Highly efficient red iridium(III) complexes based on phthalazine derivatives for organic light-emitting diodes

Two novel bis-cyclometalated iridium(III) complexes, Ir(ECPC) ₂(pic) and Ir(TPC)₂(pic) (HECPC, 3-(4-(9H-carbazol-9-yl) phthalazin-1-yl)-9-ethyl-9H-carbazole; HTPC, 4-(4-(9H-carbazol-9-yl)phthalazin- 1-yl)-N,N-diphenylaniline, pic = 2-picolinic acid) were synthesized in moderate yield under mild synthetic conditions, and their electrical and photophysical properties were characterized with respect to their application as a phosphorescent emitter in polymer light-emitting diodes (PLEDs). The devices based on these complexes with the structure of ITO/PEDOT:PSS (40 nm)/70%PVK:30%PBD:x% iridium(III) complex (70 nm)/TPBI (30 nm)/Ba (1.5 nm)/Al (120 nm) were fabricated with highly external quantum efficiency. The device based on Ir(ECPC)₂(pic) exhibited a maximum external quantum efficiency of 16.3% and a luminance of 1484 cd/cm²; while the device based on Ir(TPC)₂(pic) showed a maximum external quantum efficiency of 11.9% and a Commission International de L'Eclairage (CIE) coordinates of (0.695,0.289). The results showed that the two new bis-cyclometalated iridium(III) complexes can be used as emitters and applied in saturated red phosphorescent organic light-emitting diodes (PHOLEDs).