Charge transport in twisted organic semiconductor crystals of modulated pitch

Yongfan Yang, Lygia Silva de Moraes, Christian Ruzie, Guillaume Schweicher, Yves Henri Geerts, Alan Kennedy, RV Kohn, Hengyu Zhou, Stephanie S Lee, Bart Kahr, Alexander Shtukenberg

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)
13 Downloads (Pure)

Abstract

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 monocomponent 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 possible a correlation of twist strength with carrier mobility. Films are 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 are five times higher when the crystals are grown with the smallest pitches (most twisted), compared to those with the largest pitches, along the fiber elongation direction. A tenfold increase is observed along the perpendicular direction. Simulation of electrical potential based on scanning electron microscopy images 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 permit better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.
Original languageEnglish
Article number2203842
Number of pages20
JournalAdvanced Materials
Volume34
Issue number38
Early online date19 Aug 2022
DOIs
Publication statusPublished - 22 Sept 2022

Keywords

  • organic semiconductor
  • twisting morphology
  • charge transport
  • crystallite organization

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