Improvement of brightness and efficiency in organic light-emitting diodes using 1,3-bis(4-tert-butylphenyl-1,3,4-oxadiazoyl) phenylene as the hole buffer layer

We have reported the efficient Poly (2-methoxy, 5-(2-ethylhexoxy)-1,4-phenylene vinylene) (MEHPPV) organic light-emitting diodes based on 3-bis(4-tert-butylphenyl-1,3,4-oxadiazoyl) phenylene (OXD-7) and ITO bilayer anodes. OXD-7 was inserted between ITO anode and MEHPPV and acted as a hole buffer layer. The results demonstrated that the efficiency and brightness of the devices with ITO/OXD-7/MEHPPV/LiF/Al were four factors higher than that of devices with ITO/MEHPPV/LiF/Al. However, the efficiency and brightness of devices with ITO/OXD-7/MEHPPV/Al were worse than that of devices with ITO/MEHPPV/Al. Our results suggested that the better performance of devices should have not only the balance of hole and electron injection, but also higher hole and electron density in the emissive layer. OXD-7, as an electron-transporting material, was demonstrated to be a good candidate for hole injection buffer layer. (C) 2006 Elsevier B.V. All rights reserved.