An experimental study of poly(9,9-dioctyl-fluorene) and its interfaces with Li, Al, and LiF

The chemical and electronic structure of a new conjugated polymer, poly(9,9-dioctyl-fluorene), has been studied by photoelectron spectroscopy. The polymer films were free of oxygen contamination (within the detection limits of photoelectron spectroscopy). X-ray and ultraviolet photoelectron spectroscopy was carried out on Li- and LiF-deposition on poly(9,9-dioctyl-fluorene), as well as, on LiF deposition on aluminum. In the case of Li-deposition on poly(9,9-dioctyl-fluorene) films, doping occurred resulting in the formation of polaronic charge carriers at low doping levels and bipolaronic charge carriers at high doping levels. LiF-deposition on poly(9,9-dioctyl-fluorene) did not cause doping of the polymer films, nor did the LiF dissociate at the interface. No significant shifts in a binding energy of the core levels nor any changes in the work function occurred. LiF-deposition on sputter-cleaned aluminum may cause the surface dipole formation, though LiF dissociation was not detected. Al-deposition on LiF/PFO films did not cause dissociation of LiF, unlike the case in Alq(3). (C) 2000 American Institute of Physics. [S0021-9606(00)70230-3].