High performance blue and white phosphorescent organic light-emitting diodes obtained by sensitizing both light-emitting and electron transport layers

In this work, novel blue and white organic light-emitting diodes (OLEDs) were designed by utilizing iridium(III) bis(4-(tert-butyl)-2,6-diuoro-2,3-bipyridinne)acetylacetonate (FK306) as sensitizer in both light-emitting and electron transport layers. Analysis of device configuration demonstrated that FK306 molecules work as electron trappers in view of their low-lying energy levels and triplet energy, which broaden the width of recombination zone, thus enhancing carriers' recombination probability and suppressing the annihilation of excitons. Consequently, blue and white devices with low turn-on voltages were reported with current efficiencies of 71.95 and 72.23 cd A-1, external quantum efficiencies of 32.62% and 31.30%, power efficiencies of 74.85 and 70.80 lm W-1 and brightness of 43171 and 37848 cd m- 2, respectively. Within electron transport layer, the optimal doping concentration of FK306 is 2 wt%, which can be easily controlled in device manufacture processes. In addition, it is much more flexible in terms of sensitizer choice for doped electron transport layer compared with light-emitting layer.