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 asan alternativemethod of producing highly crystalline and pure semiconducting solarSi. The use of liquid catalysts for the electrochemical growth ofsemiconductors has been suggested to improve their quality. In thisstudy, the role of liquid catalysts during the direct electrochemicalgrowth of Si from SiO2 in CaCl2-based moltensalts was investigated by comparing the crystallinity, purity, andphotoresponse of Si deposited with and without liquid catalysts. Aliquid catalyst was introduced into Si via the codeposition of Auor Ag, thereby forming a eutectic liquid mixture with Si during electrochemicalgrowth. The use of liquid catalysts did not affect the growth rateof Si. Conversely, the liquid catalysts cause significant morphologicalchanges associated with an approximately 2-fold increase in the grainsize 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 analysesrevealed that Al from the SiO2 feedstock was the primaryimpurity within the Si deposit and that its amount decreased whena liquid catalyst was used to filter the impurities during Si growth.Subsequently, the enhanced crystallization and purification of theliquid catalysts increased the photoresponse of the Si deposit, asconfirmed by photoelectrochemical measurements. These results suggestthat the electrochemical growth of Si using liquid catalysts can enhancethe quality of Si, reflecting its potential to replace the conventionalprocess of Si production.