Iridium(iii) phosphors with bis(diphenylphorothioyl)amide ligand for efficient green and sky-blue OLEDs with EQE of nearly 28%

Abstract

In this study, a new ligand, bis(diphenylphorothioyl)amide (Stpip), containing phosphorus–sulfur (PS) bonds was synthesized as an ancillary ligand. Four iridium(III) complexes (Ir(ppy)₂(Stpip), Ir(tfppy)₂(Stpip), Ir(ttppy)₂(Stpip) and Ir(tntppy)₂(Stpip) with phenylpyridine derivates (ppy = 2-phenylpyridine); tfppy = 2-[4-(trifluoromethyl)phenyl]pyridine; ttppy = 2-[3,5-bis(trifluoromethyl)phenyl]pyridine; tntppy = 2-[2,6-bis(trifluoromethyl)-4-pyridyl]pyridine) as the main ligands were investigated. Due to the stable S–Ir bonds, these complexes emitted green or sky-blue photoluminescence with high quantum yields (Ir(ppy)₂(Stpip): λ_max = 490 nm, Φ = 44.7%; Ir(tfppy)₂(Stpip): λ_max = 495 nm, Φ = 85.4%; Ir(ttppy)₂(Stpip): λ_max = 477 nm, Φ = 92.1%; Ir(tntppy)₂(Stpip): λ_max = 516 nm, Φ = 90.8%) and good thermal stability. Using these compounds as emitters, all organic light-emitting devices (OLEDs) showed satisfactory performances. Notably, the device with the Ir(tfppy)₂(Stpip) emitter achieved a maximum luminance of 37 321 cd cm⁻² as well as maximum current efficiency, power efficiency and external quantum efficiency of 61.7 cd A⁻¹, 48.5 lm W⁻¹ and 21.8%, respectively. Moreover, the device with the Ir(ttppy)₂(Stpip) complex exhibited the highest EQE value of nearly 28%. These results showed that bis(diphenylphorothioyl)amide is a promising ancillary ligand for efficient phosphorescent Ir(III) complexes and OLEDs.