N,N-Diphenylpyridin-4-amine as a Bipolar Core Structure of High-Triplet- Energy Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes

摘要

High-triplet-energy bipolar host materials with both holetransport and electron-transport units in the molecular structure have been developed to improve the quantum efficiency of blue phosphorescent organic light-emitting diodes (PHOLEDs) through charge balance in the emitting layer. The use of the bipolar host materials enabled the fabrication of high-efficiency blue PHOLEDs with a quantum efficiency above 20%. Several chromophores have been used as the core structures of bipolar host materials. Fluorene was one bipolar core structure for host materials, and several derivatives of fluorene were synthesized as bipolar host materials for blue PHOLEDs. Modification of fluorene with hole- and electron-transport units yielded various bipolar host materials. Diphenylsilane was another common core structure for high-triplet-energy bipolar host materials. Diphenylsilane could be easily modified with hole- and electron-transport moieties by nucleophilic substitution reactions. The other core structure which has been widely used is phenylcarbazole. As phenylcarbazole is a hole-transport core, it was modified with an electron-transport substituent for better electron-transport properties. Phenylcarbazolebased bipolar host materials were effective as host materials for blue PHOLEDs.