Highly efficient iridium(iii) phosphors with phenoxy-substituted ligands and their high-performance OLEDs

Abstract

Two new iridium(iii) cyclometallated complexes (1 and 2) based on the 2-(1-phenoxy-4-phenyl)-5-methylpyridine ligand have been developed. By attaching a flexible phenoxy group on the phenyl ring of 2-phenylpyridine (Hppy), the light-emitting properties of the resulting Ir^III complexes have been improved, while the introduction of an electron-donating methyl group on the pyridyl ring of Hppy can keep the triplet emission in the green region by compensating for the reduced energy gap caused by the phenoxy group. Owing to the unique electronic structures induced by the ligand, the vacuum-evaporated organic light-emitting devices (OLEDs) of the type [ITO/NPB (40 nm)/(1 or 2):CBP (20 nm)/BCP (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm)] furnished peak OLED efficiencies at 10.0%, 31.1 cd A^-1 and 14.5 lm W ^-1 for 1 and 11.7%, 38.1 cd A^-1 and 31.8 lm W^-1 for 2. By replacing the electron-injection/electron-transporting materials (BCP and Alq₃) with TPBi, the green-emitting devices based on 1 gave outstanding peak efficiencies at 22.5%, 76.2 cd A^-1 and 72.8 lm W^-1. Extremely high peak efficiencies of 24.5%, 84.6 cd A ^-1 and 77.6 lm W^-1 were even obtained for the 2-doped devices and both of them are superior in performance to the benchmark dopants Ir(ppy)₃ and Ir(ppy)₂(acac). Moreover, polymer light-emitting devices were also fabricated using 1 and 2via the spin-coating method, and their device performances are characterized by 14.4%, 39.5 cd A ^-1 and 12.4 lm W^-1 for 1 and 12.6%, 29.6 cd A^-1 and 18.1 lm W^-1 for 2. When 2 was used to make three-color white-light OLEDs, respectable device efficiencies of 15.3 cd A^-1, 7.5% and 9.1 lm W^-1 were achieved and their white color CIE coordinates are improved relative to Ir(ppy)₃.