Morphology of composites of semiconducting polymers mixed with C60

The morphology of polymer composite films of poly[2-methoxy,5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and buckminsterfullerene (C60) has been systematically studied over a wide range of concentrations (10–81 wt.% of C60) using transmission electron microscopy (TEM). Phase separation in films prepared from solutions in 1,2-dichlorobenzene results in nano-scale crystallites of C60 (dimensions approximately 10 nm or even less), embedded in amorphous MEH-PPV. A very fine bicontinuous network structure forms for MEH-PPV:C60 compositions near 1:1 by weight. This homogeneous nanostructured network morphology in the polymer composites confirms the formation of a bulk heterojunction material as inferred from the improved optical and electronic properties of these composites in device applications.