Organic photovoltaics(OPVs)utilizing conjugated polymers as donor materials have received an increasing attention in the research community due to their potential advantages,such as low cost,flexibility,ease of processing and so on.[1-3] However,their highest power conversion efficiency,which reached up to 10.6%,[3] always lagged behind that of inorganic solar cells.Therefore,it is our expectation that this work could provide theoretical guideline for the further optimization and design of organic copolymer donor materials.In this manuscript,the 3D geometries,electronic structures and optical properties of 1 and 2,which are composed of the same dithienosilole(DTS)donor moiety and different acceptor moieties(benzothiadiazole(BT)unit for 1,and bithiopheneimide(BTI)unit for 2),were systematically characterized.Based on these results,we designed a new donor-acceptor copolymer 3 which was theoretically investigated within the same method.Moreover,the rates of charge transfer(CT)and charge recombination(CR)for all donor/PC71BM heterojunctions have also been characterized using Marcus theory.All the results indicate that 3 will be a promising donor material for high performance of the OPV due to its high Jsc and Voc,fast CT rate and slow CR rate.