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

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Physics

Background:

• Organic semiconductors (OSCs) readily form metastable polymorphs, but achieving stable, reversible transformations has been challenging due to weak intermolecular forces and poor phase control.
• Existing OSCs lack the stability and homogeneity required for reliable applications involving external stimuli-induced phase transitions.

Purpose of the Study:

• To fabricate a stable, thermally reversible polymorph in organic semiconductors.
• To investigate the potential of this polymorph for applications in nonvolatile multivalue memory devices.

Main Methods:

• Fabrication of a single crystalline 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene polymorph on low molecular weight poly(methyl methacrylate) using solvent vapor annealing.
• Characterization using in situ grazing incident wide angle X-ray scattering (GIWAXS).
• Computational analysis including visualization for electronic and structural simulations and density functional theory (DFT) calculations.

Main Results:

• A novel OSC polymorph was created where molecules exhibit a slight tilt towards the substrate, increasing resistivity.
• The polymorph demonstrates a stable, reversible resistivity change of 5.5 orders of magnitude with thermal cycling and hysteresis.
• Diverse resistivities near room temperature were achieved by varying cycling temperatures, suitable for multivalue memory applications.

Conclusions:

• Molecular tilt is the key factor governing charge transport and reversible phase transformations in this OSC polymorph.
• The fabricated material offers stable, tunable resistivity, paving the way for advanced nonvolatile memory technologies.
• A homogeneous, single-crystalline phase is maintained at each temperature during cycling, ensuring reliable performance.