Stable efficiency roll-off in red phosphorescent organic light-emitting diodes using a spirofluorene–benzofluorene based carbazole type host material

Red phosphorescent organic light-emitting diodes (PHOLEDs) with stable efficiency roll-off were developed using a spirofluorene–benzofluorene based carbazole type host material. 9-(Spiro[benzo[c]fluorene-7,9′-fluorene]-2′-yl)-9H-carbazole with a spiro[benzofluorene-7,9′-fluorene] and a carbazole unit was synthesized and it was used as the host material for the red PHOLED. The quantum efficiency of the red PHOLED was optimized at a doping concentration of 1% and the efficiency decrease at 10,000 cd/m2 from the maximum efficiency was less than 10%.