Hybrid interfaces in polymer-based electronics

Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and Al/CsF/p oly(9,9-dioctyl-fluorene) have been studied using X-ray and ultraviolet pho toelectron 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-d eposition. No significant shifts in binding energy of the core levels, or a ny changes in the work function were detected. However, for the Al/LiF/poly (9,9-dioctyl-fluorene) interface, there was no degradation of the pi -elect ronic structure, unlike the case for Al deposited directly unto poly(9,9-di octyl-fluorene). For the Al/CsF/poly(9,9-dioctyl-fluorene) interface, the C sF dissociated upon Al deposition, with the Cs likely n-doping the polymer at the interface. When deposited onto an Al surface, CsF also was found to dissociate at the interface but remaining in the CsF form away from the Al surface. Vacuum level alignment occurs for poly(9,9-dioctyl-fluorene) films spun onto 'metal' substrates. The hole-injection barrier in poly(9,9-dioct yl-fluorene)-based LEDs is hence determined by the difference between anode work function and the polymer ionization potential.