An experimental study of poly(9,9-dioctyl-fluorene) and its interface withLi and LiF.

The chemical and electronic structure of a new conjugated polymer, poly(9,9 -dioctlyl-fluorene) (PFO), has been studied by photoelectron spectroscopy. The polymer films were free of oxygen contamination (within the detection l imits of photoelectron spectroscopy). X-ray and ultraviolet photoelectron s pectroscopy was carried out on Li- and LiF-deposition on PFO as well as on LiF-deposition on aluminum. In the case of Li-deposition on PFO films, dopi ng occurred resulting in the formation of polaronic charge carriers at low doping levels and bipolaronic charge carriers at high doping levels. LiF-de position on PFO did not cause doping of the polymer films, nor did the LiF dissociate at the interface. No significant shifts in binding energy (BE) o r work function occurred. LiF-deposition on sputter-cleaned aluminum showed evidence of surface dipole formation. though LiF dissociation was not dete cted. Al-deposition on LiF/PFO films did not cause dissociation of LiF, unl ike the case in Alq(3). (C) 2000 Elsevier Science B.V. All rights reserved.