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Abstract The surface potential of a prototypical organic semiconductor, pentacene, is chemically modified by the addition of a dipole monolayer on top of the thin film. Changes are afforded by reacting the topmost layer of pentacene to generate the monolayer, and the reactant structure provides a high degree of tunability for surface potential, with shifts up to 800 mV possible. Despite the complexity of the adsorbed layer, the surface potential shift displays a near‐linear dependency between dipole strength and surface potential change, and a good degree of predictability via the Helmholtz equation. The large changes in surface potential should be enough to access electron injection in thisp‐type semiconductor, but deviceI–Vcharacteristics are not consistent with this behavior. Interactions between the metal top contact and a chemical functional group within the monolayer are the likely culprit, with spectroscopic evidence presented. While tailoring the surface potential of organic surfaces is achievable, maintaining the integrity of surface energetics upon metal deposition remains challenging.