Understanding the grain-growth mechanism of high-performance organic semiconducting diphenyl-dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene molecules

Abstract

We report here our investigation on the grain-growth mechanism of diphenyl-dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene (DPh-DBTTT), which was recently published as a high-performance organic semiconductor. Atomic force microscopy revealed that unconventional needle-like structures grew on the surface of DPh-DBTTT thin films, and these structures became more dominant as the film thickness increased and the deposited film's surface temperature decreased. In combination with the crystal structure simulations, the grazing-incidence wide-angle x-ray scattering data indicated that the DPh-DBTTT molecules preferred an edge-on orientation near the interface between the substrate and DPh-DBTTT thin film, while the needle-like structures consisted of a face-on arrangement of the molecules. We suggest that this structural change originates from the large step-edge energy barrier of the DPh-DBTTT molecules. Our findings would be highly valuable to the design of new high-performance organic semiconducting materials and optimization of the conditions of thin-film deposition.