A novel low-bandgap polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H- cyclopenta[2,1-b;3,4-b́]-dithioplene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) which is the first candidate of a new class of copolymers, was presented. The polymer shows improved charge transport properties as well as fitting electronic energy levels and good processability. The bulk heterojunction (BHJ) utilizing a conjugated polymer and a fullerene derivative for ultrafast charge transfer at the donor/acceptor interface with a photoinduced charge generation is regarded as the ideal system for photovoltaic applications. An important prerequisite for efficient photovoltaic operation is good transport properties of the individual composites of the blend. The phenomenon of ambipolar transport in pristine conjugated polymers has been reported for various conjugated polymers.