Electrochemical Formation of Si Films by Co-deposition of Si and Zn in Molten KF–KCl–K₂SiF₆–ZnCl₂ Systems (Supporting Information)

Crystalline silicon solar cells have become the leading technology in solar cell manufacturing. However, conventional solar cell manufacturing methods are energy-intensive and inefficient. We previously developed an electrodeposition method that improved crystalline Si film production but faced limitations in grain size, which is crucial for minimizing recombination losses in polycrystalline Si solar cells. In this study, the co-deposition of Si and Zn on a graphite substrate is investigated to obtain large grain-sized Si films. Electrochemical measurements and electrolysis are conducted at 923 K in molten KF–KCl–K₂SiF₆–ZnCl₂ systems. Reduction currents corresponding to the reduction of Zn(II) and Si(IV) ions are observed at approximately −2.6 V vs. Cl₂/Cl⁻ and −3.1 V, respectively in the cyclic voltammogram on a glassy carbon electrode. The optimal conditions for obtaining highly crystalline Si films are investigated by varying the ZnCl₂ concentration and current density. During co-deposition, a Si–Zn liquid alloy is deposited. Post-electrodeposition cross-sectional images reveal a Si layer on the graphite substrate with a Zn layer on top. After Zn removal, the Si films exhibit larger crystal sizes than those obtained without ZnCl₂, indicating deposition through liquid alloying with Zn.