http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7933 Scanning transmission X-ray microscopy has been used to quantitatively map the composition of P3HT:PCBM blend films in the vicinity of PCBM crystals formed during annealing at 140°C. The observed PCBM concentration profiles around these crystals have been fitted to Fick’s second law of diffusion and the diffusion constant found to be 2.5 x 10⁻¹⁴ m² s⁻¹. The PCBM concentration at the crystal boundary was found to be 19% (v/v) and is interpreted, together with the annealing temperature of 140°C, as a point on the bimodal line of the composition-temperature phase diagram. The diffusion ofPCBM through P3HT is observed to be bulk-dominated, in contrast to the surface/interface-dominated diffusion observed in MDMO-PPV:PCBM blend films by Yang et al. 2011-06-23T23:31:45.967Z ]]>