Light extraction from OLEDs using volumetric light scattering

One of the limitations on OLED performance is the optical extraction efficiency, eta(ex), which is the ratio of light generated within the device to light emitted into the ambient. Ideally eta(ex) is equal to unity. Typical estimates for this efficiency factor in OLEDs range between 0.17-0.5. We present a simple radiative transport model that quantifies the effect of volumetric light scattering on light output in terms of a small set of readily measured parameters. Our methodology is sufficiently general to parameterize and describe many of the light extraction schemes found in the literature. We will present a set of model calculations using parameters typical of many OLEDs, and show that the introduction of light scattering sites within the otherwise transparent substrate can increase light extraction efficiencies by at least a factor of 1.4. We also present experimental data to validate our analysis and demonstrate a high level of agreement between model and experiment.