Extracting light from polymer light-emitting diodes using stamped Bragg gratings

In this paper, we describe a method for increasing the external efficiency of polymer light-emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft-lithography technique that minimizes changes to the conventional LED structure. Using one-dimensional and two-dimensional gratings, we were able to increase the forward-directed emission by 47% and 70%, respectively, and the external quantum efficiency by 15% and 25%.