Ultrafast laser patterning of OLEDs on flexible substrate for solid-state lighting

Rapid developments in the organic LED technology on flexible foils promise to deliver thin, lightweight and power-efficient light sources for intelligent lighting applications. Laser patterning of OLEDs on glass for display applications has been widely reported. However, fewer reports discuss patterning of OLEDs on flexible substrates, which presents a novel optical engineering challenge. Our aim here is to quantify the potential of picosecond lasers for this application and determine a robust laser process window for large area selective OLED electrode patterning. This should involve the complete removal of (i) 130 nm thick ITO anode on a barrier layer stack and (ii)
100 nm thick Ba/Al cathode on 180 nm thick LEP/PEDOT:PSS active organic layers while leaving intact all underlying layers. Detailed laser ablation studies at 532 and 355 nm reveal that ps lasers uniquely facilitate roll-to-roll OLED manufacturing by providing fine resolution. Damage thresholds, process quality and process speed limitations will be discussed. Careful crater examination reveals that the choice of laser pulse duration is more important than wavelength for a given layer thickness. A photomechanical stress-induced ablation mechanism is believed to be key for this process and debris-free, low temperature patterning can be achieved.
Keywords: OLED, ITO, thin-film patterning, picosecond laser ablation, stress-assisted ablation