Ultrafast laser patterning of OLED stacks on a multilayered 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 [1] Laser patterning of OLEDs on glass for displays or other plastic electronics applications has been widely reported [2] However, fewer reports have discussed patterning OLEDs on multilayer barrier stacks on flexible substrates, which presents a novel engineering challenge. We discuss here recent experimental results from a detailed laser ablation study using different wavelength (1064, 532 and 355nm) ultrafast lasers (ps and fs) for this application. We aim to establish an industrially robust laser process window for large area selective OLED patterning. This should involve in separate steps the complete removal of (i) a 130nm thick ITO anode track on barrier layers [3] and (ii) a 100nm thick Al cathode patterning on 180nm thick PEDOT:PSS and LEP active organic layers while preserving the integrity of all other underneath stack layers. The results reveal that picosecond and femtosecond lasers facilitate uniquely roll to roll OLED manufacturing by providing ultra fine ablation resolution. Damage thresholds, process quality and process speed limitations will be discussed. Careful examination with optical profilometry and SEM reveals that the choice of laser pulse duration is more important than wavelength for a given layer thickness. A photomechanical stress induced ablation mechanism [4] is believed to be key for this process and debris free, low temperature patterning can be achieved with demonstrably no detrimental effects to the OLED performance.
CLEO/Europe EQEC 2009 European Conference on Lasers and Electro Optics and the European Quantum Electronics Conference