Solution-processed oxadiazole-based electron-transporting layer for white organic light-emitting diodes

Abstract

A novel alcohol-soluble electron-transporting small-molecule material comprising oxadiazole and arylphosphine oxide moieties, ((1,3,4-oxadiazole-2,5-diyl)bis(4,1-phenylene))bis(diphenylphosphine oxide) (OXDPPO), has been synthesized and characterized. Its single crystal structure, together with the photophysical, electrochemical and thermal properties, has been investigated. This material not only possesses a wide bandgap with a low HOMO level but also exhibits a strong π–π stacking with a distance of 3.35 Å. Moreover, this compound shows excellent thermal stability with a high glass transition temperature of 104 °C and a decomposition temperature of 384 °C. The unique solubility in 2-propanol makes it a good candidate for fabricating fully solution-processed multilayer organic light-emitting diodes (OLEDs). Efficient solution-processed white OLEDs have been fabricated with this compound as an electron-transporting layer (ETL). It was found that this ETL can greatly balance the electrons and holes in devices with the high work-function metal cathode (Al) and an increase in luminous efficiency of ∼70-fold can be achieved. The maximum luminous efficiency of devices with an ETL/Al configuration is even higher than that of devices using a Ca cathode.