Understanding grain growth mechanism of high-performance organic semiconducting DPh-DBTTT molecule

Abstract: We report here our investigations of 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. By atomic force microscopy, it is detected that unconventional needle-like structures are grown on the surface of DPh-DBTTT thin films and theses structures are more dominant as the film- thickness increases and the film-deposited surface temperature decreases. In combination with the crystal structure simulations, the grazing incidence wide angle x-ray scattering data indicate that DPh-DBTTT molecules prefer an edge-on orientation near the interface between the substrate and DPh-DBTTT thin film, while the needle-like structures consist of a face-on arrangement of the molecules. We anticipate that this structural change originates from the large step-edge energy barrier (0.47 eV) of DPh-DBTTT molecules. Our findings would be highly precious to designing new high performance organic semiconducting materials and optimizing the condition of thin film deposition process.