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

We have fabricated a red electrophosphorescent top-emitting organic light-emitting device using the phosphorescent bis[2-(2(')-benzothienyl)-pyridinato-N,C-3']iridium(acetylacetonate) doped in 4,4(')-N,N-'-dicarbazole-biphenyl host and Alq(3) electron injection layer. The emission spectrum shows a strong peak at 620 nm accompanied with a small peak at 675 nm in the red region. Time evolution of electrophosphorescence reveals a decay time of 703 mus at a voltage pulse of 5 V in a device with an emitting area of 20 mm(2). Rise and delay times vary from 450 to 14 mus and 73 to 3 mus, respectively, as the voltage amplitude increases from 4.5 to 10 V. These results are compared with the red emitting device without an electron injection layer. (C) 2004 American Institute of Physics.