Increased order and improved hole mobility in MEH-PPV thin films by removing shortest chains

Abstract

The effect of polydispersity on morphology and charge transport in MEH-PPV drop-cast films was investigated using grazing incidence X-ray diffraction and time-of-flight. Removing short chain segments promoted the capability of crystallization resulting in higher hole mobility and non-dispersive transport down to lower temperatures. The slope for the Poole–Frenkel relationship at 298 K was increased, and its change with temperature decreased, indicating reduced spatial inhomogeneity. Analysis using Bässler’s Gaussian disorder model, found minimal impact on energy disorder and infinite temperature zero field mobility. A good fit for hopping site separation and spatial disorder was only possible for the lower polydispersity device, suggesting that the lower polydispersity films have less mesoscopic inhomogeneity.