Different configurations of phosphorescent yellow emissive layer in white organic light-emitting device

We fabricated white organic light-emitting devices (WOLEDs) based on three different configurations for yellow emissive layer (Y-EML), using phosphorescent yellow bis[2-(4-tert-butylphenyl)benzothiazolato-N,C 2 ’]iridium (acetylacetonate) [(t-bt) 2 Ir(acac)]. The Y-EML was formed as undoped ultrathin layer, doped ultrathin layer with low (tbt) 2 Ir(acac) concentration and doped thin layer with the same amount of (t-bt) 2 Ir(acac) molecular as the undoped YEML. The results showed that the difference in configurations of the Y-EML affected not only the operating voltage but also the luminance and efficiency characteristics of the devices. Comparing device performance, it was found that devices based on the doped Y-EML showed low efficiency and yellow-dominated light emission, due to triplet exciton hopping caused by different triplet energy. On the other hand, a device with the undoped Y-EML demonstrated the highest efficiency (79.0 cd/A at 1 550 cd/m 2 and 40.5 lm/W at 1 000 cd/m 2 ), attributing to well confined charge carriers and excitons.