Aromatic Sulfides as Conjugation-Break Spacers for Designing Stretchable Donor–Acceptor Semiconducting Polymers in Photovoltaic Applications

This study reports the successful design of a series of semiconducting polymers through the incorporation of aromatic sulfide-based conjugation-break spacers (CBS), namely, diphenyl sulfide (DPS) and thianthrene (TA), into both p -type and n -type polymer backbones. These CBS moieties introduce localized conformational flexibility via rotatable C–S–C linkages while maintaining an effective π-conjugation system, enabling precise regulation of the balance between mechanical robustness and optoelectronic performance. Ternary organic photovoltaic (OPV) devices based on PBDB-T-DPS and PBDB-T-TA demonstrated excellent power conversion efficiency (PCE) retention of 97% and 93%, respectively, while increasing the crack-onset strain (COS) from 10% to 20%. Likewise, devices based on PNDI2T-DPS and PNDI2T-TA achieved up to 30% higher COS while preserving 89–91% of initial PCE. Unlike previously reported alkyl- or hydrogen-bond-based CBS systems, which typically require multistep synthetic routes and partially interrupt π-conjugation, the aromatic sulfide-based CBS units developed herein are commercially available or readily synthesized in a single step and enhance intermolecular interactions through S–S bonds and S–π interactions. This significantly enhances mechanical flexibility without compromising the charge transport or light absorption properties. This study proposes a simple and versatile molecular design strategy to impart structural flexibility to semiconducting polymers, opening promising avenues for developing intrinsically stretchable and mechanically stable OPVs suitable for next-generation wearable and implantable electronics.