Interfacial electronic structures of WO3-based intermediate connectors in tandem organic light-emitting diodes

Interfacial electronic structures of WO3-based intermediate connectors used in tandem organic light-emitting diodes were studied with photoemission spectroscopy. Important factors controlling their functional effectiveness for charge carrier generation and injection were analyzed. By systematically characterizing the electronic properties and chemical structures for various intermediate connectors, it is identified that the WO3 interlayer is capable of pronouncedly modifying the energy level alignment of the intermediate connectors and thereby the adjacent emission units. Substantial interface dipole and energy level bending caused by the oxide connector are shown to be beneficial to carrier injection into the suitable molecular energy levels of adjoining emission units.