Metal-dependent charge transfer and chemical interaction at interfaces between 3,4,9,10-perylenetetracarboxylic bisimidazole and gold, silver and magnesium

Ultraviolet photoelectron spectroscopy (UPS) is used to investigate interfaces between the organic semiconductor 3,4,9,10-perylenetetracarboxylic bisimidazole (PTCBI) and Mg, Ag and Au. The metals span a range of work function and reactivity that leads to the formation of three different types of interfaces. The PTCBI-on-Au interface is abrupt and unreacted, and the relative position of energy levels across the interface precludes charge exchange and occupation of gap states. The lower work function of Ag leads to a metal-to-organic charge transfer and formation of polaron-like states at the PTCBI-on-Ag interface. Finally, the PTCBI-on-Mg interface shows clear evidence of a strong chemical interaction, which alters the electronic structure of the organic molecules at the interface and results in the formation of a different type of gap states. Dipole barriers consistent with the energetic and chemical characteristics of each interface are seen in all three cases. Finally, the three interfaces exhibit nearly identical Fermi level positions with respect to the organic highest occupied and lowest unoccupied molecular orbitals.