Optical Measurement Of The Emission Zone In Organic Light-Emitting Diodes

Optical interference (weak microcavity) effects are used to measure the location and width of the emission zone in mixed-host phosphorescent organic light-emitting diodes. The consequences of varying composition and varying current density are evaluated quantitatively for the width of the emission zone, the internal quantum efficiency, and the outcoupling efficiency. The devices that are used here are optimized for optical interference effects. The conclusions should carry over to devices that are optimized for practical performance.