the electrostatic surface potential to strengthen intermolecular π ‐ π interactions. Meanwhile, it also reduces the overlap of electron and hole in the singlet excited state to promote charge separation. Thus, the asymmetric DQx‐FCl‐based binary device achieved a superior power conversion efficiency (PCE) of 19.11% along with improved stability, relative to its symmetric DQx‐F. More notably, DQx‐FCl‐based ternary device achieves a record PCE of 20.27% among reported back‐to‐back dimer‐based OSCs. Furthermore, the reinforced intermolecular interactions also enhance the mechanical robustness of OSCs. Flexible devices based on the PM6:L8‐BO:DQx‐FCl attain a PCE of 17.27% with a crack‐onset strain of 14.6%, while the intrinsically stretchable OSC retains 80% of its initial efficiency under a tensile strain exceeding 23%. This study demonstrates the great potential of asymmetric back‐to‐back dimeric acceptors for improving efficiency, stability, and mechanical flexibility toward high‐performance OSCs.