Manipulating the Crystallization of Methanofullerene Thin Films with Polymer Additives

Trace amount (1% to 5%) of polymers [polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(3-hexylthiophene) (P3HT)] are utilized as additives to manipulate the cold crystallization of [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) thin films. Highly crystalline PCBM films made up of well-connected domains and isolated spherulites with tunable size are produced by adjusting the type, molecular weight, and amount of polymer additives. In the nucleation stage, the polymer additives are demonstrated to have a depressing effect on PCBM nucleation. In the growth stage, we suggest that the PCBM growth rate is determined by PCBM molecular diffusion, which is demonstrated to have close correlations with the molecular mobility and crystallinity of the polymer.