Mono-dispersed droplets formation from capillary jet of liquid metal by applying an electric field

Abstract

Purpose of our research is to develop a manufacturing process of mono-dispersed metal balls for spherical silicon solar cell. The spherical solar silicon cell is a solar cell that uses silicon spheres of 1 mm in diameter and has drawn great attention due to its high productivity. Silicon spheres are manufactured by a jet dropping method. In this method, silicon droplets are generated from breakup of a capillary jet of molten silicon. The droplets are solidified while failing in a cooling tower, and then spherical silicon balls are obtained. However, it is found to occur that the silicon balls are not mono-dispersed due to coalescence of the droplets during falling. In order to solve this problem, we proposed the droplet electrification method by applying high voltage electric field. A repulsive force will act between each charged droplets and prevent them from coalescence. In our experiments, capillary jets of water, glycerol and molten gallium were used instead of molten silicon to investigate the effect of the electrification. The experimental results are found that coalescence frequency is depending on a dimensionless parameter, which represents a ratio of electrostatic potential over kinetic energy of droplets.