High T_g Triphenylamine-Based Starburst Hole-Transporting Material for Organic Light-Emitting Devices

This paper reports the synthesis of a new starburst molecule, 4,4′,4′′-tris[(2,3,4,5-tetraphenyl)phenyl]phenylamine (TTPPPA) and its application as a hole-transporting material in organic light-emitting devices (OLEDs). Although TTPPPA has almost the same ionization potential as 1,4-bis(1-naphthylphenylamino)biphenyl (NPB), the TTPPPA-based device of ITO/TTPPPA/Alq 3 /LiF/Al yields much better efficiency of 5.3 cd/A and 4.3 lm/W than the standard ITO/NPB/Alq 3 /LiF/Al device (3.0 cd/A and 2.9 lm/W). The remarkable performance enhancement is attributed to a better balance of hole and electron injection in the TTPPPA-based device. Further, TTPPPA has a much higher glass-transition temperature ( T g, 202 °C) than NPB ( T g, 98 °C), suggesting that TTPPPA can be an alternative material to NPB especially for high-temperature applications of OLEDs and other organic electronic devices.