Low-bandgap pi-conjugated polymers that consist of alkyl thiophene/alkoxy phenylene and 2,3-diphenylthieno[3,4-b]pyrazine units have been prepared in high yields by a Sonogashira polycondensation. The copolymers are characterized by NMR, IR, UV, GPC, and elemental analysis. Thin films of the polymers P1, P2, and P3 exhibit an optical bandgap, of approximate to 1.57-1.60 eV. Under simulated AM 1.5 conditions P2/PCBM devices on polyester foil provide a short circuit current of I-SC = 10.72 mA . cm(-2), an open circuit voltage of V-oc = 0.67 V, and a power conversion efficiency of 2.37%.