Alternating small band gap it-conjugated polymers consisting of alkylated cyclopentadithiophene or dithienopyrrole units linked via ethynylene bonds to 2,3-diphenylthieno[3,4-blpyrazine or 2,1, 3-benzothiadiazole have been prepared in high yields by Sonogashira condensation polymerization. The copolymers were characterized by NMR, GPC, UV-vis, and cyclic voltammetry. In thin films these polymers exhibit an optical band gap of similar to 1.46-1.72 eV. In bulk heterojunction solar cells with PCBM as an acceptor these donor polymers provide estimated power conversion efficiencies of 1.34-1.74%. Because of the ethynylene bonds, the polymers lead to the solar cells with a relatively high open circuit voltage (0.72-0.82 V) in relation to the reduced optical band gap, which helps in reducing energy losses. (C) 2010 Elsevier B.V. All rights reserved.