We have investigated the bifunctional properties using ambipolar low band gap conjugated copolymer in organic bulk-heterojunction (BHJ) solar cells. Ambipolar copolymer, poly[3,6-dithien-2-yl-2,5-di(2-decyltetradecanyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-5',5 ''-diyl-alt-benzo-2,1,3-thiadiazol-4,7-diyl] (PDT-DPP-alt-BTZ), successfully works as the bifunctional material acting as both donor or acceptor. However, because of fast recombination nature and broken charge balance of hole and electron, solar cell performances were significantly limited. The results indicate that having distinct role of each component might be better for the high performance BHJ solar cells rather than bifunctional property based on good charge transport properties of both hole and electrons. (C) 2011 Elsevier B. V. All rights reserved.