Reversible Polymorphic Transition and Hysteresis-Driven Phase Selectivity in Single-Crystalline C8-BTBT Rods

Min Woo Kim, Sooncheol Kwon, Jehan Kim, Changhoon Lee, Ina Park, Ji Hoon Shim, Il Seok Jeong, Yong Ryun Jo, Byoungwook Park, Joo Hyung Lee, Kwanghee Lee, Bong Joong Kim

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Organic semiconductors (OSCs) are highly susceptible to the formation of metastable polymorphs that are often transformed by external stimuli. However, thermally reversible transformations in OSCs with stability have not been achieved due to weak van der Waals forces, and poor phase homogeneity and crystallinity. Here, a polymorph of a single crystalline 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothio-phene rod on a low molecular weight poly(methyl methacrylate) (≈120k) that limits crystal coarsening during solvent vapor annealing is fabricated. Molecules in the polymorph lie down slightly toward the substrate compared to the equilibrium state, inducing an order of greater resistivity. During thermal cycling, the polymorph exhibits a reversible change in resistivity by 5.5 orders with hysteresis; this transition is stable toward bias and thermal cycling. Remarkably, varying cycling temperatures leads to diverse resistivities near room temperature, important for nonvolatile multivalue memories. These trends persist in the carrier mobility and on/off ratio of the polymorph field-effect transistor. A combination of in situ grazing incident wide angle X-ray scattering analyses, visualization for electronic and structural analysis simulations, and density functional theory calculations reveals that molecular tilt governs the charge transport characteristics; the polymorph transforms as molecules tilt, and thereby, only a homogeneous single-crystalline phase appears at each temperature.

Original languageEnglish
Article number1906109
JournalSmall
Volume16
Issue number3
DOIs
StatePublished - 1 Jan 2020

Keywords

  • 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothio-phene (C8-BTBT)
  • nonvolatile multivalue memory
  • organic semiconductors
  • polymorph
  • single crystal

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