Microcavity effects on emissive color and electroluminescent performance in organic light-emitting diodes

Microcavity organic light-emitting diodes having a top metal mirror and a bottom dielectric mirror, which was distributed Bragg reflectors (DBR) fabricated by using TiO2–SiO2 alternative dielectric multilayer with a central stop-band and two sub-stop-bands, were fabricated. In the devices, the active layers consisted of a hole-transporting layer N,N′-di(naphthalene-l-yl)-N,N′-diphenylbenzidine (NPB) and an electron-transporting/emitting layer tris(8-hydroxy-quinoline) aluminum (Alq3). The relationship of the electroluminescent (EL) spectrum and efficiency with the thickness of the active layer and metal layer was studied. It was found that the EL emissive color did not strongly depend on the thickness of the organic layer and metal layer, which was attributed to the excellent photon confinement role of the narrow stop-band of the used dielectric mirror. Thus, high efficiency microcavity organic light-emitting diodes were achieved, and the peak wavelength and color purity were not obviously changed, via optimizing the thickness of organic layer and metal electrode.