Understanding the Interface Dipole of Copper Phthalocyanine (CuPc)/C60:   Theory and Experiment
  Interface dipole determines the electronic energy alignment in donor/acceptor interfaces and plays an important role in organic photovoltaics. Here we present a study combining first principles density functional theory (DFT) with ultraviolet photoemission spectroscopy (UPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate the interface dipole, energy level alignment, and structural properties at the interface between CuPc and C60. DFT finds a sizable interface dipole for the face-on orientation, in quantitative agreement with the UPS measurement, and rules out charge transfer as the origin of the interface dipole. Using TOF-SIMS we show that the interfacial morphology for the bilayer CuPc/C60 film is characterized by molecular intermixing, containing both the face-on and the edge-on orientation. The complementary experimental and theoretical results provide both insight into the origin of the interface dipole and direct evidence for the effect of interfacial morphology on the interface dipole. 
Na Sai, Raluca Gearba, Andrei Dolocan, John R. Tritsch, Wai-Lun Chan,   James R. Chelikowsky, Kevin Leung, Xiaoyang Zhu
cond-mat.mtrl-sci physics.chem-ph