Diphenylphosphine oxide-based host materials for green phosphorescent organic light-emitting devices

e., (4-(9,9′-spirobi[fluoren]-2-yl)phenyl)diphenylphosphine oxide (SPDPPO) and (9,9′-spirobi[fluorene]-2,7-diylbis(4,1-phenylene))bis(diphenylphosphine oxide) (SBPBDPPO). Furthermore, 3,6-disubstituted spirofluorene possesses better thermal stability performance, for instance, higher glass transition temperatures (SPDPPO of 140 °C and SBPBDPPO of 172 °C). The phosphorescent organic light-emitting devices (PhOLEDs) were fabricated by doping tris(2-phenylpyridine)iridium (Ir(ppy)3) in hosts as light-emitting layer. The PhOLEDs employed SPDPPO as host exhibited a low turn-on voltage of 3.0 V and the maximum current efficiency of 36.5 cd/A, power efficiency of 32.8 lm/W and a maximum external quantum efficiency (EQE) of 10.5%, respectively.