Acetic-acid-assisted washing-free synthesis of Cu nanoparticles from CuO for low-temperature sintering of conductive films

Copper nanoparticles (Cu NPs) are promising low-cost alternatives to Ag-based conductive fillers for printed electronics; however, conventional synthesis routes often require low precursor concentrations, large amounts of dispersants, and post-synthesis purification, with the associated increase in costs and waste liquid generation limiting their practical scalability. Here, we investigate the role of molecular additives in the high-concentration, washing-free synthesis of Cu NPs from CuO and evaluate the low-temperature sintering behavior of the resulting particles. Among the additives examined, acetic acid effectively reduced the particle size, yielding Cu NPs with an average diameter of 89.2 nm. Thermogravimetric analysis indicated that acetic acid-derived species were removed at relatively low temperatures, whereas long-chain or multifunctional additives such as oleic and citric acids remained to higher temperatures and adversely affected sintering. The unwashed acetic-acid-assisted Cu NP paste exhibited pronounced interparticle neck formation and achieved a low volume resistivity of 1.9 × 10 -5 Ω·cm (9.1% International Annealed Copper Standard(IACS)) after sintering at 250 °C for 60 min under nitrogen without applied pressure. These results suggest that acetic acid plays a dual role in particle-size reduction and low-temperature sintering, possibly by providing removable surface species that facilitate particle contact and neck growth. The CuO-derived washing-free process combined with acetic acid addition enhances process sustainability by reducing washing steps, associated costs, and washing-related liquid waste, thereby offering a practical route for preparing low-cost Cu conductive films under mild sintering conditions.