Novel Patterning Method for Nanomaterials and Its Application to Flexible Organic Light-Emitting Diodes.

We present a simple, low-cost, and scalable method to form various patterns of nanomaterials with different dimensions and shapes using capillary and centrifugal forces. The desired patterns were formed on the surfaces of poly(dimethylsiloxane) (PDMS) stamps, and the PDMS stamps were conformally contacted with the surfaces of flexible polymer substrates. Solutions of nanomaterials, such as metal nanowires and nanoparticles, were then drop-casted at one open end of the microchannels formed at the interface of the polymer substrate and PDMS stamp. The nanomaterial solutions penetrated the microchannels due to capillary force interactions between the surfaces and the fluid. The solvents of the nanomaterial solutions exfiltrated from the entrance of microchannels because of the coffee ring effect. Then, the solvent remaining in the microchannels was discharged by applying a centrifugal force by spinning the polymer substrate/PDMS stamp system. Because of the synergistic effect of the capillary force, coffee ring effect, and centrifugal force, uniform patterns of the nanomaterials with clearly defined edges were formed for a variety of pattern shapes and substrates. Furthermore, the direct patterning approach resulted in a significant reduction in the amount of wasted materials. Finally, flexible organic light-emitting diodes were successfully fabricated on the finely patterned nanowire electrodes.