Energetics at Au top and bottom contacts on conjugated polymers

Photoelectron spectroscopy was employed to examine the energetics, and therefore charge injection barriers, at top and bottom contact configurations of gold and conjugated polymers, i.e., polymer spin coated on gold and vapor-deposited gold on polymer interfaces. Very similar results are obtained for both ex situ (contaminated) and in situ (clean) prepared interfaces: a 0.7–0.8eV decrease in the vacuum energy levels is consistently observed as compared to bare polycrystalline gold. These observations are explained by changes of the metal work function upon contacting either polymers or contaminants, associated with the reduction of the electron density tail that extends outside the metal surface.