Investigation of an efficient YbF3/Al cathode for tris-(8-hydroxyquinoline)aluminum-based small molecular organic light-emitting diodes

Efficient tris-(8-hydroxyquinoline)aluminum (Alq₃)-based organic light-emitting diodes (OLEDs) using YbF₃ as the electron injection layer have been investigated. With an YbF₃ (3.0 nm)/Al cathode, the device with Alq₃ as the emitting layer achieved a better performance than the control device with a LiF (0.5 nm)/Al cathode. The release of the low-work-function metal Yb is responsible for the performance enhancement. From the analysis by atomic force spectroscopy and X-ray photoemission spectroscopy, it is observed that the Alq₃-cathode interface could be well covered by YbF₃ at an optimum thickness of 3.0 nm, which helps to prevent the contact between Alq₃ and Al, and to reduce the destruction of Alq₃ by Al.