Increased stripe density of slot-coated PEDOT:PSS using a meniscus guide with linearly tapered μ-tips for OLEDs

We have performed slit coatings using a slot-die head with μ-tips in various shapes (rectangular-shaped, partially tapered, and linearly tapered μ-tips) to achieve high-density fine organic stripes for potential applications in solution-processable organic light-emitting diode (OLED) displays. The fluid dynamics of an aqueous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) in the presence of those μ-tips has been analyzed based on the electronic–hydraulic analogy. It is demonstrated that both line breakup occurring at low coating speeds with the rectangular-shaped narrow μ-tip and line broadening appearing with the rectangular-shaped wide μ-tip are avoidable using the linearly tapered μ-tip. It is attributed that the hydraulic resistance inside the slot-die head is decreased and the meniscus is well controlled by the linearly tapered structure. It also has a big advantage in the fabrication of multiple PEDOT:PSS stripes that the spacing between stripes can be kept constant. To fabricate high-density fine PEDOT:PSS stripes, we have devised a slot-die head with two meniscus guides embedded, each of which has 175 linearly tapered μ-tips. Using such a slot-die head, we have successfully fabricated 350 PEDOT:PSS stripes and 300 OLED stripes (59 stripes per inch) with the luminance of 350 cd/m2 at 5 V.