Polymers using 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI) with high planarity were synthesized and utilized for the photovoltaics. Push-pull types of conjugated polymers (PTTICN, PTTICNR and PTTIFR) containing TTI as electron pushing unit and 2-pyriminecarbonitrile or 2-fluoropyrimidine as electron pulling unit were synthesized. We designed pyrimidine derivatives with strong electron-withdrawing group (C N or fluorine) for the generation of strong electron pulling property. By the combination with the electron pushing unit, the pyrimidines with strong electron pulling units will provide low highest occupied molecular orbital (HOMO) energy levels for higher open-circuit voltages (V-OC). For the syntheses of the polymers, the electron pushing and the electron pulling units were combined by Stille coupling reaction with Pd(0)-catalyst. The polymers of PTTICN and PTTICNR with CN unit show higher V-OC than the polymer with fluorine unit. The device comprising PTTICNR and PCBM (1:4) with diiodooctane (DIO) additive showed a V-OC of 0.82 V, a J(SC) of 6.38 mA/cm(2), and a fill factor (FF) of 0.53, giving a power conversion efficiency of 2.81%. (C) 2015 Elsevier Ltd. All rights reserved.