High-contrast top-emitting organic light-emitting devices

In this paper we report on a high-contrast top-emitting organic light-emitting device utilizing a moderate-reflection contrast-enhancement stack and a high refractive index anti-reflection layer. The contrast-enhancement stack consists of a thin metal anode layer, a dielectric bilayer, and a thick metal underlayer. The resulting device, with the optimized contrast-enhancement stack thicknesses of Ni (30 nm)/MgF₂ (62 nm)/ZnS (16 nm)/Ni (20 nm) and the 25-nm-thick ZnS anti-reflection layer, achieves a luminous reflectance of 4.01% in the visible region and a maximum current efficiency of 0.99 cd/A (at 62.3 mA/cm²) together with a very stable chromaticity. The contrast ratio reaches 561:1 at an on-state brightness of 1000 cd/m² under an ambient illumination of 140 lx. In addition, the anti-reflection layer can also enhance the transmissivity of the cathode and improve light out-coupling by the effective restraint of microcavity effects.