Enhancing Photovoltaic Performance of Ladder‐Type Heteroarene‐Based Electron Acceptors by Modulating Molecular Packing†

Comprehensive Summary The development of novel building blocks with sp 3 ‐hybridized‐carbon‐free conjugated skeletons is important to further advance and enrich nonfullerene acceptors (NFAs), but this remains a challenge due to the lack of strategies to effectively modulate the aggregation behavior of resulting NFAs. Herein, two novel nitrogen‐bridged octacyclic ladder‐type heteroarenes end‐capped with thiophene rings (BTPS) or selenophene rings (BTPSe) are designed and synthesized as the donor cores for constructing NFAs (MQX‐2 and MQX‐4). It is found that replacing the sulfur atoms (MQX‐2) at the outer positions of the heteroarene core with selenium atoms (MQX‐4) can effectively modulate the molecular packing mode of the NFAs. The incorporation of selenium atoms induces stronger O···Se noncovalent interaction than O···S, thus promoting the formation of mixed H/J‐type aggregates in MQX‐4. Benefiting from more electron hopping channels, MQX‐4 exhibits higher electron transport (more than 1‐fold enhancement) and photovoltaic properties compared to MQX‐2, which forms only H‐type aggregates.