Scale-up of Thermal Evaporation Processes for Large-Area Coatings of ' Small Molecule' Organic Light-Emitting Diode Materials

摘要

Small-scale thermal vapor deposition of "small molecule" organics for organic light-emitting diodes (OLEDs) is readily achieved by standard "point sources" using electrical heating of small resistive containers or "boats." One approach to large-area coatings is to extend the source in one dimension and scan the substrate with respect to the source in the direction perpendicular to the long axis of the source. Long runs are accommodated by making the source capable of holding a sufficient amount of material to last for the desired run time. Two practical issues that arise with this "line source" approach to scale up are coating uniformity and degradation of the organic material from exposure to high temperatures for long times. Proper consideration of conductances internal to the source and appropriately nonuniform heating of the evaporant material are applied to address these issues. The evolution of linear sources from web-coating applications to OLED applications will be discussed, and simple design rules for achieving stable and robust uniformity performance while minimizing the thermal exposure of the organic materials will be presented.