Preparation of Superfine Spherical Silver Powders for Solar Cell Silver Paste via Non-wetting Effect of the Liquid/Solid Interface

Superfine silver powders are building blocks of silver paste, which plays a vital role as a conductive material in solar cells. The conductivity of silver paste is greatly affected by the shape, size, and homogeneity of silver powders. In this paper, superfine spherical silver powders with good sphericity and smooth surfaces were prepared by using the non-wetting effect of the liquid/solid interface. Hexagonal boron nitride and magnesium oxide were chosen as dispersants for the preparation of the silver powders. Hexagonal boron nitride with low surface energy was beneficial for the sphericity of the silver powders, and magnesium oxide with high density and hardness was beneficial for their size distribution. The result of scanning electron microscope (SEM) images showed the powders prepared via the non-wetting effect of the liquid/solid interface exhibited better sphericity and smoother surfaces than powders prepared by the liquid phase chemical reduction method, which is by far the most commonly used method. The size distribution of silver powders using magnesium oxide as dispersant was 0.2—2.4 µ m, which meets the requirements of solar cells. After sintering at 500°C, the sheet resistance of the silver film was as low as 12.71 mΩ/sq, implying good electrical conductivity.