Method for Forming Semiconductor Polymer Thin Films Using Spin Coating

Semiconductor Polymer Thin Films with Enhanced Uniformity and Crystallinity via Ultra-Short Spin Coating

This technology is a method for forming semiconductor polymer thin films by spin-coating a P3HT semiconductor polymer solution onto a substrate, limiting the spinning time to approximately 3 seconds. This allows the coating to finish before the thin film fully solidifies, followed by the evaporation of residual solvent in a vacuum. The residual solvent induces a slow growth process that facilitates the self-organization of polymer chains, resulting in a thin film with a nano-fibrillar network structure.

While spin coating is effective for creating uniform thin films, it often results in low crystallinity, whereas drop casting offers high crystallinity but poor uniformity. Furthermore, most processes simply set spinning times between 40 and 180 seconds without investigating the impact of spinning duration on organic field-effect transistor performance. Additionally, these methods typically require post-processing steps such as thermal or solvent annealing to improve performance.

This technology achieves both the uniformity of spin coating and the high crystallinity of drop casting by spin-coating a chlorobenzene-based 1 wt% P3HT solution at 1500 rpm for just 3 seconds. It forms a smooth thin film with a surface roughness of 3–4.5 nm without the need for additional annealing. Transistors using this thin film as an active layer demonstrate an average field-effect mobility of 1.4×10-2 cm2/Vs and low interface trap density with high reproducibility. This technology can be applied to the manufacturing of active layers for flexible printed electronics and organic integrated circuits, reducing process steps while minimizing performance variations between devices.

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Key Features:

• A method of spin-coating a semiconductor polymer solution onto a substrate, where P3HT with a molecular weight of 20–30 kDa is dissolved at a 1 wt% concentration in chlorobenzene (boiling point 131°C).
• A process of spin-coating at 1500 rpm for 3 seconds, completing the coating before the point of full solidification, which occurs 10 seconds after the start of spinning.
• A configuration that involves evaporating residual solvent from the thin film under vacuum after coating, without performing separate post-processing such as thermal or solvent annealing.
• A conductive organic active layer for organic field-effect transistors that forms a nano-fibrillar network structure and has an average root-mean-square surface roughness of 3–4.5 nm.

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This invention was developed with support from the Ministry of Education for the analysis of charge transport mechanisms in π-electron molecular-based n-dimensional nanostructures.

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