Electrodeposition of Si Film from Water-Soluble KF-KCl Molten Salt and Feasibility of SiCl₄ as a Si Source

Abstract

Toward an establishment of a new production method of solar cell substrates, electrodeposition of Si was investigated in molten KF–KCl (eutectic composition, 45:55 mol%) after the introduction of SiCl₄. Gaseous SiCl₄ was directly introduced into the molten salt at 1023 K by a vapor transport method using Ar carrier gas. The dissolution ratio of SiCl₄ exceeded 80% even with the use of a simple tube for the bubbling. Galvanostatic electrolysis was conducted at 923 K on a Ag substrate at 155 mA cm⁻² for 20 min in molten KF–KCl after the dissolution of 2.30 mol% SiCl₄. Although compact Si layer was formed, the smoothness was lower compared to that obtained from the melt after the addition of K₂SiF₆. The anionic molar fraction is probably one of the factors affecting the morphology of deposit.