Recently, the development of high performance non-fullerene acceptors (NFA) has made an impressive breakthrough in polymer solar cell (PSC) research. To date, many different donor polymers have been extensively studied for the NFA-based PSCs. However, only a few donor polymers have exhibited high power conversion efficiency (PCE) with the NFAs. Therefore, development of new donor polymer that can show high performance in both fullerene- and NFA-based PSCs is highly demanded.
Previously, we developed a series of donor polymers bearing 1,5-naphthyridine-2,6-dione (NTD) as a novel electron accepting building block which showed high PCE (> 9%) in fullerene-based PSC devices. Those NTDT polymers uniquely showed a large absorption coefficient, high structural coplanarity, and high crystallinity, which cooperatively contributed to the high short circuit current (Jsc) and fill factor (FF) values in thick active layer PSC. However, they showed a very low efficiency (<1%) in NFA-based PSCs due to their high crystallinity induced by linear backbone.
Herein, we present a newly designed NTD-based donor polymer (PNTD4T-o-2FB) which holds high coplanarity but with curved conformation by introducing 2,2'-(2,3-difluoro-1,4-phenylene)dithiophene as a comonomer unit. It is shown that the curved backbone conformation lowered the crystallinity but enhanced the face-on orientation of the polymer chains, which led to high PCEs in both NFA- and fullerene-based PSCs.
 WS Yoon, DW Kim, M-W Choi, J-M Park, SY Park, Adv. Energy. Mater. 2017, 1701467