Efficient sky-blue OLEDs with extremely low efficiency roll-off based on stable iridium complexes with a bis(diphenylphorothioyl)amide ligand

Abstract

The lack of efficient blue-emitting materials is one of the most important issues faced when extending the application of organic light-emitting diodes (OLEDs). Therefore, in this study, the ancillary ligand bis(diphenylphorothioyl)amide (Stpip) was utilized in iridium(III) complexes with 2-(2,4-difluorophenyl)pyridine (dfppy) and 2-(2,4-difluorophenyl)pyrimidine (dfppm) as the main ligands, respectively. The two complexes, (dfppy)₂Ir(Stpip) and (dfppm)₂Ir(Stpip), exhibit sky-blue emission peaks at 466 and 474 nm with photoluminescence quantum yields of 12% and 89%, respectively. Due to the strong coordination capability between sulfur and iridium atoms, both complexes can be prepared with extremely high production yields under mild conditions. Furthermore, a double light-emitting layer device using (dfppm)₂Ir(Stpip) as the emitter exhibits a maximum external quantum efficiency (EQE_max) of 19.4% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.13, 0.27). Specifically, the EQE remains at 19.2% at a practical brightness of 1000 cd m⁻², indicating an inappreciable efficiency roll-off.