A series of conjugated polymers were designed and synthesized via the alternating copolymerization of the electron-donating monomer 2,7-carbazole and electron-accepting monomers of naphthalene diimide (NDI), dithienyl-naphthalene diimide (DTNDI), perylene diimide (PDI) and dithienyl-perylene diimide (DTPDI), respectively. The obtained four copolymers showed good thermal stability as well as broad absorptions in visible region and narrow optical band gaps (1.86-1.59 eV). Through cyclic voltammetry (CV) measuremnts, it was found that all copolymers were n-type semiconductive materials. The copolymers' photovoltaic properties were evaluated when the blends of poly(3-hexyl thiophene) (P3HT) and copolymers were used as the active layers of polymer solar cells (PSCs): among four copolymers, the copolymer alternating 2,7-carbazole and DTPDI units (PCDTPDI) exhibited the best photovoltaic performance with an open-circuit voltage (V-oc) of 0.48 V. a short circuit current density (J(sc)) of 3.40 mA/cm(2), fill factor (FF) of 0.42, and a power conversion efficiency (PCE) of 0.68%. (C) 2012 Elsevier B.V. All rights reserved.