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

Abstract

ABSTRACT 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.