New Bipolar Host Materials for Realizing Blue Phosphorescent Organic Light-Emitting Diodes with High Efficiency at 1000 cd/m²

Abstract

New host molecules such as 9-(6-(9<i>H</i>-carbazol-9-yl)­pyridin-3-yl)-6-(9<i>H</i>-carbazol-9-yl)-9<i>H</i>-pyrido­[2,3-<i>b</i>]­indole (pPCB2CZ) and 9-(6-(9<i>H</i>-carbazol-9-yl)­pyridin-2-yl)-6-(9<i>H</i>-carbazol-9-yl)-9<i>H</i>-pyrido­[2,3-<i>b</i>]­indole (mPCB2CZ) were designed and synthesized for blue phosphorescent organic light-emitting diodes (PhOLEDs). The glass transition temperatures of two host molecules were measured higher than 120 °C, and the identical triplet energies were determined to be 2.92 eV for both molecules. The bis­(3,5-difluoro-2-(2-pyridyl)­phenyl-(2-carboxypyridyl)­iridium­(III) (FIrpic)-doped mPCB2CZ-based PhOLED exhibited practically useful driving voltage of 4.8 V in a simple organic three layer device configuration which has a smaller number of interfaces in conventional multilayer PhOLEDs. Also, the high quantum efficiency of 23.7% is reported at the practically useful brightness value of 1000 cd/m²