Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Efficient thermally activated delayed fluorescence (TADF) has been characterized for a carbazole/sulfone derivative in both solutions and doped films. A pure blue organic light emitting diode (OLED) based on this compound demonstrates a very high external quantum efficiency (EQE) of nearly 10% at low current density. Because TADF only occurs in a bipolar system where donor and acceptor centered (3)ππ* states are close to or higher than the triplet intramolecular charge transfer ((3)CT) state, control of the π-conjugation length of both donor and acceptor is considered to be as important as breaking the π-conjugation between them in blue TADF material design.

Organic electroluminescent devices are light-emitting diodes in which the active materials consist entirely of organic materials. Here, the fabrication of a white light-emitting organic electroluminescent device made from vacuum-deposited organic thin films is reported. In this device, three emitter layers with different carrier transport properties, each emitting blue, green, or red light, are used to generate white light. Bright white light, over 2000 candelas per square meter, nearly as bright as a fluorescent lamp, was successfully obtained at low drive voltages such as 15 to 16 volts. The applications of such a device include paper-thin light sources, which are particularly useful for places that require lightweight illumination devices, such as in aircraft and space shuttles. Other uses are a backlight for liquid crystal display as well as full color displays, achieved by combining the emitters with micropatterned color filters.