Effect of hole transporting materials in phosphorescent white polymer light-emitting diodes

We have investigated the effect of hole transporting materials in phosphorescent white polymer light-emitting diodes. The doping of a hole transporting material TCTA (4,4',4 ''-tris(N-carbazolyl)-triphenylamine) resulted in enhanced luminance and efficiency while the doping of other hole transporting materials degraded the device performance. The effect of hole transporting materials on the performance of the device has been explained with the triplet energy level, HOMO (highest occupied molecular orbital)/LUMO (lowest unoccupied molecular orbital) level, and hole mobility of the materials. The doping of TCTA into an emissive layer increased the maximum current efficiency by 43%. Simultaneous utilization of TCTA both as an interlayer and a dopant in an emissive layer has been found to enhance the device performance further. The optimized phosphorescent white polymer light-emitting device showed the current efficiency of 20.5 cd/A with the luminance of 1800 cd/m(2) at an operating voltage of 11.5 V. (C) 2009 Elsevier B.V. All rights reserved.