Deep blue, efficient, moderate microcavity organic light-emitting diodes

Two types of microcavity blue organic light-emitting diodes (OLEDs) with a dielectric Bragg mirror (two different center wavelengths, type-A approximate to 465, type-B approximate to 470 nm) were designed to achieve the color coordinates of NTSC blue standard and enhance the quantum efficiency in the normal direction. A moderate microcavity OLED was defined as a microcavity OLED with a single pair of TiO2/SiO2 high/low dielectric layers inserted between an indium tin oxide (ITO) layer and a glass substrate. The moderate microcavity blue OLED doped with 9,10-bis(3',5'-diphenylphenyl)-10-(3',5'-diphenylbiphenyl-4 ''-yl)anthracene (TAT) exhibited excellent color coordinates (type-A; x=0.143, y=0.068, type-B; x=0.139, y=0.081), which were better than the color coordinates of the NTSC standard (0.140, 0.080) and the TAT-doped conventional noncavity OLED (0.156, 0.094). There were approximately 60% and 54% improvement in the relative quantum efficiency of the type-B TAT-doped moderate microcavity OLED, respectively, compared to those of the conventional noncavity reference OLED (ITO = 150 nm) and other reference type-II with an identical ITO layer thickness (ITO = 85 nm). These improvements in color coordinates and the relative quantum efficiency were attributed to the optimization of narrowed spectrum bandwidth and enhanced integrated spectrum intensity in the TAT-doped blue OLED, resulting from the effective microcavity effect. (C) 2009 Elsevier B.V. All rights reserved.