A new method for electroplating Si using a water-soluble KF-KCl molten salt electrolyte and high-purity gaseous SiCl 4 has been proposed. To gain a fundamental understanding of the process, the electrodeposition of Si from Si(IV) complex ions on a Ag electrode in a molten KF-KCl-K 2 SiF 6 system was investigated by cyclic voltammetry at 923 K. The reduction of Si(IV) ions to metallic Si was observed as a single 4-electron wave, which is explained by an E q E r (quasireversible-reversible electron transfer reactions) mechanism. The diffusion coefficient of the Si(IV) ions in the electrolyte was determined to be 3.2 × 10 −5 cm 2 s −1 at 923 K by chronoamperometry.

To establish a new Si-electrodeposition process, the optimum conditions for obtaining adherent, compact, and smooth Si films using molten KF-KCl-K 2 SiF 6 were investigated at 923 K. Galvanostatic electrolysis was conducted on a Ag substrate in eutectic KF-KCl (45:55 mol%) with various current densities (10-500 mA cm −2) and K 2 SiF 6 concentrations (0.5-5.0 mol%). Cross-sectional scanning electron microscopy (SEM) of the deposits revealed that compact and smooth Si films form at intermediate K 2 SiF 6 concentrations and current densities. The relationship between the deposition conditions and Si morphology is discussed in terms of the electrodeposition mechanism.

The electrodeposition of Si was investigated in a molten KF–KCl salt mixture (eutectic composition, 45:55 mol%) after the introduction of SiCl4 to demonstrate a new production method for solar cell substrates. Gaseous SiCl4 was introduced directly into the molten salt at 1023 K by a vapor transport method using Ar as a carrier gas. The dissolution efficiency of SiCl4 exceeded 80% even when a simple tube was used for bubbling. Galvanostatic electrolysis was conducted at 923 K on a Ag substrate at 155 mA cm−2 for 20 min in the molten KF–KCl salt mixture after the dissolution of 2.30 mol% SiCl4. Although a compact Si layer was formed, its smoothness was inferior to that obtained from the melt after the addition of K2SiF6. The molar fraction of the fluoride anion is suggested as one of the factors affecting the morphology of the deposits.

Toward the establishment of a new electrodeposition process of Si, the optimum conditions for obtaining adherent, compact and smooth Si film in molten KF–KCl–K2SiF6 were investigated. Galvanostatic electrolysis was conducted on an Ag substrate in eutectic KF–KCl (45:55 mol%) with various current densities (10–500 mA cm−2) and K2SiF6 concentrations (0.50–5.0 mol%) at 923 K. Cross-sectional SEM observation of the deposits revealed that compact and smooth Si films form at intermediate K2SiF6 concentration and current density. The morphology of the Si deposit changed into nodular at higher current density. At lower current density, detachment of Si layer from the Ag substrate occurred during the water washing. The relationship between the deposition conditions and Si morphology is discussed from the view point of electrodeposition mechanism.

Melamine or melem forms a coordination compound with Pr(III). From detailed measurements of electronic absorption and luminescence spectra reported here, it can be concluded that the excitation energy transfer of the Pr(III)-melamine complex occurs via an electron exchange mechanism, whereas the Pr(III)-melem follows a Coulomb mechanism.