Investigation of calcium as high performance cathode in small-molecule based organic light-emitting devices

While calcium has a low work function, its detrimental reaction with organic molecules such as tris-(8-hydroxyquinoline) aluminum $({\mathrm{Alq}}_3)$ has hindered its applications as cathode in small-molecule based organic light-emitting devices. In this article, we explore the feasibility of using calcium as a high performance cathode in ${\mathrm{Alq}}_3$ based devices by inserting a thin cesium fluoride layer at the ${\mathrm{Alq}}_3/\mathrm{Ca}$ interface to suppress the damaging effects of Ca to the organic material. Standard ${\mathrm{NPB/Alq}}_3$ devices were fabricated with various cathodes including Mg:Ag, Ca, and CsF/Ca. The device with the CsF/Ca cathode outperforms those with the other two electrodes in terms of both efficiency and stability.