Abstract
White organic light-emitting diodes (WOLEDs) have attracted increasing attention for having great potential in high-quality display and area illumination, especially since relatively high power-efficiency phosphorescent WOLEDs have been fabricated. Although the efficiency is sufficient for some applications, WOLEDs with high efficiency at high operable brightness are desired before their maximum potential can be truly realized. Four basic approaches are employed to fabricating a high-efficiency fluorescent WOLED; i.e. forming a hole-transporting/ emission/electron-transporting tri-layered structure with low injection barriers to facilitate the injection of carriers to the emissive layer, providing in the same structure high blocking barriers to confine the entered carriers, blending in the emission host a co-host to generate cascading routes with lower carrier injection barriers, and doping in a blue host a red dye and an efficient electro-luminescent greenish-blue dye, both with high Förster energy transfer efficiency. The result is a bright and stable white emission with a maximum power efficiency of 16 lm/W at 14 cd/m2 and currency efficiency of 19.2 cd/A at 300 cd/m2 or 18.7 Cd/A at 10,000 cd/m2, sufficient to fabricate full-color displays and approaching that of incandescent bulbs. Also to be presented is the fabrication of an efficient flexible pure-white OLEDs, based on a transparent and high glass-transition polymer film surface-modified by a thin dielectric layer and then over-deposited a transparent conducting oxide at elevated temperature. The brightness and efficiency of the device along with its relatively high colour stability are sufficient to fabricate flexible active matrix, or even passive matrix, colour-displays.