Highly efficient bluish green organic light-emitting diodes of iridium(iii) complexes with low efficiency roll-off

Abstract

Two novel iridium(III) complexes Ir(BTBP)₂mepzpy and Ir(BTBP)₂phpzpy were successfully synthesized, in which 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine (BTBP) was used as the main ligand, and 2-(3-methyl-1H-pyrazol-5-yl)pyridine (mepzpy) and 2-(3-2-(3-phenyl-1H-pyrazol-5-yl))pyridine (phpzpy) were introduced as the ancillary ligands, respectively. Both Ir(III) complexes displayed bluish green emission peaks at 486 and 487 nm with high quantum efficiencies of 0.73 and 0.69, respectively. The organic light-emitting diodes (OLEDs) with the structure of ITO/HATCN (hexaazatriphenylenehexacarbonitrile, 5 nm)/TAPC (bis[4-(N,N-ditolylamino)-phenyl]cyclohexane, 40 nm)/Ir(BTBP)₂mepzpy or Ir(BTBP)₂phpzpy (10 wt%): 2,6-DCzPPy (2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene, 30 nm)/LiF (1 nm)/Al (100 nm) exhibited high efficiencies with low efficiency roll-off. Especially, the device based on the Ir(BTBP)₂mepzpy complex achieved a maximum current efficiency of 58.17 cd A⁻¹ and a maximum external quantum efficiency of 25.33% with Commission Internationale de 1′Eclairage coordinates of (0.19, 0.43). These results indicate that novel cyclometalated Ir(III) complexes for high efficiency OLEDs with low efficiency roll-off were obtained by our rational design.