Method for Improving Structural and Electrical Properties of Polythiophene Thin Films Using Sequential Solvent Coating

Process for Improving Mobility of Polythiophene Thin Films via Binary Solvent Spin-Casting without Thermal Annealing

This technology involves post-processing a pre-formed P3HT polythiophene thin film, created via spin-coating, by spin-casting a binary solvent mixture of methylene chloride (a marginal solvent) and toluene (a good solvent) in a 2:1 ratio. By simply adjusting solubility to enhance molecular alignment and crystallinity, gold electrodes are then deposited to construct a field-effect transistor.

Conductive polymer thin films produced through solution processes often suffer from low crystallinity, which hinders inter-chain charge transport and reduces charge mobility. Conventional methods to address this, such as thermal annealing or solvent vapor annealing, are limited by long processing times and the risk of damaging the thin film.

This technology induces polymer chain rearrangement by exposing the thin film to a mixed solvent that partially dissolves it, thereby increasing crystallinity and charge mobility in a short time without high-temperature heat treatment. After treatment, the thin film thickness decreases from 44.5 nm to 40.4 nm, while achieving an average field-effect mobility of 3.5×10^-3 cm2/Vs. It can be applied to organic thin-film transistor manufacturing on heat-sensitive flexible substrates, ensuring device performance even in low-temperature process lines.

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Key Features:

• Spin-coating a 10 mg/mL P3HT solution dissolved in anhydrous chlorobenzene onto a gate dielectric substrate to form a 44.5 nm thick thin film
• Spin-casting a binary solvent mixture of methylene chloride and toluene in a 2:1 volume ratio onto the polythiophene thin film for direct exposure
• Depositing gold electrodes onto the solvent-treated polythiophene thin film through a shadow mask
• A non-thermal treatment method that reduces thin film thickness to 40.4 nm and achieves an average transistor field-effect mobility of 3.5×10^-3 cm2/Vs

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This invention was developed with support from the Ministry of Science, ICT and Future Planning for the development of high-performance organic electronic devices using the self-assembly of π-electron molecules.

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