Polarizer-free, high-contrast-ratio organic light-emitting diodes utilizing microcavity structures and neutral-density filters

Polarizer-free, high-contrast-ratio organic light-emitting diodes (OLEDs) are demonstrated using a microcavity structure in conjunction with neutral-density (ND) attenuation filters. The reduction of the OLED efficiency associated with the ND filters is compensated for by the enhancement of the microcavity resonance. Furthermore, the absorption of photons from a cavity eases the requirement of the optical density (OD) of the ND filter. The reflectance of the proposed OLED devices using the ND filter with an OD of 0.4 is less than 20% throughout the visible-wavelength region, and their luminous reflectance is as low as 10%. These devices exhibit current efficiency comparable to those of the non-cavity-based OLEDs without any filter or polarizer.