Interface Analysis of Naththyl-substituted Benzidine Derivative and tris-8-(hydroxyquinoline) Aluminum Using Ultraviolet and X-Ray Photoemission Spectroscopy

摘要

Naththyl-substituted Benzidine derivative (NPB) and tris-8-(hydroxyquinoline) aluminum (Alq) organic materials have been used to demonstrated highly efficient bi-layer light emitting devices (LEDs). In such a device, the holes from the NPB layer are injected into the electron transporting Alq and recombine with emission characteristics of Alq. Thus, the interface between the Alq and NPB layers are crucial to the device performance. We will report the interface studies between Alq and NPB using ultraviolet and x-ray photoemission spectroscopy (UPS) and (XPS), respectively. The UPS results have shown a vacuum level shift of more than 0.2 eV when thin layers of NPB are deposited onto Alq. The XPS results also show a shift as a function of NPB thickness, corresponding to the vacuum level shift. Finally, we will speculate on the local band alignments close to organic layer interface and possible impact on device performance.