Tris-(8-hydroxyquinoline)aluminum-based organic light-emitting devices with Al/CaF2 cathode: Performance enhancement and interface electronic structures

The device characteristics and the interface electronic structures of organic light-emitting devices based on tris-(8-hydroxyquinoline)aluminum were investigated with ${\mathrm{Al/CaF}}_2,$ Al/LiF, and Al-only cathodes. Similar to the Al/LiF cathode, the ${\mathrm{Al/CaF}}_2$ cathode greatly improved the performance of the device over the Al-only cathode. However, a photoelectron spectroscopy study revealed that despite the performance improvement, the evolution of the new peaks during the ${\mathrm{Al/CaF}}_2$ cathode formation closely resembled those of the Al-only cathode rather than the Al/LiF cathode.