High-luminance top-emitting organic light-emitting diodes using CsAlAu as the semitransparent multimetal cathode

Top-emitting organic light-emitting diodes (TEOLEDs) using an ultrathin cesium (Cs) layer capped with a semitransparent AlAu layer as an effective, electron-injecting cathode were fabricated by vacuum evaporation. The optical properties of Cs (20 nm)Al (20 nm)Au (20 nm) at a wavelength of 520 nm exhibited a transmittance of 59% and a reflectance of 14%. The CsAlAu cathode showed lower power consumption and higher luminance at the same forward bias voltage than the CsAlAg cathode. Using a tris(8-quinolinolato)aluminum(III) (Alq3) layer as the emissive material, a TEOLED based on the CsAlAu cathode showed a maximum luminance of 66,200 cd m2 at 9.8 V. An external quantum efficiency and the power efficiency of 1.6% and 2.1 lmW, respectively, at a luminance of 1000 cd m2 (corresponding to a bias voltage of 6.2 V) was obtained. The good driving performance of this TEOLED was attributed to the excellent optical properties such as high transmittance and efficient-electron injection from the CsAlAu to the adjoining organic layer.