Transient electrophosphorescence in red top-emitting organic light-emitting devices

Abstract

We have fabricated a red electrophosphorescent top-emitting organic light-emitting device using the phosphorescent bis[2-(2′-benzothienyl)-pyridinato-N,C3′]iridium(acetylacetonate) doped in 4,4′-N,N′-dicarbazole-biphenyl host and Alq3 electron injection layer. The emission spectrum shows a strong peak at 620nm accompanied with a small peak at 675nm in the red region. Time evolution of electrophosphorescence reveals a decay time of 703μs at a voltage pulse of 5V in a device with an emitting area of 20mm2. Rise and delay times vary from 450to14μs and 73to3μs, respectively, as the voltage amplitude increases from 4.5to10V. These results are compared with the red emitting device without an electron injection layer.