Method for Forming Polymer Thin Films Using Non-Solvent Floating

Method for Forming High-Mobility Polythiophene Semiconductor Thin Films Using Non-Solvent Diffusion Crystallization

This technology utilizes a Non-Solvent Floating (FNS) process. Polythiophene is dissolved in a dense chlorinated good solvent, such as chloroform, and placed at the bottom. A non-solvent, such as acetonitrile or dimethyl sulfoxide, is floated on top to create a two-phase solution. A substrate is then dipped and withdrawn to obtain the thin film. The upper non-solvent slowly diffuses into the lower solution, inducing polymer crystallization.

While organic field-effect transistors are gaining attention for flexible and wearable electronics, polymer thin films produced via solution processes often suffer from low crystallinity, which limits charge transport performance. Existing printing processes, such as dip coating, have limitations in precisely controlling the crystal growth and nanostructure of conjugated polymers.

This technology controls diffusion rates and P3HT nanofibril growth by adjusting the Hansen solubility parameter difference (5.5–7.7) between the good solvent and non-solvent, as well as the aging time (3–12 hours). Thin film thickness can also be adjusted via the non-solvent's boiling point. This results in semiconductor polymer thin films with improved crystallinity and field-effect mobility on glass, silicon, or plastic substrates. It can be applied to flexible display driving circuits and printed organic transistor manufacturing, enabling high-performance devices through low-cost solution processing.

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Key Features:

• Dissolving polythiophene in a dense chlorinated good solvent—either chloroform, chlorobenzene, or dichlorobenzene—and placing it at the bottom
• Placing a non-solvent, such as acetonitrile or dimethyl sulfoxide, on the solution surface to form a two-phase system through phase separation, then dipping and withdrawing a substrate
• Setting the Hansen solubility parameter difference between the non-solvent and good solvent to 5.5–7.7, where a larger difference delays diffusion and crystallization
• Aging the two-phase solution system for 3–12 hours to grow poly(3-hexylthiophene) nanofibrils based on the aging time

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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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