Nitrogen heterocycle-containing materials for highly efficient phosphorescent OLEDs with low operating voltage

Since their discovery, phosphorescent organic light-emitting diodes (PHOLEDs) have been developed for more than ten years. To improve the electricity-to-light conversion efficiency of PHOLEDs, it is of great importance to improve their external quantum efficiency and to decrease their operating voltage. The improvement of functional materials such as host materials and carrier transport materials, especially electron transport materials, plays the most important role in reaching these targets. In this feature article, we provide a brief review of the recent developments in nitrogen heterocycle-containing functional materials for PHOLEDs. Special attention is paid to the issue of how to utilise the molecular design strategy in achieving the development of high-performance host and electron transport materials and of how to use these nitrogen heterocycle-containing materials to create PHOLEDs with efficiencies and operating voltages that reach the theoretical limits.