Formic Acid-Driven Enhancement of Copper Metal Organic Decomposition Films: Achieving Record-High Conductivity at Low-Processing Temperature

In this study, we introduce formic acid (FA) as a highly effective reducing atmosphere for the thermal decomposition of copper metal organic decomposition (Cu MOD) ink, thereby significantly enhancing the resulting film conductivity and lowering the processing threshold to 120 °C. By employing an FA vapor mole fraction close to its saturation in nitrogen (∼5 mol %) at a moderate temperature of 200 °C, we achieved copper films with remarkable electrical conductivity, reaching up to 80% of the bulk copper. This performance surpasses the commonly reported ∼50% conductivity plateau for low temperature processing and, to the best of our knowledge, represents the highest conductivity reported to date for Cu MOD films processed at or below this temperature. The underlying mechanism was investigated systematically. Our results reveal that the FA atmosphere facilitates the reduction process from copper(II) complex to metallic copper (Cu(0)) while simultaneously promoting the removal of organic residues. As a result, the FA atmosphere yields highly conductive Cu MOD films with reduced organic residues and a more continuous conductive network. This work provides fundamental insights into the role of FA as a reactive atmosphere for achieving highly conductive Cu MOD films and offers practical guidelines for large-scale, low-cost, printed electronics manufacturing.