Highly efficient, color-stable white top-emitting organic light-emitting diodes

Top-emitting white organic light-emitting diodes (WOLEDs) have potential applications in lighting and full color displays due to the potential realization of a large aperture ratio and a high resolution when recombining top-emitting WOLEDs with active-matrix driving circuits. In the present paper, the authors fabricated top-emitting WOLEDs based on the red/blue dual-phosphorescent emitting layers and improved luminous efficiency and color stability in WOLEDs through inserting an tris(phenypyrazole)iridium (Ir(ppz)₃) thin film as an electron-blocking layer between the red layer and the blue one. The insertion of an Ir(ppz)₃ thin film can easily generate white emission through the enhancement of doping concentration of the red dopant, thus reducing the serious requirements of manufacture technology and improving the reproducibility of process technology. In addition, the authors analyzed the mechanism of color stability, optimized the concentrations of the red and blue phosphorescent dopants, and realized a luminous efficiency of as high as 7.9 cd·A^-1 in the authors' top-emitting WOLED. The white emission lies in the warm-white region with a very small chromaticity change of (0.006, 0.01) under a wide brightness range of 87~2403 cd·m^-2.