Interface studies of Aluminum, 8-hydroxyquinolatolithium (Liq) and Alq3 for inverted OLED application

This study examined the interfaces of Alq3 on a thin 8-hydroxyquinolatolithium (Liq) layer deposited on aluminum using X-ray and ultraviolet photoemission spectroscopy. A thin layer of Liq reacted with the underlying aluminum surface. As a result, the molecular orbital features of Alq3 shifted to a higher binding energy and a new gap state was created. This effect is believed to lower the barrier height for electron injection. An organic light emitting device with a structure of ITO/Al/Liq/Alq3/NPB/WO3/Al was fabricated.The device performance showed characteristics that were consistent with the results of the photoemission studies. It is proposed that Al/Liq can be used as an efficient electron injection layer for inverted organic light emitting devices.