Interface formation between poly(9,9-dioctylfluorene) and Ca electrode investigated using photoelectron spectroscopy

Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to study the interface formation between poly(9,9-dioctylfluorene) (PFO) and Ca electrode. As the Ca coverage increases, the vacuum energy level of PFO decreases gradually in order to match the Fermi level (E-F) of Ca. The original highest occupied molecular orbital of PFO moves away from the E-F, and vanishes eventually. Bipolaron states with 1.8 eV in peak interval are formed in the former energy gap. The original lowest occupied molecular orbitals of PFO are broadened resulting in a featureless shake-up in the XPS Cls core level. (C) 2000 Published by Elsevier Science B.V.