Graphene-enhanced intermolecular interaction at interface between copper- and cobalt-phthalocyanines

Area of Science:

• Materials Science
• Surface Science
• Organic Electronics

Background:

• Understanding interfacial electronic structures is crucial for designing organic electronic devices.
• Phthalocyanines (CuPc, CoPc) are widely studied organic semiconductors.
• Graphene serves as a promising substrate due to its unique electronic properties.

Purpose of the Study:

• To investigate the interfacial electronic structures of CuPc and CoPc on graphene.
• To elucidate the role of sequential deposition of CuPc and CoPc on graphene.
• To understand the molecule-substrate and molecule-molecule interactions at these interfaces.

Main Methods:

• Photoelectron spectroscopy (PES) was employed to probe the electronic structures.
• X-ray photoelectron spectroscopy (XPS) provided elemental and chemical state information.
• Density functional theory (DFT) calculations were performed for theoretical analysis.

Main Results:

• The CuPc/graphene interface exhibited a flat band structure with a negligible interfacial dipole, indicating weak interaction.
• The CuPc/CoPc/graphene interface displayed a large interfacial dipole and significant energy level bending.
• Intermolecular interactions between CuPc and CoPc were found to be enhanced by the CoPc-graphene interface properties, leading to a work function decrease.

Conclusions:

• The electronic properties of phthalocyanine films on graphene are strongly influenced by the presence of an intermediate CoPc layer.
• The CoPc layer modifies the graphene work function, which in turn affects the CuPc layer.
• This study highlights the potential for tuning organic semiconductor interfaces through controlled molecular layering.