Single Crystallization of an Organic Semiconductor in Hydrogel Capillaries for Transferring onto Substrates

We propose a single crystallization and transfer technique of organic semiconductors using a hydrogel capillary (gel capillary crystallization method). Single crystals of the C8-BTBT thienoacene-based organic semiconductor were prepared by crystal growth in a glass capillary filled with C8-BTBT solution in the supersaturated condition. By adjusting the concentration and temperature, selective nucleation was induced only at the air/liquid interface in the capillary. From the multiple nuclei generated at the interface, polycrystalline C8-BTBT formed near the interface. Subsequent continuous crystal growth in the capillary allowed the polycrystals to transform to a single crystal, because crystal growth was regulated along one direction in the capillary. Single-crystal growth was also induced at the air–liquid interface in an agarose gel capillary, which was made by piercing with a plastic sheet, similar to that in the glass capillary. After formation of a single crystal in the gel capillary, the single crystal was removed from the capillary and transferred onto a solid substrate by dissolution of the capillary with NaI solution.