Investigation of an efficient YbF 3/Al cathode for tris-(8-hydroxyquinoline)aluminum-based small molecular organic light-emitting diodes

Abstract

Efficient tris-(8-hydroxyquinoline)aluminum (Alq 3)-based organic light-emitting diodes (OLEDs) using YbF 3 as the electron injection layer have been investigated. With an YbF 3 (3.0 nm)/Al cathode, the device with Alq 3 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 Alq 3-cathode interface could be well covered by YbF 3 at an optimum thickness of 3.0 nm, which helps to prevent the contact between Alq 3 and Al, and to reduce the destruction of Alq 3 by Al.