Improved external coupling efficiency in organic light-emitting devices on high-index substrates

High-index-of-refraction substrates are shown theoretically and experimentally to increase the external coupling efficiency of organic light-emitting devices (OLEDs) by using a quantum mechanical microcavity model. This increase is due to the elimination of those modes waveguided in the ITO/organic layer. Bi-layer OLEDs were fabricated on standard soda lime glass and high-index glass substrates, and their far-field intensity pattern was measured. Among the devices optimized for external efficiency, those on shared high-index substrates exhibited a 53% improvement in external quantum efficiency over the devices on shaped standard glass substrates, and an increase by a factor of 2-3 times over those on planar glass substrates. This principle is applicable to any backside patterning technique in conjunction with other OLED structural improvements.