We describe the design and synthesis of a sterically hindered yellow dopant, tetra(l-butyl)rubrene (TBRb) which, when doped in either 1,4-bis[N-(1-naphthyl)-N'-phenylamino]-biphenyl or aluminum tris(8-hydroxyquinoline) (Alq(3)) as emitter, shows nearly 25% increase in luminance efficiency over that of the state-of-the-art rubrene (Rb) device without significantly effecting its corresponding color. At 5% doping in Alq3 and 20 mA/cm(2) current drive condition, the electroluminescence efficiency of TBRb reaches 8.5 cd/A and 2.8 1m/W with a yellow color of Commission Internationale de l'Eclairage chromaticity coordinates (CIEx,y)=[0.52,0.48], which is among the best ever reported for yellow electrofluorescence in organic light-emitting devices. (c) 2005 Elsevier B.V. All rights reserved.