Uniform and Reliable Dip-Coated Conjugated Polymers for Organic Transistors as Obtained by Solvent Vapor Annealing

Dip-coating is a useful technique to prepare a thin film of an organic semiconductor; however, achieving homogeneous film properties is sometimes challenging because of the experimental configuration of dip-coating under the strong influence of solvent vapor. In this work, we studied the effect of solvent vapor on dip-coated film uniformity during the dip-coating process. We demonstrate that solvent vapor released from the solution reservoir strongly affects film crystallinity at each relative position in the vertical direction. We also propose a novel method that utilizes the inevitable solvent vapor to anneal dip-coated films by adding some residual time during the dip-coating process, which results in highly uniform and crystalline films. Field-effect transistors constructed using films prepared by this dip-coating technique show a uniform, reliable field effect. This work provides a general principle and systematic guideline to prepare highly crystalline and uniform films of organic semiconductors via dip-coating. This method substantially reduces operational complexity in the dip-coating process, enables easy operation, and thus meets the demands of being low-cost for large-area fabrication without a postprocess. We therefore expect this method to be highly meaningful for the fabrication of organic electronics as well as for the assembly of other materials via solution processes.