• Multilayer copper–carbon nanofilms fabricated via plasma immersion deposition achieve up to 30.20% higher conductivity than pure copper.
• Effective medium theory, first-principles calculations, and density of states analysis reveal the critical roles of copper atom adsorption sites and electron migration pathways in enhancing conductivity.
• High-density electrons from copper migrate into the nanocarbon film under an applied electric field, forming efficient electron transport channels.
• Large-scale electrode coating equipment was developed, enabling industrial production of copper–carbon nanocomposite films for high-conductivity applications.