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

Abstract

Two novel host materials based on the diphenylphosphine oxide (DPPO) and spirofluorene were designed and facilely synthesized by tuning the ratio of donor spirofluorene units and acceptor DPPO units from 1: 1 to 1: 2, i. 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.