Light extraction from organic light emitting diode substrates: Simulation and experiment

The extraction of light from the glass substrate of bottom emitting organic light emitting diodes by structured substrate surfaces is investigated by modelling and experiment. The angular intensity distribution emitted by the oled into the substrate is taken front measurement or calculation and the extraction enhancement by various microrefractive and scattering outcoupling structures is evaluated by Monte Carlo raytracing and experiment. Diagrams for the characterization of outcoupling structures are presented and discussed. It is concluded that the reflectance of the oled stack ultimately limits the amount of light which can be transferred from the oled through the substrate into air and that the transfer can be increased from about 50% for unstructured to about 80% and more for structured substrates and that the theoretical limit can be reached, e.g., with simple microlens structures. To further increase the efficiency of oleds the light guided and absorbed in the oled stack itself has to be tapped. The influence of the outcoupling structures on the angular light distribution emitted from the substrate into air is also studied.