Pulse Electrodeposition of Polycrystalline Si Film in Molten CaCl2 Containing SiO2 Nanoparticles

The high cost of Si-based solar cells remains a substantial challenge to their widespread adoption. To address this issue, it is essential to reduce the production cost of solar-grade Si, which is used as raw material. One approach to achieve this is Si electrodeposition in molten salts containing Si sources, such as SiO2. In this study, we present the pulse electrode-position of Si in molten CaCl2 containing SiO2 nanoparticles. Theoretically, SiO2 nanoparticles with a diameter of less than 20 nm in molten CaCl2 at 850 degrees C have a comparable diffusion coefficient with that of ions in aqueous solutions at room temperature. However, we observed a slower-than-expected diffusion of the SiO2 nanoparticles, probably because of their tendency to aggregate in the molten CaCl2. This led to the formation of a non-uniform Si film with low current efficiency during direct current electrodeposition. We overcome this issue using pulse electrodeposition, which enabled the facile supplementation of SiO2 nanoparticles to the substrate. This approach produced a uniform and thick electrodeposited Si film. Our results demonstrate an efficient method for Si electrodeposition in molten CaCl2 containing SiO2 nanoparticles, which can contribute to a reduction in production cost of solar-grade Si.