New Dopant and Host Materials for Blue-Light-Emitting Phosphorescent Organic Electroluminescent Devices

摘要

Organic triplet-state light-emitting materials (organic phos-phorophores) have been one of the most important recent developments in the field of organic fight-emitting diodes (OLEDs). Organic electrophosphorescent materials provided one of the major breakthroughs in electroluminescence efficiency, which is usually limited to an external quantum efficiency (EQE) of around 5 % for devices based on singlet-state fluorescent materials. Owing to its thin-film, lightweight, fast-response, wide-viewing-angle, high-contrast, and low-power attributes, OLEDs promise to be one of the major flat-panel-display technologies that can compete with the now-dominant liquid-crystal displays (LCDs) in the new millennium. Since the discovery of efficient OLEDs by Kodak in the late eighties, many researchers in both academia and industry throughout the world have been working on the improvement of their emissive constituent materials, luminance and power efficiencies, red-green-blue (RGB) color emissions, device structures, and operational stabilities. It was not until the discovery of organic phosphorophores that researchers began seriously looking into white-light-emitting OLEDs (WOLEDs) for the possibility of thin-film solid-state lighting, where efficiency is one of the most important concerns for practical usage (e.g., power efficiency of 10-15 lm W~(-1) is typical for a conventional white-light-emitting incandescent lamp, and 70 lm W~(-1) is typical for tube fluorescent lamps). Highly efficient organic phosphorescent OLEDs based on cy-clometalated iridium complexes are well known, where electroluminescence (EL) efficiencies as high as 19 % (or 70 lm W~(-1)) for green- and 10% (or 8 lm W~(-1)) for red-light- emitting devices have been reported in the literature. However, the development of highly efficient blue-light-emitting phosphorescent emitters in OLEDs, indispensable for the realization of RGB full-color displays and WOLEDs, is still in its infancy, and blue-light-emitting phosphorescent EL performance lags far behind that of the green- or red-light emitters.