Recently, we have used terthiophene side chain to modify benzo[1,2-b:4,5-b']dithiophene (BDT) to form novel building block for BDT polymers. In this paper, this building block is used to copolymerized with thieno[3,4-c]pyrrole-4,6-dione (TPD) and thieno[3,4-b]thiophene (TT). This building block and TPD- or TT-based polymers (P1 and P3) show high open circuit voltage (V-OC) (ca. 0.9-0.95 V) and low energy loss (E-g-eV(OC)) in solar cells devices compared with similar polymers without bulky side chain. We further introduce thiophene pi bridge into these polymers backbone to form two other polymers (P2 and P4). We find this thiophene pi bridge does contribute to this bulky side chained benzodithiophene polymer photovoltaic performances, especially for power conversion efficiencies (PCEs). The polymer solar cells (PSCs) performances are moderate in this article due to the serious aggregation in the PSCs active layer. (C) 2015 Wiley Periodicals, Inc.