Transformation of SiO₂ Particles to Si Film via Al-Assisted Electrochemical Reduction in Molten CaCl₂

Abstract

A Si film was formed from SiO2 particles in CaCl2 molten salt by electrochemical reduction using liquid Al-Si alloys. The liquid Al-Si alloys, formed from electrochemically reduced Si and metallic Al during the electrochemical reduction of the SiO2 particles, not only promoted electrochemical reduction, but also induced Si thin film formation. The Si film growth was observed by optical imaging, while the morphology and composition of the films were characterized by scanning electron microscopy and X-ray diffraction analysis. A pulse reduction technique was introduced to promote SiO2 reduction. The effect of the on/off time ratio on the Si film formation was investigated, with efficient SiO2 reduction achieved via on/off time ratio optimization. At the optimized ratio, a 0.9-mm-thick Si film with a Si purity of 96 at% was obtained. This effective Si production system might contribute to the fabrication of low-cost solar cells and Si-related electronic devices that require Si films.