Purity and Minority Carrier Lifetime in Silicon Produced by Direct Electrolytic Reduction of SiO₂ in Molten CaCl₂

Abstract

Si powder was produced by direct electrolytic reduction of SiO 2 in molten CaCl 2 at 1123 K. From the Si powder, Si ingots were obtained by a floating zone method. The concentrations of most metallic elements and of P in the Si ingots were lower than the acceptable levels for solar grade Si. The minority carrier lifetimes in the Si ingots were measured using a microwave photo conductivity decay method. The obtained values of ca. 1.0 µs were two orders of magnitude shorter than those observed in an Si ingot prepared from 10N purity Si.

Silicon Electrochemistry in Molten Salts

“…Highly pure silicon was obtained by SiO 2 reduction in the form of Si powder and subsequent forming of ingots by the floating zone method. 83 Purity of the produced silicon was higher than that of SoG-Si. The minority carrier lifetimes in the ingot was 2 orders of magnitude shorter when compared to 10N Si.…”

“…The p-n samples were contaminated by W, which originated from the electrode leads, whereas Al contamination was released from the quartz crucible . The purity was increased when using Si contacting electrodes instead of the foreign metal electrode. , The electro-reduced silicon was upgraded to SoG-Si by subsequent zone melting purification. , …”

“…Highly pure silicon was obtained by SiO 2 reduction in the form of Si powder and subsequent forming of ingots by the floating zone method . Purity of the produced silicon was higher than that of SoG-Si.…”

“…80,81 The electro-reduced silicon was upgraded to SoG-Si by subsequent zone melting purification. 82,83 Contamination by calcium originates either from the molten salt entrapped in the surface structure or the calcium metal deposited at negative polarization. As discussed in section 2, calcium silicides can form under UPD conditions (8) that are at E > E 0 Ca/Ca 2+ .…”

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

“…Since the development of the electrochemical reduction of SiO 2 to Si in molten CaCl 2 , − numerous researchers have assessed the feasibility of the direct electrochemical production of pure, highly crystalline, semiconducting Si films from SiO 2 . − Electrochemically grown Si is also expected to meet the requirements of purity and crystallinity. The primary strategy for achieving high crystallinity and purity during electrochemical growth is the appropriate choice of electrode material because it has a crucial influence on the nucleation and growth of Si.…”