High-Efficiency Organic Solar Cells Based on Asymmetric Acceptors Bearing One 3D Shape-Persistent Terminal Group

Three asymmetric non-fullerene acceptors (LL2, LL3, and LL4) are designed and synthesized with one norbornyl-modified 1,1-dicyanomethylene-3-indanone (CBIC) terminal group and one chlorinated 1,1-dicyanomethylene-3-indanone (IC-2Cl) terminal group. The three-dimensional shape-persistent CBIC terminal group can effectively enhance the solubility and tune the packing mode of acceptors. Compared with their symmetric counterparts (LL2-2Cl, LL3-2Cl, and LL4-2Cl) bearing two IC-2Cl terminals, the asymmetric acceptors show improved solubilities, giving rise to enhanced crystallinity and favored nanomorphology for charge transport in the blend films with PBDB-T. Asymmetric acceptors based organic solar cells (OSCs) also show much lower voltage loss due to their higher E-CT and EQE(EL) values. Therefore, they exhibit 17-27% higher power conversion efficiency (PCE) than OSCs based on the corresponding symmetric acceptors. Among these six acceptors, LL3 with a central benzotriazole core shows the best PCE of 16.82% with an outstanding J(sc) of 26.97 mA cm(-2) and a low nonradiative voltage loss (Delta V-nr) of 0.18 V, the best values for PBDB-T based OSCs. The J(sc) and Delta V-nr also represent the best reported for asymmetric non-fullerene acceptors-based OSCs to date. The results demonstrate that the combination of the unique CBIC terminal group with the asymmetric strategy is a promising way to enhance the performance of OSCs.

Automated summary

Three asymmetric non-fullerene acceptors incorporating a unique CBIC terminal group were synthesized, leading to improved solubility, enhanced crystallinity, and higher power conversion efficiency in organic solar cells compared to their symmetric counterparts. The combination of the CBIC terminal group with the asymmetric strategy shows promise in enhancing the performance of OSCs.