Insight into crystallization process of rubrene by binary solvent mixtures

Abstract

Solution-processing rubrene crystals were fabricated by blending an amount of high-boiling-point solvent into a dilute solution of rubrene in chloroform. The crystallization processes were investigated by the analysis of morphology and crystalline structures. The trajectory to the dendrite-like crystals grown was clearly observed by controlling the ratio of the binary solvent mixtures. Tremendous, compact dendrite-like crystals and sheet-like crystals were obtained by further decreasing the evaporation rate through a drop-casting method. The results indicated that the crystalline process was significantly influenced by the binary solvent ratio and the fabrication method. The crystallinity of rubrene films could be tuned from disorder, with pure chloroform solvent, to high crystallinity, with binary solvent mixtures. The formation mechanism of rubrene crystals was proposed as a competition between the impetus of slow evaporation by high-boiling-point solvent and the self-assembly force of rubrene molecules to the crystal. These results, which exhibit the concrete possibility of growing crystalline and ordered rubrene thin films, open pathways to organic thin film technology and devices.