Quinoxaline-based π-conjugated donor polymer for highly efficient organic thin-film solar cells

A quinoxaline-based π-conjugated donor polymer, poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5′,8′-di-2-thienyl-2′,3′-diphenylquinoxaline)] (N-P7), was synthesized to achieve a high power conversion efficiency (PCE) of bulk heterojunction (BHJ)-based solar cells. The optical band-gap and highest occupied molecular orbital level of N-P7 were 1.95 and −5.37 eV, respectively. BHJ-based solar cells using N-P7 as a donor and phenyl C71 butyric acid methyl ester as an acceptor gave a PCE as high as 5.5% under AM 1.5G 100 mW/cm2 illumination. We also investigated the effects of substituent groups of quinoxaline-based polymers on the morphology of the BHJ layer.