Conformation Locking on Fused-Ring Electron Acceptor for High-Performance Nonfullerene Organic Solar Cells

In this work, sidechain engineering on conjugated fused-ring acceptors for conformation locking is demonstrated as an effective molecular design strategy for high-performance nonfullerene organic solar cells (OSCs). A novel nonfullerene acceptor (ITC6-IC) is designed and developed by introducing long alkyl chains into the terminal electron-donating building blocks. ITC6-IC has achieved definite conformation with a planar structure and better solubility in common organic solvents. The weak electron-donating hexyl upshifts the lowest unoccupied molecular orbital level of ITC6-IC, resulting in a higher V-OC in comparison to the widely used ITIC. The OSCs based on PBDB-T:ITC6-IC reveal a promising power conversion efficiency of 11.61% and an expected high V-OC of 0.97 V. The weaker - stacking induced by steric hindrance affords ITC6-IC with enhanced compatibility with polymer donors. The blend film treated with suitable thermal annealing exhibits a fibril crystallization feature with a good bicontinuous network morphology. The results indicate that the molecular design approach of ITC6-IC can be inspirational for future development of nonfullerene acceptors for high efficiency OSCs.