High efficiency organic white-light-emitting diodes with dual electrophosphorescent layers

Organic white-light-emitting diodes have received much attention in the last few years due to their potential appli- cations in solid-state lightings and as back-light sources for liquid crystal displays. In this report, we prepared and characterized high efficiency electrophosphorescent white-light-emitting diodes possessing dual emitting layers. The novel device structure contained an effective host material tris[4-(9-phenylfluoren-9-yl)phenyl]amine (TFTA), doped with iridium complex: blue phosphor iridium(III) bis(4,6-di-fluorophenyl)-pyridinato-N,C-picolinate (FIrpic) and red-light-emitting osmium phosphor [Os(fptz)(PPhMe); fptz = 3-trifluoromethyl-5-(4-tert-butyl-2-pyridyl) tri- azolate] in the nano-scale emitting layers. The device exhibited a white-light emission with the Commission Internationale de l'Eclairage coordinates (CIE) of (0.34, 0.38), when the blue layer thickness was 30 nm and the red layer was 2 nm. The device efficiency was about 5.05 lm/W at 100 mA/cm. In addition, the device structure was further optimized by improving the charge transport characteristics using 2,2′,2″-(1,3,5-phenylene)tris(1- phenyl-1H-benzimidazole) (TPBI) as the new electron transport layer. The organic white-light-emitting device showed a high luminou 51.2 lm/W and the CIE coordinates of (0.33, 0.36). © 2013 American Scientific Publishers All rights reserved.