The butterfly-effect of flexible linkers in giant-molecule acceptors: optimized crystallization and aggregation for enhancing mechanical durability and approaching 19% efficiency in binary organic solar cells†

Abstract

Achieving a balance between power conversion efficiency (PCE) and mechanical robustness in flexible organic solar cells (OSCs) remains a significant challenge for small molecule acceptors (SMAs) and polymer acceptors. Here, we developed a series of flexible linker giant-molecule acceptors (GMAs), DSY-C4 to DSY-C10, by incorporating flexible linkers of varying lengths at side chain sites. The optimized DSY-C10-based device demonstrated both high efficiency (PCE = 18.89%) and exceptional mechanical resilience (crack-onset strain (COS) = 9.95%) in binary OSCs, representing a new benchmark for highly ductile acceptors. The linkage at side chain sites makes the molecules exhibit butterfly-like conformations and the flexible linker reduces spatial site resistance, significantly improving the crystallinity and aggregation of GMAs. As a result, the PM6:DSY-C10-based device exhibits superior short-circuit current density (J_SC = 27.51 mA cm⁻²) and fill factor (FF = 0.785) compared with the PM6:DSY-C4-based device (J_SC = 26.65 mA cm⁻² and FF = 0.728). Additionally, the longer flexible linker enhanced donor–acceptor interactions, leading to a 65% higher COS for the PM6:DSY-C10 blend film compared to PM6:DSY-C4 (COS = 6.04%), approaching the performance of a polymer acceptor (PT-IY). In addition, the incorporation of DSY-C10 into the PM6:BTP-eC9 binary blend achieved an efficiency of 19.91% (certified 19.39%), underscoring the potential of flexible linker GMAs for high-efficiency flexible OSCs. These results demonstrate that flexible linker GMAs provide an unprecedented balance of PCE and mechanical robustness in binary OSCs, paving the way for durable flexible OSCs.