Polymer blend aging is a crucial processing step leading to improved performance of poly((4,8-bis (octyloxy) benzo (1,2-b:4,5-b') dithiophene-2,6-diyl) (2-((dodecyloxy) carbonyl) thieno(3,4-b) thiophenediyl)):[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunction (BHJ) solar cells. The optimum aging time of the polymer mixture is found by storing the completely dissolved blend solution of the donor and acceptor for certain periods of time before device fabrication. Increased aging times improves microphase separation morphology and the and bicontinuous interpenetrating network, as proven by close inspection of the polymer mixture. As a consequence of such a synergistic increase, the resulting solar cells show an enhancement in short-circuit current. Power conversion efficiencies as high as 5.16% are found in devices fabricated with aged blends, which is a significant improvement exceeding 19% over the efficiency of 4.32% obtained in devices without polymer blend solution aging. This simple procedure has the potential to boost the maximum efficiencies exhibited by this technology.