Increased electrophosphorescent efficiency in organic light emitting diodes by using an exciton-collecting structure

A phosphorescent dye, tris(1-phenylisoquinoline) iridium (III) [Ir(piq)3] doped interface of 4,4′,4″-tris(carbazol-9-yl)-triphenylamine (TCTA) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) has been studied in organic light emitting diodes. Two devices with different emissive interfaces, TCTA+6%Ir(piq)3∕BCP and TCTA+6%Ir(piq)3∕BCP+1%Ir(piq)3, exhibited nearly the same red Ir(piq)3 emissions and I–V characteristics. However, the second device showed higher efficiency and luminance than the first device over the whole voltage range. The maximum efficiency of 6.0cd∕A reached at 0.026mA∕cm2 in the second device was 30% higher than that of 4.6cd∕A reached at 0.032mA∕cm2 in the first device. The improved performance of the second device is attributed to the fact that the excitons can be formed on both sides of the TCTA/BCP interface and can be more efficiently collected with the additional 1% Ir(piq)3 doped in the BCP layer. Therefore, the exciton-collecting structure, doping phosphorescent dyes into both sides of the TCTA/BCP interface, is believed to be a very useful way to optimize the performance of phosphorescent organic light emitting diodes.