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

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.