Understanding the Interface Dipole of Copper Phthalocyanine (CuPc)/C60: Theory and Experiment

TL;DR

This study combines theoretical DFT calculations with experimental UPS and TOF-SIMS techniques to investigate the origin and characteristics of interface dipoles in CuPc/C60 interfaces, revealing the influence of morphology and ruling out charge transfer as the cause.

Contribution

It provides a comprehensive analysis of the interface dipole in CuPc/C60, integrating theory and experiment to clarify its origin and the role of interfacial morphology.

Findings

DFT predicts a sizable interface dipole for face-on orientation.

UPS measurements confirm the theoretical predictions.

Interfacial morphology involves molecular intermixing with different orientations.

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.