Stable dinitrile end-capped closed-shell non-quinodimethane as donor, acceptor and additive of organic solar cells

Non-fullerene acceptors exhibit great potential to improve photovoltaic performances of organic solar cells. However, it is important to further enhance chemical stability and device durability for future commercialization, especially for Y6-series small molecule acceptors with 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) type as ending group. In this work, an IC-free photovoltaic material YF-CN consisting of 2-fluoren-9-ylidenepropanedinitrile terminal was designed and synthesized by stille coupling. YF-CN exhibited closed-shell chemical structure with enhanced photostability and improved morphological compatibility with the binary PCE10:Y6 blend. The moderate energy level makes YF-CN could serve as a multifunctional material, such as donor, acceptor and the third component. When adding YF-CN as second donor into PCE10:Y6 system, an improved power conversion efficiency of 12.03% was achieved for as-cast device. Importantly, the ternary PCE10:YF-CN:Y6-devices showed enhanced storage durability maintaining 91% of initial PCE after the 360 hours. This work provides new perspective to understand the open-shell character of donor and closed-shell structure of acceptors, respectively, as well as promising design concept of stable IC-free acceptors for organic solar cells.