Photovoltaic properties of solution-processed semiconducting polymer blends have been studied. It is demonstrated that photoinduced charge transfer occurs in binary mixtures of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV). Further, it is shown that the photovoltaic performance is improved by a thermal treatment which alters the morphology of the photoactive layer. The temperature necessary to achieve the enhanced performance is related to transition temperatures of the pure polymers. Device optimization yields solar cells with a power conversion efficiency of 0.75% under standard test conditions (AM 1.5, 1000 W/m2).