Versatile Host Materials for Highly-Efficient Green, Red Phosphorescent and White Organic Light-Emitting Diodes

To build up efficient host materials, two novel organic small molecules ICz-PPI and 2ICz-PPI were designed and synthesized, in which phenanthro[9,10-d]imidazole (PI) is proposed as a potential luminophore with high stability, while the indolo[3,2,1-jk]carbazole (ICz) has a high triplet energy and excellent thermal stability. Both exhibited weak intramolecular charge transfer, high decomposition temperature (T-d) and high quantum yield. ICz-PPI and 2ICz-PPI can act as the emitting layer in non-doped organic light-emitting diodes (OLEDs), which achieved an external quantum efficiency (EQE) of 2.47 and 1.94 % with CIE coordinates of (0.153, 0.121) and (0.161, 0.102), respectively. In addition, the high triplet energy allows them to be used as hosts for phosphorescent OLEDs (PhOLEDs). Accordingly, high performance for green (62.5 cd A(-1), 70.9 lm W-1, 17.8 %) and red (25.7 cd A(-1), 26.9 lm W-1, 19.4 %) had been achieved from the ICz-PPI-based PhOLED. Particularly, the ICz-PPI-based red PhOLED showed surprisingly low roll-off and maintained an EQE of 14.9 % at 10 000 cd m(-2). Furthermore, an ICz-PPI-based white OLED (WOLED) exhibited warm white light (CIEx,y=(0.427, 0.468)) and high efficiencies with a CEmax of 31.8cd A(-1), PEmax of 37.0lm W-1 and EQE(max) of 14.4 %.