Topology Engineering Regulates Free Volume to Decouple Efficiency-Mechanical Performance Trade-Off in Intrinsically Stretchable Organic Solar Cells

초록

Intrinsically stretchable organic solar cells (IS-OSCs) hold great promise for wearable electronics, yet their development is severely hindered by the trade-off between efficiency and mechanical robustness, remaining a critical challenge. Herein, three polymerized small-molecule acceptors (PSMAs) with distinct molecular topologies: linear PYIT, star-shaped BTPPYIT, and dimer-star-shaped 2BTPPYIT were synthesized with different free volume ratio (FVR), following the order of PYIT > BTPPYIT > 2BTPPYIT. The FVR can acts as a detector to reflect intermolecular interactions and chain entanglement, thereby governing the balance between photovoltaic and mechanical properties. Among these polymers, the star-shaped BTPPYIT with suitable FVR enables most optimal film morphology for efficient charge transport, while possesses strong chain entanglement for mechanical stretchability. Consequently, the BTPPYIT-based binary device achieves a record efficiency of 17.36% among star-shaped PSMAs, and a ternary device reaches a high efficiency of 20.05%. Notably, the BTPPYIT-based IS-OSCs achieve both a high efficiency of 12.58% and excellent stretchability (80% PCE retention at 22.65% strain), representing one of the best comprehensive performances reported for IS-OSCs. Overall, the star-shaped architecture of BTPPYIT with suitable FVR is very effective for decoupling the efficiency-flexibility trade-off in stretchable organic electronics.

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