Stepwise Extended -Conjugation Lengths of Chlorinated Oligomeric Non-fullerene Acceptors Accessed via Direct C.H Arylation

Low-cost and efficient synthesis of acceptors plays a key role in the commercialization of organic optoelectronic devices. So far, the unfused-ring acceptors (UFRAs) with chlorine terminal groups has rarely been reported in the past years. In this work, a series of A-D-A type chlorinated oligomeric UFRAs with the stepwise extension of pi-conjugation lengths (DFPC-2Cl-n (n = 1. 3)) are designed and successfully synthesized via direct C.H arylation. The conjugation length dependence of optoelectronic properties and photovoltaic performances have been systematically investigated, revealing that DFPC-2Cl-2 achieves the highest power conversion efficiency (7.55%) due to the significantly enhanced open voltage (V-OC), short current (J(SC)), and fill factor (FF). The broadest and highest EQE and suitable BHJ morphology of DFPC-2Cl-2-based OSC enabled the highest J(SC) and FF among the three UFRAs. The combination of chlorine terminal group with the regulated pi-conjugation lengths can finely tune the frontier molecular orbital (FMO) levels to obtain new-type oligomeric UFRAs with the elevated V-OC, J(SC), and FF. The current work demonstrates that direct C-H arylation is a robust and atomeconomic strategy to tailor the pi-conjugation lengths of UFRAs, which will provide a guidance for the design, synthesis and screening of high-performance non-fullerene acceptors for organic solar cell applications. [Graphics] .