Relationship between dopant energy levels and device performances of triplet mixed host devices

Device performances of phosphorescent organic light-emitting diodes (PHOLEDs) with triplet mixed host structure were correlated with dopant energy levels and mixed host composition. A mixed host of 4,4′,4″-tris-(N-carbazolyl)triphenylamine (TCTA) and spirobifluorene type host (PH1) was used and three different dopants with different bandgap were doped in the mixed host. Optimum quantum efficiency was obtained in TCTA:PH1 (50:50) mixed host device in the case of green dopants, while the optimum host composition for red and orange dopants was TCTA:PH1 (25:75).