Manipulating Molecular Conformation Enables Non‐Fused Ring Electron Acceptors with Compact 3D Molecular Packing and Weak Electron‐Phonon Coupling for Efficient Organic Solar Cells

Abstract Non‐fused ring electron acceptors (NFREAs) promise to meet the requirement of scale‐up fabrication of organic solar cells (OSCs), due to potentially lower synthetic complexity and cost. Nevertheless, the rotational conjugated backbone and weak intermolecular interaction negatively impact the molecular stacking of NFREAs, leading to inferior photovoltaic performance, compared to their fused counterparts. Herein, an NFREA, TTIC‐PhX, having asymmetric structure is developed to manipulate molecular conformation via replacing half of phenyl chains on TTIC‐BPh with alkyls. The larger steric hindrance and superior flexibility of alkyl chains endow TTIC‐PhX with improved molecular conformation modulation to achieve 3D packing model having more compact molecular stacking and stronger electronic coupling. TTIC‐PhX presents larger dielectric constant and enhanced intramolecular/intermolecular interaction to afford weaker electron‐phonon coupling and higher crystallinity, compared to TTIC‐BPh. Thus, D18:TTIC‐PhX based devices achieve lower trap density, higher mobilities, reduced charge recombination rate, and smaller recombination‐to‐extraction ratio to facilitate exciton dissociation and suppress charge recombination. Therefore, D18:TTIC‐PhX based OSCs realize higher J SC and FF (81.05%, the record for NFREAs) for impressive power conversion efficiencies (PCEs) of 17.71%, among the highest values for NFREAs. It indicates that manipulating molecular conformation is an efficient strategy to regulate the molecular aggregation of NFREAs for higher PCEs.