Drastic drop of external quantum efficiency at liquid nitrogen temperature in a bilayer blue phosphorescent organic light-emitting device

Abstract

We have investigated substantial drop of external quantum efficiency (EQE) at liquid nitrogen temperature in a bilayer blue phosphorescent organic light emitting device with a structure of ITO/TAPC: FirpiciTAZ/LiF/A1, where TAPC, Firpic, and TAZ represent 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane, iridium(111)bis1(4,6-difluorophenyl)-pyridinato-N,C2Ipicolinate, and 3-(biphenyl-4-yl)-4-phenyl-5-(4tert-butyl-phenyl)-1,2,4-triazole, respectively. The device exhibits a high EQE of 17.2% at room temperature although it has a simple bilayer structure. However, the quantum efficiency drops drastically to 0.8% at liquid nitrogen temperature. We studied this drastic drop of EQE in viewpoints of carrier conduction, carrier recombination, photoluminescence quantum efficiency, and energy transfer. (C) 2016 Elsevier B.V. All rights reserved.