Simple non-fused ring electron acceptors with well-controlled terminal group stacking

Producing high-performance and inexpensive non-fullerene acceptors is a great challenge in the field of organic photovoltaics. Herein, three non-fused ring electron acceptors (NFREAs), TT-O-2F, TT-S-2F, and TT-Se-2F, have been designed and can be modularly synthesized with a few high-productivity steps. According to our results, TT-S-2F and TT-Se-2F have planar molecular backbones because of the existence of S⋅⋅⋅O and Se⋅⋅⋅O intramolecular non-covalent interactions, whereas TT-O-2F has a twisted molecular backbone. In particular, TT-S-2F exhibits the largest terminal group overlapping area and exciton diffusion length among these acceptors, which could facilitate charge transport. The devices based on TT-S-2F can generate an excellent power conversion efficiency (PCE) of 15.29%, much higher than TT-O-2F (10.43%) and TT-Se-2F (12.23%), which are also among the highest PCEs based on NFREAs. Our work highlights the importance of well-controlled terminal packing in designing high-performance NFREAs.