Enhanced light out-coupling of organic light-emitting devices using embedded low-index grids

The application of organic light-emitting devices to reduce the energy consumption of interior lighting, which now costs more than $230 billion annually, is attracting interest due to the high efficiency of these devices. Indeed, electrophosphorescent organic light-emitting devices with an internal quantum efficiency eta(IQE) of 100% ( refs 2,3) already approach the efficiency of fluorescent lamps(4-6). However, because of the high refractive index of organic materials and the optical confinement and internal reflection that results, the light out-coupling efficiency eta(out) for conventional organic light-emitting devices is limited to similar to 20% (refs 2,7). Here we demonstrate that embedding a low-index grid in the organic layers can enhance the out-coupling of the waveguided light without spectral distortion. When combined with microlenses that out-couple the glass modes, the external quantum efficiency eta(EQE) and power efficiency of a white organic light-emitting device are improved to 34 +/- 2% and 68 +/- 4 lm W-1. The resulting eta(out) is 2.3 +/- 0.2 times that of a conventional organic light-emitting device used as a comparison, and simulations indicate that the enhancement can be further increased to 3.4 +/- 0.2.