Article révisé par les pairs
Résumé : Many molecular crystals (approximately one third) grow as twisted helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance charge transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a mono-component organic semiconductor 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT) that forms twisted crystals with varied helicoidal pitches and makes a possible correlation with carrier mobility. These films were analyzed by X-ray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field effect transistors were five times higher when the crystals were grown with the smallest pitches (most twisted) compared to those with the largest pitches along the fiber elongation direction. A ten-fold increase was observed along the perpendicular direction. Simulation of electrical potential based on scanning electron micrographs and density functional theory suggests that the twisting-enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permits better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.

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