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)2Ir(Pppy) and (MPQ)2Ir(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)2Ir(acac), was also synthesized for comparison. The geometrical configuration of the heteroleptic complex (MPQ)2Ir(acac)is N,N-trans, whereas (MPQ)2Ir(Pppy) and (MPQ)2Ir(TMSppy)show all-facial geometries. Among the iridium(III) complexes, red OLEDs using the (MPQ)2Ir(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 (EQEmax) 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-C2,N](picolinato)iridium(III) [FIrpic], tris(2-phenylpyridine)iridium(III) [Ir(ppy)3], and (MPQ)2Ir(Pppy), and it is one of the highest values among the reported three primary color component WOLED. Also, the WOLED fabricated using the (MPQ)2Ir(Pppy) showed excellent spectral stability at different voltages.