Container-Free Microfluidic Chemical Reduction for Synthesizing Ultrafine Silver Powder and Fabricating Silver Paste

As an important interconnecting material for solar cells, photovoltaic silver paste is in high demand. The silver powder, used as the conductive phase, greatly influences the conductivity of the paste. In this study, microfluidic technology was employed to achieve rapid and uniform mixing at the molecular level and the influence of microfluidic process conditions and reaction rates on silver powder morphology was investigated. Particularly, microfluidic technology can prevent the heterogeneous nucleation on wall of container. Using a 1.5 mol/L ascorbic acid concentration, spherical silver powder measuring 0.70–0.80 μm was produced through the convection reaction of two microflows at a 10 mL/min flow rate. This silver powder exhibited better shape regularization compared to that produced by macromixing. When mixed with micron flake silver powder in a 1:1 mass ratio and sintered at 150℃ for 45 min, the microfluidically prepared silver powder achieved a resistivity of 2.72 × 10⁻⁵ Ω.cm. This work introduces a new approach for preparing submicron silver powder, which has important applications in the solar cell silver paste field.