In time, solid-state devices should provide inexpensive, environmentally friendly illumination that changes the way we think about using artificial light.

A method of generating white light by combining a blue organic light-emitting diode with a down-conversion phosphor system is presented. It is demonstrated that the use of the down-conversion phosphor system actually leads to an overall power efficiency increase, an effect attributed to the high quantum efficiency of phosphor materials and the presence of light scattering in the phosphor layers. It is also shown that this approach permits the generation of illumination quality white light over the full range of color temperatures required for lighting applications. For the model device demonstrated in this work, an overall electrical to optical power conversion efficiency of 1.3% was achieved at a brightness of 1080 cd/m2.

A set of experimental measurements of scattering films and organic light emitting devices (OLEDs) is presented. We measure the reflectance, transmission, and emission characteristics of scattering media and OLED devices separately, and use this data as input into a simple radiative transfer model to predict the effect of light scattering on OLED light output. We find quantitative agreement between the radiative transfer model predictions and experimental results. We find that the introduction of volumetric scattering mechanisms increases the output of OLEDs by as much as 40%, which corresponds to over 70% of the light within a typical glass substrate being coupled to air.

One limitation on organic light emitting diode (OLED) performance is the optical extraction efficiency ηex, which is defined as the ratio of light generated within the device to light emitted into the ambient. Typical estimates for ηex, in OLEDs range between 0.17 and 0.5. We develop a simple radiative transport model that quantifies the effect of volumetric light scattering on light output in OLEDs in terms of a small set of readily measured parameters. The methodology is sufficiently general to parametrize and describe many of the light extraction schemes found in the literature. A set of model calculations is presented using typical OLED parameters; these calculations show that the introduction of light scattering sites within the otherwise transparent substrate can increase light extraction efficiencies to values between 0.55 and 1.

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