Novel conjugated polymers with planar backbone bearing acenaphtho[1,2-b]quinoxaline acceptor subunit for polymer solar cells

Dialkoxy substituted acenaphtho [1,2-b]quinoxaline (AQx) is demonstrated to be a promising electronic acceptor subunit for constructing high performance donor-acceptor (D–A) photovoltaic copolymers. Using it as acceptor and benzo[1,2-b:4,5-b′]-dithiophene (BDT) or thiophene (T) as donor units, two D–A conjugated polymers (abbr. as PB and PT respectively) are synthesized via Stille coupling reaction. The incorporation of alkoxy groups with quinoxaline moiety is found to be beneficial to both the enhanced solubility and the maintained coplanarity of the backbone due to strong S⋯O attractive interaction. UV–vis absorption and XRD characterization results indicate that the presence of planar AQx moiety could lead to well-ordered packing in solid state, and PB bearing planar BDT electron-donating subunit exhibits more intensified molecular self-organization. Both PB and PT possess deep HOMO energy level of −5.4∼−5.5 eV, and PB-based photovoltaic devices show maximum PCE value of 1.20% (Voc = 0.78 V, Jsc = 3.58 mA cm−2, FF = 0.43) under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW cm−2.