Ultrasonication-mediated self-assembly method for polythiophene thin films via controlled residual solvent evaporation

Method for Fabricating Highly Aligned Polythiophene Thin Films via Ultrasonic Post-Treatment in Low-Boiling-Point Solvent Vapor

This technology is a self-assembly method that involves subjecting a wet polythiophene thin film coated on a substrate to ultrasonic treatment in a sealed container filled with solvent vapor, followed by a drying process. The solvent vapor is generated by placing a separate solvent with a lower boiling point than the coating solvent into the sealed container and allowing it to evaporate.

Conjugated polymer thin films produced via solution processing have historically faced limitations in charge transport due to structural defects and irregular chain alignment. Existing methods to address this, such as thermal or solvent annealing, typically require at least 30 minutes and are often limited to specific materials.

This technology utilizes ultrasonic treatment for several tens of seconds on a chlorobenzene-coated thin film under a methylene chloride vapor pressure of 34–55 kPa. This enhances the interaction between the polymer and the solvent and controls the evaporation rate of residual solvent, thereby untangling polymer chains and promoting reorganization. Applicable to the active layer formation process of organic field-effect transistors, this method enables high production efficiency by boosting charge mobility through a post-treatment process lasting only 1–2 minutes, eliminating the need for long-duration annealing.

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Key Features:

• Forming a polythiophene thin film by spin-coating a poly(3-hexylthiophene) solution in a chlorobenzene solvent onto a substrate
• Subjecting the wet polythiophene thin film on the substrate to ultrasonic treatment in the presence of solvent vapor, followed by drying
• Creating a solvent vapor environment by introducing and evaporating a low-boiling-point solvent—with a lower boiling point than the coating solvent—into a sealed container housing the thin film
• Using chlorobenzene as the coating solvent and methylene chloride as the low-boiling-point solvent, and performing ultrasonic treatment at 42 kHz for 60–90 seconds under a solvent vapor pressure of 34–55 kPa

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This invention was developed with support from the Ministry of Education for the development of high-performance gas sensors based on phase-separated MOF/conjugated polymer hybrid thin films.

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