Efficient bluish green electroluminescence of iridium complexes with good electron mobility

Abstract

Two novel iridium(III) complexes (Ir1 and Ir2), synthesized using 2′-(trifluoromethyl)-2,5′-bipyrimidine and 5-fluoro-2′-(trifluoromethyl)-2,5′-bipyrimidine as the main ligands, and tetraphenylimidodiphosphinate (tpip) as an ancillary ligand, were investigated. The introduction of a nitrogen heterocycle and CF₃ substituent improves the electron mobility of the Ir(III) complexes, which is beneficial for device performance. Both of the complexes emit bluish green photoluminescence with very high quantum efficiency yields (Ir1: λ_max: 485/516 nm, η_PL: 89%; Ir2: λ_max: 482/513 nm, η_PL: 95%) and good electron mobility. Organic light-emitting diodes (OLEDs) constructed with an 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 complex (6 wt%):PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenyl-phosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) structure showed good device performances. Device G1 based on Ir1 showed a η_c,max value of 62.99 cd A⁻¹ with an EQE_max value of 23.5%. Owing to the slightly higher PL efficiency and lower LUMO levels of Ir2, which are beneficial for electron injection, the device based on Ir2 displayed a slightly better performance with a η_c,max value of 71.18 cd A⁻¹ and an EQE_max value of 27.7%. Even at a practical brightness of 1000 cd m², values of 57.39 cd A⁻¹ and 22.3% could still be reached.