Effect of surface morphology of slot-die heads on roll-to-roll coatings of fine PEDOT:PSS stripes

One of key components in the roll-to-roll slot-die coating system for the fabrication of fine stripes using poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) aqueous solution is the slot-die head with a shim and meniscus guide embedded together. We have fabricated the meniscus guide with 150-μm-wide μ-tips using an easily processable film for potential application in solution-based organic light-emitting diodes (OLEDs) displays. However, the success or failure of fine stripe coatings is shown to depend sensitively on the surface morphology of slot-die heads. We have investigated the coating behaviors of two slot-die heads with different surface morphology by changing the configurations of the shim and meniscus guide. Using the slot-die head with good surface roughness but local scratches, it is not feasible to fabricate 100 stripes within the effective coating width of 150 mm. We have demonstrated through computational fluid dynamics (CFD) simulations that the continuous fluid flow is interrupted and thus the fluid velocity is reduced in the presence of scratches, a phenomenon related to coating defects (line breakup and merging). Using the slot-die head with uniformly rough surface but no scratches, however, we can fabricate 150 stripes without defects by reducing the μ-tip length and the shim thickness. It is observed that the inter-stripe width and thickness uniformities are degraded with increasing number of stripes due to the degraded uniformity of the pressure distribution inside the cavity (ink distribution chamber). Finally, we have fabricated OLEDs on the conductive PEDOT:PSS stripes and successfully achieved light emission from 125 OLED stripes.