Morphology determination of functional poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene]/poly[oxa-1,4-phenylene-1,2-(1-cyanovinylene)-2-methoxy,5-(3,7-dimethyloctyloxy)-1,4-phenylene-1,2-(2-cyanovinylene)-1,4-phenylene] blends as used for all-polymer solar cells