Highly efficient and spectrally stable white organic light-emitting diodes using new red heteroleptic Iridium(III) complexes

Abstract Highly efficient red phosphorescent iridium(III) complexes, (MPQ) 2 Ir(Pppy) and (MPQ) 2 Ir(TMSppy) based on 4-methyl-2-phenylquinoline (MPQ) as a cyclometalated main ligand and 2-[(1,1′-biphenyl)4-yl]pyridine (Pppy) or 2-[4-(trimethylsilyl)phenyl]pyridine (TMSppy) as a second cyclometalated ligand were synthesized for use in organic light-emitting diodes (OLEDs). The iridium(III) complex with MPQ and acetylacetone (acac) as an ancillary ligand, (MPQ) 2 Ir(acac), was also synthesized for comparison. The geometrical configuration of the heteroleptic complex (MPQ) 2 Ir( acac )is N , N -trans, whereas (MPQ) 2 Ir(Pppy) and (MPQ) 2 Ir(TMSppy)show all- facial geometries. Among the iridium(III) complexes, red OLEDs using the (MPQ) 2 Ir(Pppy) exhibited significantly more improved luminance and external quantum efficiency with markedly prevented concentration self-quenching at high doping concentration by introduction of Pppy. Moreover, a high maximum external quantum efficiency (EQE max ) of 28.0% with a high color-rendering index (CRI) of 81 was achieved in the white OLEDs (WOLED) fabricated using the bis[2-(4,6-difluorophenyl)pyridinato-C 2 , N ](picolinato)iridium(III) [FIrpic], tris(2-phenylpyridine)iridium(III) [Ir(ppy) 3 ], and (MPQ) 2 Ir(Pppy), and it is one of the highest values among the reported three primary color component WOLED. Also, the WOLED fabricated using the (MPQ) 2 Ir(Pppy) showed excellent spectral stability at different voltages.