Electronic and Chemical Properties of Tin-Doped Indium Oxide (ITO) Surfaces and ITO/ZnPc Interfaces Studied In-situ by Photoelectron Spectroscopy

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Abstract
The chemical and electronic properties of tin-doped indium oxide (ITO) surfaces and its interface with zinc phthalocyanine (ZnPc) were investigated using photoelectron spectroscopy partly excited by synchrotron radiation from the BESSY II storage ring. Preparation and analysis of ITO and ITO/ZnPc layer sequences were performed in-situ without breaking vacuum. The Fermi level position at the ITO surface varies strongly with oxygen content in the sputter gas, which is attributed to an increase of surface band bending as a consequence of the passivation of the metallic surface states of ITO. The shift of the Fermi level is accompanied by a parallel increase of the work function from 4.4 to ∼5.2 eV. No changes in the surface dipole are observed with an ionization potential of IP = 7.65 ± 0.1 eV. The barrier height for hole injection at the ITO/ZnPc interface does not vary with initial ITO work function, which can be related to different chemical reactivities at the interface.