Novel conjugated polymers incorporating thieno[3,4-c][1,2,5]-thiadiazole (TTD) and 2,1,3-benzothiadiazole (BT) were synthesized. The TTD-BT copolymers displayed broad absorption bands in visible-near-infrared regions with optical band gaps of 1.1-1.2 eV. The HOMO energy levels were lower than those of TTD-oligothiophene alternating copolymers due to the electron-deficient nature of the BT unit. The photovoltaic device consisting of the polymer and a fullerene derivative ([70]PCBM) showed power conversion efficiencies of 0.01-0.08% under simulated AM 1.5G irradiation of 100 mW cm(-2).