Introduction of photonic crystal structure into organic light-emitting diode

An Organic light-emitting diode (OLED) is very promising device for a flat panel display and an illumination applications due to the possibility of very thin and flexible structures, large area emission, high brightness and low power consumption. To realize a high efficiency is one of the most important issues for these applications. Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) structures, which are expected to realize the versatile control of light. We fabricate two-dimensional PC structures in the organic and indium-tin-oxide anode layers in which most of the light is confined. This results in light extraction from the waveguide mode. Improvements of 20 and 130% are observed in the spectrally-integrated intensity and the peak intensity, respectively, in comparison with samples without PCs. As the thickness of the organic layer is reduced, lower operating voltages are found to maintain the light-extraction efficiency. We can expect further improvement in the overall efficiency by optimizing this structure.