Control of galvanic replacement reaction between Cu nanowires and Ag species under vacuum filtration for transparent conductive films with long-term durability

Abstract Ag coatings on Cu nanowire (NW) surfaces are widely studied for making durable transparent conductive films. Although the galvanic replacement reactions (GRRs) between Cu NWs and Ag species were usually employed, non-uniform Ag layers were obtained due to their rapid reaction rates, leading to non-durable films. Herein, the GRR between Cu NW surfaces and Ag complexes in citric acid solutions was controlled by vacuum filtration, obtaining uniform Ag-coated NWs for durable films. Citric acid removed the surface impurities from the Cu NW surfaces and also modified the surfaces. While adsorbed to the NWs, citric acid delayed the Cu dissolution in aqueous solution, enabling regulation of the Ag concentration, solution volume, and temperature of the GRR. The GRR was precisely controlled by lowering some or all of these three factors under vacuum filtration. In the controlled reactions, the slow reaction rates caused partial Ag crystal growth on the surfaces. The heterogeneity of the growth increased with solution volume, producing large surface irregularities. At fast reaction rates with high Ag concentrations, the Ag species uniformly reacted with the Cu NW surface within a short time, leading to Cu NWs with fewer surface irregularities and thicker Ag layers than at slow reaction rates. After the GRR, the sheet resistance of the Cu NWs was lowered because the Ag crystal growth between the Cu junctions decreased the contact resistance. In transparent Cu NW films with a thick Ag layer, the sheet resistance was retained for 300 h at high-temperature (130 °C) and under standard harsh conditions (85 °C and 85% relative humidity).