23.4: Photoemission Investigation of Cesium‐Doped tris(8‐hydroxyquinoline) aluminum (Alq3) and the Effect of Dopant Diffusion

Abstract

AbstractThe chemical and electronic effects of Cs‐doped Alq3 have been investigated using X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). XPS reveals the formation of a new nitrogen species shifted to lower binding energy that increases in intensity as a function of Cs doping. UPS reveals the formation of a new gap state in the previously forbidden band gap of Alq3 after Cs doping. Both results are consistent with the formation of a Cs‐Alq3 charge‐transfer complex. The thermal stability of the charge‐transfer complex was also evaluated using angle‐resolved XPS (ARXPS). The XPS data suggests that one Cs atom attached to an Alq3 molecule is thermally stable, but the addition of a second or third Cs atom to an Alq3 molecule produces a thermally unstable complex. OLED device data also confirms the thermal instability of the Cs‐Alq3 complex.