Polymer solar cells (PSCs) having donor-acceptor bulk heterojunction (BHJ) is one of the convenient solution for meeting the world's current energy demands. Herein, we report the fabrication and characterization of bulk heterojunction solar cells using the blend of PCDTBT and PC70BM in 1,2-dichlorobenzene (o-DCB) with the device structure of ITO/PEDOT:PSS/PCDTBT:PC70BM/BCP/Al. The effect of dipolar dopants such as dimethylsulfoxide (DMSO) and dimethylformamide (DMF) and common dopants such as 1,8-diiodooctane (DIO) and 1,8-octanedithiol (OT) as processing additive solvents on the performance of PCDTBT:PC70BM based BHJ solar cells were studied and compared with the device without additive in terms of current density, open-circuit voltage and power conversion efficiency (PCE). The addition of additives significantly leads to the aggregation of PCDTBT molecule, thereby controlling the morphology of PCDTBT:PC70BM films enhancing an efficient exciton dissociation and charge transport. Among the additives used the device containing DMSO showed the best performance with a PCE of 7.3%.