Relationship between doping concentration and recombination zone in green phosphorescent light-emitting diodes

Device performances of green phosphorescent light-emitting diodes (PHOLEDs) were investigated according to the doping concentration of tris(2-phenylpyridine) iridium in electron transport type spirobifluorene-based host. Recombination zone was shifted from hole transport layer side to inside light-emitting layer as doping concentration was increased. Luminance efficiency of the green PHOLEDs was improved from 14 cd/A to 33 cd/A by increasing doping concentration from 5% to 10%.