Silicon electrodeposition in a water-soluble KF–KCl molten salt: Utilization of SiCl₄ as Si source

The electrodeposition of Si was investigated in a molten KF–KCl salt mixture (eutectic composition, 45:55 mol%) after the introduction of SiCl₄ to demonstrate a new production method for solar cell substrates. Gaseous SiCl₄ was introduced directly into the molten salt at 1023 K by a vapor transport method using Ar as a carrier gas. The dissolution efficiency of SiCl₄ exceeded 80% even when a simple tube was used for bubbling. Galvanostatic electrolysis was conducted at 923 K on a Ag substrate at 155 mA cm⁻² for 20 min in the molten KF–KCl salt mixture after the dissolution of 2.30 mol% SiCl₄. Although a compact Si layer was formed, its smoothness was inferior to that obtained from the melt after the addition of K₂SiF₆. The molar fraction of the fluoride anion is suggested as one of the factors affecting the morphology of the deposits.