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We study the evolution of the electric surface potential for small molecular organic semiconductors adsorbed on different high‐work function substrates using photoelectron spectroscopy. Usually, the surface potential of these materials shows a typical progression in dependence of the adsorbate layer thickness indicating the formation of a space charge region near the interface. We discuss the surface potential evolution on the basis of the commonly used Schottky model and a second model using a density of states distribution (DOS) in the adsorbed semiconductor energy gap. In order to derive an analytical solution, we simplify an existing approach for space charge regions at polymer contacts. This approach is based on tailing gap states in polymer adsorbates. We simplify it using a constant DOS distribution. The differences between the Schottky model and the simplified distributed states model will be discussed. Finally, both models are applied to measured values of the surface potential evolution of some exemplary organic molecules on different substrates. We find that the surface potential evolution of the simplified distributed states model describes the measured potential development more accurately than the Schottky model. The DOS is estimated in the framework of the model being between 1018 and 1019 cm−3 eV−1.

We investigate the electronic interface properties of an organic bilayer heterojunction solar cell, built of CuPc/BPE‐PTCDI as donor/acceptor system. Band alignment of this interface and interface potentials were measured using synchrotron induced photoemission spectroscopy (SXPS) on stepwise deposited BPE‐PTCDI on doped and non doped CuPc. Using non doped CuPc at thermodynamic equilibrium the bands bend at the interface in a direction that hinders dissociation of geminate pairs. As a measure to form a band bending that supports geminate pair separation p‐doping of CuPc is tested. As dopant WO3 was applied being a promising material for p‐doping of CuPc due to its high ionization potential. At the doped CuPc/BPE‐PTCDI interface the internal field is actually reversed now driving holes in CuPc and electrons in BPE‐PTCDI away from the interface.

BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF interfaces with zinc phthalocyanine (ZnPc) were studied by photoelectron spectroscopy. BaCuChF compounds oxidize when exposed to ambient atmosphere. Se capping layers were studied as a means to produce representative surfaces for photoelectron spectroscopic measurements. Decapped BaCuSeF surfaces remain O-free and C-free when the Se layer is evaporated but they become F-deficient. The resulting surfaces have work functions of 4.85 eV and Fermi levels located 0.25 eV above the valence band maximum. In situ stepwise deposition of ZnPc on a BaCuSeF film surface produced a chemically inert interface with a hole-injection barrier of 0.11 eV.

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