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

Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and Al/CsF/poly(9,9-dioctyl-fluorene) have been studied using X-ray and ultraviolet photoelectron spectroscopy. The polymer films were free of oxygen contamination (within the detection limits of photoelectron spectroscopy). In the case of LiF-deposition on poly(9,9-dioctyl-fluorene) films, doping did not occur, nor did the LiF dissociate upon Al-deposition. No significant shifts in a binding energy of the core levels, nor any changes in the work function were detected. However, for the Al/LiF/poly(9,9-dioctyl-fluorene) interface, there was no degradation of the π-electronic structure, unlike the case for Al deposited directly unto poly(9,9-dioctyl-fluorene). For the Al/CsF/poly(9,9-dioctyl-fluorene) interface, the CsF dissociated upon Al-deposition, with the Cs likely n-doping, the polymer at the interface. When deposited onto an Al surface, CsF also were found to dissociate at the interface but remaining in the CsF form away from the Al surface.