Enhanced hole injection and improved performance in organic light-emitting devices by utilizing a novel composite hole injection layer

Organic light-emitting devices (OLEDs) with MoO(x) Ag(2)O and a composite layer consisting of Ag(2)O//MoO(x) as hole injection layers (HIL) have been investigated. We have observed that the insertion of such a composite layer leads to a striking improvement in the electrical properties with lower driving voltage, higher power and current efficiencies. At a current density of 20 mA/cm(2), the driving voltage of the device using an Ag(2)O//MoO(x) composite HIL (Cell-AM) is 5.9 V, which is 2.2 V, 3.8 V and 4.5 V lower than that of the devices using MoOx (Cell-M), Ag(2)O (Cell-A) as HIL and the device (Cell-I) without HIL, respectively. Its power efficiency is 2.56 Lm/W, which is 1.8, 2.4 and 3.6 times higher than that of Cell-M, Cell-A, and Cell-I, respectively. The current efficiency is 4.88 cd/A, which is 33.7%, 58.4% and 110.3% higher than Cell-M, Cell-A, and Cell-I, respectively. These improvements are attributed to its high hole injection ability. The result is verified by using the J-V curves of 'only' devices and further explained with the help of the Fowler-Nordheim (F-N) tunneling theory. (C) 2010 Elsevier Ltd. All rights reserved.