Phosphorescent organic light-emitting diodes fabricated using iridium complexes with carbazole-based benzothiazole ligands

We designed and synthesized two novel red-emitting iridium complexes, (2-Btc)₂Ir(pic) and (2-BtcPh)₂Ir(pic), that contain 2-(9-ethylcarbazol-2-yl)-benzothiazole (Btc) and 2-(9-phenylcarbazol-2-yl)- benzothiazole (BtcPh) as the main ligands, respectively, and picolinic acid (pic) as an ancillary ligand. Red emissions at 637 and 624 nm were observed from (2-Btc)₂Ir(pic) and (2-BtcPh)₂Ir(pic), respectively, in dichloromethane solution. Red phosphorescent organic light-emitting diodes (OLEDs) with ITO/PEDOT:PSS (40 nm)/TAPC (30 nm)/TPBi:TCTA:red dopants (x%) (25 nm)/TSPO1 (35 nm)/LiF (1 nm)/Al structure were fabricated. Red phosphorescent OLEDs using (2-BtcPh)₂Ir(pic) as a dopant at a 5% doping ratio exhibited a maximum external quantum efficiency of 10.5%, maximum power efficiency of 11.0 lm/W, and maximum luminance of 1145 cd/m² with CIE coordinates of (0.65, 0.34). Moreover, a white phosphorescent OLED with an ITO/PEDOT:PSS (40 nm)/TAPC (20 nm)/mCP:FIrpic (3%) (20 nm)/TPBi:FPQIrpic (10%):(2-BtcPh)₂Ir(pic) (1%) (5 nm)/TPBi (25 nm)/LiF (1 nm)/Al structure exhibited a maximum external quantum efficiency of 11.7%, maximum power efficiency of 28.8 lm/W, maximum luminous efficiency as high as 29.0 cd/A, and maximum luminance of 16,020 cd/m² with CIE coordinates of (0.44, 0.49).