Ultrafast Carrier Dynamics of Nonfullerene Acceptors with Different Exciton–Phonon Coupling: Impact of Intramolecular Noncovalent Interactions

In organic solar cells (OSCs), strong exciton-vibration (exciton-phonon) coupling can hinder exciton transport, thereby limiting exciton dissociation and resulting in significant nonradiative recombination energy losses. Here, we investigate the suppression of exciton-phonon coupling in OSCs by modulating intramolecular noncovalent interactions. Using three non-fused-ring electron acceptors, TT-O-2F, TT-S-2F, and TT-Se-2F, we reveal an intrinsic correlation between molecular conformation and exciton-phonon coupling. Experimental results elucidate that TT-S-2F and TT-Se-2F, featuring intramolecular S···O and Se···O noncovalent interactions, exhibit quasi-planar backbones that weaken exciton-phonon coupling, whereas TT-O-2F exhibits a twisted backbone. When blended with the polymer donor D18, TT-S-2F delivers superior hole transfer efficiency (84.67%) and Förster resonance energy transfer efficiency (53.80%), leading to the highest power conversion efficiency of 15.29%. These findings demonstrate that intramolecular noncovalent interactions can significantly enhance molecular planarity and effectively mitigate exciton-phonon coupling, which promotes charge transfer and separation, offering a molecular design strategy for high-efficiency OSCs.