• donor–acceptor (D–A) conjugated copolymers;
  • low bandgap;
  • near-infrared absorption;
  • polymer solar cells;
  • tetracyclic acceptor units
Thumbnail image of graphical abstract

Two electron-deficient tetracyclic monomers, 6,9-dibromo-7,8-bis(octyloxy)-11H-indeno[2,1-b] quinoxalin-11-one (M1) and 1,3-bis(5′-bromo-4′-hexylthiophen-2-yl)-9H-indeno[1,2-b]thieno[3,4-e]pyrazin-9-one (M2), are synthesized through condensation of ninhydrin with aromatic diamines in good yields. Copolymerization of M1 with thiophene (Th) and dithieno[3,2-b:2′,3′-d]silole (DTS), and M2 with DTS affords three new D–A conjugated copolymers, P1P3, respectively. The optical, electrochemical, and photovoltaic properties of P1–P3 are investigated. P3 exhibits a broad absorption (300–1100 nm) and a low bandgap of 1.24 eV. Solar cells based on P3/[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) blends afford a power conversion efficiency of 1.93% and a very broad spectral response (300–1020 nm).