Completely non-fused electron acceptor with 3D-interpenetrated crystalline structure enables efficient and stable organic solar cell

Non-fullerene acceptors (NFAs) based on non-fused conjugated structures have more potential to realize low-cost organic photovoltaic (OPV) cells. However, their power conversion efficiencies (PCEs) are much lower than those of the fused-ring NFAs. Herein, a new bithiophene-based non-fused core (TT-Pi) featuring good planarity as well as large steric hindrance was designed, based on which a completely non-fused NFA, A4T-16, was developed. The single-crystal result of A4T-16 reveals that a three-dimensional interpenetrating network can be formed due to the compact pi-pi stacking between the adjacent end-capping groups. A high PCE of 15.2% is achieved based on PBDB-TF:A4T-16, which is the highest value for the cells based on the non-fused NFAs. Notably, the device retains similar to 84% of its initial PCE after 1300 h under the simulated AM 1.5 G illumination (100 mW cm(-2)). Overall, this work provides insight into molecule design of the non-fused NFAs from the aspect of molecular geometry control.

Automated summary

Non-fullerene acceptors based on non-fused conjugated structures have potential for low-cost organic photovoltaic cells, but their efficiencies are lower than those of fused-ring NFAs. A new bithiophene-based non-fused core, TT-Pi, was designed, leading to the development of a completely non-fused NFA, A4T-16, which achieved a high PCE of 15.2% with 84% retention after 1300 hours under simulated AM 1.5 G illumination. This work provides insight into molecule design of non-fused NFAs through molecular geometry control.