Unraveling the Role of Liquid Metal Catalysts in Electrochemical Growth of Solar Si from SiO₂ in CaCl₂-Based Molten Salt: Enhancement of Crystallization, Purity, and Photoresponse

Abstract

The electrochemical growth of Si has been developed as an alternative method of producing highly crystalline and pure semiconducting solar Si. The use of liquid catalysts for the electrochemical growth of semiconductors has been suggested to improve their quality. In this study, the role of liquid catalysts during the direct electrochemical growth of Si from SiO2 in CaCl2-based molten salts was investigated by comparing the crystallinity, purity, and photoresponse of Si deposited with and without liquid catalysts. A liquid catalyst was introduced into Si via the codeposition of Au or Ag, thereby forming a eutectic liquid mixture with Si during electrochemical growth. The use of liquid catalysts did not affect the growth rate of Si. Conversely, the liquid catalysts cause significant morphological changes associated with an approximately 2-fold increase in the grain size of Si, as estimated from X-ray diffraction and Raman analyses, by offering a low interface energy for Si nucleation. In addition, secondary ion and inductively coupled plasma mass spectroscopy analyses revealed that Al from the SiO2 feedstock was the primary impurity within the Si deposit and that its amount decreased when a liquid catalyst was used to filter the impurities during Si growth. Subsequently, the enhanced crystallization and purification of the liquid catalysts increased the photoresponse of the Si deposit, as confirmed by photoelectrochemical measurements. These results suggest that the electrochemical growth of Si using liquid catalysts can enhance the quality of Si, reflecting its potential to replace the conventional process of Si production.