Low roll-off power efficiency organic light-emitting diodes consisted of nondoped ultrathin phosphorescent layer

Abstract

Low roll-off power efficiency (ηp) organic light-emitting diodes at high current density were fabricated using a nondoped ultrathin bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) phosphorescent layer and thin N,N′-di(naphthalene-2-yl)-N,N′-diphenyl-benzidine separate layer. A maximum ηp of 8.48lm∕W and luminance efficiency of 20.26cd∕A at 2014cd∕m2 were obtained from the device. The ηp roll-off percentage of ultrathin phosphor layer device was reduced to 20% at a current density of 20mA∕cm2, which is about 40% for conventional phosphorescent device. The low roll off of efficiency was attributed to the direct carrier trapping and confining emission zone function of the ultrathin phosphor layer.