Interface formation between the Al electrode and poly[2,7-(9,9-dihexylfluorene)-co-alt-2,5-(decylthiophene)] (PFT) investigated in situ by XPS

The interactions of thermally evaporated aluminium with spin-casted film of poly[2,7-(9,9-dihexylfluorene)-co-alt-2,5-(decylthiophene)] (PFT), a novel blue light-emitting copolymer, were studied in situ by X-ray photoelectron spectroscopy (XPS). The changes in the C 1s, S 2p, O 1s and Al 2p core-level spectra, with the progressive deposition of aluminium, were carefully monitored. Aluminium was found to interact extensively with the bulk-adsorbed oxygen to form a layer of metal oxide and Al-O-C complex at the Al/PFT interface. Migration of the bulk-adsorbed oxygen to the surface occurred in response to the deposition of aluminium onto the polymer. The changes in the C 1s and S 2p lineshape suggested the formation of aluminium carbide and sulfide species, promoted by the electron transfer from the deposited aluminium atoms to the conjugated carbon and sulfur atoms of PFT. The deposited aluminium atoms did not diffuse to a significant extent into the sub-surface region of the polymer film, but aggregated in the form of island-like clusters before forming a metallic layer.