Electroluminescence characteristics of a novel biphenyl derivative with benzoxazole for organic light-emitting diodes

Green-emitting biphenyl derivative with benzoxazole (4,4′-bis[2-(1,3-benzoxazol-yl-1-ethenyl)]-2-hexyloxybiphenyl) was newly synthesized. The benzoxazole, due to its electron-rich and good thermal stability, is introduced to enhance organic light-emitting diodes(OLEDs). This paper reports the optical and electrical characteristics by utilizing new biphenyl derivative with benzoxazole as the emitting layer for OLEDs. According to Thermogravimetric Analyzer (TGA) analysis, the weight ratio of that biphenyl derivative with benzoxazole starts to decrease at 350 °C, which suggests relatively good thermal property. The structure of the device is ITO/TPD or α-NPD (50 nm)/biphenyl derivative (50 nm)/LiF (0.5 nm)/Al (150 nm). The maximum luminance of the device using α-NPD is about 74,700 nW/cm2 at 9.6 V. With increase of applied voltage, the emitting zone changes from green to blue due to the influence of emission from α-NPD. On the other hand, the device based on TPD is 217,900 nW/cm2 at 6.4 V and the emitting zone of the device is constant regardless of the driving voltage.