Novel iridium complexes as high-efficiency yellow and red phosphorescent light emitters for organic light-emitting diodes

A series of novel biscyclometallated iridium complexes based on spirobifluorene ligands and acetyl acetonate (acac) ancillary ligands have been synthesized and characterized. Their electrochemical properties were investigated by cyclic voltammetry (CV). HOMO, LUMO, and energy band gaps of all the complexes were calculated by the combination of UV-vis absorption spectra and CV results. TGA and DSC results indicated their excellent thermal stability and amorphous structure. All the iridium complexes were fabricated into organic light-emitting devices with the device configuration of ITO/PEDOT:PSS (50 nm)/PVK (50 wt %):PBD (40 wt %):Ir complex (10 wt %) (45 nm)/TPBI (40 nm)/LiF (0.5 nm)/Ca (20 nm)/Ag (150 nm). Yellow to red light emission has been achieved from the iridium complexes guest materials. Complex C1 (yellow light emission) achieved an efficiency of 36.4 cd/A (10.1%) at 198 cd/m2 and complex C4 (red light emission) reached external quantum efficiency of 4.6%. The slight decrease of external quantum efficiency at high current density revealed that the triplet-triplet (T1-T1) annihilation was effectively suppressed by the new developed complexes.