Manipulating Crystal Stacking by Sidechain Engineering for High-Performance N-Type Organic Semiconductors

Y-series non-fullerene acceptors (NFAs) have achieved great progress in organic solar cells (OSCs). Most research attention is currently paid to their molecular engineering to improve the efficiency of OSCs. However, as n-type organic semiconductors, the relationship between their molecular packing structures and charge transport properties is mostly ignored. Herein, it is clarified how the molecular packing of Y-series NFAs fundamentally determines their charge transport properties by manipulating their crystal stacking via sidechain engineering. Therefore, branched alkyl/alkoxy substitutions are taken on a reference NFA (Y6-1O), affording three derivatives, namely 1OBO-1, 1OBO-2, and 1OBO-3. Results show that while the replacement of branched alkyl/alkoxy sidechains has little impact on optical properties and energy levels, it can change crystal stacking motifs significantly. The single crystal of Y6-1O with all linear sidechains forms a 2D-brickwork structure and shows lower mobility. In contrast, 1OBO-2 with all branched sidechains exhibits a favorable 3D interpenetrating porous network, displaying an electron mobility of 1.42 cm2 V-1 s-1 in single-crystal organic field-effect transistors (SC-OFETs). This value is among the highest for NFA-based n-type OFETs. This study not only reveals the fundamental structure-property relationships of Y-series NFAs, but also suggests the potential of Y-series NFAs for high-performance n-type organic semiconductors. How the molecular packing of Y-series non-fullerene acceptors fundamentally determines their charge-transport properties is clarified by manipulating their crystal stacking via sidechain engineering. Therefore, the all-branched-chains-substituted derivative, namely 1OBO-2, exhibits single crystal structure with a favorable 3D interpenetrating porous network. It thus results in an excellent electron mobility of 1.42 cm2 V-1 s-1 in organic single-crystal transistors.image