Crystal size

The size of organic semiconductor crystals can be controlled using a solution shear system based on inorganic polymer micropillars

October 30, 2018

(Nanowerk News) Recently, solution processable organic semiconductors have been highlighted for their potential application in printed electronics, becoming a feasible technique for fabricating large area flexible thin films at low cost.

The field-effect mobility of organic small-molecule semiconductors depends on crystallinity, crystal orientation, and crystal size. A variety of solution-based coating techniques, such as inkjet printing, dip coating, and solution shear have been developed to control crystallinity and crystal orientation, but a development method Techniques to increase the size of organic semiconductor crystals are still needed.

To overcome this problem, the KAIST research team developed a solution shear system based on inorganic polymer micropillars to increase the crystal size of an organic semiconductor with the size of the pillars. By using this technique, the crystallization process of organic semiconductors can be precisely controlled, and hence a large area organic semiconductor thin film with controlled crystallinity can be made (Advanced materials, “Solution shear based on inorganic polymer micropillars of thin layers of large surface organic semiconductors with a crystal size dependent on the size of the pillar”).

Chemical structure of inorganic polymer (AHPCS) and method of manufacturing a microstructured AHPCS shear blade. (Image: KAIST)

A variety of solution-based coating techniques cannot control the fluid flow of solutions appropriately, so the solvent will randomly evaporate on the substrate, which has difficulty in manufacturing thin films. organic semiconductors with large crystal size.

The research team integrated inorganic polymer microstructures into the solution shear blade to address this problem. The inorganic polymer can easily be microstructured via conventional molding techniques, has high mechanical durability and resistance to organic solvents.

Using the inorganic polymer-based microstructure slide, the research team controlled the size of organic small-molecule semiconductors by adjusting the shape and dimensions of the microstructure. The microstructures in the blade induce the regions of sharp curvature in the meniscus line that has formed between the shear blade and the substrate, and therefore nucleation and crystal growth can be regulated.

Therefore, the research team made an organic semiconductor thin film with large crystals, which increases the mobility of the field effect.

The research team also demonstrated a process of solution shearing on a curved surface using an inorganic polymer-based flexible shear blade, which extends the applicability of solution shear.

Professor Park said, “Our new solution shear system can control the crystallization process precisely during solvent evaporation. He added, “This technique adds another key parameter that can be used to adjust the property of thin films and opens up a wide variety of new applications.

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