Synthesis and photovoltaic properties of conjugated copolymers bearing planar acenaphtho[1,2-b]quinoxaline moiety with deep HOMO level

A series of alternating copolymers (PC-AQx, PT-DTAQx, PC-DTAQx, PF-DTAQx, and PBDT-DT AQx) bearing novel planar acenaphtho[1,2-b]quinoxaline (AQx) or 8,11-di(thiophen- 2-yl)acenaphtho[1,2-b]quinoxaline (DTAQx)-acceptor cores have been synthesized via Suzuki or Stille coupling reactions. UV-vis absorption and GIXRD characterization results indicated that the presence of planar DTAQx unit is favorable for the promotion of well-ordered interchain packing in the solid state, and the incorporation of planar electron-donating benzo[1,2-b: 4,5-b0]-dithiophene (BDT) moiety would be propitious to the molecular self-organization. Electrochemical measurement results suggested that four copolymers possess deep HOMO energy level of -5.5 ∼-5.6 eV. The polymer solar cell with structure of ITO/PEDOT: PSS(30 nm)/polymer: PCBM (60 nm)/Bphen(10 nm)/Ag(100 nm) exhibited the highest V∞ of 0.84 V with PF-DTAQx as p-type polymer, while the best power conversion efficiency (PCE) of 0.9 % was obtained using a blend of PBDT-DTAQx and PCBM(1: 4) as active layer.