The design of quinoxaline based unfused non-fullerene acceptors for high performance and stable organic solar cells

Unfused non-fullerene acceptors with the merits of easy synthesis, high yields and low cost have attracted much attention in recent years. And the development of new unfused acceptors with high performance and stability is urgently demanded. In this work, we designed and synthesized two unfused non-fullerene acceptors (UF-Qx-2F and UF-Qx-2Cl) with an electron-deficient quinoxaline (Qx) as the central unit linking with the electron-donating cyclopentadithiophene (CPDT) as the conjugated backbone. With different end groups, the crystallinity and packing behaviors of molecules were finely tuned. UF-Qx-2Cl, which is capped with 2-(5,6-dichloro-3-oxo-2,3dihydro-1H-inden-1-ylidene)malononitrile (IC-2Cl), possesses more red-shifted absorption, higher crystallinity and more ordered molecular packing. The J52:UF-Qx-Cl based devices achieved a higher power conversion efficiency of 10.81% and better thermal and air stability than those of J52:UF-Qx-2F based devices. Our results indicate that the use of electron-deficient core units (Qx) is a promising way to design unfused NFAs, and the unfused non-fullerene acceptors hold a bright future to carry out high performance and stable organic solar cells with low cost for commercial application.