Resonance‐Based Directional Light Emission from Organic Light‐Emitting Diodes: Comparing Integrated Nanopatterns and Color Conversion Waveguide Gratings
Tailoring the angular emission pattern of organic light-emitting diodes (OLEDs) is a promising approach to increase device performance in many applications. In miniaturized point-of-need sensor systems using organic light sources and photodetectors, directional illumination of specific sensing spots may enhance overall sensitivity by improved light utilization. Periodically nanopatterned waveguides forming photonic crystal slabs are oftentimes employed to obtain directional resonant light outcoupling from OLEDs. This work compares emission directionality for two types of devices utilizing the same polymer compounds as the emissive material: OLEDs comprising a nanopatterned bottom electrode and conventional OLEDs featuring a dedicated nanopatterned color conversion layer (CCL) for directional light outcoupling. Simulated and experimentally measured emission characteristics show that resonant outcoupling effects from a separate CCL are significantly stronger due to spatial separation from the lossy electrode layers as well as high optical contrast at the waveguide interfaces. While OLEDs with nanopatterned electrodes exhibit only small deviations from the Lambertian emission profile, the nanopatterned CCL induces high outcoupling peaks at specific viewing angles leading to increased emission directionality.