Improved electron injection of OLEDs with a thin PBD layer at Alq3/Cs2CO3 interface

In this study, the effect of one oxadiazole derivative (PBD) using as an electron injection layer (EIL) at Alq3/Cs2CO3 interface has been investigated. The present of PBD EIL was showed an interesting enhanced electron injection for OLEDs although the nominal electron injection barrier for PBD based OLEDs is much larger, because PBD owns an obvious higher intrinsic the Lowest Unoccupied Molecular Orbital level (2.3 eV) than that of Alq3 (3.0 eV). For example, the current density of OLEDs at 8 V was increased from 54 mA/cm2 to 168 mA/cm2 when inserting a thin PBD layer (5 nm) at Alq3/Cs2CO3 interface. Here the increased current is suggested associating with the changed electronic structure of PBD when it contacts with Cs2CO3.