Donor-acceptor semiconducting polymers containing benzodithiophene and benzodifuran have been synthesized and tested in bulk heterojunction solar cells with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The solar cells were fabricated using a conventional device structure ITO/PEDOT:PSS/polymer:PCBM/Ca/Al. The solvent employed for solution processing and concentration of blend were optimized. Tapping mode atomic force microscopy (TMAFM) and transmission electron microscopy (TEM) analysis indicated an improved phase separation between the polymer and PCBM which resulted in an increased PCE upon additive used. The highest power conversion efficiency (PCE) of 5.55% obtained was the polymer containing benzo[1,2-b:4,5-b']difuran with furan substituent as donor unit and furan-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione as acceptor unit.