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Oxygen plasma treatment of indium tin oxide ͑ITO͒ results in a change in work function and electron affinity by ϳ0.5 eV. This change correlates with the measured increase in injected current in simple ''hole-only'' organic devices with O-plasma treated ITO electrodes. Neither addition nor removal of surface hydroxyl functionality accounts for the observed work function and electron affinity changes. X-ray and ultraviolet photoelectron spectroscopies show a new type of oxygen species is formed. Oxidation of surface Sn-OH to surface Sn-O ᭹ units is proposed to account for the observed changes in O-plasma treated ITO; this proposal can explain a wide variety of previously described ITO surface activation results.

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We have used photoelectron spectroscopies to study the metal/organic semiconductor interfaces formed by depositing three different metal–quinolate derivatives on Ag, with the goal of better understanding the initial stages of interface formation. We find very consistent results at all three interfaces, which exhibit strong energy level shifts within the first molecular layer, followed by a nearly “flat-band” condition. These results were analyzed in the context of the interface dipole and “band-bending” models. We conclude that the interface dipole model, extended to account for the differences in polarization screening in the first molecular layer, most accurately describes our findings. In this article we present the most thorough description of the early stages of metal/molecular organic semiconductor interfaces to date.