Electronic structure, diffusion, and p-doping at the Au/F₁₆CuPc interface

Interfaces formed by evaporating Au on copper hexadecafluorophthalocyanine (F₁₆CuPc) and F₁₆CuPc on Au are studied via ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy. The energy position of the molecular levels is found to depend on the deposition sequence. The Au-on-F₁₆CuPc interface exhibits a lower hole injection barrier than the F₁₆CuPc-on-Au interface. This behavior is attributed to the diffusion of Au into the organic matrix at the Au-on-top interface, in which they behave as acceptors. Band bending consistent with p doping, i.e., upward away from the metal interface, is observed in Au-doped F₁₆CuPc films. Current-voltage measurements on Au/F₁₆CuPc/Au sandwich structures show a higher electron injection barrier at the top Au electrode contact than at the bottom electrode contact, also consistent with p-type doping F₁₆CuPc by Au.