Efficient electroluminescence of bluish green iridium complexes with 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine and 2-(3,5-bis(trifluoromethyl)phenyl)-5-fluoropyrimidine as the main ligands

Abstract

We thoroughly investigated four iridium(III) complexes (Ir(tfmphpm)₂(acac), Ir(f-tfmphpm)₂(acac), Ir(tfmphpm)₂(tpip), and Ir(f-tfmphpm)₂(tpip)) using 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine (tfmphpm) and 2-(3,5-bis(trifluoromethyl)phenyl)-5-fluoropyrimidine (f-tfmphpm) as the main ligands and 2,4-pentanedionate (acac) and tetraphenylimidodiphosphinate (tpip) as the ancillary ligands. All complexes showed bluish green emissions peaking at 473–480 nm with very high photoluminescence quantum efficiencies in the range of 85–95%. The organic light-emitting diodes (OLEDs) using these emitters exhibited good performances. Especially, the device using Ir(tfmphpm)₂(tpip) with the structure of ITO (indium-tin-oxide)/MoO₃ (molybdenum oxide, 3 nm)/TAPC (di-[4-(N,N-ditolyl-amino)phenyl]cyclohexane, 50 nm)/mCP (1,3-bis(9H-carbazol-9-yl) benzene, 5 nm)/Ir(tfmphpm)₂(tpip) (6 wt%) : PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 50 nm)/LiF (1 nm)/Al (100 nm) displayed the best performances with a maximum luminance of 28 194 cd m⁻², a maximum current efficiency of 74.70 cd A⁻¹, and a maximum external quantum efficiency up to 35.0%, and the efficiency roll-off ratio was small. The current efficiency of the device remained as high as 66.46 cd A⁻¹ at the brightness of 1000 cd m⁻², suggesting that they are potential materials for applications in OLEDs.