The performances of simplified single-layer phosphorescent organic light-emitting diodes (SL-PhOLEDs) have significantly increased and they now appear to be a promising alternative to multi-layer PhOLEDs. The blue and white emissions, far more challenging than all the other colours, are still particularly desired. Herein, a high efficiency host material for blue emitting SL-PhOLED using the blue emitter FIr6 is reported, which is particularly interesting as it displays an emission at shorter wavelengths than the well-known FIrpic emitter, almost exclusively reported in the SL-PhOLEDs literature. The host material investigated herein is constructed on the electron-rich quinolinoacridine and displays when incorporated in FIr6-based SL-PhOLEDs, an external quantum efficiency (EQE)⟩10% and a low Von of 3.1 V. This is the first work passing an EQE of 10% with FIr6 as an emitter. This host also reaches a very high EQE of 19% when used with the green emitter Ir(ppy)2acac, this performance being among the highest recorded for green SL-PhOLEDs. Finally, as white SL-PhOLEDs involve blue emitting SL-PhOLEDs, this host is also used with a combination of blue and yellow emitters. An extremely high EQE of 24% is reached with CIE coordinates of (0.40;0.48). These findings show the real potential of the quinolinoacridine fragment to reach high performance multi-colour SL-PhOLEDs. A high-efficiency host, constructed on electron-rich quinolinoacridine, for blue and green-emitting simplified single-layer phosphorescent organic light-emitting diodes (SL-PhOLEDs), is reported. The performance is among the highest recorded for green SL-PhOLEDs. To gain insights in the development of challenging white SL-PhOLEDs, this host is also used with a combination of blue and yellow emitters, providing a very high external quantum efficiency of 24%.image