Regio-Specific N-Alkyl substitution Tuning the Molecular Packing of High-Performance Non-Fullerene Acceptors

The rapid development of non-fullerene acceptors (NFAs) with strong near-infrared absorption has led to remarkably enhanced short-circuit current density (Jsc) in organic solar cells (OSCs). The NFAs based on benzotriazole (Bz) fused-ring π-core have great potential in delivering both high Jsc and decent open-circuit voltage due to their strong intramolecular charge transfer with reasonably low energy loss. In this work, we have designed and synthesized a series of Bz-based NFAs, PN6SBO-4F, AN6SBO-4F and EHN6SEH-4F via regio-specific N-alkyl engineering based on the high-performance mBzS-4F that was reported previously. The molecular packing of mBzS-4F, AN6SBO-4F and EHN6SEH-4F single crystals were analyzed by X-ray crystallography in order to provide a comprehensive understanding on the correlation between molecular structures, charge-transporting properties, and solar cell performances. Compared with the typical honeycomb single-crystal structure of Y6 derivatives, these NFAs show distinctly different molecular packing patterns. The strong interactions of terminal indanone groups in mBzS-4F and J-aggregation-like packing in EHN6SEH-4F lead to the formation of ordered 3D networks in single-crystals with channels for efficient charge transport. Consequently, OSCs based on mBzS-4F and EHN6SEH-4F show efficient photo-to-current conversions, achieving a highest power conversion efficiency of 17.48% with a Jsc of 28.83 mA/cm2.