title: Understanding the Interface Dipole of Copper Phthalocyanine (CuPc)/C60: Theory and Experiment.
abstract: 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.
authors: †Energy Frontier Research Center (EFRC:CST), The University of Texas, Austin, Texas 78712, United States.
authors: Na
authors: N
authors: Sai
authors: †Energy Frontier Research Center (EFRC:CST), The University of Texas, Austin, Texas 78712, United States.
authors: Raluca
authors: R
authors: Gearba
authors: ‡Texas Materials Institute, The University of Texas, Austin, Texas 78712, United States.
authors: Andrei
authors: A
authors: Dolocan
authors: John R
authors: JR
authors: Tritsch
authors: †Energy Frontier Research Center (EFRC:CST), The University of Texas, Austin, Texas 78712, United States.
authors: Wai-Lun
authors: WL
authors: Chan
authors: James R
authors: JR
authors: Chelikowsky
authors: ∥Sandia National Laboratory, MS1415, Albuquerque, New Mexico 87185, United States.
authors: Kevin
authors: K
authors: Leung
authors: †Energy Frontier Research Center (EFRC:CST), The University of Texas, Austin, Texas 78712, United States.
authors: Xiaoyang
authors: X
authors: Zhu
keywords: density-functional theory; electronic level alignment; interface dipole; morphology; organic photovoltaics; time-of-flight secondary ion mass spectrometry; ultraviolet photoemission spectroscopy