Planarization of slot-die coated multilayer stripes via pre-drying by a heating roll for organic light-emitting diodes

摘要

Micro-patterning of single-layer thin films in the cross-web (transverse) direction is feasible using a slot-die coating system. For its practical applications in organic light-emitting diodes (OLEDs), however, the fabrication and planarization of multilayer thin-film stripes are indispensable. We have coated multilayer stripes using an aqueous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and non-aqueous poly(N-v-inylcarbazole) (PVK) and planarized them via pre-drying by a heating roll in a roll-to-roll slot-die coating system. It is demonstrated that the PEDOT:PSS stripe can be planarized at a pre-drying (heating roll) temperature of 40 degrees C. At higher temperatures, it is found that there appear the evaporation-induced inward and/or outward capillary flows depending on the wet film thickness. Using a low-boiling-point solvent, the PVK stripe coated atop the planarized PEDOT:PSS stripe is shown to be planarized at a pre-drying temperature of 65 degrees C, the step coverage and thickness uniformity by which are substantially enhanced. Such a planarization scheme also brings in the positive effect on the surface morphology of those stripes. To verify the planarization effect at the device level, we have fabricated phosphorescent OLED stripes. Without planarization, the light-emitting area shrinks and a spot with strong light emission appears, increasing the probability of a short circuit in OLEDs. With planarization, however, we can achieve brighter light emission from OLED stripes with high inter-stripe emission uniformity.