Clean Synthesis and Formation Mechanisms of High‐Purity Silicon for Solar Cells by the Carbothermic Reduction of SiC with SiO2

Abstract Metallurgical synthesis of solar grade silicon (SoG−Si) is an existing challenge due to the strict chemical composition of silicon for solar cells. Here, we report a green and facile approach to synthesize high‐purity silicon (99.98 wt%, 0.12 ppmw B and 0.18 ppmw P) for solar cells by the carbothermic reduction of SiC with SiO 2 in a vacuum graphite resistance furnace. Catalyst of Fe 2 O 3 plays the role of reducing the concentration of CO (g) , lowering the energy consumption and improving the purity and yield of silicon. The present work is one‐step to obtain silicon with less B and P, but it is composed of silicon synthesis, oxidation refining, vacuum refining and blowing refining, which discloses an innovative chemical concepts of in‐situ synthesis combined with refining. According to the characterizations of the reacted SiC particles performed by XRD, Raman, PL, XPS, SEM and TEM, the morphologies and formation mechanisms of the in‐situ silicon from the horizons of atomic scale were revealed for the first time. It was evidenced conclusively that the Si−C bonding is broken from the (006) planes of 6H‐SiC at 1850°C by the reaction of SiC (s) + 2SiO 2(l) =3SiO (g) + CO (g) , and then the silicon nucleates on the (101) planes of 6H‐SiC and grows along the [111] direction at 1950°C via the vapor‐solid reaction of SiO (g) + SiC (s) =2Si (l) + CO (g) .