Far-field luminous intensity distribution depending on the outcoupling structure of organic light-emitting diodes

The finite-difference time domain method was combined with the ray tracing technique to investigate the viewing angle characteristics of organic light-emitting diodes (OLEDs) with various optical structures for improving the outcoupling efficiency. The angular dependence of the far-field luminous intensity on OLEDs with a basic structure and on the one with scattering particles in the glass substrate exhibited an almost Lambertian distribution at their optimized conditions. The pillow lenses applied onto the front surface of the glass substrate made the intensity distribution complex with local-intensity maxima appear. This was attributed to the interactions between the curved lens surfaces and the rays emitted from the light source. This study suggests that both the microcavity in the organic layers and the optical structure for efficient outcoupling should be optimized to realize appropriate viewing angle characteristics for display or lighting applications.