We fabricated high efficiency yellow-color organic light-emitting diodes (OLEDs) by co-doping 2,8-di(t-butyl)-5,11-di[4-(t-butyl) phenyl]-6,12-diphenylnaphthacene (TBRb) and tris(8-hydroxyquinolinato) aluminum (Alq(3)) guests in a N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) host. Co-doping of electron-transporting Alq3 with yellow dopant TBRb in hole-dominant NPB layers resulted in substantial luminance-yield improvement compared to TBRb-only counterparts without color contamination from Alq3 green emission. The luminance yield of 11.4 cd/A, corresponding to the co-doping of 8% TBRb and 2% Alq(3), is larger than previously reported luminance-yield values of conventional TBRb-based yellow OLEDs. Another advantage of the TBRb-Alq(3) co-doped OLEDs is an insignificant roll-off of efficiency at high current-density and/or brightness levels. (C) 2015 Elsevier B.V. All rights reserved.