Electroluminescence enhancement in blue phosphorescent organic light-emitting diodes based on different hosts

Abstract

Blue phosphorescent organic light-emitting diodes (OLEDs) are fabricated by utilizing the hole transport-type host material of 1,3-bis(carbazol-9-yl)benzene (MCP) combined with the electron transport-type host material of 1,3-bis (triphenylsilyl) benzene (UGH3) with the ratios of 1:0, 8:2 and 6:4, and doping with blue phosphorescent dopant of bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic). The device with an optimum concentration proportion of MCP:UGH3 of 8:2 exhibits the maximum current efficiency of 19.18 cd/A at luminance of 35.71 cd/m2 with maintaining Commission Internationale de L’Eclairage (CIE) coordinates of (0.1481, 0.2695), which is enhanced by 35.7% compared with that of 1:0 with (0.1498, 0.2738). The improvements are attributed to the effective carrier injection and transport in emitting layer (EML) because of mixed host materials. In addition, electron and exciton are confined in the EML, and 4,4′,4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) and Di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) have the high lowest unoccupied molecular orbital (LUMO) energy level and triplet exiton energy.