Suppression of Capillary Flow in Slot-Die Coating for the Fabrication of Fine OLED Stripe

Due to lateral and vertical capillary flows appearing in a slot-die head with $\mu $ -tip for fine line coating, line breakup occurs at a relatively low coating speed, making it difficult to narrow the stripe. Through computational fluid dynamics (CFD) simulations, we demonstrate that capillary flow can be substantially suppressed by increasing the contact angle of the head lip and forming the microscale groove patterns in the dual plate (shim and meniscus guide). It is shown that the corresponding contact angle of the groove patterns increases up to 120°. Based on the simulation results, we have coated the head lip with a hydrophobic material and embedded the dual plate with micropatterns fabricated by a laser cutter into the slot-die head. Using such a hydrophobic slot-die head, we can suppress the lateral capillary flow of an aqueous poly(3,4-ethylenedioxythiophene):poly (4-styrenesulfonate) (PEDOT:PSS) to a great extent and, hence, increase the coating speed, rendering the stripe narrow ( $\approx 76~\mu \text{m}$ ). To demonstrate its applicability to organic light-emitting diodes (OLEDs), we have also fabricated fine red, green, and blue OLED stripes and successfully achieved light emission from them with the emission area of $80\,\,\mu \text{m}\,\,\times {5}$ cm.